largecar379

this has probably been beat to death, but I'm not having any luck with the search button, so here goes....

I would like to know which way to go when building a 928 stroker, hopefully nothing stupidly exotic, maximum cc's without removing cylinders and putting in liners, but build one at a reasonable cost.

crank?
rods?
pistons?

I have a fresh 'drilled' stock stroke 5.0L crank (do these hold up to having them welded up and reground to 95.25 stroke? or should I just bite the bullet and buy a new one already stroked and drilled? if so, which crank supplier should I contact?)

I have read that a 5.85 rod is the way to go? if so, recommendations? or, can I go to a 6 inch rod and move the piston pin further up? How much total length (stroke, plus rod, plus piston top) can it handle or is recommended?

any recommendations for pistons? 968 or aftermarket, skirt or not? one way or another, they'll have to be 16V notched for my Euro 16V heads. Compression ratio to be less than 11:1.

I have a M28/44 block to build with, will bore to 104mm and Nicom coat at US Chrome. Already talked to US Chrome----overbore/coat/finish hone/ready to go, $1300 plus shipping and 3 weeks (as of this week)

The parts I have are from Stan Shaw, purchased the past summer. He an I have talked about going the stroker route, but he and I agreed I need further input......

Thanks ahead for the help-----

--Russ

Vilhuer

Get Scat or Moldex crank only when you have exact and final piston and rod weights on hand. This will save you from lot of problems. Forget any stock crank weldings etc.

Since you are not using Alusil block go with aftermarket pistons. There is no point in geting yourself problems caused by 968 pistons. They are expensive even when they are used and then you still need to modify them and rods too to make them fit together with 2 valve heads and Chevy rod pin holes. With aftermarket pistons you can also get compression ratio to whatever you want. Also get pistons even before you have block machined so that they will fit the block even if they will not turn out exactly like specs.

When you go with aftermarket pistons you can choose rod lenght based on that. So basically you need to select pistons which will need 5.85" or 6" rods and then get rods accordingly. Longer the better for rod angles so if you find pistons which will work with 6" rods go that route.

Total possible and desirable stroke + rod + piston compression height is obviously determined by block dimensions. You can calculate this from stock Porsche parts. Rods are 150mm long and I have piston compression height numbers somewhere if you don't find them from some previous message.

largecar379

Thanks Erkka,

Scott at US Chrome wanted a piston sent with the block.......

Glad to hear you say a 6 incher is the way to go, as my long time drag racing buddy said the same---leaves the piston at TDC longer, makes more power, he says......

I have your dimensions written down somewhere.....believe it was 232.35mm for total.

Looks like pistons first, then the other stuff....crank last.

Thanks--

--Russ

atb

Russ,

I don't know if Scat does single stroker cranks, I've only heard of them producing batch orders. Moldex does single order cranks. One of the advantages you have with the Moldex is that you can have the crank balanced to your specific set up. All of the Scat cranks required a significant amount of heavy metal to balance when using steel rods. If you get your pistons and rods first, you could supply the weight to Moldex and maybe they could get you at least in the ballpark for producing a pre-balanced unit.

Errka is right on shooting for 6.0 rod. When you calculate the rod ratio using a 5.85, it is almost a freak of physics that these stroker motors work, and that they can be spun as high as they are. A 6" rod gets you back into the zone of more conventionally accepted performance specs, let alone the other advantages you mention. Since you are starting with a clean slate, you have the advantage of using off the shelf chevy rods. Going with a Chevy LS-7 ti conrod would be very cool, and save on balancing costs later. I had a discussion with Dennis Kao awhile back about this, and he had stated a concern that the big end of these rods may be too narrow to work with the 928 bore spacing, but wasn't sure. I'd definitely be looking into it if I were starting a stroker motor now with a clean slate. If not an LS-7, maybe just an aftermarket SBC ti rod off ebay. I don't know what ti prices are these days, so it may not be in the budget.

Since you are designing your own piston, you will find that you will have a better selection of rings if you go with a size different than 104mm. For some reason this size is in a dead zone for conventional pistons, somewhere between a small block and a big block I guess. The good thing is by going a little smaller, you will have thicker cylinder walls after the boring process, and you will just be a little smaller then using a 968 piston. Probably worth the trade from a durability perspective. Reynolds put a .250" minimum thickness requirement on their alusil blocks. I think the majority of strokers have at least some part of their cylinders walls narrower than this limit. I think the thinnest documented is about .220", but no one is really talking. I think the majority of stroker owners don't sonic check their blocks after boring because they feel they are "committed" at that point. Haven't heard of a cylinder failure yet, so these blocks are probably tougher then Reynolds gave them credit for. The Nikasil coating should help strengthen the cylinders towers in this regard I would imagine.

My first block prepped for stroker had too thin a cylinder wall overall after boring, and had been decked. The Pistons weren't manufactured correctly and so the pistons had a lot of negative deck height. I've been working on stripping a second block and will be sending it out to US Chrome as well. This one has thicker cylinders to begin with, and hasn't been decked, so I'm hoping to cure two problems at once.

Good luck Russ, I've been at it for years trying to get this motor together. Its amazing how far stroker development has come along in the last few years. I've often told others when talking about my project that if I started a second stroker project right now, I would have the second one done first since I wouldn't have to go through all the hassle of making parts fit that I have on my current project. It's a learning experience, and a fun one at that despite all the work arounds.

LT Texan

Hummm, the engine will live longer, but make more power? Some of those drag guys like short rods, high leverage rates and piston acceleration. But hey, my subscription to Hot Rod Magazine expired long ago.

That's good. He can get the piston to wall clearance right that way. But he should want all the pistons.

Dan

Mike Simard

Moldex is the way to go for a crank, it takes 4 months so get it on order, call them with balancing specs if you get your pistons while it's still on order. The quality is great and you get the best possible oiling. Remember to get a grooved #3 bearing.

Using a nikasiled block opens up an opportunity for custom pistons. Everyone is making custom pistons nowadays. It should be mandatory, why compromise features to use an existing design? A custom piston allows a better rod length and you can have valve notches that fit, the skirt can be where you want it, you can use thinner ring pakages if you'd like. It's a great way to build an engine!

The LS7 titanium rods have the universal Chevy big end size and width. That width is narrower than the Porsche but it doesn't create a problem, it just makes the crank counterweights thicker.

Mike Simard

Don't use up valuable brain space to work over the long/short rod debate. it's not worth it. Just run the longest rod that will fit conveniently and save your brain cells for remembering anniversaries etc. You can also obsess over piston acceleration rates but at the end of the day nobody really knows if anything works better than if it were slightly different and it just doesn't matter much.

123quattro

The longer the rod ratio the better assuming you can fit them in the block. Short rods mean more piston acceleration, which raises internal forces. F=ma. That said, plenty of engines continue to run with bad rod ratios.

Edit -> Mike covered this in the time it took me to type it.

Vilhuer

Use 968 piston as model for skirts as they will fit into block at bottom dead center. Full skirt will not.

If 6" rod will move pin too high its possible to use pistons where oil ring is at pin height. I would do it unless difference in piston price gets really high.

LT Texan

I agree. For crazy racing like holding revs at 10k and dropping the clutch - anything goes and who knows? But for us tracking cars and street driving, long is better.

Jim bailey - 928 International

Which is better is somewhat a moot point since I doubt that there EVER will be another SCAT batch of 928 cranks , EVER ! Greg Brown now orders Moldex cranks 5 at a time...

largecar379

That's good to know......

I reckon I'll get with Greg when I'm headed that way---just gathering info right now.

Thanks Jim--

--Russ

BC

Why Jim? I have a scat crank on my shelf still. Should I sell it on ebay and get a moldex?

Jim bailey - 928 International

Scat is into high volume the only way the last batch ever got built was they combined the Devek "order" which had languished for well over a year with our order of cranks and that plus one for a guy in Australia was enough to get them to finally make some 928 cranks but that was years ago ! I only put together that special order because so many people were complaining about not being able to get a crank. Plus I wanted to correct the market value Now we just send anyone who is interested direct to Moldex 313-561-7676 ... Greg Brown builds stroker engines so he orders cranks ahead of time so he has them on hand when he needs one....novel concept !

928SS

you could always use a custom pauter rod. super strong, low windage profile, custom length as needed. carrillo is still claiming 75hp/cyl =600bhp in a V8 for their A series rods in std lengths, but one broke a while ago for someone w/a stroker around 400rwhp. so now they are mumbling something about chevy sideloading and just using H beams or custom rods in some kind of CYA mode. IMO, could have been a detonation thing, maybe. H beams haven't been broken yet in a stroker as far as I know, but after the A beam blowup, pauter or a TI rod seems like the super conservative ticket, to me anyway.