Quench, separated thread.

[BRUTAL64]

I think C6 made the recommendation first, but yeah. FelPro or Cometic, whatever is right for what you need. Then buy some used 1.8 rockers and see if it'll pass.

Don't know if you really need another dyno re-tune, I'd just pull the AFR down lower. If I remember right your motor was stoich at WOT. I'd bring it down a point or two, should help the ping prob.

Drop the CR 1/2 a point, colder plugs, more gas in the mix... should run on 91 all day. If you care about that sort of thing. I would def bet the plug fouling was a result of the Torco.

You guys keep forgetting about quench. Yep, that'll bite you in the ass. Quench should be around .045. Much bigger than that and you're right back to pre-ingition with your lower compression. :drink:

I don't see where that plug was fouled. It had a lot crap on it, but that didn't mean it wasn't firing. I'd have to look at that plug close up. To be sure.:)

[BRUTAL64]

I forgot, what's quench again? I'll bring the plugs with me this Saturday. I already ordered a set of copper autolites on the colder end of the spectrum.

The distance the piston flat (closest to head) is from the flat area of the head. 045. is considered the optional distance. Anything much more than this will contribute to engine pre-ingition.

Mine is .054 on current 400. On my first LT1 I had a .068 quench and it pinged like a MF. I closed it up on the next build (everything else being the same--except even higher cr) with the piston .005 below deck and the head gasket was .042 I had no pinging at all. Quench is VERY important.:bigthumbsup:

[94cobra69ss396]

Here's some info on quench from United Engine and Machine's website.

"Excessive cylinder pressure will encourage engine destroying detonation, and no piston is immune to its effects. An important first step is to set the assembled quench ("squish") distance to .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance (the distance your piston is down in the bore). If your piston compression height (not dome height) is above the block deck, subtract the overage from the gasket thickness to get a true assembled quench distance. The quench area is the flat part of this piston that would contact a similar flat area on the cylinder head if you have zero assembled quench height. In a running engine the .040" quench usually decreases with RPM to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity across the combustion chamber. This movement tends to cool hot spots, average the chamber temperature, and speeds flame travel after TDC to increase power. On the exhaust cycle, some cooling of this piston occurs due to the closeness of the hopefully cooler cylinder head. The power increase occurs because the shock wave occurs at exactly TDC on all cylinders, every time. It tends to make all cylinders alike and receive more identical flame travel speed. Spark scatter tends to be averaged with the TDC kick received from a tight quench.

Some non-quench engines, such as '68 and later Chrysler V-8's, can be converted to quench type with pistons such as the KB278, KB280, KB372, and KB373. Most Mopar cylinder heads recess the quench area into the head, so a raised area on the piston is necessary to get the close collision. If you are building an engine with steel rods, tight bearings and pistons, modest RPM, and automatic transmission, a .035" quench is the minimum practical to run without engine damage. The closer the piston comes to the cylinder head at operating speed, the more turbulence is generated. Unfortunately, the operating quench height varies in an engine as RPM and temperatures change. If aluminum rods, loose pistons (they rock and hit the head), and over 6000 RPM operation is anticipated, a static clearance of .055" could be required. A running quench height in excess of .060" will forfeit most of the benefits of the quench head design and can push the engine into severe detonation.

The suggested .040" static quench height is recommended as a good average dimension for stock rod engines up to 6500 RPM. Above 6500 RPM, rod selection becomes important. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or thick head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will likely create more ping at 9.5:l than you had at 10:1. One way to cheat the system is to make sure the piston of choice is light on quench side and to make sure the piston of choice is light on quench side and heavy on spark plug side. As RPM increases the piston tries to cock away from quench surface, allowing a tighter quench at most all RPM. The suitable way to lower the compression is to use a KB Dish Piston. KB Dish Pistons (reverse combustion chamber) are desinged for maximum quench area. Having part of the combustion chamber in the piston can improve the shape of the chamber and flame travel. The Step Dish is sort of an upscale version of our reqular configuration. It allows some piston weight reduction and allows the quench action to travel further across the chamber. It is especially favored when large dish cc's are required."

[enkeivette]

Ben, do you know how much lift your valve springs can take? How about your piston to valve clearance? I wouldn't go installing a set of 1.8 rockers until you know these measurements. If you’re going to replace the head gaskets with thicker ones then you'll gain some piston to valve clearance over what you have currently but you will still want to clay the piston and make sure.

Always good to check. I'd use Playdo over clay. Clay is filled with fine sand that hardens at high temp. Don't like the idea of that on my cylinders and under my rings.

But I doubt you'll have an issue with this.



Brutal, I do forget about quench because with my app, lower CR was more important to avoid detonation than proper quench. I know 40-45 is ideal but I think the lower compression would be better for Ben in avoiding detonation than having ideal quench, don't you? In fact, he prob doesn't have proper quench now.

Ben, how thick is your current HG? Any idea how far down the pistons are?

[94cobra69ss396]

Always good to check. I'd use Playdo over clay. Clay is filled with fine sand that hardens at high temp. Don't like the idea of that on my cylinders and under my rings.

Funny you mention that because that is what I use. Since I have kids it's readily available to me.

[enkeivette]

I've been nailing my motor at 13lbs of boost on only 91 octane up to redline multiple times every weekend since June to tune it... and enjoy it. No detonation yet with the now proper AFR.

...I have a .086 quench.

[94cobra69ss396]

Brutal, I do forget about quench because with my app, lower CR was more important to avoid detonation than proper quench. I know 40-45 is ideal but I think the lower compression would be better for Ben in avoiding detonation than having ideal quench, don't you? In fact, he prob doesn't have proper quench now.

Read the info I posted, it answers this question. It was written by John Erb the Chief Engineer at KB Pistons.

[94cobra69ss396]

I've been nailing my motor at 13lbs of boost on only 91 octane up to redline multiple times every weekend since June to tune it... and enjoy it. No detonation yet with the now proper AFR.

...I have a .086 quench.

You also said you didn't have detonation before you broke the piston. Just because you can't hear it doesn't mean it's not happening.

[BRUTAL64]

Always good to check. I'd use Playdo over clay. Clay is filled with fine sand that hardens at high temp. Don't like the idea of that on my cylinders and under my rings.

But I doubt you'll have an issue with this.



Brutal, I do forget about quench because with my app, lower CR was more important to avoid detonation than proper quench. I know 40-45 is ideal but I think the lower compression would be better for Ben in avoiding detonation than having ideal quench, don't you? In fact, he prob doesn't have proper quench now.

Ben, how thick is your current HG? Any idea how far down the pistons are?

Ford in the early 70's did away with closed chamber heads and used completely OPEN chambers. No quench at all. The ratios were around 8 to 1.

They pinged like a MF under load.

[enkeivette]

You also said you didn't have detonation before you broke the piston. Just because you can't hear it doesn't mean it's not happening.

True, but in hindsight I think I did feel it. I used to think I had an ignition problem, sort of a rough acceleration... you can search back and find threads about it. Now I don't have that any more. I'm thinking that was detonation.

My piston blew because of the 36 degrees of timing and the excessively high AFR. It was 15:1 at 5lbs, when I sealed it up and it boosted like it does now... who knows what the AFR went up to. :boggled:

Also quench is less important in blown apps so I hear.



If Ben has less than ideal quench right now, which is likely with his high compression franken-LSX, than he can kill two birds with one stone. Lower the CR and get ideal quench.

[BRUTAL64]

Here's some info on quench from United Engine and Machine's website.

"Excessive cylinder pressure will encourage engine destroying detonation, and no piston is immune to its effects. An important first step is to set the assembled quench ("squish") distance to .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance (the distance your piston is down in the bore). If your piston compression height (not dome height) is above the block deck, subtract the overage from the gasket thickness to get a true assembled quench distance. The quench area is the flat part of this piston that would contact a similar flat area on the cylinder head if you have zero assembled quench height. In a running engine the .040" quench usually decreases with RPM to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity across the combustion chamber. This movement tends to cool hot spots, average the chamber temperature, and speeds flame travel after TDC to increase power. On the exhaust cycle, some cooling of this piston occurs due to the closeness of the hopefully cooler cylinder head. The power increase occurs because the shock wave occurs at exactly TDC on all cylinders, every time. It tends to make all cylinders alike and receive more identical flame travel speed. Spark scatter tends to be averaged with the TDC kick received from a tight quench.

Some non-quench engines, such as '68 and later Chrysler V-8's, can be converted to quench type with pistons such as the KB278, KB280, KB372, and KB373. Most Mopar cylinder heads recess the quench area into the head, so a raised area on the piston is necessary to get the close collision. If you are building an engine with steel rods, tight bearings and pistons, modest RPM, and automatic transmission, a .035" quench is the minimum practical to run without engine damage. The closer the piston comes to the cylinder head at operating speed, the more turbulence is generated. Unfortunately, the operating quench height varies in an engine as RPM and temperatures change. If aluminum rods, loose pistons (they rock and hit the head), and over 6000 RPM operation is anticipated, a static clearance of .055" could be required. A running quench height in excess of .060" will forfeit most of the benefits of the quench head design and can push the engine into severe detonation.

The suggested .040" static quench height is recommended as a good average dimension for stock rod engines up to 6500 RPM. Above 6500 RPM, rod selection becomes important. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or thick head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will likely create more ping at 9.5:l than you had at 10:1. One way to cheat the system is to make sure the piston of choice is light on quench side and to make sure the piston of choice is light on quench side and heavy on spark plug side. As RPM increases the piston tries to cock away from quench surface, allowing a tighter quench at most all RPM. The suitable way to lower the compression is to use a KB Dish Piston. KB Dish Pistons (reverse combustion chamber) are desinged for maximum quench area. Having part of the combustion chamber in the piston can improve the shape of the chamber and flame travel. The Step Dish is sort of an upscale version of our reqular configuration. It allows some piston weight reduction and allows the quench action to travel further across the chamber. It is especially favored when large dish cc's are required."

Some good info there.:thumbs_up:

[enkeivette]

...I'll pull out my plugs and measure the gaps to see if they've opened up at all in the last couple of months.

[94cobra69ss396]

...I'll pull out my plugs and measure the gaps to see if they've opened up at all in the last couple of months.

Look for white specs in the plugs. That's a sign of detonation.

Check out this article with pictures http://www.stockcarracing.com/techarticles/40118_reading_spark_plugs/index.html

[94cobra69ss396]

Here's a good article on quench for a SBC. http://www.chevyhiperformance.com/techarticles/94138_piston_head_clearance_guide/index.html

[enkeivette]

Look for white specs in the plugs. That's a sign of detonation.

Check out this article with pictures http://www.stockcarracing.com/techarticles/40118_reading_spark_plugs/index.html

Will do.

My plug was cracked when I blew the piston, in just the one cylinder. And that was the first time I got on it fully after sealing it up. Those intake manifold gaskets had a short life.

That's why this time I didn't get on it fully till I got my WOT AFR into the 12s.



But back to Ben, post your piston to deck height and your compressed HG thickness. If you don't know them... you might be SOL. Unless you can find the HGs in some build list and the pistons are stock. Stock piston to deck should be an easy find for an LS1.

[BRUTAL64]

Here's a good article on quench for a SBC. http://www.chevyhiperformance.com/techarticles/94138_piston_head_clearance_guide/index.html

Every one should read this.:p


I wish the people I talk to at work were as smart as you guys. You people are a pleasure to share info with.

[enkeivette]

Here's a good article on quench for a SBC. http://www.chevyhiperformance.com/techarticles/94138_piston_head_clearance_guide/index.html

That artcile says not to run any tighter than .05 from a pro engine builder!!!

"According to Ken Duttweiler, the tightest quench he recommends is around 0.050-inch."

I wonder how much is really known about quench. When I called AFR and FelPro with my quench vs. compression questions, they both told me to go with the thicker HG. AFR's opinion was basically that yeah quench matters, but having proper compression is way more important. But once again, in a boosted app.

[BRUTAL64]

That artcile says not to run any tighter than .05 from a pro engine builder!!!

"According to Ken Duttweiler, the tightest quench he recommends is around 0.050-inch."

I wonder how much is really known about quench. When I called AFR and FelPro with my quench vs. compression questions, they both told me to go with the thicker HG. AFR's opinion was basically that yeah quench matters, but having proper compression is way more important. But once again, in a boosted app.

So, look at it this way. A pro builder is looking at much higher rpms than the average Joe. My 400 is set up with .054 quench--cause I was always spinning them over 7000 rpm. So rod material, rpm and piston clearance set the final closest quench spec. :thumbs_up:


So a low rpm engine with close piston clearances could go .035 quench with a steel forged rod.

[Damian]

ODBII. I ordered some cheapy copper colder plugs.

I might be able to use my Tactrix cable and datalog and see whats going on.

[enkeivette]

Looks like it was actually Cometic that I talked to. Searched for my old thread. All of the gurus said that with boosted apps it is not important at all.

Not sure about NA.



You should have added, in a blown application. It is a different world than N/A.
Cometic is correct.

A 3100 lb car 6-71 blown 327 was built 20+ years ago with the piston .125 down the hole and still runs 11.0 quarter. Uses no oil and is driven most the time on the street. I agree it is not the best squish but the timing works well with this one. The rings are the Old TRW plasma ceramic! I wish they still made them!!!!

It's not unusal to get conflicting tech info from different companies on the same item. I've even seen it within the same company. It boils down to who you are talking too at these companies.

For your application (blower) the .071 Cometic will work for you.
PS..I run a F3R.

Blessings.........Ron.

All of the serious effort boosted engines we've done use (and will continue to use) dished pistons with basically no "quench" at all, and some have very thick head gaskets also. You wont have anything to worry about using a thick head gasket.

Jason

Cometic is right we have done it many times go for it.

With a blower, it is NOT important at all.PERIOD

[enkeivette]

Going to theorize.

If quench is just basically a matter of mixing the air and gas and moving it all around evenly on top of the cylinder before combustion to promote even combustion (thereby eliminating hot spots, or spots more prone to detonation) then it wouldn't matter with a blower. Blowers mix the air and gas and move the air all around in the cylinder before the 'quench' happens. (Pushing the air in, rather than drawing it in) So with blower motors, there should be practically no hot spots.

With the same line of reasoning, on FI cars, expecially those of a relly good design like the LS engines, it shouldn't matter as much because the fuel and air would be mixed better than in a carb app. Not saying it's the same as a blower motor, just better than carb motors.

[BADDASSC6]

I read the quench post it was really good, but my interpretation was that they were discussing setting quench with the correct compression ratio. I'm not saying it's not important, but I will say that it's not as important as correcting the CR.
my $.02

[enkeivette]

So, look at it this way. A pro builder is looking at much higher rpms than the average Joe. My 400 is set up with .054 quench--cause I was always spinning them over 7000 rpm. So rod material, rpm and piston clearance set the final closest quench spec. :thumbs_up:


So a low rpm engine with close piston clearances could go .035 quench with a steel forged rod.

Is this 7k 400 in your Vette? It's not the one with balance issues is it? Cuz I really want to feel what a 7K rpm SBC is all about. Mine has some expensive parts and even it chokes out at 6K.

[94cobra69ss396]

Is this 7k 400 in your Vette? It's not the one with balance issues is it? Cuz I really want to feel what a 7K rpm SBC is all about. Mine has some expensive parts and even it chokes out at 6K.

Your engine shouldn't choke at 6000. I run the 454 in the Chevelle to 6500 and I have about the same size cam as you do 246 @.050 with a .623 lift with a longer stroke. You may not have enough valve spring pressure if it's choking at 6000. That's what happened to me with the old valve springs on the 454. They were the stock Edelbrock ones that are for a flat tappet cam and I'm running a solid roller. Since I only run it to 6500 they had enough pressure for a couple years but then the car started to choke past 6000. I haven't run it down the track yet to see how it pulls but I jumped on it in second gear with the new springs and with the tires blazin I quickly shifted it to third when the tack hit 6800.

[enkeivette]

Your engine shouldn't choke at 6000. I run the 454 in the Chevelle to 6500 and I have about the same size cam as you do 246 @.050 with a .623 lift with a longer stock. You may not have enough valve spring pressure if it's choking at 6000. That's what happened to me with the old valve springs on the 454. They were the stock Edelbrock ones that are for a flat tappet cam and I'm running a solid roller. Since I only run it to 6500 they had enough pressure for a couple years but then the car started to choke past 6000. I haven't run it down the track yet to see how it pulls but I jumped on it in second gear with the new springs and with the tires blazin I quickly shifted it to third when the tack hit 6800.

Hmmm... I got the upgraded springs from AFR (heavier) not sure what rate they are. I do have 1 5/8ths headers and catalytic converters though. Could this have anything to do with it?

I think the motor made peak hp at 6.1K

It feels like it pulls hard past 6K now, but it's so damn powerful it's hard to tell when it chokes out. I remember it choked after 6K when NA so that's where I shift now to be safe. To be honest I could be shifting at 5.5K one time and 6.5K the next, like I said, and I'm sure you empathize, the rpm moves up quicker than my senses can follow. Or you might have more time to react with a wider gear set (3 speed auto right?)

[enkeivette]

Also, don't forget that my cam is a hyd roller. Heavy as they come.

[94cobra69ss396]

Hmmm... I got the upgraded springs from AFR (heavier) not sure what rate they are. I do have 1 5/8ths headers and catalytic converters though. Could this have anything to do with it?

I think the motor made peak hp at 6.1K

It feels like it pulls hard past 6K now, but it's so damn powerful it's hard to tell when it chokes out. I remember it choked after 6K when NA so that's where I shift now to be safe. To be honest I could be shifting at 5.5K one time and 6.5K the next, like I said, and I'm sure you empathize, the rpm moves up quicker than my senses can follow. Or you might have more time to react with a wider gear set (3 speed auto right?)

I was in second gear (1.48) and you're correct that it goes quick. I just caught the tack as I was shifting. When I drag race the car and this goes for the Cobra as well I shift from first to second by the sound of the engine. I don't even look at the tack until I'm shifting from second to third and from third to fourth on the Cobra. So I completely understand. Also, I'm kind of out in the middle of no where so I was on a deserted street going straight.

If you're going off what your car was doing before when it was lean then that would make sense.

[enkeivette]

If you're going off what your car was doing before when it was lean then that would make sense.

Sarcasm?

[94cobra69ss396]

Sarcasm?

No. Your car wouldn't make power up in the higher rpms due to it running lean so it would feel like it was running flat. If you are still feeling this now that the AFR is correct then I'd say you don't have enough valve spring pressure.

[BRUTAL64]

Is this 7k 400 in your Vette? It's not the one with balance issues is it? Cuz I really want to feel what a 7K rpm SBC is all about. Mine has some expensive parts and even it chokes out at 6K.

Yes, It was suppost to be a 7,000 rpm motor, BUT, that damn vibration it has limits my big rpm blasts. The 12 dollar motor went to 7,000 -all the way around my dash tach- anytime I wanted. I balanced that motor with a UPS scale.:o
I should have balanced this motor myself.:sm_up_there:

I once rode in a 69 Z28 that would spin over .........ready........8,000 rpm. I didn't believe it either till I rode in it. Yep, quite the sound. Nascar tone to it.:drink:

[enkeivette]

No. Your car wouldn't make power up in the higher rpms due to it running lean so it would feel like it was running flat. If you are still feeling this now that the AFR is correct then I'd say you don't have enough valve spring pressure.

But if it does pull harder past 6K, it might have just been the AFR?

[enkeivette]

Btw Ben, you already have a pretty big cam for having just ported heads, I just looked last night. You might not gain anything, depends on how big your heads were ported.

[Vettezuki]

Btw Ben, you already have a pretty big cam for having just ported heads, I just looked last night. You might not gain anything, depends on how big your heads were ported.

The cam is pretty moderate.

224/224 114LSA

The ports are huge, supposedly 305cfm. :huh:

[BRUTAL64]

The cam is pretty moderate.

224/224 114LSA

The ports are huge, supposedly 305cfm. :huh:

305 cfm flow are Big Block numbers.:thumbs_up:

[Vettezuki]

305 cfm flow are Big Block numbers.:thumbs_up:

Like I said, this motor with an LS1 intake (I have an LS6) and headers made 432 on an aggressive tune in the car it came out of. I don't think the driveline loss is so much higher on a C3 than a C5 (if at all), so with some headers and a good tune, I should be at least back to 430, maybe higher. :huh: Just speculation until it's done.

[Damian]

I think its just your a/f is out of whack.

[Vettezuki]

I think its just your a/f is out of whack.

Looks pretty good on the dyno. :huh:

http://motorgen.com/pic/data/515/BirdRunDyno1.jpg

[enkeivette]

Btw Ben, I don't know why nooo one has mentioned this, but you can significantly drop your compression without changing your cry baby quench, by changing only the head gasket.

Should I elaborate, or should I be a dick and let you guys figure it out?



And yeah, you can use more lift. Those are some big ass ports. Don't worry about duration changing. Duration as measured wll change with different rockers but actual duration doesn't change. Review the duration article I stickied if you don't know what I mean.

I wouldn't say your AFR is out of whack, but you could def make some more power and resist pinging with a 12.5 at WOT.

[Vettezuki]

Btw Ben, I don't know why nooo one has mentioned this, but you can significantly drop your compression without changing your cry baby quench, by changing only the head gasket.

Should I elaborate, or should I be a dick and let you guys figure it out?



And yeah, you can use more lift. Those are some big ass ports. Don't worry about duration changing. Duration as measured wll change with different rockers but actual duration doesn't change. Review the duration article I stickied if you don't know what I mean.

I wouldn't say your AFR is out of whack, but you could def make some more power and resist pinging with a 12.5 at WOT.

If going to a thicker gasket to drop CR, the only way to maintain quench (assuming I even have vaguely correct quench as it is), would be to change pistons right? If not, you need to elaborate.

[enkeivette]

If going to a thicker gasket to drop CR, the only way to maintain quench (assuming I even have vaguely correct quench as it is), would be to change pistons right? If not, you need to elaborate.

You change the bore of the HG.

I went from a .041 to a .061, but that only got me half way to 9:1, the rest was the 4.166 bore over the old 4.03 bore.

But really, you need to know your measurements. What could happen here for example is that you'll find that you have a .03 HG and quench right now, and that you can go up to a .05 HG/ quench with a bigger HG bore and that'll bring you way down while keeping your crybaby quench. Which for the record, I think there is too much hype about.

The HG bore change alone will prob not drop your CR enough, so you really need some specs to see if you could increase the thickness. Even a few 10/1000 in combination with a bigger bore will make enough of a difference. I think when Brutal did the math to determine my new CR but left out the bigger bore, it made a difference of about .2 points.

[BRUTAL64]

If going to a thicker gasket to drop CR, the only way to maintain quench (assuming I even have vaguely correct quench as it is), would be to change pistons right? If not, you need to elaborate.

If you pull the heads, some chamber work---a little cutting here and a little grinding there and with a little smoothing of the cast Iron chambers ......... we could get a 1/2 point drop easy. With anything close to a 11cr--- quench is important. :judge:


Don't forget we would have the piston tops to work on also.

[enkeivette]

I'm willing to bet the original compression happy owner of this LS went with the thinnest HG he could find and you might not even have enough quench. Which could also cause pinging.

[Vettezuki]

I'm willing to bet the original compression happy owner of this LS went with the thinnest HG he could find and you might not even have enough quench. Which could also cause pinging.

The motor was reassembled and we used stock GM MLS gaskets.

[BRUTAL64]

I'm willing to bet the original compression happy owner of this LS went with the thinnest HG he could find and you might not even have enough quench. Which could also cause pinging.

Not ENOUGH quench would mean the piston would hit the head.:D

[enkeivette]

Not ENOUGH quench would mean the piston would hit the head.:D

Could hit the head.


Bem, how far down are stock LS1 pistons?

[enkeivette]

And is your motor/ HG earlier than 2003?

[Vettezuki]

And is your motor/ HG earlier than 2003?

Yes.

Bem, how far down are stock LS1 pistons?

Don't know. Maybe a question for LS1Tech?

[enkeivette]

With some quick research it looks like you'd have a 3.91x.051 HG. 2003 and later ran a .054 HG so I think we can all agree that .054 would be fine. Cometic makes a .054 x 4.19 HG which should drop your CR .25 points while keeping your quench the same as 03+ LS engines.

But this is just rough math without knowing a lot. You really should get all of the specs before you take anything apart. I'm assuming the pistons are flush with the deck, otherwise the quench would be more than .054 stock. Which wouldn't surprise me. I'll bet GM thinks about it less than we do.

[Damian]

Looks pretty good on the dyno. :huh:

I honestly think your colder plugs will help out quite a bit. Looking at the dyno sheet, I doubt quench is really a problem. You pulled out your spark plugs and they looked like crap. I wouldnt touch anything until you put the new plugs in and drive around the block.

I would even try and richen it up a bit as well.

[Vettezuki]

The plugs I got Autolite 5144 are very slightly longer than the plugs I had. The 5144 are supposed to be the colder version of the 5245, which is defined as the stock replacement for my plugs. Should I be concerned about this .01 or so extra length?

[Damian]

I doubt it. You looking almost in the realm of the difference in plug gaps.

[enkeivette]

I doubt your plugs are that close, but crank it to TDC stick your pinky in there and see if there's reason for concern.

[enkeivette]

Word on the street is that stock pistons come out of the block a bit. So you might be able to go bigger than .054. And obviously drop more than .25 points.

[94cobra69ss396]

If going to a thicker gasket to drop CR, the only way to maintain quench (assuming I even have vaguely correct quench as it is), would be to change pistons right? If not, you need to elaborate.

Guys, here's a picture of the quench area that I outlined and have an arrow pointing to. It is where the flat area of the piston meets with the flat area of the head. It can only be changed by using a thicker/thinner HG or by resurfacing the block so that the piston is not as far down in the hole.

http://www.motorgen.com/pic/data/500/Quench.jpg

I'm just starting to assemble the 355 for our Camaro and need to order bearings and head gaskets so I measured to see how far down the piston is. On our new block the piston is .029 down so I'm going to go with the thinnest gasket I can find to try and get the quench as close to .050 as possible. We are using a forged piston with a long skirt and a tight piston to wall clearance so we could go tighter than .050.

[BRUTAL64]

I'll bet GM thinks about it less than we do.

Bet they don't. Why do you think they came up with a FAST BURN chamber?


Well, actually, Smoky designed that chamber in the Sixites.:sm_up_there:

[BRUTAL64]

Guys, here's a picture of the quench area that I outlined and have an arrow pointing to. It is where the flat area of the piston meets with the flat area of the head. It can only be changed by using a thicker/thinner HG or by resurfacing the block so that the piston is not as far down in the hole.

http://www.motorgen.com/pic/data/500/Quench.jpg

I'm just starting to assemble the 355 for our Camaro and need to order bearings and head gaskets so I measured to see how far down the piston is. On our new block the piston is .029 down so I'm going to go with the thinnest gasket I can find to try and get the quench as close to .050 as possible. We are using a forged piston with a long skirt and a tight piston to wall clearance so we could go tighter than .050.

Good illustration. I use a .032 copper head gasket.:drink:

[94cobra69ss396]

Good illustration. I use a .032 copper head gasket.:drink:

I found a .021 one but it says the block must be O-ringed. I'm still looking.

[enkeivette]

Ben, you can also retard the cam 4 degrees, which would bleed off compression and lower your dynamic compression ratio. Then just rock it back when it's time to smog if you would even need to.

And for fun you could even rock it forward 8 degrees (4 degrees advanced) for the track, fill up with Torco and see if you run faster. Cornfed did this if I remember correctly.

[enkeivette]

http://www.motorgen.com/pic/data/500/Quench.jpg

Black arrows show how you can increase HG bore, decreasing CR, without changing quench.

http://i34.tinypic.com/309ps8w.jpg