I'm building a motor for my rear engine dragster, I have just bought a set of Venolia pistons (nice) however they gave me for free (: a set of Jahns cast pistons with rings and a 15cc dome (3.80) would these be runable in a back up motor? they look heavy, I don't like cast pistons and a old design.

They are heavy and most likely use the old style thick rings. Modern pistons with metric rings provide less friction according to Ted's dyno test. Mummert offers forged pistons in stock stroke as well stroker pistons and kits. The old parts are nice to look at and talk about, but modern stuff is proven to make more power. But to answer your question, yes they will run, I think Tim just built a motor using a set of Jahns for a customer.

Glen Henderson



Freedom is not Free

Letohatchee, AL

Rear engine dragster with a Y? you have to keep us updated on that!

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

Cliff, the Jahns pistons required lots of clearance, probably .007-.008". Measure the skirt, its probably 3.793". Rings are likely 5/64 5/64 3/16".
Will we see it at the West Y-Block Shootout next year???

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Hi John, yes I am planning to be there with a car, These pistons look scary to me however it looks like a few guys run them with no problems, I am building 3 motors, a short rod, a standard rod and a long rod, I may use them in the standard rod motor, I am looking to turn them to at least 8 (cast piston?), I am still waiting for some parts (crank adaptor) this is an NHRA legal car (I just passed cert for 7.50 and slower) I am going to try to run this with the big boys, I think I will have to be a better driver, I know they will be faster, all of my friends just smile when I tell them I removed a Big Chevy and going to run a 300 inch Y block Ford, It needs to run a 8.90 dial in, (I think I have a lot of learning coming)

Cliff: IMHO, turning Jahn's cast pistons 8 grand wouldn't seem like a good idea. If they're similar to the ones sold many years ago, we found their specs on my buddies race engine were a bit iffy. Also, after some use, due to the design & postion of the dome, we suspected that they weren't exactly great for an even flame spread either.  Maybe best used on a hi po street engine?     


Paul

Sell them to somebody building a street engine, then Get some forgings from Ted or John.The cast pistons will not last in that serious a motor. By the way 8.90's are going to be tough on gasoline. We only have three cars capable of this an they're all Professionally built.

Frank/Rebop

Bristol, In ( by Elkhart) 

Another problem with cast pistons is their growth rate/expansion from race heat temperature.  You will not be as consistent with cast pistons as with forged.  I found that water temperature, oil temperature, and quick turn around for next race all caused my engine/car to slow down with a cast piston engine.  I ran electric fan, dual batteries, trans cooler, ram-air, everything to try to keep the car consistent, but if the temperature could not be controlled during heat races, then the car slowed down.  That problem went away with forged pistons, and the car became dead consistent.  Joe-JDC

JDC

Good idea Joe, I have a lot of parts, the only reason I was thinking of running these pistons is they were free and I cut can cut the dome to my liking

Cliff, I doubt the Y-Block will efficient past 7000-7400 rpm. The heads and intakes just don't seem to like higher revs. I think running it from 5000-7200 is realistic. Is it a powerslide or turbo trans or maybe you're going to C4??

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico