Spacer vs NO for 4mill

[Ieat4strokes]

was having a debate with a buddy today, he was telling me i wasted money getting stock cylinders "ported for a 4 mill when i couldve just went with a spacer plate setup. Whats the power difference? Is there one? I went with a 4 mill FAST setup and i basically didnt have any ammo to fire back at him other than its what most ppl on here are doing. He said he's going with a 4mill longrod and a plate "since its cheaper and he wont have to get some cylinders ported....thanks guys

[AKheathen]

a ported stock stroke will make more power than a stroker with a spacer plate. not porting really short-circuits alot of power, and restricts some flow, basically.

[broncbob]

From what info I can find on this, the pistons used on the long rod set up change the port timing a bit, and the spacer plate only makes it worse. No I have talked to has told me it's a good idea to run the spacer.

[jbooker82]

Just drag race him and see who wasted there time and money.

 

When you put a 2mm thick spacer plate under the cylinders your physically raising the cylinders. That in turn causes you to raise all the ports 2mm. So they don't open when they should when compared to degrees of crank shaft rotation.

 

A 4 mill crank will cause the piston to fall 2mm farther down in to the cylinder, and pop up 2mm out of the cylinder. You cant have the pistons hitting the head so you have to space the jugs up off the cases, or run a cylinder head that has been cut. (usually a cool head with stroker domes). So when you put a 2mm thick spacer under the cylinders, the piston now doesn't pop out 2mm out of the top, but it falls 4mm farther down the cylinders. So now the piston falls 2mm farther down below the ports which isn't good for performance.

 

The best way (the way you did it), is to run no spacer plate. Most builders that port for a 4 mill start off by lowering the ports. That way the piston isn fallen 2mm below the transfer and intake ports. Then they don't have to raise the top of the transfer ports very much because they opened them up down wards already.

 

That is why you hear guys say once you port your cylinders for a stock stroke crank you can't have them reported for a 4 mill. When they port for a stock stroke crank they just raise the top's of the ports. Then when you go to a 4 mill they need to lower the ports back down to they are level with the piston. Now you have transfer ports that are way to big and performance suffers.

 

Yea if you don't have a very aggressive stock stoke port job you might be able to have them reported for a 4 mill, but the builder will have to determine that.

 

josh

[Ieat4strokes]

Thanks everyone. I did tell his dumbass that he had a race waiting on him when he got ready.

[Alex29573]

i was told that for example, in a 4mm stroke you would port each window 2mm down and 2mm up

 

after that you would have to do w.e else you would do for the regular drag/dune port

[AKheathen]

down 1.5-2mm to match the piston, yah, but up 2mm-it doesn't work like that. you set them at the desired degree of durration, so you can get like .5mmon the transfers, and 2.4mm on the exhaust, for example...just what ever matches durration to run right