Clearancing: 92mm AA Pistons, 76mm Stroker, & 5.325"

[Dan Ruddock]

You are off on this. The effective stroke and engine displacement stay the same with a rod length change. A long rod engine will have a little more top end power and a short rod will have better torque down low.

Cam choice can compensate for this to some degree and many believe long rod motors are easier on the pistons and cylinders.

For street use I like short rods because the engine fits better and they drive nice. As long as you keep the rod length to stroke ratio between 1.6 to 2.0 you are good to go. Dan

[palmettofx]

It doesn't help that I'm drunk off toilet wine, so I appreciate your responses.

[GodJockey]

[palmettofx]

I was really hoping to get away with stock pushrod length, will 74/76 be requiring cut-to-length pushrods?

I just remembered my new heads were flycut to accept 94mm jugs so I'd need them anyway, right?

[bugguy1967]

He thinks the shorter rods are reducing stroke. They're not. Regardless of your rod choice, a piston will still travel 74mm with a 74 stroke. We use different rods to change ratios or to achieve a certain length.
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"A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine"

[Danwvw]

If your heads are cut for 94mm cylinders then you have a choice of still using the 92 ThickWalls. at Least with a 69 or 74 mm crank, the 76 mm crank pushes it though the piston is on the verge of coming right out the bottom of the cylinder with these A stroke cylinders: http://vwparts.aircooled.net/Piston-Cylinder-Set-92mm-x-69mm-Machine-In-p/vw9200t1k.htm

A shorter rod does not take away stroke because the rod is at 90' to the crank. They do cause the piston to move faster at TDC and BDC though.
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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[David Wayne]

I am throwing my intended combo out there for suggestions and comments. I have 94mm AA pistons now, 50cc combustion chamber, Engle 110 with 1.25 rockers. Current deck is .110 so I intend to go with a 76mm crank, adding .275 of an inch of stroke, but only .138 inches to the top. Then I will go with the 5.325 rods subtracting .070 inches. If I calculate correctly, that should render a deck of about .038, from which I will shim .020 inches to get my compression ratio, which might be a wee bit high for my cam, but I intend to deal with it in my lightweight street buggy. This is on paper, but I think I am calculating correctly. Your opinions please.

[modok]

math seems correct.
You know the reason you have .110 deck is because when you bore a case for 94 cylinders you are supposed to deck each side .060 too.

Watch out for leaks at the case -savers

[modok]

[palmettofx]

I'm between the following

76 / 5.4
74 / 5.3

I don't think I'd be able to tell the difference when driving between the two though.

[modok]

what heads and carbs and exhaust?

[palmettofx]

New OEM heads machined to 94 - standard sized valves
dual 1bbl empi 34's (came with the car - they look like the weber 1bbls i think, and yes I knoew EMPI carbs are crap)
The best way to describe the exhaust is each port has its own pipe, never meeting, baffled. They basically turn around and point backwards.

This is on a sandrail.

I'm basically having to build this motor from the bottom on, and replace everything according to the machine shop. The only thing he said that was usable were the rocker arms, everything else was warped. The only thing I currently have is the new 94 heads and 92mm thick wall AA's. I'd rather not deal with returning those because I'm trying not to waste money (return shipment) because I'm gonna have to spend a lot on the rest of the motor.

[modok]

I'd use a 74 stroke then.
74 is a good size for "small" heads and carbs.

76 is just an odd size, it is the least handy of them all. 80 would be a handy size but why 76? I have no idea why we have 76 stroke cranks.

[palmettofx]

Fair enough, I am very excited to be putting this motor together, and it isn't my first, just I haven't gone through replacing every aspect of the motor before and never quite had as many "cheap" options as far as engine building has gone so being flooded with aftermarket parts it's overwhelming as hell.

Thank you for your advice and such, I appreciate it.

[palmettofx]

Afterthought, if I go with the 74, is it likely that I'll need non-standard pushrods? If I could I'd prefer to go ahead and order those too if there's a good chance I won't need cut ones.

[Danwvw]

My 5.325" Rods with a 74mm crank uses standard length push rods, It's one of the reasons I chose to go with the combination.
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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[palmettofx]

Suite, thanks!

There are too many combinations to these things, which is great, but I'd really just like to order as few times as possible since the holidays equals extended shipping/handling times it seems.

[Bret Young]

Paging mightymouse regarding medium length stroker cranks.....

76mm is considered sort of an odd size when considering stroker cranks. Some people say go stock, 78 or 82. But to each their own.

I like what mighty had to say about medium stroker's, and its what I have sitting on my shelf waiting for me to actually build it.

RIMCO stroker clearanced case set up for 82x90.5, 92mm thick walls (B pistons) turned down to 90.5 at the case, 76mm DPR crank and 5.5" I-beam rods. I haven't mocked mine up yet, but guys that have used that combo say it goes together really easy, deck is very close out of the box and is VERY close to stock width.

Lot of people say I should have just gone with an 82mm crank since my case was clearanced, but I got the crank brand new (still in plastic wrap from DPR) for 1/3 the price.

[modok]

The piston ends up near .060 in-the-hole with that combo only if you forgot to deck the case for the 94's to begin with, but then the engine is .060 wider per side. so no, but it does appear so in some cases.
Your engine will be .060 wider each side.

78 stroke with stock rods and AA B pistons or 94 cima, or cima 92 decked .020", or cima 90.5 decked .040" is stock width, IMO, that's easier. Cima making the pistons different heights does complicate matters tho, but it's always been that way.

[Bret Young]

I will have to look at the case spec's on the card thats still attached to it from RIMCO, but I know the case was decked for the thick walls. The case is setup to be built as a 82x92 thick wall engine.

They have to deck it different for 92's/94's compared to 90.5's?