90.5 vs 92

AirJose · Post by **AirJose** » Mon Dec 10, 2001 7:10 pm

I need your opinion on these pistons. I am building an ocassional driver (2 to 3 days a week) with no more that 2 hours driving distance. I like more power but some durability also. Are 92's ok now, it seems that some years ago they did had some problems and did not last too long, I like the engine to last several years. Input please...

Matt Harris · Post by **Matt Harris** » Mon Dec 10, 2001 7:33 pm

Screw em both and go 94's! Don't be scared of them. They will last as long as the valve job at least (usually 40,000) miles at which time you can hone them, new rings, new set or whatever. $200 is cheap for 40,000 miles of service. Don't be scared of 94's, I was and for no reason!! You can drive as long as you want just make sure the engine is working in harmony as a whole. An external cooler doesn't hurt either

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Matt Harris
78 x 90.5
2007cc
1971 Super

Eaallred · Post by **Eaallred** » Mon Dec 10, 2001 8:30 pm

I've got well over 10K on my 94's, with most of those being hard street miles, or track time. Daily driven everyday, even in +110 degree weather we see in the summer time here in Vegas.

I pulled my engine down to swap to a larger cam, and bigger heads, and my cylinders still look brand new on the inside. Plenty of cross-hatch on these puppies.

I will no doubt, run 94's in everything else I run from now on.

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Eric
64 Bug

jmillheiser · Post by **jmillheiser** » Mon Dec 10, 2001 10:22 pm

ive herd of 94s lasting 50k-70k on street engines (milder cam, CR in the 8s). they are definately worth it on a cruiser/track car. for 2-3 days a week type stuff 94s should be well worth it.

on a daily driver (everyday) id still use 90.5s

evil_vw · Post by **evil_vw** » Mon Dec 10, 2001 10:39 pm

hey airhose-- a bit more $$$ but worth the effort would be to stroke the motor rather than up the bore to 94's. it is fact that the bigger the bore, the thinner the walls of the cylinder and this reduces the cylinders ability to dissipate heat. also, quite simply, less metal means less strength at higher rpm's. if you want lots of power, especially at lower rpm's, than opt for a 78 or 82mm crank and leave your pistons at a much more durable and reliable 90.5-- this would make a 2007cc and a 2110cc, respectively. the 2110 is very popular with guys who want the power and keep the heat and stress down. of corse, if you want LOTS of power, up the bore to 92 or 94 bore and stroke it out, but dont do this if you plan to use your car as a daily driver, even if only on the highway. i know theres always those people who will say "i drove may car with 94's for a 100 years blah blah blah", but a good rule of thumb- less driving more motor, more driving less motor. unless your really into spending money and have lots of free time!!!

Shad Laws · Post by **Shad Laws** » Mon Dec 10, 2001 10:49 pm

Hello-

it is fact that the bigger the bore, the thinner the walls of the cylinder and this reduces the cylinders ability to dissipate heat.

Not quite...

It is a fact that the thinner the walls, the less groovy things are. This is due to STRENGTH, not heat dissipation. Hell, for heat dissipation, the thinner the better! However, the former argument is superior over the latter... case in point: machine-in 88s outlive slip-in 88s by quite a bit.

It is also a fact that 85.5, 90.5, and 94 all have almost if not exactly identical wall thicknesses

Take care,
Shad

Eaallred · Post by **Eaallred** » Mon Dec 10, 2001 11:01 pm

Not being able to use 94's for daily use is, in my opinion, hogwash.

They got a bad rap years ago, but has anyone heard any bad news with them recently? Everyone I've talked to that is running 94's has been very happy with them, and aren't suffering the blow-by, or other symptoms that 'thin wall' cylinders are known for. Over 10K on mine, countless 14 second runs (test n' tune night every friday night in the summer), 700 mile round trips to Phoenix to race it (run what ya brung!), and mine still look new.

94's are fine. More than fine IMHO.

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Eric
64 Bug

JohnConnolly · Post by **JohnConnolly** » Mon Dec 10, 2001 11:23 pm

I was scared (10 years ago) too. Early 94s did have a problem, they were thinner than today's 94 cylinders. 94s are fine, but I wouldn't run them on a bus or T-3, those are my only reservations.

IMO, when hotrodding a 1600, I go to 94s first, then heads, then a stroker crank if you can still afford it. UNLESS you drive like a grandma, then get the crank before the heads.

John
Aircooled.Net Inc

Bent · Post by **Bent** » Tue Dec 11, 2001 3:51 am

Check out those 94s at the Bottom of the barrels , they are TO THIN. The required hole in case is TO BIG. Use 90.5s with stroker.We have in stock 75.5 stroker cranks tested to 10,000rpm.
Ben
Ben Automotive Engineering

Oz-made and designed

These run stronger and longer than U.S. 78 strokers.

Bent · Post by **Bent** » Tue Dec 11, 2001 3:54 am

Hey John,
I am scared of poeple like scat , from previous experience.
Ben

Eaallred · Post by **Eaallred** » Tue Dec 11, 2001 7:19 am

Too thin at the base?
Did you know people are starting to have them machined down so they can fit them in thier engine case that they were previously running 90.5/92's? They are not too thin. They may be thin to the eye, but not the application.

I can see the hole in the case being too big if you were running 10mm headstuds with case savers, seeing as they cut into them, but if you run 8mm chromoly and casesavers, the hole does not cut into them at all. It's all about the right combonation.

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Eric
64 Bug

69bug4me · Post by **69bug4me** » Tue Dec 11, 2001 10:32 am

i would go with the 94's also,i have ran the same set in my sandrail for 4 years and i abuse the hell out of it,it's been over heated,over revved and so on when i tore it down i just honed and added new rings and it was ok,my friend used 92's in his engine and was blowing smoke after one season.

case hole wont be to big i'm even using a case with 10mm studs and no case savers,but then again it's an offroad engine.

Marty · Post by **Marty** » Wed Dec 12, 2001 7:18 pm

94's being thin at the base means absolutely nothing. At BDC your rings are maybe halfway down the cylinder and that is where all of the wear and heat are (in the top half of the cylinder). The bottom part of a cylinder just supports the piston skirts. Now if you cut your skirts way down or have worn out used pistons, they will slap around and wear everything out.
Case bore ID is another issue and its user preference. I run 10mm studs with a 94mm bore with no problems but there are limits before you start cracking the case at the stud holes or start pulling studs. 28 pounds of boost is around the limit.
Street cars should have no problems.

JohnConnolly · Post by **JohnConnolly** » Wed Dec 12, 2001 7:53 pm

Bent,

10,000 RPM? What engine is this, where?

Please give us more information and specifics on this engine.

John
Aircooled.Net Inc.

Tom Simpson · Post by **Tom Simpson** » Wed Dec 12, 2001 8:48 pm

Yeah really... 10,000rpm scares me too... All I can think about is cases getting sawed in half and blood and teeth everywhere.... 94's are OK.... They have plenty of thickness at top and bottom. If you are running 10mm studs, you can have the cyl bases cut down to the 90.5mm base dia. I have done this for several people and it works great. There is no stress in this area, therefore it doesn't fail. I will run 94's in every motor I can from now on. They just make too much power for the money not to use them.... It really amounts to the cheapest, most reliable HP you can add.....