Ideal e85 compression
Id say 9.5 as it retains good low speed response but does not limit you when you start running higher boost levels. Even E85 can only support so much. Try running 11 to 1 and 20 pounds of boost and its not going to be easy.
The last one I tuned that was approx 11:1 compression sure seemed like it was giving up early with how much timing it would take once it got up around 13-14 psi. Even with E85 I still like to see the static compression ratio kept in check around 10:1 max. You give up so much headroom as far as the effective compression ratio goes when you up the static compression ratio by a point or two it's crazy. Considering most turbos are more efficient up at the higher pressure ratios it usually pays to keep it a bit lower anyways so you can let the turbo do the work if it's capable. Of course like hellbents10 said, it really depends on the combo and what it's going to be used for.
The combo I am planning is 86 Grand National 5.3 w/ 317 heads stock 99 camaro cam Precision 6765 turbo likely lots of 1/8 mile and if I'm lucky enough to get someone to pass me on visual for smog check light street cruising to car shows and the track. With a cat I figure my combo should pass smog emission wise. Visual is a whole other story. Because I got a new block for only 99 dollars and the heads for 75 I am going to gamble with some speed pro or keith black hypers and some new stock rods w/ arp pro rod bolts.
Last edited by TurbopigB4C; Jun 23, 2011 at 05:21 PM.
On The Tree
Joined: Sep 2014
Posts: 144
Likes: 2
Even though this thread is dated, I have to say that when calculating ECR and fuel stability you would be very surprised at how far you can go.
If you calculate some of the builds on the stock bottom end reliability sticky thread, you would see some people running
ECRs in excess of 15:1 on pump 93 and even 91 successfully. Way over the recommended 12.5 for premium pump gas.
If you analyze the stats based on
High static compression/high boost vs. Low static compression/high boost. You will find that the former nets way more power all over the curve. And way better part throttle response.
There is a big misconception that more timing is more power. That is WRONG. We as tuners have to find the ideal timing for the set up and on high static comp/high boost it happens to be lower.
Now by no means it doesn't have its drawbacks. Definitely there is a lot less head room and you would have to be on top of the maintenance religiously. But if your up to it it will be seriously intense power.
If you calculate some of the builds on the stock bottom end reliability sticky thread, you would see some people running
ECRs in excess of 15:1 on pump 93 and even 91 successfully. Way over the recommended 12.5 for premium pump gas.
If you analyze the stats based on
High static compression/high boost vs. Low static compression/high boost. You will find that the former nets way more power all over the curve. And way better part throttle response.
There is a big misconception that more timing is more power. That is WRONG. We as tuners have to find the ideal timing for the set up and on high static comp/high boost it happens to be lower.
Now by no means it doesn't have its drawbacks. Definitely there is a lot less head room and you would have to be on top of the maintenance religiously. But if your up to it it will be seriously intense power.
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From: Ohio
Ive had a lot of luck before at 10.5:1 on E85 around 18 lbs of boost. I usually sacrifice either compression or timing. Same amount of compression as a gas build... Run more timing. More compression than a gas build... Run the same timing.
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Depends how much power you want to make and how responsive you want the engine out of boost. Boost is more efficient at making power than a high SCR. Bumping a full point of SCR raises the CC temps a ton and only adds roughly 4% power. 1lb of boost adds less heat than a point of SCR, and makes more power. Dropping a full point of compression also allows much more than 1 additional pound of boost. So it's a "no brainer".
IMO it's pointless to run a ton of SCR. Around 8.75 ish is ideal IMO. Pump gas... race gas... or e85. With methanol you can squeak by with 10:1 or so. Tuning window and error margin gets smaller and smaller the more SCR you add.
My JY 8.6:1 5.3 went 8's at 25lbs or so. I'd love to build a super low CR engine and shut up all the guys whining about low SCR engines being "dogs". I'm working on it now. I have the 08 5.3 block and rods. Looking for the 4.8 crank. Should be around 7.6:1 depending on the heads I use.
IMO it's pointless to run a ton of SCR. Around 8.75 ish is ideal IMO. Pump gas... race gas... or e85. With methanol you can squeak by with 10:1 or so. Tuning window and error margin gets smaller and smaller the more SCR you add.
My JY 8.6:1 5.3 went 8's at 25lbs or so. I'd love to build a super low CR engine and shut up all the guys whining about low SCR engines being "dogs". I'm working on it now. I have the 08 5.3 block and rods. Looking for the 4.8 crank. Should be around 7.6:1 depending on the heads I use.
