Max Compression Ratio for NA LSx Motors on E85?

[Vettezuki]

So, if they make E85 more readily available in CA, I'm tempted to make my lil' ole 346 a forged 383, bump the cam one size up and crank up the CR as far as I dare.

E85 seems to vary in Octane rating between 100-105. It also has wonderful cooling effects being 85% alcohol and all.

So, who can calculate a highest safe potential CR. I was thinking at least 13:1, but maybe 14:1. :huh:

[94cobra69ss396]

So, if they make E85 more readily available in CA, I'm tempted to make my lil' ole 346 a forged 383, bump the cam one size up and crank up the CR as far as I dare.

E85 seems to vary in Octane rating between 100-105. It also has wonderful cooling effects being 85% alcohol and all.

So, who can calculate a highest safe potential CR. I was thinking at least 13:1, but maybe 14:1. :huh:

You won't be able to predict the exact compression ratio that you can use. There are a lot of other things to consider such as cam specs, combustion chamber design, timing, etc. I can tell you that with 100 octane race fuel I’m able to run 12.25:1 compression on the Chevelle with 40° total timing with a cam that has a .623 lift, 242° @ .050 on a 110° lobe separation with an aluminum head without detonation. I also know that I’m right at the edge from detonating because I’ve tried mixing pump gas and race fuel for less octane and the car detonated. If I were to run E85 I think I could get away with a little more compression (12.5:1 or so) with a 112 lobe separation and still not detonate. However, I do think I would be right at the edge but that’s just my opinion I do not know for sure.

I'm not sure what design the heads you have are but I've heard that the LS6 combustion chamber design is great so you might be able to get away with 13:1 if your heads have the same design.

[Vettezuki]

Is there any reason port injection vs. carburation would make a difference?

[94cobra69ss396]

Is there any reason port injection vs. carburation would make a difference?

I don't think it would make a difference as long as both were properly tuned.

[Vettezuki]

What's the most CR those Cometic gaskets can drop? Maybe something like targeting 13.5:1 as a start place, then dropping if necessary would be a good strategy.

[94cobra69ss396]

I ran these on Comp Cams Camquest dyno program. I used the same setting and just changed the compression from 12:1 to 13:1. The difference was about 15 more hp and 10 more tq. The average differences were only about 4hp and 4 tq. I'm not sure it would be worth adding the extra compression unless you were going to be installing a huge cam and porting the crap out of the intake and heads. Here's the links to the graphs.

12:1 (http://www.motorgen.com/pic/data/500/12_to_1.JPG)
13:1 (http://www.motorgen.com/pic/data/500/13_to_1.JPG)

[Vettezuki]

I ran these on Comp Cams Camquest dyno program. I used the same setting and just changed the compression from 12:1 to 13:1. The difference was about 15 more hp and 10 more tq. The average differences were only about 4hp and 4 tq. I'm not sure it would be worth adding the extra compression unless you were going to be installing a huge cam and porting the crap out of the intake and heads. Here's the links to the graphs.

12:1 (http://www.motorgen.com/pic/data/500/12_to_1.JPG)
13:1 (http://www.motorgen.com/pic/data/500/13_to_1.JPG)

Does it allow you to select E85 for fuel and dial-in various ignition curves? But I get the point. Somehow I would have expected the toruqe/hp to be more different between 12:1 and 13:1 all other things being equal, though it was just a hunch.

[94cobra69ss396]

Does it allow you to select E85 for fuel and dial-in various ignition curves? But I get the point. Somehow I would have expected the toruqe/hp to be more different between 12:1 and 13:1 all other things being equal, though it was just a hunch.

It doesn't. There is such a thing as having too much compression.

[Vettezuki]

It doesn't. There is such a thing as having too much compression.

Please to explain. I know some of the NA drag boys move over from Gas (110 - 117) to pure alcohol at around 14:1, before the take it up any higher.

[94cobra69ss396]

Please to explain. I know some of the NA drag boys move over from Gas (110 - 117) to pure alcohol at around 14:1, before the take it up any higher.

Just like head selection, cam selection, etc you need to balance the compression with the rest of the components. Say you have a stock 350 with a stock cam, heads and exhaust manifolds it doesn't make any since to run 12:1 compression. It will probably run better on 9-9.5:1 and wouldn't need race fuel to keep from detonating.

[Vettezuki]

I'm having a harder time wrapping my head around the relationship of compression to the other parameters. I totally get the relationship of intake to head flow, cam and exhaust and that it doesn't make any sense to have huge intake and restricted exhaust for example. That's all related to air flow. But compression (except for the effects on cylinder filling and scavenging I guess) seems somehow independent of the air flow issues of intake through exhaust. :huh: Basically I was under the impression all things equal in an engine that is breathing adequately, more compression equals more cylinder pressure equals more torque equals more power. Where am I going wrong? What physically causes the diminishing return?

[94cobra69ss396]

I'm having a harder time wrapping my head around the relationship of compression to the other parameters. I totally get the relationship of intake to head flow, cam and exhaust and that it doesn't make any sense to have huge intake and restricted exhaust for example. That's all related to air flow. But compression (except for the effects on cylinder filling and scavenging I guess) seems somehow independent of the air flow issues of intake through exhaust. :huh: Basically I was under the impression all things equal in an engine that is breathing adequately, more compression equals more cylinder pressure equals more torque equals more power. Where am I going wrong? What physically causes the diminishing return?

You are correct. I'm not saying you won't gain hp and tq by adding compression. As you know cam timing plays part in not only airflow but also cranking compression. Because of the low static compression ratios that are used manufactuers use cams with wider lobe seperations (115-120) to build cylinder pressures at lower rpms. Now if you leave that same cam in the engine but add a lot more compression cylinder pressures get too high and you end up with an engine that will detonate at low rpms.

What I'm trying to say is that there gets to be a point where adding more compression just isn't worth it. I think that if you are going to keep everyting the same as you have now and just add more compression I would stick with around 12 - 12.5:1 and no more on E85.

[Vettezuki]

You are correct. I'm not saying you won't gain hp and tq by adding compression. As you know cam timing plays part in not only airflow but also cranking compression. Because of the low static compression ratios that are used manufactuers use cams with wider lobe seperations (115-120) to build cylinder pressures at lower rpms. Now if you leave that same cam in the engine but add a lot more compression cylinder pressures get too high and you end up with an engine that will detonate at low rpms.

What I'm trying to say is that there gets to be a point where adding more compression just isn't worth it. I think that if you are going to keep everyting the same as you have now and just add more compression I would stick with around 12 - 12.5:1 and no more on E85.

My cam is 224/224 .566 lift, 114LSA. This is about the limit of cam size and maintaining emissions compliance, but maybe a custom grind just a tiny bit bigger could fly. :huh: Of course I don't know what effects E85 (technically an illegal swap) would have on measured emissions. Carbons should be lower but NOX probably higher as I understand it. Anyway, for sake of argument let's say the emissions is not a problem. What about compression for my cam or a tiny bit bigger?

Thanks for pointing out the cam timing cranking pressure issue. I didn't plug that into the equation.

[BADDASSC6]

Is there any reason port injection vs. carburation would make a difference?

Port injection is better. The injectors allow for more accurate and even deliver of fuel to each individual cylinder. Carburators will allow you to set your air/fuel ratio, but not for the entire rev band.

I met a guy at the 1/8mile drag at barona that LOVED E85! He stated that he didn't pick that much up top end, but was able to make a bunch of mid range power by advancing the timing.

[Vettezuki]

I met a guy at the 1/8mile drag at barona that LOVED E85! He stated that he didn't pick that much up top end, but was able to make a bunch of mid range power by advancing the timing.

That's what it looks like on the C6R too. The difference in torque and power under the curve for the E85 vs. Gas setup is shocking. But what all they're doing in addition to the fuel and obviously timing, I don't know. :huh:

[TimAT]

FWIW: Shafiroff has a SB and a BB that are setup for E-85. Link to the BB:

http://www.shafiroff.com/sportsman/540_825_e85.asp

Looks like he's running that one at 14:1. I just did a quick look maybe his cam specs are there too.

[Vettezuki]

FWIW: Shafiroff has a SB and a BB that are setup for E-85. Link to the BB:

http://www.shafiroff.com/sportsman/540_825_e85.asp

Looks like he's running that one at 14:1. I just did a quick look maybe his cam specs are there too.

Thanks Tim. :thumbs_up:

[94cobra69ss396]

Nice find. However, it looks like he is using 13:1. Below are the specs for the 540. This also isn't your run of the mill street engine that he just added compression to and is running on E85. It has a custom solid roller cam, Dart Pro 1 heads and is making 825hp at 6800rpms. Take a look at his 540 pump gas motor that makes 695hp at 6300. It uses 10.5 compression and a smaller cam.

Dart Big "M" 9.8" Low Deck 4 Bolt Race Prepped Block w/Splayed Caps
Eagle 4340 4.250" Stroke Steel Crank
Eagle 4340 6.385" H-Beam 3D Steel Rods
Clevite 77 "H" Series Main & Rod Bearings
JE/SRP 13.1 CR Forged Aluminum Pistons
Speed Pro Plasma Moly Ring Set
SSRE Custom E85 Grind Steel Billet Roller Cam
Comp Cams Heavy Duty Solid Roller Lifters
Cloyes Billet True Roller Timing Set w/Torrington Bearing
Dart "New Design" Pro 1 345 Aluminum Heads
Manley Nextek® 1.640" Roller Springs w/Titanium Retainers & 10° Locks
ARP Head Stud Kit w/Parallel Ground Washers
Comp Cams Ultra-Gold 1.7 Aluminum Roller Rockers
FelPro HP Head Gaskets w/Pre-Flattened Steel Wire
Merlin X "New Design" Dominator Intake Manifold
SSRE/Moroso Custom Stroker Oil Pan w/Windage Tray
Moroso Race Prepped Pump w/Tig Welded HD Pickup
GM Performance Chrome Front Cover w/Billet Pointer
SFI Approved Harmonic Balancer
Complete Assembly Internally Balanced


Ben, I personally don't think it is worth the trouble to add compression and run your engine on E85. I also don't think it will pass a sniffer test with 13:1 compression. If you want to experiment with E85 do it on RxSnake and don't ruin your reliable Vette.

[BADDASSC6]

^^^^^Concur!

[Vettezuki]

True nuff.

The truth is that I think I have a fair bit of power sitting on the table as it is in the form of tune and headers. I have a very conservative tune for pump gas (something like 18 degrees total). I'm still running stock manifolds. With this I'm getting 391 WHP.

The same basic engine (exactly the same long block) was putting down 432 in a C5 vs. my C3. The difference is that he had an aggressive tune and headers. But he also had an LS1 intake, not an LS6 like I have. Bottom line, I *should* be able to hit something like 420+ with some decent headers and a better tune with everything I have right now. While this wouldn't be a mountain of extra power, a lot of it would fall under the curve and be noticeable.

I just have a soft spot for kick ass NA motors.

[jsup]

True nuff.

The truth is that I think I have a fair bit of power sitting on the table as it is in the form of tune and headers. I have a very conservative tune for pump gas (something like 18 degrees total). I'm still running stock manifolds. With this I'm getting 391 WHP.

The same basic engine (exactly the same long block) was putting down 432 in a C5 vs. my C3. The difference is that he had an aggressive tune and headers. But he also had an LS1 intake, not an LS6 like I have. Bottom line, I *should* be able to hit something like 420+ with some decent headers and a better tune with everything I have right now. While this wouldn't be a mountain of extra power, a lot of it would fall under the curve and be noticeable.

I just have a soft spot for kick ass NA motors.

Don't get sucked into the "under the curve" stuff. IMO it's marketing crap.

[Vettezuki]

Don't get sucked into the "under the curve" stuff. IMO it's marketing crap.

Well, what do you mean? If the torque reaches a higher level lower in the RPM band, that means more power sooner. I would think this is desirable compared to the opposite, especially in a street driven car, and super especially if it's not at the expense of peak torque up in the rev range (i.e., peak HP). :huh:

[BRUTAL64]

:popcorn::popcorn:

[Damian]

I know no one has posted in here for a month or so, but I love E85. I have one a couple blocks away from my work (Santa Monica), but none around my house. When I was running it, I was up to +44 timing advance at WOT with 12.1 a/f ratio with NO knock with 9.5-1 compression ratio. i could have easily gone more timing, but I was still testing on E85. I might go back to it, I will if I do finish my turbo build.

I wouldnt really say its fully worth the changes and tune to run E85 on a N/A engine, but FI will make you smile like no other.