jpshepley

The engine combo is a 572ci BBC 345cc heads & a max rpm of around 6000 & running around 10 psi on 98 fuel.
I know a 8/71 will do it but would it be worth going to a 10/71?
Its mostly street driven.

Josh

promod45

buy going up one step in a blower will only give you about 1 to 2 lbs more boost, that is what BDS told me as i was going to do the same as you..

suicidebomb

MAN! A 6/71 is big, an 8/71 is huge, I'll bet a 10/71 is like Godzirra! :shock: :lol:
suicidebomb

OneBadGMC

If you want to build boost without spinning the snot out of it, you'll need a 14-71...

1:1 on an 8-71 is going to be about 7 PSI.

1:1 on a 10-71... 9.3

12-71... 10.8

14-71... 12.2

The slower you can turn it, the cooler the air.

Here's the 14-71 on our 568 with Dart 360 heads...

us7race

I believe my friends 10-71 at 1:1 was 22 lbs.
But not confirmed..He runs Mooneyham blowers.
The one he has now is a 14-71 Hi-Helix Superman but it is a Kolbelco.
At 20% over it makes 36-37Lbs. On the data Logger.
Always but bigger as far as a blower if your budget allows, like someone already said the less you overdrive it the cooler the air.

jpshepley

bigger blower means cooler air at the top end but they can leak alot down low, loosing bottom end.
Theres no point having a 14-71 if its only good for a 2000 rpm rev range?
Please correct me if I am wrong I'm no expert on blowers (or anything really).

Josh

OneBadGMC

If they leak at the bottom, they'll leak at the top.

A street blower is going to leak like a hole in an aorta no matter what. They simply don't have tight tolerances...If they did, when they heated up the rotors would seize against the case.

If the motor is going to be dual carbed, get two big ass dominators, and a 14-71 with 15" top/bottom openings.

If it's going to be EFI, get a 9.5" opening top and whatever size bottom. The smaller the top opening the quicker it makes boost. Run dual fuel above and below the blower. Feed just enough through the top to keep the blower cool, and use the lower injectors to control EGT balance for each cylinder.

jpshepley

It will be a dual carb motor & yeah I was planning on 2 1050cfm carbs.
Thanx for the info

Josh

OneBadGMC

1050 aint big enough.

The thing with a blower is... You can never have too much carb, only too little. The blower will pull constant vacuum on the carb.

Think about it this way. The blower is trying to run in full boost all of the time. The butterflies strangle down the airflow to what you want.

If the carbs are too small, there is increased vacuum under the carb, which means that the blower is pulling harder on the fuel system. Too much vacuum and the smallest of changes on the carb make huge unintentional changes.

Go with 1250s or bigger if you can find them.