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

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 ?

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 ?

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.

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 ?

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.

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

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 ?

I think the amount of boost an engine will "take" is going to be dictated by things like compression, chamber design, type of fuel, cam, tune, timing, etc...all after the fact of whatever the source of forced induction is. I think those types you mentioned are more efficient and will make more power for the same amount of boost (I think mainly because of less heat generated under boost) but I think the amount of boost (cylinder pressure) will be the same...but I could be wrong...haven't really built and tested enough different blower deals to know. I'm building a (non marine) Vortec blown 540 BB Chev right now that will be on alky, MFI/blow through and should make around 2500. I'm also building a twin turbo 511 BB Chev EFI pump gas deal so when we get this on the dyno I'll remember to take notes on all this.

My point was, lets say you have a roots combo making 1200hp at the flywheel, and a turbo making 1200hp at the flywheel. The roots will probably have quite a bit more parasitic loss , and making more cylinder pressure to net the same power at the flywheel. Not sure if im making sense the way im explaining it lol

I dont know much about BMEP except its a calculated number? I will say this about BSFC/vs load/vs boost/vs hp/vs what makes the boost. I am making these numbers for sake of discussion but they are supported by some past testing I have done/read about, they just will be exaggerated a little. Heres the example: we build (2) 1200 hp blower motors, motor A has the worst example of a roots supercharger on it, motor B has whatever centrifugal that is most efficient. The roots motor has a BSFC of .625 (typical in real life), the centrifugal motor has a bsfc of .520 (have observed this personally a few months ago), REMEMBER, this is for sake of discussion, not to start a fight about. So both motors are giving us 1200 hp at crankshaft, BUT motor A is using 750 lbs per hr of fuel, motor B is using 624 lbs per hr of fuel. For sake of discussion I will over simplify this too, boost equals extra hp, this motor B in our example makes 650 hp on its own, we give it 14.7 lbs of boost the hp doubles minus parasitic losses so roughly motor now makes 1300 but takes 100 hp to turn supercharger so we see 1200 at the crank. So the cylinders are making 162.5 hp and using that amount of fuel, shedding that many btus, cylinder pressure goes with this accordingly, i'm sure at some point the BMEP could be calculated from this. Motor A also makes 650 hp on its own, and 1200 crank hp boosted but is using 20% more fuel to do it, which in turn means each cylinder to do it has to make 195 hp, equals extra btus, more load per cylinder, more detonation etc. Now we could start arguing about latent cooling from the fuel going thru the blower rotors and a whole lot of other things, this is just a example, not complete fact. In reality though, for motor A to make that same hp as motor B it would need to run MORE boost to make that extra hp per cylinder to get us our same crank hp so at same boost motor A would make LESS crankshaft HP, same boost, probably same cylinder pressure prob same amount of detonation, at same hp level however, more prone to detonation, FWIW, Smitty

Makes sense to me. ^^^

In that regard, yes absolutely. Artic explained it pretty well but I think the discussion would have to go in the direction of WHY the centrifugal makes more power with less boost. It's not 100% parasitic drag, i's also efficiency in the compression of the air/fuel. Compare a Whipple or PSI to a traditional roots and you'll see what I mean. The physical demand to turn the rotors is equal for all discussion purposes and doesn't take much HP at all but if you look at the charge efficiency of both, you can see where they drastically differ.

In my example though a old school roots supercharger uses signifigantly more hp to turn, I recently "dynoed" a procharger at less than 75 hp parasitic loss to make 14 psi of static boost at 5800 engine rpms, hence the reason why you can drive a centrifugal with a 8 or 12 rib serpentine and old school roots blowers need a much larger drive belt, they would shred/slip a 8 rib unmercifully. There are DEFINATELY other issues with pumping losses between rotors, heat generated if sized small and turned up high too on roots but overall the main reason bsfcs are so much higher on it takes more hp to physically turn the roots, fwiw, Smitty

I've heard this argument for years and it just isn't true. Think about it...how much mass is there really in a pair of aluminum rotors? None to speak of...certainly not what we see HP wise in the difference between types of blowers, especially when you start comparing the rpm those other blowers have to turn and the mechanical disadvantage they have. You take away the fact that a roots is technically a compressor...remove that load form the rotors and it doesn't take squat to turn them. You're not measuring parasitic loss due to the mechanics of the blowers, you're measuring parasitic loss in efficiency of how they treat the air. Do the same calculation on a turbo, where there is ZERO mechanical loss and you'll see what I mean.

Ive been running a 10 rib serpentine belt on my b&m 420s with no slipping issues, and the belt lasts quite a while. Mercs 600/ 800sc used the same setup, many guys put intercoolers on them and ran 8-10lbs with 10 rib, although some did the 16 rib swap.

I dont think the roots are as bad as people think as far as power to turn at low boost. Now, 35lbs of boost, they definitely do take some power.

The majority if marine and street roots blown setups, dont need a cog belt.

The other thing is, look at the pulley sizes. A roots might run a 5 inch rib pulley on top, and 5 or 6 inch rib on the bottom. Where a procharger runs what, a 8 or 10 inch crank pulley, with a tiny top pulley? I think that plays a part in pulley slippage issues with the centrifiguls due to their massive overdrive

I turn my centrifugal 58,000 rpms, its internally stepped up 4.4 to 1 and overdriven by the crank over 2to1 also, fwiw, smitty

Do you get decent belt life ? My buddys procharged setup was hard on belts . Like you, he was turning it pretty hard . That dam belt had to be like a guitar string or he lost a significant amount of boost.

I called Procharger to see what they recommended for pulleys to make 10 lbs of boost at 5800 RPM....

They said with my 7.5" crank pulley to run a 5.25" blower pulley.. Puts me at 36,789 rpm impeller speed at 5800 rpm...

Don't think I'll have to worry about belt slip. :)

I ran 12 psi on 93 with my 598 it made 1200 hp and I ran 32 deg timimng I also ran a m4 with a cog belt drive

You will have to watch for it there to...even 5-6psi belt needs to be kept very tight and watch for black dust

Im turning my procharger 8 to 10,000 rpms past its rating because of the hp level im at, really in m4 or m5 territory but never upgraded. With 12 rib i never had belt problems at 48 000 to 50,000 rpms, at 58,000 everything has to be perfect and i had to re-enforce mounting bracket to eliminate flex and was still marginal, fwiw, Smitty

What ? A 5.25 upper pulley

7-lbs of boost and I'd have an efi system that can knock retard.thats why I like the mefi4b,you can watch the knock sensor and spot problems.I use the knock and o2 sensor to dial the tune in.

Great discussion. Is there a preferred system or plug and play setup for knock sensing especially on a low tech carb setup without efi/computers?

I have a pair of 572s with 14-71s on top, intercooled and twin 850 carbs in between 1000-1100hp running 93 and Boostane to get it around 99octane for safety. I really wanna add the O2s (have the FAST kit already), but love the idea of knock sensing, and how to prevent bad things from happening. I am by no means an engine expert, and had them built for me, just curious, might be a nice add-on before I start running the thing hard.

When I dynoed the procharger head unit it was static boost throttled to achieve same load as it would be on motor at wot. I DO disagree on your opinion of "load" from supercharger. I dont really care how much hp it would take to free spin a old school roots, I am talking about under a load. So back to BSFC's, two identical motors, cams, heads etc, one with a centrifugal with BSFC's in the .520 range, the old school roots blower motor with bsfc's in the .625 range, its a fact the roots motor is using 10-20% MORE fuel to make same crankshaft hp, if its NOT from hp required to turn the blower then what is it from? We got a 1200 hp centrifugal motor using 1300 hp worth of fuel to make 1200 at crank, and on the low side at only 10% more we have a old school roots motor using 1430 hp worth of fuel to make 1200 hp, for sake of discussion both tuned to same exact afr also. BTW, these BSFC's are from personal observations of dyno sessions I have been part of. I love a good technical discussion, this ISN'T a argument, Smitty
I thought about the comparison between the 2 drives, hard to compare one drive thats turning suprcharger 10 to 1 at 58,000 rpms vs 1-1 on a roots , I do know the impellor shaft in y M-3 is 20 mm in dia (less than 7/8ths of a inch), I dont think you could spin a old school roots with a shaft that small without shearing it off.

Ill add i have never seen anyone double keyway a crank snout on a marine centrifigal. Those heavy billet lobes are geared on a roots too,and swing some inertia ,but still ...

Yes.. 7.5" lower & 5.25" upper pulleys is what they suggested...

I'm only shooting for 8-10 PSI on a 555 cid engine..

Have not fooled with any of the big m4's but a 5.25 on the smaller chargers even with the 7.5 lower would be utterly gutless on a 555 . Thats a huge upper pulley for a procharger.prob would never slip though for shure

What SC is that using?

M3 and M4 SC are big blowers for big airflow and power.

It's an M4 Non self contained...

Sucks that Procharger doesn't publish compressor maps. Their tech guys say to figure it as a direct equation to max output and you'll be close...

So, in my case with a 7.5 crank and 5.25 blower pulley and a 4.44:1 step up ratio it puts me at 36,789 impeller speed at 5800 rpm...

The blower is rated at 2500 CFM at 48,000 rpm, so at 36,789 rpm it should produce about 1916 CFM ... :)

Here is a good site to compare different Procharger supercharger outputs and pulleys and projected boost. Fun to play with.

http://zero2sixtymotorsports.com/pro...st-calculator/

Unfortunately it doesn't have the M4 supercharger listed.
With these big blowers, output is not linear. They are relatively inefficient at lower blower rpm's in making boost. It is a logarithmic increase.
So 3/4 rpm is not 3/4 cfm and hence boost. 36,789/48,000 x 2500cfm -- Does NOT equal 1916cfm but something much less.
It will also depend on your choice of TB/carb, intake manifold, heads, cam and all their flow ratings.

I suspect your pulley combination will possibly yield lower boost numbers than you think especially if all your other components are optimized.
No big deal, So you will just need a smaller SC pulley to achieve your boost target.
Procharge is playing is safe and very conservative. "Start low, Go slow" and proceed from there.

What kind of power do you expect?
Predictions--> 555 CID x 1.15hp/cid = 640hp x 8pounds boost(8/16) = 950hp, x 10pounds boost(10/16) = 1040hp if everything is optimized.
So how much CFM is needed for 1000hp?

When will you be building your engine?

I'm sort of a newbie when it comes to tuning, but can you really run 10 lbs of boost on 91 octane? I always thought you needed 1 more octane for every pound of boost?
Am curious for my own application too. I run 91 octane. 540 with v4 race vortec charger, electromotive ecu, 72 lbs injectors (mulitport). I pull 6lbs at 5000 rpm and thought I was making 775hp. So to get more hp, I can run a bigger pulley, larger injectors and flash ecu? I've got dart pro 1s, je pistons, calles crank, Carrillo rods, 741 cam. And be safe on 91?

Depends on base compression, cam, fuel and timing curve etc. I run 13 psi in my 540 on 93 octane, and did some dyno pulls on 92 octane BUT i went with dished blower pistons ( 8.3/ 8.4 compression) and they are swain tech coated on skirts,and crowns

does the electromotive ecu have the ability to run a knock sensor.thats what I would be looking at.you can use the afr meter but its tricky trying to see the knock events.

775 is a lot of power and wanting more. What drives are your using?

Your injectors are plenty big and you could easily make 100 200 more horsepower if you have enough boost and run some more rpms

I have 02 sensors, but I believe knock is supported . Can run closed or open loop as well. I have Huber 1350 trannies and SSM3s. Data logging is part of it too. Incidentally I need to retune since it looks like I'm a little lean (just did top ends and some valves were toast ).