Effects of Dropping Compression on HP

[Vettezuki]

I'm just north of 11:1. I need roughly 93 octane to be safe (especially in the hotter/crappier gas summer).

My cam is moderate at 224/224 LSA 114, lift .566 AIR.

If I use a cometic gasket to drop CR .5-1 full point (I think that's the max possible) and all other things being equal, how much power could I expect to lose?

[94cobra69ss396]

I'm just north of 11:1. I need roughly 93 octane to be safe (especially in the hotter/crappier gas summer).

My cam is moderate at 224/224 LSA 114, lift .566 AIR.

If I use a cometic gasket to drop CR .5-1 full point (I think that's the max possible) and all other things being equal, how much power could I expect to lose?

Don't, you may end up making it detonate more. Do you know what your current quench is?

[Vettezuki]

Don't, you may end up making it detonate more. Do you know what your current quench is?

Nope. And why would dropping CR make it ping/detonate? I sorta remember what quench is, but I thought the upshot was that it's a detail, nice to dial in perfect, but not a mega deal breaker.

More CR means more heat, cuz that's what happens when gases get compressed. Less compression means less heat. :huh:

Ideally I want two things.
- maintain power as much as possible (all else being equal)
- get to a pump gas only situation


Other things I'm thinking of doing will and/or may not effect the situation.
- 160 T-stat. (I'm running stock which I *think* is 190.)
- Shorties (certainly retain less heat against the heads that the cast OE manifolds)
- Hi flowing cats -> hopefully less back pressure, better scavenging, less heat in combustion chamber ???
- If I take off the heads I have sodium filled vales I could use.

[enkeivette]

Ron is right, you may end up detonating more. BUT, as I remember from that last quench thread we started for you, you may be able to go thicker and still stay within the .055, which is the LS1 stock GM spec if I remember correctly. So you'd be fine.

The way to do it is to increase the bore of the HG as much as possible while only increasing the thickness 10 or 15/1000ths. That way you keep decent quench.

If I remember correctly you're WOT AFR was around 14:1 wasn't it? 12:1 would allow a lower octane too. It would run cooler. You can also try colder plugs.



As far as the hp goes, I don't know. I can e-mail you a desktop dyno program if you want to play around.

[big_G]

That much compression could support a bigger cam, IMO. Crunch the DCR numbers and see if will get you there. A larger lobe profile will reduce the DCR and more than likely fend off pinging/detonation.

[Vettezuki]

Here's (http://motorgen.com/forum/showthread.php?t=8771&highlight=Quench) the thread on quench for reference. I remember now. I have no idea what my current quench is. It should be OE. I'm using standard thickness HGs (AIR) and the internals are stock. The higher CR is from milled heads.

enkei, I am running colder copper plugs and that seems to have made some difference. The colder stat and shorties should help quite a bit too.

Big_G. My cam is the biggest I can get away with in CA for my engine combo. I would like to have run a slightly larger cam, but that would almost certainly push me out of bounds for the sniffer.

[enkeivette]

Here's (http://motorgen.com/forum/showthread.php?t=8771&highlight=Quench) the thread on quench for reference. I remember now. I have no idea what my current quench is. It should be OE. I'm using standard thickness HGs (AIR) and the internals are stock. The higher CR is from milled heads.

enkei, I am running colder copper plugs and that seems to have made some difference. The colder stat and shorties should help quite a bit too.

Big_G. My cam is the biggest I can get away with in CA for my engine combo. I would like to have run a slightly larger cam, but that would almost certainly push me out of bounds for the sniffer.

Swap out some 1.7s every two years. And order those HGs with the huge bore. I prob posted a link for them somewhere.

There's only one real way to find out if it will make enough of a difference.

[Vettezuki]

Swap out some 1.7s every two years. And order those HGs with the huge bore. I prob posted a link for them somewhere.

There's only one real way to find out if it will make enough of a difference.

I'm 99% sure stock rocker ratio is 1.7. Why change every two years?

[94cobra69ss396]

I'm 99% sure stock rocker ratio is 1.7. Why change every two years?

If it won't pass tail pipe.

[enkeivette]

I'm 99% sure stock rocker ratio is 1.7. Why change every two years?

Like you were 99% sure about port frequency and smogging an LS1 in an RX7? Hahahahaha. JK.

I guess they are 1.7ish, sort of. You can go to a 1.8 then, you get my point. Looks like Crane 1.7s are effectively 1.8.
http://www.chevyhiperformance.com/techarticles/14148_0506_chevy_ls1_gold_race_rocker_arms/index.html

[Vettezuki]

Like you were 99% sure about port frequency

I was wrong.

and smogging an LS1 in an RX7?

I'm right. It's not so much the "law" as how the guidelines are typically interpreted. Punk. :p

I guess they are 1.7ish, sort of. You can go to a 1.8 then, you get my point. Looks like Crane 1.7s are effectively 1.8.
http://www.chevyhiperformance.com/techarticles/14148_0506_chevy_ls1_gold_race_rocker_arms/index.html

Oky doky.

[enkeivette]

I think you need to quit crying about your high compression, sell those heads, buy some AFRs and drop the CR down to 9:1, and install a CARB legal Procharger.

Then you will own this forum, in more ways than one.

[Vettezuki]

I think you need to quit crying about your high compression, sell those heads, buy some AFRs and drop the CR down to 9:1, and install a CARB legal Procharger.

Then you will own this forum, in more ways than one.

I've thought about it . . . It's just money. I've got some but it goes to business first, Snake 2nd, the Vette about last and there isn't enough to stretch that far now. I've also thought about selling the Vette and just focus on biz for a while and come back to hobby stuff later. :huh: The market is crap though and wouldn't bring much of a price. Fortunately I'm not desperate so I don't have to move anything. Decisions decisions.

[jsup]

Like you were 99% sure about port frequency and smogging an LS1 in an RX7? Hahahahaha. JK.

I guess they are 1.7ish, sort of. You can go to a 1.8 then, you get my point. Looks like Crane 1.7s are effectively 1.8.
http://www.chevyhiperformance.com/techarticles/14148_0506_chevy_ls1_gold_race_rocker_arms/index.html


I'm not a fan of that publication as I don't trust their testing.

[jsup]

I think you need to quit crying about your high compression, sell those heads, buy some AFRs and drop the CR down to 9:1, and install a CARB legal Procharger.

Then you will own this forum, in more ways than one.

See above, I also don't trust AFR and their big claims. All I hear from them is "imagine this" and "what if" that...... no hard evidence unless they control the pre determined outcome.

Look at Profiler heads, at least they were developed by a professional.

OR Dart heads. I spent a few days with the CEO of Dart not too long ago, he took me on a personal tour of all their factories and such. I think they are a great product.

Additionally, I am involved with running probably the biggest head test ever done, and the most fair, and I know the demands made by companies. Let's just say Dart and Profiler gave heads unconditionally. Others had all kinds of stipulations......

[Vettezuki]

See above, I also don't trust AFR and their big claims. All I hear from them is "imagine this" and "what if" that...... no hard evidence unless they control the pre determined outcome.

Look at Profiler heads, at least they were developed by a professional.

OR Dart heads. I spent a few days with the CEO of Dart not too long ago, he took me on a personal tour of all their factories and such. I think they are a great product.

Additionally, I am involved with running probably the biggest head test ever done, and the most fair, and I know the demands made by companies. Let's just say Dart and Profiler gave heads unconditionally. Others had all kinds of stipulations......

Here in the People's Republic everything visible that's aftermarket has at have an E.O. No. (CARB cert.) I don't know if any of those heads are, though I think AFRs are. Heck, I'm running ported and milled truck heads that I had stamped with the correct casting numbers just in case any ref/smogger go nosey.

[jsup]

Here in the People's Republic everything visible that's aftermarket has at have an E.O. No. (CARB cert.) I don't know if any of those heads are, though I think AFRs are.

Lots of indefinates there! :D Should find out, I suspect if one is they all will be and vice versa.

[Vettezuki]

Lots of indefinates there! :D Should find out, I suspect if one is they all will be and vice versa.

A quick look indicates Profiler and Dart are not CARB legal, TrickFlow and AFR are.

[jsup]

Get the TFS.

[enkeivette]

I've heard only good things about Trick Flow. The AFRs that came out after mine did have some valve issues, but that was for a 1st gen SBC. I have no idea about their LS stuff.

[BRUTAL64]

Quench is the issue on a NA motor. I think some chamber work on your current heads would help greatly.

BTW- a one point drop in CR is about (give or take) 25 to 35 hp.