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Old 08-15-2019, 07:58 PM   #29
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If E85 was plentiful, pump gas was rarely going to happen, 400whp was the limit forever, the car never saw a track day and long commutes required fuel economy then I would totally say leave the stock compression, but in any other scenario I would say drop compression.

This quote from post 14 says it all:
@Bach415

Right on! Thanks; Yeah E85 is plentiful around me. I dont really see making any changes for more power after this. I might want to do a track day maybe a couple times a year, and weekend autoXs. Its going to be my daily for the spring, summer, fall but my commute is very easy. Only 12 miles, mostly highway... Only thing is i really wanted to be able to drive it cross country out to CA to visit my buddy and do a track day out there with him. But I might just need to buy a trailer and haul it if I want to do that...
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Old 08-15-2019, 08:15 PM   #30
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Quote:
Originally Posted by Irace86.2.0 View Post
His tuner is saying it is a bad idea. You are saying at 400whp is not needed, but he is building the motor so why not? Can you give one reason why he shouldnít? Wouldnít the improved reliability, improvement power on pump gas and overhead for more power in the future more than warrant lowering compression?
His 2nd post clearly stated he is running e85 and occasional 91. So no lowering compression for him would be a step back.
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Old 08-15-2019, 08:36 PM   #31
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@Bach415

Right on! Thanks; Yeah E85 is plentiful around me. I dont really see making any changes for more power after this. I might want to do a track day maybe a couple times a year, and weekend autoXs. Its going to be my daily for the spring, summer, fall but my commute is very easy. Only 12 miles, mostly highway... Only thing is i really wanted to be able to drive it cross country out to CA to visit my buddy and do a track day out there with him. But I might just need to buy a trailer and haul it if I want to do that...
No reason you couldn't drive it to CA, even if you ran out of E85. You could just run a lower boost map.

I would just read that link I posted. Here it is again, but read more about what others said than myself; those who lowered compression:

http://www.ft86club.com/forums/showt...pression+ratio

In the beginning I was in the camp that E85 was enough for 400whp, that it only made sense to drop compression when wanting more power than that, or if someone was going to spend a lot of time on 91 octane, but it seems like if anyone is going to be doing track days, wants more power off E85, more power potential down the road, etc then might as well drop the compression. In fact, several guys with lower compression motors chimed in and their responses confirmed the benefits. You are in the E85 capital of the country, practically, so access isn't an issue, but for reliability, I would consider dropping compression, especially if you will be doing track days.
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Old 08-15-2019, 08:55 PM   #32
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His 2nd post clearly stated he is running e85 and occasional 91. So no lowering compression for him would be a step back.
There might be more turbo lag and less fuel economy and less power off of boost, but if those detriments were 200rpms, 3mpg and 15hp@2k, respectively, then wouldn't the reliability improvement be worth it, especially for track days?
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Old 08-16-2019, 04:21 AM   #33
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Originally Posted by Irace86.2.0 View Post
There might be more turbo lag and less fuel economy and less power off of boost, but if those detriments were 200rpms, 3mpg and 15hp@2k, respectively, then wouldn't the reliability improvement be worth it, especially for track days?
There's a post on here from Delicious somewhere explaining that they opt for customers to use a stock compression or 12:1 compression built block when going FI, because there was no need to lower compression. I have a buddy locally who just built his block through CSG via Bluemoon Performance, and they opted for a 12:1 compression. Both of these companies are regarded as companies that know their stuff, and both chose to use stock-ish compression.

Just sharing some knowledge about what those companies prefer, not trying to tell you you're wrong. Many different ways to make power.
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Old 08-16-2019, 06:19 AM   #34
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Or simply there are more ways to skin a cat, netting same result/output at end.
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Old 08-16-2019, 08:51 AM   #35
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When these cars first came out, it was commonly thought that even 10:1 compression was high compression, and people thought with 12.5:1 that no way this can handle any boost, then people tried it and thought, OK it can handle it but 7psi is the limit, and then they kept testing it and pushing it and its been shown that even 12-13psi is pretty reliable on a stock engine. Many tuners in recent years now have changed their thoughts on needing to lower the CR stating its not really necessary, and often times not recommended.

New tuning methods, the cars ability to monitor so many parameters and give instant feedback, being able to adjust and tune so many parameters, and having both PI and DI, has allowed tuners to safely push these cars closer to the edge, as well as push the edge further out, allowing for safe reliable power with out needing to drop the CR.

400whp on E85 is easy to get with stock CR, I would possibly consider 12:1 for a slight added margin of safety and being able to push the car more in the future if desired. but much lower doesn't seem necessary or worth it on these cars, unless your shooting for some crazy numbers.

Hearing from people who dropped CR stating its worth it or recommended doesn't really say much. I would much prefer hearing from people with built engines and kept stock CR and what their tuner said was the limiting factor for reliable power.
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Old 08-16-2019, 10:50 AM   #36
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I remember 35 years ago doing 10 to 1 on a 351 Windsor in my 73 Bronco. At the time that was a premium gas only engine.
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Old 08-16-2019, 11:25 AM   #37
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Originally Posted by FunnyGopher View Post
There's a post on here from Delicious somewhere explaining that they opt for customers to use a stock compression or 12:1 compression built block when going FI, because there was no need to lower compression. I have a buddy locally who just built his block through CSG via Bluemoon Performance, and they opted for a 12:1 compression. Both of these companies are regarded as companies that know their stuff, and both chose to use stock-ish compression.

Just sharing some knowledge about what those companies prefer, not trying to tell you you're wrong. Many different ways to make power.
^this. It was the dyno for TJ Hunt's car w/ Edelbrock super charger for the delicious tuning one. Long story short, the car made roughly 400 whp but had they had to dial back the power due to the amount of linear boost coming out of the super charger. IIRC eventually TJ Hunt changed over to a turbo kit instead for more power while keeping that same CR.

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When these cars first came out, it was commonly thought that even 10:1 compression was high compression, and people thought with 12.5:1 that no way this can handle any boost, then people tried it and thought, OK it can handle it but 7psi is the limit, and then they kept testing it and pushing it and its been shown that even 12-13psi is pretty reliable on a stock engine. Many tuners in recent years now have changed their thoughts on needing to lower the CR stating its not really necessary, and often times not recommended.

New tuning methods, the cars ability to monitor so many parameters and give instant feedback, being able to adjust and tune so many parameters, and having both PI and DI, has allowed tuners to safely push these cars closer to the edge, as well as push the edge further out, allowing for safe reliable power with out needing to drop the CR.

400whp on E85 is easy to get with stock CR, I would possibly consider 12:1 for a slight added margin of safety and being able to push the car more in the future if desired. but much lower doesn't seem necessary or worth it on these cars, unless your shooting for some crazy numbers.

Hearing from people who dropped CR stating its worth it or recommended doesn't really say much. I would much prefer hearing from people with built engines and kept stock CR and what their tuner said was the limiting factor for reliable power.
I agree with this. Not much people ran the 12.5:1 CR on built motors for our platform but it has been proven that it does work. I would like to see more builds with the standard CR. Pretty sure everyone has seen how TJ Hunt drives his BRZ. He has not blown his motor yet from what I can recall but had snapped a lot of belts off of the supercharger.

Another view on this are the stock motors built by Honda (I know different engine). I have seen even the type-r engines (both B and K series) push around 350-400 whp on stock blocks w/ boost (these are already running 11:1 or 11.5:1 CR iirc from factory) and still driving fine.
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Old 08-16-2019, 01:30 PM   #38
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It would be interesting to see 400whp at 10:1 and at 12.5:1 on the track. Specifically, would the temps be much different and would the cars still be putting down 400whp or would the 12.5:1 be compensating with ignition timing.

We have a few people who have blown built motors too. Curious what their compression ratio was.
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Old 08-16-2019, 03:27 PM   #39
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Maybe @Sportsguy83 can chime in. Didnít he make like 553whp on a stock block or something freaky? Maybe 400whp is nothing, even for the track.
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Old 08-16-2019, 05:39 PM   #40
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Quote:
Originally Posted by Irace86.2.0 View Post
Maybe @Sportsguy83 can chime in. Didnít he make like 553whp on a stock block or something freaky? Maybe 400whp is nothing, even for the track.


552 on stock block, but thatís just a ticking time bomb..... I pushed it on 500 whp map, the 552 map was very rarely used.

If I would have built the FA20, it would have been because I trust the shop that built it and wouldnít ace any worries tracking it at 400 whp...

but I donít know if thereís any track record out there for built cars being used hard on the track at that power level. There has to be, but I personally donít know.
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Old 08-16-2019, 06:00 PM   #41
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552 on stock block.
jeebus!
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Old 08-17-2019, 01:13 PM   #42
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What do you guys think of keeping the comppression at 12.5:1 if I'm only gonna be using 93 octane on boost at around 300-350 whp?
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