supercharger carb info needed
 

Hello
I have a 3-71 Detroit supercharger coming and might fit it to my 34 Tudor. I am contemplating what would be a good carb for the application to the 255 flathead. Don´t need to fit multiple carbs if I can have the same with one 4-barrel. I would like to have one big carb that is flowing enough for this application. Don´t need much more hp - just a little more torque up the hills.
Some of you must have already done this game so I look forward to your suggestions what is the best carb for this exercise.
As always - Thanks for all your input - highly appreciated!

Re: supercharger carb info needed
 

Your preference to use the four barrel is a smart one. For a size I would recommend a Holley 600 CFM. My experience with supercharging the Ford flatheads for street application's has proven to me that 600 CFM is spot on perfect. In reality with the 600 CFM size carb you will actually see economy as well as power to pull hills. For my all out supercharged flathead's the CFM flow I use on my little 292 cube V-8 with one four barrel would shock even the big block crowd.
Ronnieroadster

Re: supercharger carb info needed
 

First, we must be clear on whether this is blow-thru, or not? Probably not, but it makes a difference. The ideal size 4 barrel carb for a small street Flathead is the 465 CFM Holley. This is especially true where good usable low speed torque RPM is desired while maintaining good top RPM HP. But, even more important than specific CFM sizing, is the requirement for jet sizing to be safe. I suggest a good A/F ratio meter so you can start somewhere in the 11 to 12 area while seeking the ultimate for your combination. The ignition combination will be a consideration to make the best use of the new blower.

Re: supercharger carb info needed
 

465 CFM is in no way adequate for any supercharged flathead application. The throttle response as well as the lean out situation with that size carb will cause issues. Your way to lean. Be very careful because your going to burn a hole in the top of a piston being to lean. My extensive real world hands on experience has shown the minimum needed CFM is 600. Jet sizing from the out of the box Holley is an excellent point to begin with. The 600 Holley with the vacuum secondary will work perfectly. Flathead V-8 supercharged set ups using a GMC blower will easily produce 8 pounds off boost when under driven as much as 20 percent even the 371 which by the way has the carb sitting on top of the blower. With out the proper CFM damage will result.
Ronnieroadster

P.S. ignition should be a minimum of 8 to 10 degrees initial with a total of no more than 20 degrees. Ask me how I know

Re: supercharger carb info needed
 

Thank you Ronnie for this very valuable information. I will go this way. I learned a lot about supercharging and the adjustment of Hillborn injection and ignition on Max Lambky´s Vincent streamliner which I drove for 10 years. Of course this was a bit more power orientated as we were running alky and had 45 degr fixed ignition for the most power.
On my Tudor I have a Chevy distributor that has various screwthreads in the flyweight stop so I could adjust full advance there and still get 10 degr initial timing. I will get back to you when the blower is here - Thanks again for so much valuable input!

Re: supercharger carb info needed
 

I have nowhere as much experience as Ronnie, but I can say no one knows more about supercharged Flatheads in my opinion. I run a 600 CFM Holley with vacuum secondaries. It's VERY tunable. Make sure you're using an A/F meter to see what you're doing through all rpm's, loads and boost.

Re: supercharger carb info needed
 

Nearly any size or type carb can be set to provide a safe A/F mixture. The CFM rating does not control the A/F mixture.

Re: supercharger carb info needed
 

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Pay attention, Guys & Girls! Two SMART folks here passing some interesting ideas back & forth! DD
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Re: supercharger carb info needed
 

When I decide to add my 2 cents to a post I do it based off actual seat of the pants experience. When it comes to Ford flathead high performance be it horsepower or reliability I went about it by teaching myself by trial and error. This I have found while frustrating at times has been perfect for learning the correct way of doing this stuff.
My first experience with my own supercharged flathead began in the last century during 1978.
My first blower was a 671 GMC with two 600 CFM Holleys on top. Yes you read that right a 671 on my little 258 cube Flathead. The first thing I learned was how easy it was to blow head gaskets when using Edlebrock heads which were resurfaced to much. Boy the number of Victor big bore copper head gaskets i went thru in those early learning days is amazing. At least they were not expensive at $4.95 each I still remember the part number 3044 and 3045.

Next learning curve came when the dome tops of the forged pistons decided to go the other way they went down! To much advance not enough octane in the gas and to much boost will melt aluminum.

My wife and I drove our 671 blown Flattead powered Deuce roadster all over the tri state area and as far as Memphis Tenn. attending the Street Rod Nationals. On the open road miles per gallon was always 20 or more. As the years went by I learned more and more about that blower combination.

Racing at the drags that steel roadster and little 258 cube flathead would run low 13 seconds at over 100 MPH in the quarter. Many guys running overhead engines in their Hot Rods thought running heads up against my flathead was an easy win many found out it was not I beat all of them back then.

Fast forward to this Century I decided to try my hand at Land Speed Racing so my first engine i used in my race car was that little old 258 from so long ago and that 671 GMC blower and the two Holley 600 four barrels. Speeds in the race car as a Lakester 182 MPH then I converted to a rear engine roadster combination same engine 172 MPH. My little engine continued to surprise more than 30 years latter.

Above is a bit of history that most don't know about me. So when I decide to add my thoughts to certain posts its done based off experience not an attempt to just write something. I enjoy helping when I can.
Ronnieroadster

Re: supercharger carb info needed
 

Ronnie .....That is downright impressive, and rightfully-gained knowledge and wisdom through payin' your dues.

I don't know about the rest of you's guys, but I'm STILL payin' attention, and waiting for any more of this wisdom to come to light. DD
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Re: supercharger carb info needed
 

Wow!!


Thanks Ronnie for taking the time to write this up, teach us and hear some great history!


Glenn

Re: supercharger carb info needed
 

Thanks Ronnie!

Re: supercharger carb info needed
 

I have never tried building a supercharged flathead because they are not allowed in vintage circle track racing so there is no market.
However, I have wrenched on several fairly good ones over the years.
For street use with a 3-71, a 600 cfm 4 barrel carb would be ideal. I would use a Holley because they are simple to street tune. They are very simple to adapt to a GMC blower.

Here is a pic of a 36 coupe with a 3-71 and 2 Stromberg 48's back in the mid 50's. It turned 110 in the low 12's consistently.
404A cam. The guy drove it to work during the week.

Re: supercharger carb info needed
 

Interesting the pictured coupe is using about 320 CFM of carbs yet appears to be described as a good performer.

Re: supercharger carb info needed
 

I am running a Holley 600 cfm with vacuum secondary on my Mark Kirby built 286" flathead. Runs super strong after some tuning.
Details.... 12d initial advance... 26d total at 2000 rpm.... boost control retards timing
1-3d per pound of boost .... total timing @ 5 lb boost is 18d
The Holley has the Weber conversion which uses Weber jets for infinite tuning ability..

Re: supercharger carb info needed
 

That's is an excellent combination plus the fun part is the infinite tuning possibility's. Having the option of being able to come up with the best tune is overall an additional bonus.
Something else that's important to remember as the years pass the actual gasoline we buy has changed dramatically. Gasoline once actually smelled like gasoline {last century} today it smells more like kerosene in many areas. This change over the years has shown we need to be able to adjust our tune ups to compensate. To me its part of the fun staying on top of what works to make a combination perform and give some economy as well.
Ronnieroadster

Re: supercharger carb info needed
 

Yea but there's certainly more performance to gain with 600 CFM

Re: supercharger carb info needed
 

You are right and don't think we didn't ride him about that.
He was very stubborn about several things. He was also convinced that cast pistons were stronger than Forgedtrue pistons and proceeded to break a piston about 1 a month. He fixed that eventually but never did fix the asthma problem.

Re: supercharger carb info needed
 

Thanks Pete for the history


Glenn

Re: supercharger carb info needed
 

Unfortunately many of these posts have lost sight of the OP request and established standards. This was not, I thought, about what to do for maximum HP. But rather, a request for the best combination for the small cube engine to torque up a hill. I have provided the appropriate suggestion to satisfy the sought after information. There are several options for what would "work out" here but the optimum would be nearest to what I suggested. There is a very wide range of A/F mixtures and CFM options which seem to work just fine with our Flathead engines because the torque curve is flatter than most other engines. But, in many cases these are "seat of the pants" assessments which are not quantified, realistic, evaluations. Just because something seems to work "OK" does not indicate it is the best.
I do not make suggestions just to be talking. I present only the facts. People can choose to learn or not.