Hot Rods Repro Scot blower can't make real boost

Well if you have an original to copy why not copy it rite down to the nats ass?????????????????

 

Joe Abbin of RoadRunner Eng in Albuquerque has a 335 dyno h.p. Flatmotor that runs a Isky 400 jr camshaft and modified cast iron Merc heads. He is an engineer,has a flow bench, and a dyno and knows how to use them. I think he runs 4-6 lbs boost,but not positive on that figure. I know he runs a B & M blower. Flatheads Forever!

 

Here is the answer form HandH

Peter,

I have been in contact with Holley Corp. regarding your issue, since I purchase rotors from them, they will send
me another spec sheet on the rotors.

I will also do the math here on the CNC machine operations to double check measurements.
Next week when I have all the calculations before me, I will evaluate the issue you are having.
Since the SCOT Blowers are based on a specific CFM, I am sure this can be figured out, it seems to
be a mechanical/physical issue.

I have built and run over 200 blowers on Arduns, Flatheads, Dixon Headed Flatheads and some one off Buicks
etc. and have not encountered a low boost issue, except 1 where he had a physical dimensional issue and could
not fit the correct pulley size to a wide belt application he made.

Thanks Max Sr.


Hope they find a solution

 

Hope it turns out for the best Cheaterspete.
On our H&H scott we also had issues with the drive belts. My wife was enjoying a drive one day ,when she came home I noticed small bits of rubber on the chassis . Seems the toothed belts do not like being bent backwards on the idler. We used the exact same belts as H&H .
Tried numerous belts and eventually settled on an ugly pair of green Kevlar belts. We took advise from a belt drive specialist. Don’t know how long they would have lasted as we took the blower off due to unsatisfactory boost.
I know it would not look the best but would it be possible to fit pulleys to suit a serpentine belt??

 

Hmmmm , a lot of people seem to have problems making boost with the h&h blowers ...their pulleys should have a ratio to make boost at a certain displacement (cam aside)
A roadrunner weiand kit always makesgood boost . Then adjust it once to your engine size and cam and it simply works ....a few around here

 

To clarify, HandH SCoT blowers are the only ones I heard mentioned. I have their 471 and no issues making 7 pounds out of the box.

 

Yep! , i agree

 

I have a second hand set 4-71 . 12psi
Fun

 

Some one must have invented a "flow" bench machine that you would tell the out put versa the input or boost? Kinda like a head flow mach? If so and they are independent of H&H that's were I would send it. 7G's is a little much for a blower that's just a poser at the moment. All of this is of course assuming everything else is up to snuff ........................................

 

The big NHRA teams have blower dynos.
I imagine the serious racing blower companies like BDS would have one.

 

CheatersPete, did you get a chance to check the rotor to case clearances?

 

7000 is a lot for a non working hair dryer... I agree... My engine is making 125hp to the wheels, I have the dyno chart.
The blower is the issue there, Now I m waiting for a solution from HandH. I had no time to check rotor clearance but will do it asap.

 

I hope that wasn't headed my direction. I've already had to scrape off rubber from my tail pipes and quarter panels and I only have 70 miles on the flatty.

 

You have a 471, Apples & Oranges!

 

BDS says to use a 110* LSA on all their blowers on different motors. It doesn't specifically show a flathead, but the assumption is... Look at this chart.
http://www.blowerdriveservice.com/blower-cam-specs.html

 

One size does not fit all.

Physics does not back this.

 

OMG, somebody ought to tell BDS about this! But then, Physics doesn't know if it says Ford or Chevy on the hood.

 

You just don't get it. I will explain it to you, when my plane lands.

 

I get it... but then, some things just don't matter and this is one of them.

 

Agree with gimpyshotrods. LSA is a simple number... it needs duration and profile added to it before you can determine overlap (it is the overlap, not the LSA, that blows boost out the exhaust). As an example, Lunati specify various LSAs for their SBC blower cams, ranging from 110-114º. A single LSA probably makes cam stock management easier for BDS.

Cheers,
Harv

 

No you don't, and yes, it does.

The suggestion that a single LSA (and by definition overlap) is appropriate for all engines, regardless of engine design, cam profile, and intended use is intellectually dishonest and lazy.

Proper cam selection needs to take into account every single aspect of the engine's design, from displacement, to rod/crank ratio, to cam lobe profile, to intake and exhaust runner specifications, valve sizes, combustion chamber shape, piston dome/dish shape, head material, to intake design, and dozens of other variables.

One LSA will absolutely not work properly on every engine, in every use-case.

One thing that will not vary is the fact that the wider the LSA, given all else equal, and an identical cam lobe profile, the more useful boost will be made (until the point of diminishing returns is reached). This is basic physics. Remember, they are not called The Friendly Suggestions of Physics, they are the law.

So why do companies make blanket recommendations like BDS does?

Companies like BDS, Weiand, Holley, etc. are in the business of producing supercharger kits that the average Joe can bolt on, produce moderate performance gains, without the risk of destroying their engine. They have to do this. If they don't leave a substantial amount of potential performance on-the-table, there will be a decidedly increased risk of a catastrophic failure. While likely not to be the fault of the manufacturer, the manufacturer will nonetheless be blamed.

In the age of instant communication, it is VERY easy for a company to earn a poor reputation, and lose some, if not all of their business.

How do I know this to be true? I am a Senior Engineer at the world's 5th largest automaker. It is literally exactly my job to explain conditions like this to folks like Senior Executives, all the way down to line-workers, and to see to it that they do not happen. When you are sitting on $220,000,000,000.00 in assets, and produce almost 10,000,000 vehicles per-year, you can quickly become a target for litigation, if you even slightly slip. A company like BDS could be erased from the face-of-the-earth by serial litigation, even if they did not lose, just from reputation damage alone.

I have personally watched guys at Sonoma Raceway swap upper and lower pulleys (going from underdrive to overdrive), on what appear to be otherwise stock SBC's, but with blowers. On more than one occasion, the result was a rod, or rods, right out of the block, on the first pass. Each said “something wrong with the blower”, or something to that effect. This could end up being a retailer's worst nightmare.

That performance left on-the-table can be the difference between a powerful engine, and one with 50% more power, with almost the same (in design, and cost) hardware (if it is built right in the first place).

Real horsepower is built, not bought.

I can personally guarantee that if I took the 115º LSA cam out of my purpose-built to be blown Hemi, and put in an identical grind, except at 110º LSA, I would lose 150 to 175hp, or more.

Building generic, formulaic kits for the public, for engines of unknown quality, is not the same thing as building a specific engine, for maximum power and durability.

I know guys that have girdled stock-block Honda 4-cylinders, producing over 1000hp, at the crank.

Nobody sells that as a kit.

Why? Because ever slack-jawed yokel with a credit card would blow up their poorly built engine, in the first 5-minutes.

 

Gimpy, maybe I need to clarify this a little. I'm NOT in disagreement with you on overlap and LSA. CheatersPete is only looking for the reason why he has less boost with a smaller blower.

I recommended a 110* LSA using BDS as my reference for street blowers. CheatersPete is not looking to make 1000 HP flathead. He's just wondering where a couple of pounds of boost went.

Come to find out his cam choice uses a 108* LSA. A 110* LSA is a step in the right direction. Speeding up the blower is another step in the right direction. I personally think he needs another carb on top, but that's another story.

BTW, thanks for your technical input. Next time, please don't jump to conclusions that don't matter. He doesn't need a 115* LSA (or a 6-71) for only 4-7 lbs. of boost. The thing will have NO rumpity-rump that every self respecting hot rodder wants to hear.

 

Hello, Just checked the clearance, I have 0.015 between the lobes and 0.011 between case and lobes...

Dyers said that I should have 0.008 between rotors and case, but it should give more boost... waiting for HandH answer..

 

Hi Pete- I'm following along with interest. I was wondering if you have done any additional research about your cam and if it is a known good grind for a blower, or if it has too much overlap to take advantage of what the Scot has to offer. I keep thinking a rotor quality issue is less likely than perhaps a wrong cam pick, but that is only non-fact based opinion ....

 

We had the same very low boost issue and we were running a tame Max 1 cam in a very carefully built and basically blueprinted flathead. The blower seemed to get in the way of the intake charge. Waiting patiently to hear Peters outcome.

 

Subscribed.

 

My turn to jump on this:
No i do not have the perfect cam for blower application and I will now purchase another one with the specification below
Intake Duration (gross): 280
Exhaust Duration (gross): 270
Intake Duration (.050”): 242
Exhaust Duration (.050”): 234
Intake Valve Lift*: .375"
Exhaust Valve Lift*: .365"
Lobe Separation: 112

+ I just swaped my carbs for the new stromberg 250cfm. I use to have the Holley 94 rated at 165cfm.

Will have to tune and let you know.


thanks again for all you positive assistance on this

Best regards

Pete

 

Awesome Pete - can't wait to hear the result! Also I have been wondering about the new 250cfm strombergs and if they open up more power opportunity.

 

Your new cam must have less overlap to make more boost at low rpm than the L-100 cam .
Is this the case ?
I really dont think your problem is camshaft related ......
If so , i would go smaller on the cam not bigger.
Didnt make really good power years ago with
A 4-71 blower and a Max-1 cam?
Bigger carbs are a good Idea .
Anyways , its cool that you try to find the boost and not just leave it alone.

 

Sounds generous.