Coleslaw

Probably going to catch to flak for this but I just wanted to come on here and ask for opinions on having higher compression while running boost. I have an LS2 408 stroker with 11.1 c/r and was told I would only be able to run maybe 6-7 lbs safely on 93 pump gas. Was just wondering what everyone thinks of that? Is low compression and boost a thing of the past? or is it possible to run a decent amount of boost on 11.1 with a good tune? I know it's not incredibly high but im just curious. Really want a blower but want to know what parameters are acceptable.

Detoxx03

iTrader: (14)

On 93 it’s iffy. Personally I run the stock 10.7 cr on my LS3 and have been for 8 years now with boost. Half of those years I’ve been running E85. My next build will be in the 11’s but I’ll be on corn.

Mavn

iTrader: (3)

E85 you can run whatever . On 93 . I wouldn't even try it

jordoza

On 93 id keep the boost low like they advised you. On e85 i would just run it and have great off boost response.

simman22

iTrader: (25)

I am looking for similar information on a thread I created but more specifically on the dynamic compression side of things. I have ~11:1 compression and a decent N/A cam and I’ve been running at 7lbs for a while on 91 octane in Colorado (elevation helps a little). I’m looking to go up around 12-15 with meth and potentially swapping to e85 so I can keep you updated on how that goes. I do all of my own tuning and use the track and plugs to really dial it in so make sure your tune is on point and don’t try to get greedy with timing.

gametech

iTrader: (1)

You say you want a blower, but do not say if you mean a centrifugal or a PD style. A centrifugal can run higher peak boost numbers on higher compression, because those peak boost numbers happen after peak torque. Try the same boost with a twin screw, and you will have full boost during your torque peak, which would invite catastrophe. Of course if this was a high stalled auto, you would never load the engine until over peak torque rpm anyway. I hope this gives a tiny insight into the variables involved with your question.

ddnspider

iTrader: (26)

I'm 10.5:1 on 93 only and plan on at least 10 psi if not more. All about AFR and timing.

Coleslaw

Yeah I want a procharger and yeah it's a stalled auto. It made over 500whp n/a so I wanted to run some boost to up the numbers. The only way to run big numbers would be to swap pistons out and drop compression so I was hoping to get as much as I could while running meth too.

Coleslaw

Right on, let me know lol. And yeah 15 lbs would probably give me a huge bump in power with my setup. Idk if I could run that much tho because I'd have to have it tuned with Max boost without meth just in case anything went wrong with the meth kit. And then add the meth injection on top of it just to cool the intake temps.

simman22

iTrader: (25)

Will do, I have cast pistons until it lets go so it should be a good amount before yours. I have a Paxton centrifugal as well so it helps the power come in a little softer and peaks way after peak torque, like he said. For normal street duty and when I don’t intend on racing, I keep the larger pulley and restrictor (ECS way of controlling boost) to keep it at 7 psi so you could probably do something similar if a pulley change is easy. Even though it’s been done a ton of times, I wouldn’t recommend trying to do that much (over the stock 6-7) without meth injection because one bad tank of gas or excessive iat’s could be a bad time! Timing will be different at the various boost levels so think about that if you don’t tune yourself.

hillshooter

I have a 416 ls3 and last year it was around 11.5:1 and I had tons of problems. I could run 16-17 Psi but nothing higher, I tried every fuel and eventually was running e85. I would still take out spark plug tips. it was just a cluster and at the end of the season I thought it was fixed and turned it up to around 21 pounds and lifted a head.

I took the motor down last winter and put a -15CC wiseco piston and I cant tell you how much better it runs all the way around. I get way more usuable RPM, I have taken out a single plug strap, I dont get the deto like I used too. its just much much better all the way around. In fact ECT went down as well over all.

right now at just over 10:1 I am running 24 pounds of boost and am about to start sneaking it up.

JoeNova

10:1 on 93 and washer fluid, topping out a 3 bar map sensor on stock bottom end 5.3 with a billet S475. 12 degrees of timing. No MBT timing curve.

I'm my opinion, it was the perfect street setup.


I've ran 13:1 on pump E85 and high boost.

Coleslaw

Would love to run 85 but there are hardly any stations anywhere in my state let alone near me...

Coleslaw

What kind of FI ? Turbo, centrifugal ect.... And so you're saying that 15 pounds is possible with my setup? It's all forged built obviously I just don't want detonation issues. And obviously I can't run e85 like I said to the other guy. So im stuck with 93...

hillshooter

I dont think you could run 15 pounds on 93, you would need 110 or E. Mine is a twin turbo.

BCNUL8R

iTrader: (2)

I like Procharger, but with only 6-7 lbs peak I don't think it's worth the cost. If it was me and ethanol isn't an option I'd try 20% methanol in the fuel tank. I've never actually done this, but I've been researching and it looks like a good option in your case. What I have done before I switched to ethanol is to run pump gas with xylene/toluene to bump me up to 97 octane and that did work well. When mixing gas like that I've always combined the two fuels into a jug then poured into tank. This along with a return style fuel system seems to work very well with no noticeable issues with mixing. I've experimented with some other fuel blends as well and plan to experiment with water/meth injection as well soon just to learn what I want to do with fuel long term. The 20% methanol mix sounds like something worth trying in your case then run 10-12 psi. to make the Procharger worth the cost.

Kfxguy

iTrader: (1)

I have 10.5:1 compression
12-13psi
93 pump
no meth yet
13 Degrees timing before and after tq peak. at 4800 I have it at 12 degrees, 5200 i have it at 11 degrees then goes back to 13 degress at 5400. the reason is my tq peaks at 5200, my shift drop is at 5200 and the boost goes up 1 psi when i shift for a couple hundred rpm. I have all those things working against me so i have to limit the timing in that area. I get no spark retard doing that, and if I add 1 degree I get a .5 degree pulled. I shoot for zero being pulled and I didnt turn the sensitivity down much at all.

when I finally get around to installing my meth injection, I plan on spraying the iat sensor directly and set whatever temp it goes to, to have a degree or more of timing. No spray, no added timing.

gametech

iTrader: (1)

Why such a low shift rpm? I never even bent a stock pushrod until 6800rpm.

Kfxguy

iTrader: (1)

I don’t shift at 5200. I shift at 6500-6800 and the rpm drops to about 5200.

gametech

iTrader: (1)

Understood. When you mentioned going back to 13* timing at 5400rpm, but then did not mention anything higher in the rpm range, I thought you were short shifting it. I generally ramp my timing back up gradually all the way from a low at peak torque to whatever runs best at peak rpm.