Flathead Questions and concerns!!!!

F

flatheadz-forever

Senior Member
I have been searching around and looking at different threads, and could not come up with a solid answer to these following questions:

1. Do you have to run radius lifters with the 425 potvin eliminator?How many guys out there run this cam on the street and will the 425 eliminator make more power than a 400jr? also will I have to use keyway lifters with the 425 eliminator?

2. Is 3 5/16 bore, and 4 1/4 stroke a good or proven combo?

3. What is the best quality crank rods and pistons to run in a full race street motor. forged pistons?

please help
 
To answer your #2 question, yes. The #3 question, I think a scat crank with 4 1/4" stroke, scat rods and ross aluminum racing pistons will work great for a hopped up street flatty. Those are all really commonly used combinations and can be purchased as a kit from places like Speedway.....
 
Last edited:
I think you will get many valid opinions from experts here - no one answer is the right one - the right one is what you want to achieve (power level, operating efficiency, ease of start and idle, power band, operating temperature expectations, ignition type, carburetion, valves, etc. and how much money you have to spend i.e. power has a direct correlation to dollars. That said - I selected an original merc crank stroked to 4 1/4 with 3 5/16 bore (286ci) Ross racing pistons - 21A Ford rods race prepped, L100 cam, Navarro blower heads and a S.C.o.T Blower. I recommend a thorough read of Joe Abbins 335HP Flathead Ford V8 book.:cool:
 
I have the book, I would like to make 200hp 260 tq It is going into a light 1930 model a pickup any advice on the potvin

I believe your merc crank would be stroked to 4 1/8 if you have 286, I am not trying to tell you what you have but Just did the math, because I am the one in need of advice just saying
 
flatheadz-forever said:
I have the book, I would like to make 200hp 260 tq It is going into a light 1930 model a pickup any advice on the potvin

I believe your merc crank would be stroked to 4 1/8 if you have 286, I am not trying to tell you what you have but Just did the math, because I am the one in need of advice just saying
Click to expand...

Sorry - you are right 4 1/8th crank for me:D
 
19Fordy said:
I have read many posts about SCAT cranks not being balanced very well. So do your homework.
Click to expand...

I agree, in fact I would never take a manufactures word that the part is balanced. Always have any rotating engine componant balanced by a reputable machinist. New or old those engine parts should always be checked and balanced.

That being said I think scat makes a good crank, it's always good paractice to balance any/all rotating assembly.
 
flatheadz-forever said:
No need for apologies here, how heavy is the car your motor is in
Click to expand...
Its in the 3 window in my avatar - I would guess the Coupes weight at 2,600lbs?
PICT0024.jpg
 
flatheadz-forever said:
I have the book, I would like to make 200hp 260 tq It is going into a light 1930 model a pickup any advice on the potvin

I believe your merc crank would be stroked to 4 1/8 if you have 286, I am not trying to tell you what you have but Just did the math, because I am the one in need of advice just saying
Click to expand...

I posted on the Hamb site about your build, but didn't put the "numbers" up there.

It's going to take some slightly "deep-pockets" to get to the 200 HP number, however, will most definitely be around the "260" torque number with the 4.250 arm in the program!

The build I mentioned over there, at 292 C.I.'s, made 155+ (peak) HP @ 4300 and 250+ (peak) Tq @ 2200. This was with the Isky "800" cam, single 4-brl!

We used a number of small "tricks" on the build, you can read about it on the Hamb.

Some of special items performed: flycut valve pockets (for unshrouding), fire-slot spark plug holes, dowel-pin heads, lightweight (Ross) piston/ring-pack, porting the bowls below the valves, etc. There was no porting perse, only a "bowl-clean up", and the "Stainless" valves remained at the 1.510" number!

Bronze-lined guides and "Viton" valve stem seals! Decks were done on a "CNC" ("ultra-smooth" finish, much like the aluminum heads come with) which helps seal the "copper" head gaskets securely! Studded mains and studded heads.

Thanks, Gary in N.Y.

P.S. This build incorporated the "modified" oiling system, idles with 25#/30# oil pressure (hot/180*), cruises with 55#/60#, and has a "bone-stock" Melling M-19 pump!
 
Last edited:
I like the 425 Potvin, It will make a great deal of power. It's about the best cam for doing so. It requires a great deal of spring pressure and is best made form a steel billet. It uses a standard flat tappet. The cam requires a hi idle to prevent lifter/lobe failure. Unfortunately getting 200hp might not be possable. I suggest you go to a roller cam.
 
flatheadz-forever said:
I have been searching around and looking at different threads, and could not come up with a solid answer to these following questions:

1. Do you have to run radius lifters with the 425 potvin eliminator?How many guys out there run this cam on the street and will the 425 eliminator make more power than a 400jr? also will I have to use keyway lifters with the 425 eliminator?

No. Flat lifters. Stock STEEL ones are best.
Yes, the 425 will make more power than the 400 jr.
No, keyed lifters are for the 404 type cam.

2. Is 3 5/16 bore, and 4 1/4 stroke a good or proven combo?

Yes.

3. What is the best quality crank rods and pistons to run in a full race street motor. forged pistons?

Best quality crank is a billet Moldex or Crower..(A cast SCAT is adaquate for street)
Best quality rods are Carrillo H beam..(SCAT is adaquate for street)
Best pistons are ROSS. PERIOD!

please help
Click to expand...
...
 
The Potvin 425 cam is called the "ELIMINATOR" for a reason. It is a great, high RPM cam. Probably the best flat tappet cam ever designed for racing and certainly the best I have ever used. Yes, it will make more top end power than a 400jr. but it will NOT make as much power in the lower speed ranges. I would not consider it a viable option for a street cam.

3 5/16 X 4 1/4 is a good street combo. Wiseco, Ross, Arias are all about equal Flathead forged pistons. If you go with a complete Scat balanced assembly it should eliminate any concerns about the crank being difficult to balance.

As others have said it is better not to listen to the hype and inflated numbers. A 200 HP goal will take much more work than a cam and crank assembly can give you. For the street a supercharger is the most reliable way to get your 200 HP. Even with a blower a 200 HP engine must be well thought out.
 
The only cam that requires radiused lifters that I can remember is the Isky 404-A. I'm running a Potvin 415 in my flattie but have not been able to find any specs on it.
 
GOSFAST said:
I posted on the Hamb site about your build, but didn't put the "numbers" up there.

It's going to take some slightly "deep-pockets" to get to the 200 HP number, however, will most definitely be around the "260" torque number with the 4.250 arm in the program!

The build I mentioned over there, at 292 C.I.'s, made 155+ (peak) HP @ 4300 and 250+ (peak) Tq @ 2200. This was with the Isky "800" cam, single 4-brl!

We used a number of small "tricks" on the build, you can read about it on the Hamb.

Some of special items performed: flycut valve pockets (for unshrouding), fire-slot spark plug holes, dowel-pin heads, lightweight (Ross) piston/ring-pack, porting the bowls below the valves, etc. There was no porting perse, only a "bowl-clean up", and the "Stainless" valves remained at the 1.510" number!

Bronze-lined guides and "Viton" valve stem seals! Decks were done on a "CNC" ("ultra-smooth" finish, much like the aluminum heads come with) which helps seal the "copper" head gaskets securely! Studded mains and studded heads.

Thanks, Gary in N.Y.

P.S. This build incorporated the "modified" oiling system, idles with 25#/30# oil pressure (hot/180*), cruises with 55#/60#, and has a "bone-stock" Melling M-19 pump!
Click to expand...

Gary::o Information if you will please "flycut valve pockets" is this the area around the valve,cut in the block, OR above the valve in the head?? and the "fire-slot" spark plug hole, is this a open grove cut in he head toward the cylinder??and clean-up the bowls under the valves I understand, but no clean-up of the exhaust ports to the outside?? I clean up or round the dam at the out exhaust port short of round the opening both front and rear ports ?? and do you support, the center main ?? .. I will be running "the modified" oil system to, hope I get your oil prssure :)...you do build a heck of and engine... thanks,.. its a good read. ... OLD....BILL :cool:
 
flatheadz-forever said:
what are the specs side by side of the potvin "400" and 425 eliminator alongisde the 400jr
Click to expand...

400jr:
Lift (.400 .400) Valve Lash hot (.018 .018) ADV Duration (258 258) .050 Duration (244 244) LC 111.

Potvin 400:
29-75 75-29 400 284 In .011 Ex .013
Potvin 425:
26-74 74-26 410 280 In .011 Ex .013
 
You must log in or register to reply here.
Back
Top