loosing boost in M62 @ WOT
 

Alright guys had the car dynoed today and made 271whp @15lbs i do have stg 2 zzp cams and an ATI on 2.9. Seems i hit 15lbs peak around 5k, but then i slowly loose boost till redline @8k, smoke tested the intake and seems fine also running ZZP BRFPS with deleted stock regulator ball and no leaks there either. I already replaced the boost bypass valve selenoid and didnt help. any advice?

Alright i smoked again and found the evap canister to be leaking, i guess the evap wont be the issue since i dont build boost until after the blower, still stumped no leaks in the intake, no leaks in exhaust. anyone have any ideas?

How much boost are you losing? What are you going by? Gauge or hpt?

hpt and the dyno showed it as well about 1-1.5 lbs from 5-8k
i will get home in about an hr and ill upload the dyno.

Well sounds liked you've covered all the basics. Perhaps the cams are causing the slight boost drop.

Attachment 17368

Attachment 17369

I feel like im loosing too much power up top for it to be the cams...

You running valve spring upgrade?

of course and BS delete and ati fully balanced and rotated

I see no thing out of the ordinary, the cams breath better in the higher rpm's, and the boost loss is so minimal that I could only see it being attributed to the engine breathing well in that power range. Your dyno chart looks perfect and the boost looks perfectly consistent all the way up to 8k. What exactly is the problem? 271whp is fantastic for a M62 LSJ.

I build boost till redline.... never drops, but your numbers look good for an M62 on pump gas and your mods.

You have a different supercahrger :p


OP is essentially running a 2.8" pulley.
How do the rotors on the SC look?

;)

agreed with staged... what was your std correction dyno? Wouldn't be surprised if that was around ~280whp... which is on right on par with your setup and pump gas.

lol yeh i was gonna say, isnt he on a H62? This isnt uncommon for a 3rd-5th generation supercharger with those style of rotors, it just goes to speak to the inefficiency as you continue to spin them faster and faster. All your really seeing on the dyno is the fact that the motor is getting consistently more efficient at breathing in that RPM range and the M62 is not able to keep up with the airflow to maintain that backpressure in the intake manifold as the engine begins to draw it in faster then the blower can force it. If there was some drastic drop off of boost by a couple of pounds i would say belt slippage or something, but power looks very consistent and strong on that dyno. I'm more curious if the OP is actually shifting at 8k or not, because I would think that would put you past the peak of torque on the shift.

Basically, put a smaller pulley on ans shoot some nitrous.

I wasnt comparing... I was simply stating I build boost till redline.

The way you said it implies that the OP has a problem with his setup when he doesn't. Your like one of maybe 25 people who actually know what a H62 is. lol Everyone else would have just presumed you spelled M62 wrong. Don't want the OP getting the wrong idea and comparing his against yours is all im saying.

True, but the OP PM'd me, so he knows my mods now ;)

:twothumbs

I am not sure is there a calculation from sae?

The rotors are immaculent the blower has less than 20k as this is the 3rd m62 on my car all warrantied from GM

I figured out that shifting at 8k is useful for 1st and 2nd only but I have never had a need to shift past 120 into 4th. I did get pulled on by a LOUD 06 GM turbodiesal by a 1/4 length from 105-120ish before letting out
I dont think the answer would be smaller pulley and nitrous, but maybe my 3.0 pulley and nitrous with E85 :)
Ive known about your H65 for a while, very respectable for all GM parts, also my header compared to your GM honed mani might be the difference in boost drop off.


Overall I thought something was wrong as I thought the car was supposed to make more power at higher engine speeds especially with the Stg2 cams, but I am in essence past the M62's efficiency range, anyone know the guy who does the porting to the blower, I would be interested in getting mine done and seeing if it makes a difference with E50.

i would think that if you went up to a 3.0 instead of a 2.8 that the higher rpms would make more power as opposed to a smaller pulley. would definitely affect low end power, but like you said, youre already shifting first and second at 8 k

I don't think that would help at all, lowering the pulley size is just going to lower the boost level and lower power overall, the problem is merely that the M62 can only move so much air at any given time, and at that power range, his engine is starting to become more efficient then the blower can handle. The only solution to the problem is to change the blower to something that has a longer efficiency range or that moves more air per cubic meter, or however they measure airflow on these things. I'm not really up to par with my math on that.

armcclure is the guy with the porter blower cases, and I would love to see this be tested on your car to see if his porting works as claimed with a back to back test on the same pulley on your car. If you would be oh so kind to provide that dyno should you go that route, because im a big skeptic.

Positive displacement supercharger modifications | HorsepowerCalculators.net - Home of the Virtual Dyno & The comprehensive horsepower calculator

^ this sums it up, ive pumped a ton of cash into the engine to make it bulletproof and able to utilize the stock blower. Well I gave him a PM and let him know about this thread hopefully I can get this done and be able to make some power up top

i wasnt very clear on what i was trying to say. the end all be all solution would be to ditch the m62 if he wants to make power to 8k rpm. but if he went up in pulley size, the max power point of the powerband would move more towards redline and not drop off as badly near redline. it may make less power, but id be suprised if there was much of a loss. a 3 inch pulley would spin the m62 to 17000 rpm at 8 k rpm of engine speed