[LostHighway]

Its been a little while since I posted but I am enjoying my '75 Bird. So much so that she is starting to show a rear main seal leak that cannot be ignored... So I figure its time to start doing what I want to do... A nice 350.

Does anyone see any issues running a 4.25" stroke crank in a smallish bore 350? I plan on machining the bore to a 3.915" (.040") over and using the 4.25" crank for a total of 409 cubic inches. Cylinder heads will be machined and ported 5C's with roller rocker arms and a decent roller cam doing the work. The car has A/C and needs to be operable. The radiator will be upgraded and I am looking for one that has a oil cooler integrated. Thanks for your feedback, I really like this site!

LLPMD!

[blueghoast]

I think it'll be a hard running little motor.
The only thing I would do is put a little compression in it.
I strive for close to 10:0:1. It makes a big difference I know it has for me.
And with that stroke it'll be an animal. Good Luck with it.

GT.

[LostHighway]

Originally Posted by blueghoast

I think it'll be a hard running little motor.
The only thing I would do is put a little compression in it.
I strive for close to 10:0:1. It makes a big difference I know it has for me.
And with that stroke it'll be an animal. Good Luck with it.

GT.

Compression is going to be near 9.0. Maybe a little more. I like the idea of an Edelbrock head as the chamber is WAY better than the stock one, plus the weight savings and extra flow.. etc. etc. BUT... This is to be a "stock appearing" engine. Nobody knows but me. (And now you) but you get the idea. It is in no way going to be a racecar. Just a weekend cruiser thatll be fun.

[blueghoast]

Originally Posted by LostHighway

Compression is going to be near 9.0. Maybe a little more. I like the idea of an Edelbrock head as the chamber is WAY better than the stock one, plus the weight savings and extra flow.. etc. etc. BUT... This is to be a "stock appearing" engine. Nobody knows but me. (And now you) but you get the idea. It is in no way going to be a racecar. Just a weekend cruiser thatll be fun.

OK-- My 350 is 9:76:1 and still pump gas. I'll finaly be able to get it out
this summer. It sounds good and heathy unlike most 350's It's got a try
power cam and the heads have been ported and there small valves too.
Have fun sounds like a good project.

GT

[LostHighway]

Originally Posted by blueghoast

OK-- My 350 is 9:76:1 and still pump gas. I'll finaly be able to get it out
this summer. It sounds good and heathy unlike most 350's It's got a try
power cam and the heads have been ported and there small valves too.
Have fun sounds like a good project.

GT

Keep us updated. Funny enough, most Pontiac builders I have spoken to say 350's are being build a lot more these days - so your results will be interesting to say the least.

One that note, for anyone reading who cares, my local builder Glenn, (Glenns Machine in Round Rock, TX) just did an Edelbrock headed 383 Pontiac that did 432hp. It was a roller cam deal and it was NOT a race engine. Just a street car that was meant for cruising. I can get specifics if anyone is interested.

[johnta1]

The longer stroke will require special pistons - different pin height.
Might check where to get those?


If doing that maybe get special pistons to use with longer rods like the 6.7/6.8" aftermarket rods.

[LostHighway]

Originally Posted by johnta1

The longer stroke will require special pistons - different pin height.
Might check where to get those?


If doing that maybe get special pistons to use with longer rods like the 6.7/6.8" aftermarket rods.

Pistons are available - custom. Thats the plague of these 350's. Maybe in the future more will be available but for now im going to have to be the guy.

[Tom Vaught]

Speacking of 6.7 and 6.8, Some of the 6.8L F*rd V-10 stuff was small bore and large stroke and they ran very well in a street application. Cubic Inches was about 415 cid. Bore and stroke size is 3.552" in × 4.165 in. So you would have that engine covered in both dimensions (Bore and Stroke), with your 3.915 bore and 4.25 stroke. Go for it.
A engine is just a bunch of metal pieces that people years ago figured out how to do work.

Tom V.

['ol Pinion head]

Compare the performance of stock '65-67 Olds 442 400 engine to one from a '68-69 Olds 442. Also note, the Olds heads flowed better than stock flow 2.11-1.77 D port heads.

Sure it can be done, but cost/benefit, cant see anyway its smart to go to the trouble to install a 4.25" stroke crank in a Pontiac 350 Pontiac.

[dataway]

If I ever built another Pontiac engine it will be a 350. So much easier to find parts for.

[Schurkey]

Originally Posted by LostHighway

I figure its time to start doing what I want to do... A nice 350.

Does anyone see any issues running a 4.25" stroke crank in a smallish bore 350? I plan on machining the bore to a 3.915" (.040") over and using the 4.25" crank for a total of 409 cubic inches.

Originally Posted by dataway

If I ever built another Pontiac engine it will be a 350. So much easier to find parts for.

I'd have said the opposite.

I think he'd be WAY ahead to just build a Pontiac 400. Less "custom crap", simpler, easier, and the larger bore has got to breathe better.

[Gary H]

Just me but I'd source a 400 block and build it. You'd save a little on the pistons since many companies already make them for a 400 block and a 4.250 stroke. One company's pistons that I use a lot are the KB Icon pistons. Good finish & ring pack, and reasonable price compared to a custom piston such as Ross. You'll wind up with 50 - 60 CI more, depending on the end bore, by using the 400 block. It'll be worth more for resell in the end as well. No brainer.

[PAUL K]

We've built a couple of 4.25 stroke 350's lately. Every instance has been an original engine to the car. If built correctly they are good runners.

[LostHighway]

Originally Posted by PAUL K

We've built a couple of 4.25 stroke 350's lately. Every instance has been an original engine to the car. If built correctly they are good runners.

Can you elaborate on these builds? Just a “rough draft” of what was involved and how they performed? Thank you!

[ponyakr]

As others have said, it's cheaper & the engine will have more power & torque, if you build a 400 block stroker.

But also as said, a 350 block stroker is possible. It'll just cost more & have less power/torque.

Butler sells 4" & 4.25" stroker assemblies for the 350. But, they use custom Ross pistons.

https://butlerperformance.com/c-1234...413-cu-in.html

Should be able to save several hundred by going with Auto Tec pistons. A few years back, I was quoted a price of just under $500, shipped. I suspect the price today would be about $550 shipped. But the Ross pistons are at least $800, with pins.

RPM H-beam rods are $400, in either 6.7 or 6.8" length.

http://www.racingpartsmaximum.com/sa...elhbeam-2.html

5140 rods are $300. I'd say that extra $100, for H-beams, is good insurance, in case you should ever wanna really wind it up.

http://www.racingpartsmaximum.com/sa...tockrod-2.html

You may have already read this article. Ace Brewer built a 4" 350 block stroker, which made 462hp. Ace is no longer in business, & Probe don't make the 350 pistons any more. But, that's just as well, since some of the engine builders here have posted that the Probe pistons were poor quality.

https://www.hotrod.com/articles/hppp...-engine-build/

PS: You mentioned that you have a '75 model 350. If it's a late '75 350, it could have a casting #500810 block. If that's the block you have, I wouldn't stroke it. Those blocks have the thin main webs, just like the "557" 400 blocks. I know this for a fact, since I have one of the 500810 blocks. Some always argue that they built big power with 557 blocks, beat on 'em for years, & never had a problem, Many others were not that lucky. So, if you have a 500810 block, build at your own risk.

[tom s]

The last set of Autotec I got had gone way up.Like 700 plus with rings and pins.Tom

[hurryinhoosier62]

LostHighway, I like the way you think: outside the box!! Paul Carter and I had a conversation about installing a 4.21” stroke 3 inch main crank into a 350P block about four years ago. We came up a custom piston from CP/Carrillo based on an LS blank(3.905 is a standard LS oversized), 6.700 BBC rods with lightweight tool steel piston pins. The heads would be either KRE or Edelbrock “D” ports. Cometic produces 350P MLS head gaskets. This combination would give a the advantages of the 1.5/1.5/3.0 mm ring pack( less parasitic drag, light pistons and pins that are going to reduce the side loads on the thrust side cylinder walls and plenty of low speed torque with the 4.21” stroke and the correct cam.

[pontiacjeff]

Keep in mind... any valves larger than 1.96/1.66 or lift over .450, you will need to chamfer both the intake and exhaust sides of the top of the cylinders.

[ponyakr]

Originally Posted by tom s

The last set of Autotec I got had gone way up.Like 700 plus with rings and pins.Tom

I suppose it depends on who you buy from. When I called Auto Tec, they told me I could buy cheaper from one of their high volume dealers. The name they gave me was Shannon's Engineering. Shannon is the guy who gave me the price. It was either $450, or $460, + shipping.

I've noticed that he sells larger bore Pontiac pistons for $508.30 + shipping, now. That includes pins but not rings.

https://shanonsengineering.com/produ...at-top-pistons

As mentioned, the 350 pistons would be made from blanks used for other common engines, with a similar bore size. Shannon called 'em "shelf blanks".

I think it has been established here that Paul K can order Auto Tec pistons for you, as well as Paul Carter. May be others here. I don't know. Don't know what any of their prices would be.

I do know that Butler seems to do their custom piston business mostly with Ross. And the last I checked, I think the prices was around $800, with pins, + shipping. I'll look it up & post a link.

OK, they're $700+ $90 for pins, + shipping. That's well over $800, without rings.

https://butlerperformance.com/i-2445...tegory:1234850

[dmac]

Because the 350 will be drawing less air, for your purpose you may not need or want larger valves. to keep it simpler without worries about the valve notches.