4mm Stroker Crank

[duneslinger]

Hi I've got a question for the experts here, a friend of mine just bought a trick racing 4mm stroker std rod crank they cut his 18cc trinity pro domes .80 to clear the pistons. would this be the same as moving the dome up 2mm for the added up stroke of 2mm I though this was why they sell a spacer plate and wouldn't this set up require the port to be reworked. just looking for some insight. thanks

[boonman]

Yes, the porting should be re-worked. Being that you have another 2mm of stroke on either end, compression is going to raise. You are effectively at this point LOWERING the exhaust port. Thus, providing more air to be compressed, and this must be changed. With them cutting .080" out of the dome, that is a little more than 2mm. 2mm=.0788" Not much. .0012" more. Anyways, The porting is a major factor with a stroker. Also, you are correct in your belief that this is one reason they sell a spacer plate.....

[fixitrod]

I would also add as far as porting, Vitos told me you can use his spacer plate and lower your ports 2mm to keep stock timing.

[PassionRE]

Was Vito's referring to a 2 mil base spacer plate?....JIm

[D34]

I would also add as far as porting, Vitos told me you can use his spacer plate and lower your ports 2mm to keep stock timing.

if a spacer plate is put n that changes the timing... just so u know... stock exhaust height with a 2mm spacer will put u around 190* exhaust... L8r d34

[fixitrod]

Was Vito's referring to a 2 mil base spacer plate?....JIm

That would be for the base spacer yes. I'm not sure about port timing and the head spacer.

[PassionRE]

Yes I agree D34, the transfer duration is increased from 120 to around 132 degrees as well. Vito needs to ck his degree wheel again....Jim

[fixitrod]

I called vito's to verify. I didn't talk to vito this time but he said about the same thing. You run the base spacer and lower the exhaust ports. He's saying that if you take 2mm from the bottom of the ports and use the spacer, the top of the ports will close at the same time. I'd have to see it on a degree wheel. The open duration time will be high.

[PassionRE]

Vito needs to ck his degree wheel again....Jim

Stock ex. duration is 180 degrees and with plate and +4 is 190. That represents ex timing being 5 degrees advanced..Jim

[fixitrod]

Makes since because were talking about the crank moving in a circle. They talk like it's just linear.

[PassionRE]

As far as ex. port (timing) is concerned , it is linear movement in reference to movement per degree of rotation. In this area of the stroke, that rate is fairly constant. BUT, since you have increased the stroke, movement is more with the same given degrees of crank rotation. Thus, your exhaust ports open 5 degrees earlier. And since they open up 5 degrees earlier, they close 5 degrees later ,bringing up the (duration) to 10 degrees more than stock....Jim