Hi,

I have recently finished an installation of a McCulloch VS57 on a SBC in my 1940 Ford convert. I'm good now with my carburetor (https://www.theturboforums.com/threads/need-help-on-initial-pvcr-sizing.387868/) but now am trying to learn about how the s/c is affecting my engine RPM.

Boost works great but now my engine quits at about 5,100 RPM whereas it would spin up easily to 6,500 before the s/c. I know the McCulloch controls its speed to 29,000RPM and the recommended engine RPM limit is 5,100. I thought the McC s/c would protect itself by closing the pulleys up but didn't expect that it would limit my SBC RPM.

From http://vs57.y-block.info/limitations.htm

"Summary

The VS57 has the following limitations:-

1) They should not be used on an engine with a calculated true horsepower of 300 hp or more. The Heavy Duty drive VS57 units have a limitation of 350 hp.
2) Boost should be limited to between 4 and 4 ½ psi for engines with a calculated true horsepower between 210 and 300 hp.
3) Maximum boost should be 6 lbs for a calculated true horsepower of less than 210 hp and may be as much as 6 ½ lbs for a calculated true horsepower of less than 150 hp.
4) Engine rpm should be limited to below 5100 rpm for a standard installation. I’ll cover this aspect in more detail later."

I didn't find any " ... more detail later"

Any McCulloch guys that can answer this for me?

Glenn

 

Wish I had more of an answer for you, but have you monitored your AITs and seen if it runs out of compressor?

From what I recall they used these on Studebakers which means the output would likely be not spectacular these days compared to an engine with a modern head unit. How big is the impeller inducer? Also, If I was looking for big power in an original footprint I would almost think about finding a shop to cram a modern wheel in the stock unit.

 

Hi,

My AFRs are around 11 give or take when boosted. I have an AEM AFR gauge to monitor. The boost is constant at the 5,100 RPM but the engine hits a wall with no further RPM increase.

I'm not looking for huge power, it's more for a period type of installation in my 40 Ford.

Thanks

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I would say the blower is done at 5100. Not sure what your base hp is. But they had those recommendation for base hp because if the engine breathes near or more than the capacity of the blower than iats go up and the blower struggles. So the blower may have become the limiter so the engine looses overall air flow as it revs and just cant continue.

Their blower rpm limit maybe be blower speed safety.

 

Thanks tbird, the blower is definitely putting a stop to it!

I estimate my HP to be 350 - 400. I had it built by a great engine builder, blue printed and balanced, teflon buttons instead of wrist pins, forged pistons, etc. I assembled it all. It started as 65 Vette short block with fulie heads.

 

I think the page is out of order and that this paragraph under limitations is the "more detail".

"The supercharger is designed to generate it’s maximum boost at it’s maximum safe impellor speed, 5 psi at 29,000 rpm. When the supercharger goes into high drive ratio (10 to 1) at 2,900 engine rpm the supercharger produces 5 psi. When 2,900 engine rpm is exceeded the solenoid, which is preset to 5 psi, bleeds the excess pressure and uses that to drive the air piston on the variable ratio drive, consequently reducing the drive ratio as the engine rpm increases. Obviously engine rpm can increase to a point where the supercharger is incapable of reducing it’s drive ratio any further via use of the pressure bleed, which is when it reaches it’s low ratio of 5.7 to 1. Given the 29,000 rpm impellor limit this is when the engine rpm reaches 5100 rpm. Any engine rpm increase above the 5100 rpm limit will result in increased boost above 5 psi as a result of increased impellor speeds above 29,000 rpm."

I couldn't find anything detailing the adjustment of the solenoid. What boost are you seeing now and can you adjust it down to see what difference it makes?

That's a super cool car and drivetrain!

 

That's a super cool car and drivetrain![/QUOTE]

Thanks Chad!!

 

I thought that pulley looked strange, adjustable ratio to keep boost consistent!

I also love the car.

 

Thanks Russell!

Yeah, there is a solenoid and along with changing air paths, the pulley sheaves are spread; making the pulley "smaller" in diameter and spins the s/c up. Retired mechanical engineer so I love it

 

The 5100rpms is where it can no longer regulate itself, and depending on engine hp it can put too high of a load on the "ball planetary" creating more than 2% slip. When that happens it gets hot and disintegrates.

It's the compressor hp requirement that is the true limiting factor. If you lower boost you lower the lbs/min needed and therfore lower the compressors needed hp.

 

Okay, what I thought would occur is the drive pulley sheaves would close up, decreasing the boost. It seems like the s/c is choking at 5,100 and end of story.

I'm an old guy and can live with 5,000 RPM. It sure gets there fast! In my youth it was a whole different matter

The other fun thing, and it may be due to the front end lifting a little, the windshield wipers start flapping, not sweeping the windshield but oscillating up and down from the windshield real fast!

 

First off I must say your car is really cool and having the old school mccullough is awesome! From all the research I've ever done on those they were used on engines around 300 cubes or less if I'm not mistaken. I know Studebaker used them on the 289s which in its prime made around 1 hp per cubic inch at relatively low boost levels. I'm sure your sbc has far superior breathing capabilities than they did. So not only are you trying to feed a bigger engine but it also allows much more air into it based on the breathing capabilities...and it will only flow what the biggest restriction allows. Reminds me of my old smog pump supercharged Kohler single. It ran great on a stock engine. Then in a quest for more power I cleaned up the ports and added a custom ground cam for boost. I ended up having to spin the smog pump twice as fast just to feed it and it defeated itself by making the intake air temps too hot. Actually ran better with the stock engine at 7psi than the modified engine did. Never tried an intercooler due to the lack of space. Just a thought.
Joel

 

Good thoughts and thanks Joel.

My fulie heads have 2.02" intake and 1.60" exhaust valves so yes they breathe very well.

I'll live with a reduced redline. I always wanted to try an s/c so glad that I did. I was first thinking about putting it on my 32 flathead but it runs so good now and I didn't want anything sticking out from the hood so went with my 40.

 

I've made good progress with my setup. My secondary side was too rich. After going down 4 jet sizes, it revs right up to 6K now so I'm happy
I will shift at 5K or so to keep the McCulloch safe. It is real fun!

Cliff from CUNDN was a great help to me. An excellent vendor from my experience.

 

Hi,

I want to conclude this thread with my final setup for maybe a future user.

This is a list of things to watch out for, etc.
(Great site but has missing pictures in spots: http://vs57.y-block.info/index.htm)

- The Corvette McCulloch bracket (ACO-1000 or ACO-1000 B – 1955 to 1957 Corvette) will work with a Model A without a hood. This bracket hangs more to the side to get under the Vette hood. Vette has good engine bay width.
- For a tighter in mount, you need a CH-101 bracket used on 55-57 Chevy or fab your own.
- Try to have an alternator mount that mounts off of a Chevy Ram's Horn exhaust manifold. I couldn't do this due to clearances and had to modify the McCulloch idler arm and my new alternator bracket as you can see in some of my pictures. Best objective is to keep the idler arm pulley high so you don't have fan/alternator belt clearance issues.
- Watch out where the thermostat housing is on the manifold. I ended up buying three different outlets before I found one that I could modify to fit under the s/c case
- You'll need a distributor that you can re-work to control maximum advance. This needs to be decreased to prevent detonation
- You'll need an electric pump feeding the mechanical or two electric pumps if not
- You'll need a boost referenced fuel pressure regulator for the electric pumps, or a boost referenced mechanical. I'd also install an electric pump off of the gas tank feeding this mechanical and to avoid vapor lock.
- Belts, belts, belts will give you a headache. I bought four alternator belts and two McC belts in addition to one from a Kaiser before I got them to work

Blow Through Holley Mods

I started with two vent tube extensions like this:

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I was still running way too rich so twisted the secondary horn into the air stream after removing the extension

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After MANY jet changes (got so I could do it in 40 minutes) I ended up with these:

#65 Primary
#69 Secondary

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All of this took me many days to figure out. Time consuming process but well worth it!!

Glenn