1dirtyZ

iTrader: (1)

could a blower motor actually loose power after changing to better flowing heads ( from stock 6.0 heads to 320 cfm heads)and long tubes ? the boost level fell 2 psi after this swap.

could the heads actually be hurting blower performance?

mike m

iTrader: (6)

yes it could drop, you just need to use a little smaller size pulley. my car lost almost 4 lbs after a h/c swap.

MelloYellow

Agree, re: drop. Not hurting flow or performance tho. Helps reduced temps.

1dirtyZ

iTrader: (1)

so what youre saying is that performance drops even though i have less back pressure and more efficient heads??
it's not making sence to me.
and the blower is almost at it's maximum impeler speed, so that rules out a smaller pulley.

NoGo

iTrader: (2)

Your performance doesn't drop. The engine flows better, so less back pressure (ie boost) is seen when you are cramming all that air in.

As long as the compression of the heads is the same the HP that the motor made before the swap should be the same.

1dirtyZ

iTrader: (1)

that's what i don't get, the motor we were tunning lost a whole lot of power, even though the heads were the same compression.

we were expecting a gain ( worst case scenario of no gains) but we ended up loosing horsepower and torque all along the rpm band and especially up top.

CHRISPY

Are you using a boost referenced regulator?

You need to think of it in CFM not boost. You are pushing the same CFM at less boost which is very good.

If you are running a boost referenced AFPR or FMU you will see a drop in FP with less boost even though you are flowing the same or more air. This will result in a lean condition. May need to look at timing and fueling. (on a dyno with wideband and LS1edit)

I bet it is tuning related.

Cheers,
Chris

1dirtyZ

iTrader: (1)

it was on a wide band dyno with edit , and we did dail in the fule and the spark as much as we can but no luck. so that rules out the tunning.

i just can't explain why this is happening.

Pro Stock John

iTrader: (34)

Car made less power on the dyno you are saying? How much less?

1dirtyZ

iTrader: (1)

about 80 hp less.

MelloYellow

Belt slip, leaks, A/F, Timing, C/R.

JimmyKash

the heads aren't hurting you, they are only helping. Since your engine is consuming more air more efficiently (noted by your 2psi pressure loss) you are going to need to re-tune the fuel/timing.

Also check for boost leaks and/or slipping belt

1dirtyZ

iTrader: (1)

see that is the problem. this happened on the dyno with a wide band and ls1 edit and a techIII, we were retuning it.

there is no belt slippage, no leaks, A/F is between 11.5:1 and 12:1 and timing has been pushed up till i got knock then i pulled back ( almost same timing as it had before)and the compression ratio hasn't changed.

could the the owner's blower be too small now? (it's a D1-sc)

Black LS1 T/A

I would not flow the motor better without upping the boost back to where it was... or close. Boost adds a lot of horsepower... sometimes we start to take that for granted.

Get the boost back up to where it was and you will see your performance increase for the heads/headers.

Let's say heads going on an N/A motor gave you 30 more rwhp (just an arbitrary number). Let's say the difference in 7 PSI and 10 PSI was 80 RWHP (3 more PSI and headers did this for me). Guess what? You've lost power in the better heads/less boost scenario.

Get the boost back up, and you will exceed what you had before. OR.. get it close to what you had before, and you will match the power with a little less boost.

Of course, I'm assuming enough fuel and optimal tune for each situation.

My2Cents.

ChrisB

Since the crank/blower pulleys didn't change he should be flowing roughly the same CFM - since the blower essentially fixes that. The fact that his boost is lower is pretty much irrelevant - it's the amount of air coming in, not the pressure ratio that matters.

The only way I could see this hurting is if the blower became more effecient with a higher pressure ratio - but that isn't very likely for the pressure ranges we are looking at here (or with respect to thermodynamics - assuming no surge, etc.).

I would get the problem figured out before you change the pulleys - as you will only be masking a problem by upping the boost. Can you post the dyno graphs? What were the specs on the heads? Are you sure the compression ratio is the same (did you have them CC'd)? What kind of valvesprings are on them now? How was the car running - at the same tune was the a/f ratio the same, richer, leaner, etc? How is the MAF reading compared to before? The camshaft is the same?

qqwqeqwrqwqtq

Boost pressure does not equal cfm. It is a measure of backpressure in the intake tract.

If boost went down when the heads were changed, then power should have went up due to the increased CFM that the engine IS USING. (and their is less parasitic loss from the compressor).

Was the compression ratio reduced with the head change?

What size cam?

mike m

iTrader: (6)

tell us more about the heads, flow #s? what the compresion is? and what cam is it?

1dirtyZ

iTrader: (1)

the compression ratio wasn't changed according to him , i think it's about 9.6:1 ~ 9.8:1 but i'm not sure. as for the head flow numbers and cam specs i'll have to get back to him for that, but i know it has comp dual valve spings (the 987 or something like that). the air ratio was between 11.5:1 and 12:1 , in the pulls before heads and headers the A/F was 11.5:1 and rising to 13:1.

we were talking about this last night and someone said that the reason the power loss occured is that there is less air to push through the motor ( well it's the same amount of air but flowing through a bigger hole), so the ratio of air volume to size of "tunnel" the air is going through is smaller. dunno if that makes sence to any of you or even if it's physically true.

Pro Stock John

iTrader: (34)

80 is a lot.

I'm thinking there's a problem like belt slippage or valve float or something like that.

JimmyKash

I thought of a better way to post what i am trying to convey:

"boost" is just a #, you should know that. here's a small example to help you understand why we say the heads didn't "lose" you hp.

Lets say with your old heads and the blower pullied for 800cfm (just pulling out a number) it made 12psi on your gauge and made 450rwhp ok?

Now you install a better flowing intake, heads, and/or cam. Your blower is STILL putting out 800cfm but since there is less of a restriction in the intake tract the "boost #" will go down.

This doesn't get you anymore hp really it just lets the motor run more efficiently since it doesn't have the excess pressure in the intact track. Which is good for many reasons:

octane
detonation
gasket sealing
etc

Now if you were to pully that blower up to say 900cfm (again just another # for this example) the boost # would increase back to 12psi but the hp would increase from the extra 100cfm the blower is putting through the motor.

Hope that helps