Wastegate on supercharger?

ONELOWF · Jul 27, 2008

The object of the game for me is to have more boost on the low and mid part of the curve, and have the boost flatten out at a livable limit.
I datalogged temps the other day in 108* ambient temps, and showed 132* max iat with my a/a intercooler.
You have to have boost to spare to make this work at all, but also to keep from generating excessive heat.

Here's the formula for blower speed, less the correct step up ratio which will be different for each s/c. Powerdyne is 3, Paxton is 3.5, and so on....

Red line (shift) rpm x crank pulley diameter / s/c pulley x ? ( s/c step up ratio) = blower speed

mogs01gt · Jul 28, 2008

You guys are trying to band aid the main issue with Centrifugal blowers, no low end power. You arent going to gain boost down low properly with a Centri. Im not sure why anyone would go with a centri if they want low end torque... Instead of screwing around and changing the system, its easy to just install a set of gears to compensate for the lack of low end power(boost).

I understand what you guys are trying to attempted though but wouldnt bleeding the boosted air out of the intake tubes cause a vacuum leak?

BennyBlown2v · Jul 28, 2008

mogs01gt said:
I understand what you guys are trying to attempted though but wouldnt bleeding the boosted air out of the intake tubes cause a vacuum leak?

No, not with a blow through system; just put the WG before the meter. With little blowers this honestly wouldn't help, but something like a D1SC, T-trim, or big boy Novi 2k or something you could make a lot more usable power IMO.

jprovence · Jul 28, 2008

they only reason I see that you would need to bleed to boost off is because you are playing out of your league. Running a huge blower on a stock motor and just bleeding to boost off. If you running a big blower, get a motor that can handle the boost, and enjoy 17psi at 6000 rpm.

ONELOWF · Jul 28, 2008

mogs01gt said:
I understand what you guys are trying to attempted though but wouldnt bleeding the boosted air out of the intake tubes cause a vacuum leak?

No. When the WG reaches it's set point, 8.5 psi for mine, it opens and allows the excess boosted air to escape, but still maintains 8.5 psi from blower to throttle body. No vac. When you look at the boost gauge the needle pegs at 8.5 psi.

This is not a bandaid, just a way to adjust the boost curve. It can be refined further with an adjustable waste gate.

mogs01gt · Jul 29, 2008

ONELOWF said:
No. When the WG reaches it's set point, 8.5 psi for mine, it opens and allows the excess boosted air to escape, but still maintains 8.5 psi from blower to throttle body. No vac. When you look at the boost gauge the needle pegs at 8.5 psi.

This is not a bandaid, just a way to adjust the boost curve. It can be refined further with an adjustable waste gate.

Why not get the correct pulley then?

Gearbanger 101 · Jul 29, 2008

mogs01gt said:
Why not get the correct pulley then?

I believe their reasoning behind it is that the ultra small pulley will ramp up the blower much faster, improving low end torque. Which yes, will work but I think what many still fail to realized here is that although the over all boost pressure may be controlled with some sort of secondary waste gate system, it does nothing to control the increased discharge temps from over spinning the head unit itself.

The answer for some may be to just compensate with an after cooler, or not go so small with the pulley as to increase the discharge temps to any great extreme, but if that's their answer, it makes just as much sense (and cuts costs and work dramatically) to be a little more conservative with the pulley ratio and pull timing and add fuel to the curve in order to control the power output.

The 4.6L has decent head bolts and gaskets, so their top and bottom end will still take a fair bit of pressure without issues (compared to a 302 that would blow a head gasket if you looked at it the wrong way without ½” head studs). Its the slightest hint of detonation that breaks pistons and bends rods with these engines....which again can be controlled with the tune.

If it were me, I would stick with the smaller blower (since they will ramp up more quickly and continue to remain more efficient at lower blower speeds), over pulley it slightly (somewhere in the 10-12psi range) and work with the tune.

Regardless of what you guys decide, you may improve your power band to some extent, but you guys will never see the bottom end torque of a Positive Displacement blower, no matter how you attempt to work this. So you've got to make due with what you've got and compensate with the tune and gearing, or sell the whole ordeal and buy something with an Eaton or a Twin Screw unit as part of the kit.

Oh....and I just cracked 7,000 posts.

stanggt00 · Jul 29, 2008

i will show you how it works out i am going blowthrougth and setting mine up with a waste gate.........also upgrading to the t-trim from sq

with 8-rib set-up and a small pulley point is no pulley change just adj the waste gate for increase in boost...

its is true you will need a bigger blower to truly see the effects t or ysi blower

i finally got my mmr motor togetter just going to recheck my cam degreeing again before i install it and also waiting on my k-member parts to get here later this week

any ways

4.10 gears and a t-trim or ysi blower ..small pulley and wastegate to control boost is a nice set-up

.............no one ever said is was the only way to go just different

BobHyatt · Jul 29, 2008

justinschmidt1 said:
Any one know how to calculate blower RPM's?

Count the teeth on the blower pulley and the teeth on the crank pulley. Divide the blower teeth into the crank teeth. This will tell you how many revs the blower makes for one crank rev. Say the numbers are 10 and 20 for simplicity. The blower is running at exactly 2x crank speed.

My only comment on over-boost going out thru any sort of wastegate is that it takes _power_ to run the blower at higher boost levels, and dumping that power out the wastegate all the time just to get boost at lower levels is not very efficient. Just think what would happen if you had a true 10psi boost at 6K, and then a 20psi boost wastegated down to 10psi at the same speed. What produces the extra 10psi? engine horsepower and the latter case would be significantly slower.

98GTfromGA · Jul 29, 2008

there have been several threads on this at modularfords and the corral. MM&FF even did an article on it last year. Basically the only downside is that you might end up overspinning your blower and creating excess heat. personally i say go for it, hell i might even do it myself since i am already converting to blowthrough anyway.

justinschmidt1 · Jul 30, 2008

BobHyatt said:
Count the teeth on the blower pulley and the teeth on the crank pulley. Divide the blower teeth into the crank teeth. This will tell you how many revs the blower makes for one crank rev. Say the numbers are 10 and 20 for simplicity. The blower is running at exactly 2x crank speed.

My only comment on over-boost going out thru any sort of wastegate is that it takes _power_ to run the blower at higher boost levels, and dumping that power out the wastegate all the time just to get boost at lower levels is not very efficient. Just think what would happen if you had a true 10psi boost at 6K, and then a 20psi boost wastegated down to 10psi at the same speed. What produces the extra 10psi? engine horsepower and the latter case would be significantly slower.

Well, its probably gonna be setup to where I can get 10-12 psi in to my system and the blower would be spinning to 15-16 psi at 6k....its not gonna be that crazy...but enough to get into boost a little earlier and make more boost in the midrange.

Im not trying to be a PD blower but with my current setup the car pretty much has to be at like 4k to really pull.

Once I hit third gear, Im only making 5 psi at 4k and cant even tell im blown...Im in thrid gear from 80-115 at the track so making an extra 3-5 PSI from like 4-5k would really help get me through the traps quicker and keep my third gear alive.

This setup isnt gonna be crazy...its gonna be blowing off extra boost from like 5-6k most likely and wont be creating much more heat.

mogs01gt · Jul 31, 2008

justinschmidt1 said:
Well, its probably gonna be setup to where I can get 10-12 psi in to my system and the blower would be spinning to 15-16 psi at 6k....its not gonna be that crazy...but enough to get into boost a little earlier and make more boost in the midrange.
Im not trying to be a PD blower but with my current setup the car pretty much has to be at like 4k to really pull.
Once I hit third gear, Im only making 5 psi at 4k and cant even tell im blown...Im in thrid gear from 80-115 at the track so making an extra 3-5 PSI from like 4-5k would really help get me through the traps quicker and keep my third gear alive.
This setup isnt gonna be crazy...its gonna be blowing off extra boost from like 5-6k most likely and wont be creating much more heat.

What gears?

justinschmidt1 · Jul 31, 2008

mogs01gt said:
What gears?

im auto with 3.73s

First gear is fine but second gear and third gear acceleration just doesnt feel as strong as it could be since im not really in the meaty part of the powerband.

geoffsgt · Jul 31, 2008

I'd be curious to know how much more power it takes to turn the smaller pulley.

mogs01gt · Jul 31, 2008

justinschmidt1 said:
im auto with 3.73s

First gear is fine but second gear and third gear acceleration just doesnt feel as strong as it could be since im not really in the meaty part of the powerband.

crap, I thought you had a manual.

ONELOWF · Jul 31, 2008

mogs01gt said:
Why not get the correct pulley then?

The correct pulley would be the one that makes the desired amount of boost coming out of the blower regardless of how much of it you want to use or waste.

justinschmidt1 · Jul 31, 2008

geoffsgt said:
I'd be curious to know how much more power it takes to turn the smaller pulley.

mmm...I really dont think it will use that much more power

wheelstandin87 · Jul 31, 2008

i think its worth a try

i considered doing this before and i would be curious to hear some results on how it works out and downfalls like heat and over spinning the blower if you even have any problems at all..id say give it a shot if it doesnt work they way think think it will then you can take it back off its not stuck on forever.

justinschmidt1 · Aug 1, 2008

Im interested in doing it...but then again, I kinda dont want to spend 500 dollars and see no real gain from it.

Once the blower is making the peak boost and the wastegate opens it would all be down hill from there.

I would be wasting power trying to spin the blower, and creating extra heat.

How much I dont know, but 10 psi now, compared to 10 psi after, I would probably be making quite a bit less power.

ONELOWF: Do you have before and after thoughts? Before and after dynos or 1/4 miles?

ONELOWF · Aug 2, 2008

justinschmidt1 said:
Im interested in doing it...but then again, I kinda dont want to spend 500 dollars and see no real gain from it.

Once the blower is making the peak boost and the wastegate opens it would all be down hill from there.

I would be wasting power trying to spin the blower, and creating extra heat.

How much I dont know, but 10 psi now, compared to 10 psi after, I would probably be making quite a bit less power.

ONELOWF: Do you have before and after thoughts? Before and after dynos or 1/4 miles?

Sorry, I don't have any dyno or track numbers to offer.

No, you don't loose all of your boost when the WG opens, you release what you don't want going into the engine to atmosphere, but the boost is maintained at the WG setting, so it remains constant.

The biggest question I would have is the heat. My s/c is running around 70% ? of it's rpms to make 13 psi so there is not too much heat. If you plan to run yours at the max rpms or close, then you could have a heat issue, no doubt.

Yes, with good parts, you will be over $ 400, and there is no guaranty that you will have the exact power curve you want, or expected. I had to play with mine a while to get it adjusted to where I want it.

I would do it again in a heart beat. I see 5 psi around 2k rpm, and full 8.5 around 3,000 rpms with no side effects so far. Well, I do have a traction problem.

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