4 barrel upgrade

[blueroo]

I plan on going to a four barrel carb for my 170. The carb I plan on using is an Autolite 4100 from a 390, but with different jets and primaries. Has anyone done this that can offer me some tips. Additionally, is there an adapter or does one have to be made?

 

[rickwrench]

A HW32/36 and stovebolt adapter is what you really meant to say, right?
To get a 4bbl carb to fit to a 170 log head requires major hacking/welding/fabricating. The 4100 is waaaaay to big a carb for the engine. If you could rebuild the intake to accept a 4bbl, a holley 390cfm would be the carb to use.
Rick(wrench)

 

[80Stang]

4100 probably is 480cfm or even bigger as it is from a BB, and will be overkill for your engine. 390 is too much too but if you really want to go to a big carb that is the way to go. Your engine needs less than 200cfm even though it might be a little modded.

 

[blueroo]

Is there a way to "choke" the 4100 down using smaller primaries and secondaries that it wouldn't kill the motor?

 

[Mustang Boy]

i would recommend just goin with a smaller carb like a 2brl

 

[addo]

What do you want to do? Your motor will swell up like the liver of a foie gras goose...

Why not go the cheat; blank off two barrels discreetly on a Q-jet? It will impress the Fordies, annoy the GM brigade, and maintain the bluff.

 

[wsa111]

Blueroo, go with a 7448-350 holley at the most.

Anything larger is a catistropic loss of power & ecomomy, William

 

[powerband]

I've tried both the H/W 32/36 and a 7448 on a 170 with a performance built head/valves and stock cam with @9.5:1 compression. I was testing the head before using it on a 250.

The 32/36 is more drivable and a smoother operator but the 7448 has more low end grunt. The bigger 7448 is susceptible to loading and could use tuning for a 170.

Once the H/W secondary is open, the difference is small, but low speed performance is a choice worth experimenting with the two carbs.

Powerband .

8)

 

[CobraSix]

Remember one thing:

Unless you are going Direct mount (which you really can't with a log head) or changing to an Aussie head modified for a 4v carb (like I did) you still have to cram all that air through a 1v opening. The draw down from a 4v to a 1v is huge and I think you will lose more then you will gain as a result. the 2v-1v draw down isn't as extreme and offers more gains then loses.

I would seriously look at a 2v instead. Tested and proven upgrade.

Slade