[LM93]

Wallace Racing lists the I6 bore at 3.87" for the 230 and 3.88 for the 250. Stock 350 bore is 3.875 and I have a set of 3.905 TRW pistons. Would pistons for a V8 work, or does a I6 need a different skirt or something? Pin offset? Piston weight and crank counterweight?

[Stan Weiss]

What you need now is to see if any other engine has the bore you need with a compression height around what you need. If one doesn't posts them up I see if I can find my books and post them up.

A couple more which my work are SBC 283 and SBC 307

Stan

[LM93]

And the pistons would need a sizable dish in order to run pump gas.

[LM93]

Something like this? https://www.summitracing.com/parts/u...-020/make/jeep

Since most Pontiac C/R's were overrated from the factory, what are the actual combustion chamber sizes?

[LM93]

Are the rods for the Chevy and Pontiac I6 the same? Scat makes forged rods for the Chevy.

[Jack Gifford]

Originally Posted by LM93

... Wondering how much power Pontiac's straight six is capable of, strength-wise...

I don't know about "strength-wise". But back when I was on the phone a lot with Fritz Voight (Mickey's crewchief, who gave me a lot of help with my hemi V8) I asked if he and Mickey ever toyed with the OHC six. He said yes, but any attempts at serious power caused head cracking between the valves.

[mgarblik]

I saw your mention of the OHC 6 being much lighter and that was a factor in your decision to possibly build one. I don't know how much lighter that engine would be than a Pontiac V-8 with aluminum heads which is quite common now.
The OHC 6 has an iron block, iron head and a mile long crankshaft. I would check the weights to be sure. If weight is a major consideration, an aluminum block/head V-8 may be lighter yet and make more HP of course. Lots of decisions to make. A 400+ HP OHC 6 is going to be an expensive build. But really cool.

[LM93]

Originally Posted by Jack Gifford

I don't know about "strength-wise". But back when I was on the phone a lot with Fritz Voight (Mickey's crewchief, who gave me a lot of help with my hemi V8) I asked if he and Mickey ever toyed with the OHC six. He said yes, but any attempts at serious power caused head cracking between the valves.

Hard to argue with someone like Mickey. What kind of power would a pro team like his be trying to wring out of their engine? 400, 500, 600hp? Every last ounce, probably.

https://www.gomog.com/allmorgan/engineweights2.html
About weight, this website lists the I6 as 200lbs lighter than the V8. Aluminum heads save about 50lbs each right?

[LM93]

New thread started in thee OHC Tech section.

[Stan Weiss]

Look at the pictures and the caption with them.

https://www.motortrend.com/how-to/ah...-six-build-one

5.7" rod lenght. Don't know what the deck height is? But that makes the bore, stroke and rod length for the 230 ci engine is the same as a 307 ci SBC V-8.

Stan

[Stan Weiss]

Originally Posted by Stan Weiss

Look at the pictures and the caption with them.

https://www.motortrend.com/how-to/ah...-six-build-one

5.7" rod lenght. Don't know what the deck height is? But that makes the bore, stroke and rod length for the 230 ci engine is the same as a 307 ci SBC V-8.

Stan

From this article.

Stan

[Stan Weiss]

Found this while I was on Speed Talk

https://www.speed-talk.com/forum/viewtopic.php?t=13927

I have two sets of Pontiac OHC rods. The later ones appear to be a stouter rod than the early ones. The early ones look to be equivalent to Chevy rods.

Talking about 307 SBC Pistons.

You are correct on the piston interchange

Stan

[Half-Inch Stud]

AS stated a decade ago; my 1969 OHC-6 Sprint had connecting rods superior to the Chevy Pink Rod. And I reckon them GM forgings to be similar to a RA V rod design.

Cameras were not a thing for me in 1982-1985

Being a Pontiac V8 minded fella, i loathed and hated high-rpm engine spinnings, yet found the Sprint to be in its own from 4500 to 7500. 7000-7500 upshifts were a routing thing on the major roads. Mallory Dual-Point dwell beat stock dwell, but the grafted HEI was fantastic.

Maple Grove run fell onit knees at the top of 2nd gear. ran mid 14s or 15 (forget), and never did add a pusher pump.

I dunno why there was no fear of spinning the factory flywheel! yikes.

[turbo69bird]

I didn’t read through the thread for other responses but what kills engines N/A or turbocharged or blower etc. Is usually detonation. A good tune will go a long long way to making a set up last.
I don’t know much about the rods in the L6 but the blocks appear pretty stout. Id bet it’s make good HP torque and live if the rods are any good in them . Look for any short comings in oiling system too . Aside from that should live if the tune is good .

Many an engine builder has been blamed when the tuner should have been!

[JLMounce]

Having read through this thread, I can't really comment on longevity of the I6 in general, but I don't really think one of the stated goals of a lighter package is really in play here. It's pretty hard to find information on the weight of those things, but one source I've seen puts them in the 450 lb dry area, compared to about 630 dry for a v8.

An aluminum intake and heads v8 should be around 550-560 dry.

Adding a turbocharging system to the I6 is going to add anywhere between 75-130 lbs depending on the size of the turbocharger, whether it's non-intercooled, or is air-air or air-water intercooled etc. Weight wise, I think it's going to be pretty close to a wash.

The cool-factor with a turbocharged OHC 6 under the hood, is undeniable, but at the 400-500 hp performance threshold and very near or equal nose weight, you're going to be money ahead by building a typical street v8.

[Tom Vaught]

Not sure of how much a OHC Boosted 6 cylinder GM engine will support.

I do know from experience that not all 6 cylinder engines are the same.
I did a engine study with a 300 cid @ord engine with a cast iron head and dual
small (correctly sized) Turbos (many years before the ECOBOOST 6 cylinder stuff)
that destroyed the 302 and 351 Naturally Aspirated similar trucks in a 3 vehicle shoot-out.

We are talking 100 foot margins here in the quarter mile racing.
Not once not twice but throughout the whole day.

Nino Novelli, his brother Gino Novelli, and I made a bunch of V-8 guys unhappy that day in front of a large crowd of people at the test track.

We saw almost 500 hp with the 300 cid engine (less than 15 psi boost and a small inter-cooler set-up.) Far more HP vs the V-8 guys.

So could a OHC GM smaller engine with a proper turbocharger make slightly less than 500 hp with todays turbo technology? For SURE.

Charlie66 has made HP much higher than that with his 4 cylinder engine.
But he has a good flowing (not great flowing) E-Head.

Has anyone ever put a OHC 6 cylinder head on a flow bench to see what that OHC head is capable of NA??? That would be the first question.

Tom V.

[Mr Anonymous]

1968-1969 (only!) Olds 400 was 3.870 bore. 1.75 CH. However, 40 over gets you 3.91 which is 318 mopar, if you can make that work.