Frenchy4g63

So I've been doing some thinking lately about stroker motors. With all the cranks available now, K1, Eagle, Jun etc.. It seems there's a ton of options out there. I'm trying to find that perfect mix of quick spool and high rpms, as I'm sure a lot of you are as well.

So here's what I'm thinking, using the 4g63 block, what about using a 97mm crank with the stroker pistons from a 4g64 crank stroker, and then using a 1.5mm longer rod? this would help with spool and help with top end. Or take it one step further and use a 94mm crank, same stroker pistons, and a 3mm longer rod? Both of these seem like great options, am I not thinking about something that I should be?

I calculated the rod ratio of both these combo's and they are pretty desirable.

97mm stroke/1.5mm longer rod = 1.56
94mm stroke/3mm longer rod = 1.64

I'm curious to see what EvoM guru's and engine builders have to say. This would also work with the 4g64 block, but the math would be differant obviously.

Frenchy4g63

bump

anyone have any input, good or bad...?

Frenchy4g63

two days and 58 views and no comments?

comn people, someone has to have some input whether this is a good idea or not. Is everyone happy with the 100mm 4g64 crank, or spending thousands on a Jun, Cosworth or Tomei stroker?

Maybe I'll just have to try it and hope everything works out as well as I think it should.

littlemilla3

iTrader: (2)

The longer rod and slower piston speed of the 94mm crank will be more desirable...

Frenchy4g63

It would be better as far as its high rpm capability, but would suffer on the low end. They both have tradeoffs, but still seem like good options.

I'm leaning towards using the 97mm crank, as my car is going to be a street/drag/track car, and I think it would be better for my application. If somone were building a street/drag car, the 94mm option would be perfect in my opinion.

94AWDcoupe

iTrader: (125)

Changing the geometry of the rod is not worth the gains. a 300$ scat or eagle rod is all that is needed for 99% . a custom rod runs 750 and takes two to three months to get. The 2.3 in the stock 2.0 block with stock rod length works very very well. Why change what works? A 94mm or 97mm crank will be just as sweet mated to stock length rods.

Ted B

iTrader: (6)

The primary purpose of using a long stroke crank is to increase displacement. In this case, I'm not sure I agree with compromising the increase in displacement to increase the rod/stroke ratio. Not because I don't think increasing the rod/stroke ratio isn't a good thing, but not necessarily at the expense of displacement in this case. Also, as to what stands to be gained from this expensive exercise in real world terms depends heavily on the type of application.

Frenchy4g63

Wouldn't you still need a custom piston to do that? So, you would still need custom parts either way.

Frenchy4g63

Yeah I guess I was trying to think of the easiest way to use a 97mm crank. The purpose wasn't necessarily to increase the rod ratio, but to gain some high rpm capability along with the added displacement. I figured instead of making up the differance with the piston, do it with the rod, and gain a little better rod ratio.

I could certainly use the stock length rod, when I figured the rod ratio with the stock length rod it was 1.55 so not much of a differance, but like I said, if I need to get a custom part, I'd rather at least get some added benefits from it.

FWIW I got a quote from K1, with their crank, rods, and JE pistons for the same price as Buschur or AMS's stoker's with Crower/Oliver rods.

littlemilla3

iTrader: (2)

I think either option would be great, but using the 94mm crank with the longer rods would be a great middle-ground to increase displacement and keep a desirable rod ratio and piston speed, which will make the motor much more reliable long-term and make it less prone to problems when you need to rev it higher to make good use of cams and/or turbo upgrades. It would be nice to have a fat powerband from 4k to 8k.

Ted B

iTrader: (6)

FYI: Increasing the rod/stroke ratio by lengthening the rod does not decrease average piston speed. The piston travels the same distance in the same amount of time, regardless of rod length. The only ways to reduce piston speed are to shorten the stroke or turn less rpm.

littlemilla3

iTrader: (2)

Yeah I was stating the 94mm crank will result in a lower piston speed than the 97mm crank.

littlemilla3

iTrader: (2)

I was bored so ran some quick numbers. If you bore it .020 or .040 inches over , it will obviously be slightly larger.

85mm bore x 88mm stroke = 1997cc (stock)
85mm bore x 94mm stroke = 2134cc
85mm bore x 97mm stroke = 2202cc

Tell me if I made a stupid error, because I'm tired and it's possible!

Frenchy4g63

yeah that's right, for reference the 100mm/4g64 crank with stock bore is:

100mm x 85mm = 2270

What I really like about the 97mm crank option, is you could rev the 97mm crank stoker 300rpm higher, and the piston speed would be the same as the 100mm crank stroker, I doubt you would lose 300rpm in spool, so I think you would benefit from using it over the 100mm crank.

I think I'm gonna give it a try, I need to get some quotes to see how much custom 151.5mm rods are gonna run. If their too much I'll just use stock size 150mm rods and get a custom piston, which should be cheaper. I'm thinking Pauter rods, cause I know they'll hold the power and they do a lot of custom sized parts.

Also, just for fun I was doing the math using a 4g64 block, and if you added another 6mm to the rods for either the 97mm crank or 94mm crank, the rod ratio's are even better.

94mm/159mm rods gives you a 1.69 rod ratio, almost stock.
97mm/157.5 rods gives you a 1.62 rod ratio

If I used a 4g64 block, I wouldn't do this, but it's interesting just to see what's possible.

ZyBeR

iTrader: (2)

OMG... Why reinvent the wheel?

JUN Auto in Japan is and always will be the No.1 4G63 tuner in the world (period).
They use a 94mm crank, why? Maybe they just rolled two dices and made a crank with what ever stroke there number suggested.. Or NOT! R&D is what it's called.
No offense, but you will never be able to redo there work, nor get there experience.

I know I will get lot's of **** from this post from n00bs but I COULDN'T CARE LESS!

It's of a reason JUN is ranked No.1 tuner.
It's of a reason the fastest Evos uses there parts (and no I'm not talking 1/4 mil cars).

And one more thing.. No one uses a 85mm bore in a built 4G63 block, that's stock bore. Always, Always go to the first over dimension (85.5mm) and hone the cylinders to make sure you get a perfect surface.

If there is anything you like to know about JUNs products I can tell you the most as I have worked with all engine parts they supply to the 4G63.

If I had to choose another brand of stroker kit I would go with Cosworth, they make a replica (almost) of the JUN kit. Cosworth manufactures JUNs pistons after JUNs specs.
There are some differences between the JUN and Cosworth cranks, if you call Cosworth they will tell you exactly what it is, but it's also a slight price difference to Cosworth advantage.