Blower Expert Needed

I got a question for whoever can offer some advice. I got a 420 small block chevy that has custom Ross pistons for a 9.0 compression with a 0 deck height and a .039" head gasket. I got a 400 block with a 4.155 bore and a 3.875 stroke crank and 6.0 rods. I just aquired the blower off EBAY and just in time because my pistons were ordered two days before for 10:1 compression. No refund or exchange on custom $800 pistons. Now that I'm trying to tune this blower, I don't want to over do it. I have about 5-6 lbs boost when I first get on it but after about 4500 rpm my boost is falling to about 3-4 lbs. Should I adjust this setup to provide six pounds on the top side or leave it at the bottom side At cruise it has low boost which I was told is good because you dont need any boost under about 2000 rpm. This motor is built to shift a 6500 with a 7200 redline. Also this motor is topped with 215cc iron eagles, solid roller comp cam custom grind .590in. .608ex. lift and 248in. 258ex. duration@.050 tappet lift with a 112 lobe centerline. And last of all a Proform 850 double pumper. This motor runs hard but that boost loss at high rpm is troubling me. I think if I build the boost a little higher at first it could sustain 5-6lbs up high. But don't want to fry it.



Thanks, Ray

Hi Ray:
First of all, I'm not a blower expert, but assuming that you have a good sealing 6-71 & are running it at 1:1, you should be able to make about 10 lbs. of boost at 6000 rpm's. A 10:1 static compression motor with 10 lbs of boost requires some HIGH octane fuel to combat detonation, not the crappy 93 stuff & "O" ringing the block may not be a bad idea. Why is the boost falling off? Well, the single 850 DP carb maybe restricting the amount of fuel (or air) you require & most importantly, you could be leaning out the motor (you usually do this just one time). HEAT is your biggest enemy & you are building lots of heat in that motor. What do your plugs look like? Any backfiring?
Maybe Pat McCarthy can throw out some other ideas.... Don

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Originally posted by camaro_fever68
I got a question for whoever can offer some advice. I got a 420 small block chevy that has custom Ross pistons for a 9.0 compression with a 0 deck height and a .039" head gasket. I got a 400 block with a 4.155 bore and a 3.875 stroke crank and 6.0 rods. I just aquired the blower off EBAY and just in time because my pistons were ordered two days before for 10:1 compression. No refund or exchange on custom $800 pistons. Now that I'm trying to tune this blower, I don't want to over do it. I have about 5-6 lbs boost when I first get on it but after about 4500 rpm my boost is falling to about 3-4 lbs. Should I adjust this setup to provide six pounds on the top side or leave it at the bottom side At cruise it has low boost which I was told is good because you dont need any boost under about 2000 rpm. This motor is built to shift a 6500 with a 7200 redline. Also this motor is topped with 215cc iron eagles, solid roller comp cam custom grind .590in. .608ex. lift and 248in. 258ex. duration@.050 tappet lift with a 112 lobe centerline. And last of all a Proform 850 double pumper. This motor runs hard but that boost loss at high rpm is troubling me. I think if I build the boost a little higher at first it could sustain 5-6lbs up high. But don't want to fry it. Thanks, Ray

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you didn't say what size blower you have. if its a small blower you're probably playing out of air. as far as adj. the boost, i didn't know you could adj. the upper boost without changing the lower boost also. to me the boost sounds ok if you have 9:1 pistons. the reason you don't have boost at cruise is because, the carb has to be opened about 1/2 way for the blower to have any air to blow. you should have boost anytime you are at WOT. if you are running 9:1 pistons, 5 lb. of boost. 850 carb. and turning it 6500 prm's and not breaking nothing then i would leave it alone. i cant believe you're not impressed with that. sounds like a nice blown st. motor to me. not sure you need all that cam though. :HMMM:

what dyno don said sounds good . one carb one this? two afb 650 cfms or holleys i wound do. sounds like it is botteleneck. at 10 to 1 and 671 with 112 centers. 10 psi it should make easy . how good is blower sealing on intake and what is the vauuum on the top. the carb when the boost drops and is the blower in good shape?? a nosealed could take more than 1 to1 but i think it is the carb and air cleaner and i hope you have a big ex

I am no experts, but a few things that are important are, cam without to much overlap, ie stuff more air and fuel in the cylinder, exhaust which is free flowing to get rid of the gases, ignition which is boost referenced, to set fire to the air and fuel. A blower takes horsepower to drive, if combustion is not happening efficiently, then boost would drop off as well. But that combo must put a smile on your face.

Im not an expert on blower motors yet, but have been doing research cause i'm going to be buildiing one next fall. From what I have gathered thus far is that blowers can tame a big camshaft, it is the wider LSA's and narrower overlaps that help the blower maintain good boost levels throughout the intake and comresion strokes.Your camshaft has a 112 LSA, and nearly 250 Degrees @.050, pretty big overlap for a small blower. Blowers like wider LSA's the wider the LSA the less overlap, and this alone will help maintain a higher cylinder pressure. I am under the opinion you are running either a 144 or a 177 ci mini blower. The only way you can increase the boost levels is changing the pulleys, now keeping in mind that more cylinder pressures are going to increase heat, you are already running 10:1 pistons, so higher octane gas is going to be a must. You might try a smaller camshaft, I am not sure if a pulley change will be enough to maintain a higher boost level with the current cam in your set up. Just my opinion

Who manufactured the blower? What size? What pulleys?

Sounds like all good information and I thank yall all. You gave me some direction to look in. The blower I'm running is a Weiand 177 with a stock drive of 1.45:1. Holley emailed me back and said that the reason my boost is falling is because its being used good. As long as I don't go into a vacuum at high rpm the blower is working well. The more efficient the intake and exhaust the better, and boost being used up like so is better than building up high manifold pressure. I could gear the pulleys a little more and maintain a boost of about 6-7 psi down low and 5-6 up high. PS. THIS ENGINE IS 9.0:1 The cam may also be a problem like someone mentioned earlier. I'm looking into that also. And just to say THIS ENGINE DOES RUN!!!!!!!!!! The only reason I'm tinkering is just to make sure I'm not leaning it or hurting it when my psi droops. This is a big engine for a small blower but I like it because it stays under the cowl hood. STEALTH ATTACK!!!

"Holley emailed me back and said that the reason my boost is falling is because its being used good."

So, I assume that if the boost fell to 1 psi at the top, the blower would be doing an exemplary job???? Sounds like lip service to me. :whacked:

My take on it, the blower is too small for the application.

tech, your idea sound more like it. What do you think about me gearing it a little bit more. I only need about 2psi to be optimum at high rpm It is set a stock psi for stock 350, they do use this blower on big blocks If I could maintain 5-6 psi I would be happy. It only spikes 5-6 psi when I first jump on the throttle.



Ray P.

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Originally posted by camaro_fever68
tech, your idea sound more like it. What do you think about me gearing it a little bit more. I only need about 2psi to be optimum at high rpm It is set a stock psi for stock 350, they do use this blower on big blocks If I could maintain 5-6 psi I would be happy. It only spikes 5-6 psi when I first jump on the throttle.



Ray P.

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if the blower is not big enough it dont make no dif. what you do to it, you are still gonna use it up. the blower cant move enough air. you need a bigger blower.

Overdriving the blower will give you more top end boost, and low end too. Can you stand more at lower rpm? That blower would be better on a 350.

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Originally posted by R Pope
Overdriving the blower will give you more top end boost, and low end too. Can you stand more at lower rpm? That blower would be better on a 350.

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how can overdriving the blower give him more boost, he is down to 1 lb. at top end. if you speed the blower up its just gonna get to 1 lb. quicker. his blower is not big enough. in this case i cant see where speeding up the blower will do anything. :confused:

I just back from Thunder Racing, I have a new drive and driven pulley. Thunder says this should put me at about 7psi initial and maintain 5-6psi on up to 6500 rpm. I'm going from 1.45:1 to 1.90:1 which is near the max my rotors can spin and still be in the safe zone for wear and tear. It'll take me about an hour to install and test. My boost should not build up down low till the throttle is wide open according to Thunder. This design and blower set-up should come into affect above 2200rpm. Guess we'll see!!!




Ray

WER