Hot Rods Repro Scot blower can't make real boost

Dear Hambers

I have been dealing with flatheads for years, and I have pretty good results with my humble preparations... my last dyno run with the french flathead, isky max1, full ported block and 6 psi boost by a 4/71 get it to 232hp.

I have built another engine for my roadster 1932, still a french block, 255ci. full ported, literio L100 cam, Milodon 1.5 valves. light weight flywheel. dual 94, tuned with AFR. and I get 125 Hp to the wheels. Last April I decided to spend my economies and get a HandH SCOT blower kit.

I get the smallest upper pulley because my loser pulley was small in diameter. the calculation indicate that I should boost 4 PSI and in reality I only can get 2 at 4500 rpm. ( same dual 94 carbs).
I built another lower pulley in order to make the blower rotate more. I have now a 5 inches lower pulley and a 3.2 upper pulley and can't get 3 psi....

Anybody here have an idea ? what can go wrong?


thanks for your assistance

Peter

 

Blow off valve set too low?

 

no setting possible..

 

Boost is a product of back pressure and air flow. If your carbs are too small, you may not be able to draw enough air to make more boost. Or, if your exhaust is very free flowing with little back pressure it can lower boost numbers.

 

I have nothing to add except that it's too dang pretty not to work. ( I have a thing for SCoT blowers)

 

I had the same carbs set up on my coupe with the 4/71 and was able to make 6+ PSI....

I start to think that the blower is not well adjusted... rotors VS case... too much play?

 

do you know what the displacement of the blower is?

 

142 cid

 

http://www.wallaceracing.com/Basic Blower Measurements.htm

I have the last one on the list

 

It is a new ''improved'' version, Made in USA unit. should be much better than the old ones!?
Thanks for your imputs, hope we will find the solution

 

Too much internal clearance ?

 

That's what I think too.... 7000$.... what a waste of money

 

Have you talked to H&H ?

 

A pruned 3-71 with four carbs will make some suds on an engine like that

 

I have sent several email, no constructive answers at the moment., I will let know the HAMBERS how this goes, I m sure HandH are doing their best for the production parts, I m not accusing anyone, just want to find the solution of this problem

 

Measure the clearance, between the rotor tips, and the case.
Compare to the GMC factory specs.

 

Is this a street motor, or race ?

 

Mike at HandH is good people, very busy, but good to work with. He will help. I bought his pruned 471 set up for my 8ba, 7 pounds of boost and couldn't be happier. You got something wrong but I am afraid I cant help with the answer. Fantastic looking flatty! Looking forward to hearing the resolution.

 

Also check clearance between rotors...this can be adjusted by shimming. Clearance will increase/decrease with fore-and-aft adjustment of one or the other.

 

Belt Slipage??

 

I found this on the Ford Barn, SCOT rotor to case clearance is not adjustable like GM blowers

It's a straight two lobe design.

 

Possibly, only looks like 1 of the 3 belts in the pic.

 

Definitely only 1 belt in the picture and it looks like any more would interfere with the water pump belt.

 

This will only be of some use: I'm an ex-dragracer with blown fuel. I made a plate that fits the inlet flange. It had a hole drilled and tapped in it for a vacuum gauge. If you spin a blower with the starter or with another comparable standard, you will come up with a number that is relative to the condition of the unit. The clearances and timing of the rotors all affect this. In racing when we all had the same size of blower, the amount of vacuum it would pull was a general indicator of whether you had a good unit or a turd. You would have to have a good scot to come up with a number for this to be useful.

 

I will try to answer all, it is a street engine. the set up in the actual picture was with one belt, I have now 2 belts. no slippage as far as I can tell. 10 minutes ago, I have recheck, 4500rpm WOT, 2.5 to 3 PSI max

 

Mike haven't respond to my email yet

 

Mmm, you're using up some horsepower to make that 2.5 psi.

 

Try another boost gauge?????????????????????
Have you driven it yet? What does your seat of the pants feeling tell you?

 

Yes i drove almost 1000 miles already... driving everyday to commute...
It feel like more power and smoother acceleration but not like I use to get with my other engine and the 4/71 with 6 psi...

 

In your picture towards the front left of the inlet manifold what is the part that looks like a grommet with a pipe in it? I realise you have been driving it but any chance boost is being lost through that part? It looks like a non connected PCV valve.