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Procharger boost 91 octane

Old 11-29-2015, 08:09 PM
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Default Procharger boost 91 octane

How much boost can I run on 91 octane ?

Engine is 8.6:1 compression
with Aluminum heads and an M4 Procharger..


THANKS !

Doug
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Old 11-29-2015, 08:17 PM
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Cam specs? Intercooler?
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Old 11-29-2015, 08:30 PM
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Originally Posted by MILD THUNDER View Post
Cam specs? Intercooler?
AW504 Intercooler..



Just found a dynamic compression calculator.. put in 8 psi & the dynamic is 11.6:1, but what is the max for 91 octane ?


Your engine summary is as follows: Bore 4.560 inches, stroke 4.25 inches, rod c-c length 6.535 inches, with a static compression ratio of 8.6 :1. Your camshaft specifications call for an inlet valve closing of 49.7 degrees ABDC (after bottom dead center).

Your chamber volume is 149.66 cc's. With this camshaft your dynamic, or effective stroke is 3.70 inches. Your dynamic compression ratio is 7.52 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 146.67 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 8 PSI is 11.61 :1.

Last edited by Boatally Insane; 11-29-2015 at 08:37 PM.
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Old 11-29-2015, 08:38 PM
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I know articfriends smitty, ran something like 12lbs on his procharged 540's. Maybe he will chime in.

I'd invest in a good IAT gauge for the dash. Keep on eye on those intake temps....
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Old 11-29-2015, 08:53 PM
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Originally Posted by MILD THUNDER View Post
I know articfriends smitty, ran something like 12lbs on his procharged 540's. Maybe he will chime in.

I'd invest in a good IAT gauge for the dash. Keep on eye on those intake temps....
I can across these quotes from Smitty and Alex Haxby... but that's with 93 octane...
How far would I have to back it down to be 91 octane friendly ?



Originally Posted by Haxbyspeed

It really depends on your combo but I agree, 14ish lbs with conventional Procharger stuff seems to be the max safe level for 93 octane. The MAT spikes quickly because the Procharger starts to produce a lot more heat as the boost comes up. If the intercooler is sized correctly, it will level off. I usually see 135-155 after a few minutes of WOT, which is nothing to worry about. I like mid to high 11's AFR, up to 10-12 lbs, and lower as the boost goes up. On pump gas the prochargers like to be a bit richer then a Whipple to make max power, and MBT is usually lower then a similar Whipple or roots combo too


Originally Posted by articfriends

IF a Prochargerd marine motor has EFI, afr's verified/tuned on water at wot, aluminum heads and compression close to or around 8-1 along with 75-80 MAX degree lake water for innercooler 12-13 lbs is easily reliable, I have ran that kinda boost for quite a while and haven't hurt a motor yet, Smitty
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Old 11-29-2015, 09:31 PM
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On dyno when I made 1115 hp we saw 14 ish psi boost in intake (past) throttle blades, this was on 80% pump 92/93 and 20% 110 octane, I ran medium pulley at 13-14 psi on 92/93 on dyno, in boat the pulley that made 14+ made more like 13 and the pulley that made 13/14 made 12-13 roughly, I always run 93 in boat with that pulley at 8.3/ 8.4-1 compession and never logged any KR on data logger/scanner pro, even on a 5 minute /6300 rpm pull. Cam, chamber design, innercooler efficiancy, under hatch air flow, water temp to innercooler, engine block temp, timing curve, afr, etc will all have factors in how much boost you can safely run and for how long. Stuff needs to be perfect to run max boost for a given octane, off top of my head I would say 8 psi, and possibly 10/11 BUT only way I would run that much is IF you can monitor KR!
the reason I say 92/93 is we went thru quite alot of fuel on dyno, we made several trips to gas station and deliberately bought 92 instead of 93 in last couple of trips, the reason why is I always run 93 BUT wanted to see if we had KR on slightly lower gas to give some safety margin.

Last edited by articfriends; 11-30-2015 at 12:42 AM.
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Old 11-30-2015, 06:59 AM
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I only run 6psi but only on 93, even at a decent cruise you are still in boost for a long period of time...tuning with a 02 in the boat running a must, but I would think 5-6 max w/91 but too many variables here. Why only 91 ?
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Old 11-30-2015, 08:36 AM
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Steve Brule at Westec in CA taught me a long time ago that the best indicator for boost, if you're on the dyno, is to watch the BMEP number. Depending on the fuel you're using there is a max "safe" bmep. I was dynoing a 540 pump gas marine engine with a 1471 and intercooler...we were watching the IAT's because we didn't have a fresh cold water source for the intercooler and had to use dyno water, but he was watching the BMEP's more than anything. I think he said 230-235 was about max for CA 91 octane pump gas. Engine made 1021 @ 6400 (for a small Vdrive hot rod boat) and about 32* timing, right at 10# boost. I know centrifugal blowers are a lot more efficient and should make a little more power than a roots.
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Old 11-30-2015, 08:46 AM
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Originally Posted by ezstriper View Post
I only run 6psi but only on 93, even at a decent cruise you are still in boost for a long period of time...tuning with a 02 in the boat running a must, but I would think 5-6 max w/91 but too many variables here. Why only 91 ?
I'd like it to be safe to top off with 91 if needed on an extended weekend, as 93 isn't available on the water everywhere..

I'll certainly fill it 93 when it's on the trailer..


Doug
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Old 11-30-2015, 08:54 AM
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Originally Posted by horsepower1 View Post
Steve Brule at Westec in CA taught me a long time ago that the best indicator for boost, if you're on the dyno, is to watch the BMEP number. Depending on the fuel you're using there is a max "safe" bmep. I was dynoing a 540 pump gas marine engine with a 1471 and intercooler...we were watching the IAT's because we didn't have a fresh cold water source for the intercooler and had to use dyno water, but he was watching the BMEP's more than anything. I think he said 230-235 was about max for CA 91 octane pump gas. Engine made 1021 @ 6400 (for a small Vdrive hot rod boat) and about 32* timing, right at 10# boost. I know centrifugal blowers are a lot more efficient and should make a little more power than a roots.
Yes, and also a reason imo, one should not look at bsfc numbers as a fuel ratio tuning number.

I think the prochargers, turbos, and screws can get away with a little more wouldnt you say scott ?
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