Hey guys, just wanted to see what people's experiences are with higher compression street builds. I've been having fun with the stock block 20G setup for quite some time and now the engine is starting to show signs of wear, did a leak down and cylinder 3 is pretty hurt. I now have to pull everything apart and figured if I'm doing it I might as well make everything solid, I was just held up by whether or not I'm going to do 9:1 or a 10:1 setup. Coming from the Honda world it's a lot different and I have seen and noticed that most either stay near stock comp or just a small bump, but I like the idea of not feeding the motor a ton of boost to make power. This is just a streetcar, it may see a track night here or there but nothing to is too pressing, so I figured I could venture out in that world. The turbo setup would be a Tubular manifold with a T3 BL5858 looking to make somewhere around 450whp on 93oct, could potentially do E85 (closest station is a 45 min drive).

 

Pump gas = 9:1 compression, no higher.

 

The 4G63 is thirsty for boost, feed it all the B. It's what makes it a legend.

 

I’ve spent enough time in the Honda world to think I might know where you’re coming from there. Listen to these guys .
The 4G63 was designed in the mid 80s. It’s been revised and refined over the years but it’s not a K20. It likes all the boost and not all the timing/CR.

 

My 2.2 is 10:5.1 or even a little higher, running E85. Car drives fantastic out of boost, the high compression 2.2 is a win win.

 

That doesn't work with pump gas. Read the whole original post.

 

Yeah we don't have the VE numbers that Honda VTEC motors do, stay 9.0:1 or below if you aren't going to run E85 only. I would much rather a slightly lazier car off boost than always worrying whether the engine is going to detonate - it's entirely possible that you wouldn't even reach 20 psi without knock, so peak numbers wouldn't be much different. The 4G63 makes its numbers with brute force, so don't be afraid of a bit of boost.

 

1 point of compression is ~3% gain. But 10:1 will not run the boost 9:1 will on pump gas and you will lose power.

 

Raising static compression, affects dynamic compression, which is what it's all about. Raising dynamic compression is like adding timing. Depending on your engine's V.E and fuel you will be using, 1 point of static compression can add gains from 3-4% up to 10%. Of course you ain't going to gain 10% on 93 oct no matter how good your setup's V.E is, the calorific value ain't there, plus it will not allow you to run the amount of timing needed to reach the overall gains you wish from your setup. On 93 oct , I would personally keep the setup at stock static compression, and run as much timing and boost it can give me.

If you are worrying about off boost performance and about the on boost area but without being at full boost rpm point, you can still enhance your setup's performance through other ways, lowering the boost threshold and reducing spool time of the turbo as much as possible through the use of the right exhaust - intake - cooling parts(I/C and piping) dialing in your cams to a combo which favors more low and midrange load,but loses the least amount possible of hp up top, also through the right boost strategy and through proper mapping of course.








Marios

 

My car made 550 on pump 93 full flex fuel tune, obviously wouldn’t want to push it past that. A good tuner is the key to success, high compression isn’t the enemy.

 

Good luck with that.

 

most cars that are naturally aspirated have trouble running on pump 93 on 10.5-1 cr let alone a boosted car , though there are some boosted vehicles from bmw with 10.5 to 11 to 1 cr , but those are Direct injection. That’s not going to work to good on a evo unless you keep your boost down , better off going 9-1 cr for pump gas.

 

just my opinion... if you have a 10.5 : 1 motor... it needs to get nothing but quality E85 or race gas.
No pump gasoline whatsoever

 

OP is coming from the Honda world. My old-school B-series was 11:1, if I remember right. It ran all day on 91. We would then feed them about 7psi, or so of boost and up to 15psi with water/meth. WHP was only 300 on pump and 350ish on water/meth, but it was RIGHT now power. God, that car was so fun to drive.
Anyway.. Using all that as a point of reference, he also needs to understand that Honda had it "just right" and a 4g63 just can't pull off the same "magic".
I wish it could... I've often wished for a high-comp 4g63 to run on flex fuel

 

Imagine running an Evo at 7psi and being wildly disappointed the entire ****ing time.

It's simply not comparable to your honda setups. I'm sure even at 7psi it was a decently larger turbo than an Evo9 turbo as well.