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 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?
1. Don't know about the "Potvin" cam, can vouch for the Isky line! The Isky "88" would be used in a heavy ride, OEM Fords and Mercs, the "400-Jr" in a rod type (lighter) ride! Isky calls for radiused lifters, we use the "Johnson's" still. 2. The 3.312" x 4.250" is no problem. Have recent one drove from N.Y. to the James Dean Run in Indiana. Drove through the Pa. mountains in a '49 Merc convertible, probably near 4000#, give or take a few. This build was recently dynoed before delivery! Had 155 HP/265 Torque at some nice RPM band. 3. The Eagle crank is the easiest to work with, the Scat rods are also the easiest to fit in the block with the 1/4" arm (and plenty strong enough), and Ross pistons are the best choice! Ross uses a 1.5 x 1.5 x 3.0 mm ring pack! Less internal drag, more available power! (Add) Stud the mains, we use an ARP main stud kit, and stud the heads also! We have ARP kits put together for these! Thanks, Gary in N.Y. P.S. Couple tips, make certain the block gets finished honed with a "block plate", use Teflon coated cam brgs, and do the oil filter modification to the block! Also, we are probably the only shop in the country now "pinning" the heads and gaskets to the block, like the SBC's, with 5/16" dowel pins! Keeps everything stable and helps gaskets live longer! Edelbrock has increased the clearance between the bolt holes and the fasteners recently, allowing too much movement on the heads!
>> Isky doesn't specify or use radius lifters on any of the cams he currently makes. The famous cam of Isky's that DOES require radius lifters is the 404-A. It is very difficult to find a set of radius lifters - along with the drilling jig it takes to install them. The Potvin 425 Eliminator uses a standard flat-tappet lifter. The profile is actually on the ragged edge of running off the lifter, so it is a bit hard on them (edges), but it isn't a big deal. The 425 is one of the best cams out there for a bigger cube motor, that is ported/relieved for flow, has plenty of carbs, etc.. With that said, the best way to run a Potvin 425 is on a steel core (1932 if you can find one). Contact Pete1 on the HAMB - he can grind you one . . . if you find the core and he wants to do it. >> Ross supplies pistons with both the traditional style Grant rings (I think they're junk) - and on certain sizes can supply the metric ring pack listed above. I'd definitely try to go the metric route - much better rings than the old Grant crap.
I really like the dowel pin idea, even the old heads (mine are nos Sharps never used) wobble, and I seriously concidered it. Do you use exsisting w/ports at end of block, or drill and index new holes? I work with large diesels, 5/16 seems dainty
The fixture we designed (it is actually the block plate also) locates everything and allows the block, heads, and gaskets to all be drilled separately while maintaining perfect alignment! As I stated above, the 5/16" dowels get the job done, always have on the SB Chev's! The block holes (.308") allow the pins (.310") to be "pressed" into the decks, on this build none go into the water jackets, which avoids any possibility of "seepage" from the ends of the head gaskets, and finally, the head pin holes (.311") have very slight clearance! (Add) You should all consider doing the bronze-lined guides as well, never have a valve "hang" in a guide ever again, and also consider using the new "Teflon" coated cam brgs!! Thanks, Gary in N.Y. P.S. Here's a few shots, I actually have these posted in another section up here, showing the setup for pinning and the (95%) oil-modification.
So I wonmt have to do any extra work to install the 425 eliminator versus the 400jr. thanks for the reponses guys, I appreciate it. so a 4 1/4 stroke will be alright in a 30 ford pickup
Put a thin layer of modeling clay on either the piston crown or the combustion chamber, bolt down the heads, turn the engine over, remove the heads and check how squashed the clay is. Gives you an idea of piston to head clearance. Also works for piston to valve clearance on flathead engines.
Not sure if your a member over at thefordbarn but theres tons of flattie guys over there,you will get all your questions answered.
yes , it will wake up around 2800-3000 rpms Personal experience ! I would try a 400jr , only has around 260° duration but will make power from 2000 and up Or better cam is 1007B Iskys. I would still work on the ports alot as you are fighting too small ports compared to big CCs
Put a thin layer of modeling clay on either the piston crown or the combustion chamber, bolt down the heads, turn the engine over, remove the heads and check how squashed the clay is. Gives you an idea of piston to head clearance. Also works for piston to valve clearance on flathead engines Just to clear this up a bit, claying will check piston to head clearance but not piston to valve clearance. Valves are next to the piston in a flathead, not above it. You DO want to check valve to head clearance, esp with a high lift cam.
If you're having piston to valve clearance issues on a flathead that is usually because you broke a valve and the head of it is now beating the hell out of your piston . . . BAD . . . Really BAD
Huh???? I'm a hotrodder, and I'm over there. There are guys over there like Ol' Ron and Walt Dupont, plus heaps of others, who have been building flatheads with cams for decades, both for racing and for street. The knowledge there is huge! From the way you're bumping your post I get the impression impatience is a problem for you.
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