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Is anyone using a carb spacer under their Holley 94 on a 239 flathead? They are advertised to improve air/fuel vaporization through and out of the carburetor as well as changing the effective intake plenum volume. Do the phenolic ones also reduce heat transfer from the manifold into the carb? Has anyone actually seen a benefit to installing one on a stock 239 flathead? How thick a spacer did you use?
Well my Holley 94 is on a Y-block, but I have the carb spacers. These are what came on it. I think it is about 6 of the gaskets stacked.
Not sure if it helps any.
If your carb is getting too hot, just use 2 or 3 gaskets as Joe did. At one point I blocked the heat risers in the manifold due to a perceived overheating problem, and quickly found it unsatisfactory. On a 70° day, I had to run the choke for almost 10 miles, and actually had ice forming on the base of the carb.
What kind of spacer claims an increase in plenum volume? Is it open between the 2 barrels? Hard to imagine any benefit.
The articles I have read were about spacers from 1" to 2" tall by MotorTrend. Here's their quote "Spacers are said to improve air/fuel vaporization through and out of the carburetor. Anytime the air/fuel charge has to turn sharply coming off the carb, it increases the chance of separating the fuel from the air. If there's big drops of wet fuel instead of an ideal fine, homogeneous mist, performance will be adversely affected. By raising the carburetor higher, there is more time for the fuel to gently turn in to the intake runners, plus less chance of the charge bouncing sharply off the plenum floor. Additionally, changing the effective intake plenum volume and height with a spacer may change the intake manifold's tuning resonance".
From everything I've read and seen, a carb spacer is a good thing. Typically anything between 1 and 2 inches is optimum.
Check out "Engine Masters" on Motortrend. They have several episodes where they test different applications with carb spacers. Its pretty interesting.
This is kind of getting away from the main discussion but still related. I made carb spacers for the dual carb set up in my '37 Buick. The dual carb set up was only offered in the Special in '40 and '41. I have have '40 engine in the car. In '37 and '38 the engine sits level in the frame, the later models the engine sits at a slant toward the back. If you install the dual carb set up in the earlier models the carbs will be uneven and tilt forward. I made two aluminum blocks that have a angle to compensate for the slant. It was pretty easy with a piece of 1/2" thick aluminum, a drawing, hole saw and a friend with a mill. I could have rig something up in my drill press but I knew someone with a mill.
If your carb is getting too hot, just use 2 or 3 gaskets as Joe did. At one point I blocked the heat risers in the manifold due to a perceived overheating problem, and quickly found it unsatisfactory. On a 70° day, I had to run the choke for almost 10 miles, and actually had ice forming on the base of the carb.
What kind of spacer claims an increase in plenum volume? Is it open between the 2 barrels? Hard to imagine any benefit.
Ross,
When you say you blocked the heat risers, do you mean on the spot on the stock intake manifold under the carburetor on the drivers side where the paint always burns? The old trick there is to use some pennies or one penny? Is this what you are referring to?
Ross,
When you say you blocked the heat risers, do you mean on the spot on the stock intake manifold under the carburetor on the drivers side where the paint always burns? The old trick there is to use some pennies or one penny? Is this what you are referring to?
Yes, but pennies weren't a tight fit, so I used some 0.012" shim stock I had to block off at the gasket. That way I could also pull them out if I decided against running that way (which I did) without pulling the manifold. The passages are on both sides, and run thru the manifold. Blocking them also makes for popping on deceleration, which some think is cool, but I don't.
I'd like to use a carb spacer but for a different reason. I need a vacuum source for my upgrade to power brakes in my 50 F1. I'm running a stock flathead 8 with dual Holley 94's on a Fenton manifold. There is no boss on the manifol that can be drilled and tapped for a fitting, except for a small one to run the vacuum advance. I was thinking of using carb spacers and installing a vacuum hose fitting in one of the spacers. Does anyone here have experience with this? Will I have enough vaccuum this way, to run the brakes? I'd appreciate any suggestions! Thanks!
The stock distributor vacuum advance is not designed to be directly connected to the manifold vacuum. I believe this should be sourced from any single one of your carburators vacuum advance ports (blocking off the other). This would leave the manifold vacuum port open for accessories like wipers and possibly your brakes. I don't know the size of the manifold vacuum port, but the standard for boosted brakes is 11/32 hose - and yes, the oddball size of 11/32 is specific to ensure that proper DOT compliant and vacuum rated hose is used. Don't use 3/8 radiator, fuel line, or whatever as they can collapse under vacuum. This also means that the typical 1/8 NPT barbs may be too restrictive.
There are Holley/Stromberg risers that incorporate a small 1/8 NPT vacuum port, but I would wonder if that could cause some tuning/matching issues on a dual setup of the vacuum draws were not even, and again, likely too small for power brakes.
The main purpose (today) on a street vehicle is to use a phenolic spacer to somewhat isolate the carb from engine heat (intake manifold) to prevent fuel percolation (ethanol laced) (was also a problem back then) in the carb.
Differing heights can also offer different HP/torque ratings but you have to be careful of ACL height.
Thank you for your input. I got this truck in 1970 and put a 289 in it. Now putting a flathead back in. I have not worked on a flathead since 1970 ha, ha!
Yes, I can route my vacuum advance to one of the carbs. The drilled boss in the manifold was plugged when I got it. I put a threaded flare fitting in it for the vac advance but if I'm not using that port, maybe I can enlarge it and install a fitting for the brakes. If it doesn't work, I can always just plug it and try something else. Thanks for the information about the 11/32 hose. I was not aware of that..
Mike
Does your manifold have a boss right behind the carb, where the plug is in the pic below? Big Truck manifolds had that for power brakes. If you have the boss but it isn't drilled/tapped, you could put one there, but you need to be sure you don't drill into the exhaust crossover passages.
