Hi All,

I would like your opinions on which way to go with my Flathead v8
It's a stock Mercury 8BA V8 with the 4" stroke crank and a 0.030" overbore, I will have headers and a dual exhaust

I intend to drive this truck so am looking for reliability and with gas over here around $6 a gallon MPG is an issue

Carbs
I have 3 holley 94's, my plan was to use all 3 with a progressive linkage, other people have said I would be better to use just 2 what do you think ?

Will I be OK putting 1 on till I find a manifold etc?
I dont want to run this engine lean.

PCV
I will fit a PCV, I believe I need to add a vent to the oilpan. What's the best way to do this

Heads
I had a cracked head so I bought 2 good RT heads, I have read on here that these will give low compression, can these be skimmed enough to get a reasonable CR or should I find some more?

Cheers

Steve

 

Steve

Browse thru here.

http://www.btc-bci.com/~billben/flathead.htm

 

Thanks

That's a great site

 

Steve, the 49-51 merc was an 8CM. It came stock with one carb so I doubt you have to worry about running lean with one carb.

If you're concerned with mileage I'd go with one. In rare instances 2 carbs will do as well as one, but usually the more cfm you have the more fuel you use. You can't run progressive linkage with 2 carbs - that's where guys have trouble with half the engine running lean. Three works well, but uses more fuel.

PCV - if you use the late series intake manifold you do not need a pan vent. That's only necessary when using an early (32-47) intake on a late (48-54) engine.
Early flatheads pulled fresh air in the pan and expelled it from the road draft tube.

Henry improved the ventilation route with the late flathead - it pulls fresh air in the oil filler cap and expells blowby from the road draft tube for better circulation throughout the engine. The PCV can be plugged into the road draft opening and routed to the intake manifold near the base of the carb (center one if multiple carbs). Simple as that.

The RT heads will work - close to stock performance as they are or even slightly better. 52/53 Ford EAB heads have the highest CR without milling.

 

I assume you have measured the stroke and bore, so you know that you have the 4" throw crank. My truck had Mercury 8CM heads on it but was a Ford crank. The RT heads will give you a higher compressions ration than the stock heads which would have been 8CM. The 8CM heads have higher volume to compensate for the longer stroke. For your truck, don't know if that's good or bad, just be aware it will significantly increase the CR. I just took off the 8CM heads from my 239 (3.75" stroke) because they were giving me too little compression and bought a set of NOS RT heads.

 

From a chart that appeared on the msn flathead group site recently, using RT heads on a stock Merc flathead will result in an increase in CR from 6.8 to 7.2 I doubt that you'll notice a 'seat of the pants' difference.

I run EAB heads on a Merc engine which should have a cr of 7.6. This is very streetable on regular 87 octane gas.

 

Two thoughts on the carb situation

A cheap yet effective upgrade is to find a Y-block carb, Holley 2110-EE or equivalent. These have the same bolt pattern and externally look identical. But they have 1-1/16"-dia. throttle bores. The stock model 94 has 13/16". If you do the math, the 2110 has about 70% more throttle area (the venturi's are about proportionately bigger, which is really what matters) The 2110's have drillings for Load-a-Matic distributors just like the 94's, some also have an "economizer" valve that looks just like a power valve on the bottom of the body, doesn't seem to either hurt or help. (I've never been able to figure out what it really does) I'm running a 2110 on a stock 239 Ford flatty and it works well; I went to it because I'm at high altitude and the flatty needs help breathing the thin air. Usually, a bigger 2-bbl carb gets somewhat worse mileage, but I haven't noticed the difference. (mostly because mine is hardly ever on the road )

A more modern approach is the Holley 350 cfm 4-bbl. Everyone I know who has gone to it loves it, and it is a more modern design so it meters more correctly. Overall I would expect it to beat a two-deuce setup hands down for both tunability and mileage. But you have to use an aftermarket distributor with mechanical and vacuum advance, like say the MSD drop-in's.

 

edit -- Sorry --double post

 

Here are a few observations, suggestions and corrections based on about 50 years of building, driving and racing flatheads.

1. 8RT heads will result in roughly a 5.8:1 cr on a 239 and will result in around 6.7 with a 30 over 255. Common published data groups the 8RT and 8BA head together which is incorrect. Carefull measuring of all the various castings by myself and others show the 8RT to be the lowest cr of the 8BA family. Ford did not acknowledge this but he was wise to lower the cr in trucks which already had block cracking problems with the 59A. When gas octane improved light trucks eventually were shipped with 8BA heads towards the end of flathead production. The highest cr stock head is the 52-3 Ford car EAB.

2. Nothing looks better than a multi carb flathead. However unless you have a cam installed and some basic porting to make use of the increased flow all you will achieve is sooty plugs and a leaner wallet. OTOH, an early 255 used a Holley 885 backdraft carb of around 210 cfm as compared to 165 or so for the 239, 52-3 models used the teapot 1901.
Merc intakes used a 4 bolt carb & matching intake and one very easy way to get some cheap performance is to install a Rochester small base 2G series. They run in the 225-275 cfm range depending upon original application and there is plenty of internet info on decoding the part #. The 2G will have to be mounted in reverse to utilize the original throttle linkage. The 49-51 Merc intakes are aluminum and polish up nice.
OTOH, if you insist on the 3 carb intake then the suggestion of a Y block carb in the center is a good one. However I would install dummies on the ends until such a time as oil is discovered below (not on) Portsmouth Harbor or you have installed a nice lopey cam or both.

3. The fitting on the base of a Y Block carb is referred to by Ford as a spark advance valve. The purpose was to control the advance during heavy acceleration and low engine vacuum. It IS NOT an economizer valve which is also known as the Power Valve in Holley terminology. For use on a flathead, remove the spark valve and plug the hole.

4. When running multiple carbs or different type of carb it is best to upgrade the stock Lodomatic distributor to something that gives both mechanical and vacuum advance via the now conventional method of ported vacuum. The 94 family of bases can easily be modified for this feature, Rochester carbs already have it. When using 94's plug the venturi port on the rear of the bowl. Going to an electronic distributor will also improve fuel economy and they are now available in 6 and 12V versions. Some are problematic when used with sparking generators and also poor grounds.

 

Thanks for the clarification on the spark advance valve, 'Merc. As far as plugging the passages for use with a mech/vac distributor, it always seemed to me that you just wanted to plug the portion of the passage that goes down to the throttle blade area, and leave the one that connects to the venturis. If you plug the connection as you describe, where do you get a new signal?

I was confusing two different trucks here, I was thinking this was Narwhal's Merc with the Ford intake and a 94 on it. I am further confused now by the description "Mercury 8BA". Are 255 Mercs considered an 8BA? Seeing this is a British variant, were there differences in export models? This is really an EAC, isn't it?

 

Thanks for the replys, thats some really useful information

I shouldn't have called this a 8BA
I assume this is a Mercury motor, it has a 4" stroke, the block has "C1BA" cast into it, the heads are marked 8CM-C and the cam is stamped "8CM"

This motor has been rebuilt at some time so could be built from anything.
It also has adjustable lifters and came modified with a modern 2 barrel holley carb adapted to a 3 bolt manifold and a single water pump which I have junked to replace with 2 original pumps

The truck originally came from South Africa where they were assembled from parts made in the USA and Canada

Thanks again

Steve

 

You cant use any signal from a 94 on a modern dizzy. You need PORTED vacuum, not venturi and not manifold. The Lodomatic works in exact reverse of what you need.
I drill a small hole in the carb base just above the throttle plates and epoxy in a 1/8" brass tube. Only 1 carb needs that mod in multi carb setups.


Steve, that is a Canadian 1951 8BA block with Canadian 49-50 heads and cam. Original Mercs came with a 4 bolt intake and a backdraft Holley 885 carb for hood clearance in 49-51, intake was aluminum. 52-3 used a cast iron 4 bolt intake and the 1901 teapot carb.
Many swapped to the Ford 3 bolt intake & carb since rebuild kits for the Mercs were often scarce and the 1901 was known for summoning the fire brigade on numerous occasions.

Im wondering if you can elaborate on the single water pump that was on it? That would be an excellent idea for some applications. The version that uses a Chevy 409 pump is the only one Im aware of and is way overpriced IMO.

 

Carl, thanks for the updated info on the RT heads. I missed that somehow or other. From your cr info, am I right that they're a couple cc's larger than the 8CM heads?
Thanks
Tim

 

There were 2 steel plates bolted to the block over the holes where the original pumps fitted, the single pump was bolted to the plates and driven off a pulley welded to the original crankshaft pulley, a alternator was mounted on the side driven off the same belt

I put a couple of pics in my gallery "Flathead V8"

I still have the pump somewhere so could take a few close up pic's at the weekend if you're interested

Steve

 

Yep. Ron Halloran, Mike Bishop, and a few others took up my offer to do a real comparison of all of them several years ago. I wanted it that way to get a better sampling from different parts of the country. AFAIN the MSN crowd did absolutely nothing except stroke their egos and rehash old info. I dont even bother looking over there, if info is not on Fordbarn or HAMB it doesnt exist!

Since Ford casting tolerances are all over the place, Ive seen as much as a 6cc Delta, the 8RT averages 85-87 cc. I used 85 in calulating earlier in this thread.