#1  
Old 08-12-2021, 01:31 AM
LM93 LM93 is offline
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Default Turbo build options and questions.

I'm considering building a turbocharged I6 in my '79 Firebird. The T-top it has limits the power to less than 500hp, otherwise the body might permanently deform. Instead of a low boost 350 I think a high boost I6 would be a cool project, plus weigh less and handle a little better. But I have a bunch of questions before I start.

This website has a 'for sale' section for I6 parts. So does OHC6.com. Clifford's Performance has some parts available. What other sources for parts are there, aside from ebay?

Did the Sprint engines come with stronger internals? Should I look for a crank with a specific casting number?

Are the Pontiac and Chevy I6's internals the same from the head gasket down? Would new rods for a Chevy work in a Pontiac? Scat makes forged H-beams.

Do these pistons have similar dimensions to original pistons? https://www.summitracing.com/parts/u...-020/make/jeep . I would think the pistons would need a sizable dish to run on pump gas. I have 92 octane where I live.

Most Pontiac's C/R was overrated from the factory, what are the actual combustion chamber sizes for the different heads?

I have a TKO 600 conversion kit for a Pontiac V8. Would that bolt right in or is there interference, like the starter? I think I read something somewhere about the starter and fitment issues.

Are the valvetrains pretty durable? Are there know weak points I should be worried about or try to modify?

Was the factory redline for the 230 6500rpm initially? I read that they lowered it for the 250 because of QC inconsistencies from the factory. How high could a carefully assembled valvetrain rev to? What would be its main limiting factor?

I know that's a lot of question but I really want to know what I'm getting into before I start.

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Old 08-12-2021, 06:37 AM
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It's been posted before but worth a re-post.
Jon Peters Turbo engine.
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Old 08-12-2021, 08:47 AM
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I found this online and copy an pasted it .

The ohc6 was based off of Chevrolet’s 230 cubic inch L-head six-cylinder engine but nearly all components were either modified or of a completely new design. The ohc6 had a bore of 3.875 inches and a stroke of 3.250 inches with a 9.0:1 compression ratio. The crankshaft was a cast nodular-iron design supported by seven main bearings and the block was extended well below the crankshaft centerline to provide greater stiffness, improve bearing life, and minimize vibration. The steel forged connecting rods were conventional in design and attached to cast aluminum flat-headed pistons of a slipper skirt design that contained deep recesses for the valve heads. The pistons did not include any expansion control devices which differed from those found in other engines.




Looks like these engines all came with forged rods ..

If so it think this engine would definitely hold some power.

I've been looking for what rod length they have because the stroke is a half inch less then a 8cyl . But i cant seem to find any information .


The fact that it has a short stroke really gets my interest..

My question would be, can you get a cam ground for this . If not , then you're stuck with the factory spec's. Which im sure will work but not what i would want to go off of. It does have a decent amount of duration right off the bat though.. .228 degrees is not bad..

I think if you got a low compression version like the 9.0:1 which makes around 175hp you could make 500hp with 25 to 30 psi. That would be with a stock motor right out of a car with no mods..

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Old 08-12-2021, 03:18 PM
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Regarding the OHC in a gen 2 Firebird, I believe there might be a hood clearance problem. Seem to remember that being one of the reasons why they went back to the Chebby I6.

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Old 08-13-2021, 01:44 AM
LM93 LM93 is offline
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Quote:
Originally Posted by MarkS57 View Post
Regarding the OHC in a gen 2 Firebird, I believe there might be a hood clearance problem. Seem to remember that being one of the reasons why they went back to the Chebby I6.
https://forums.maxperformanceinc.com...4&d=1628590195

It's been done before. And I thought I was being original.

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1979 Esprit, Starting the Resto-Mod Process with a 350 and a TKO 600.

"And the one thing you can say about Capitalism is that, although it produces inequality-which it absolutely does-it also produces wealth, and all the other systems DON’T. They just produce inequality." Dr. Jordan Peterson
  #6  
Old 08-13-2021, 02:13 AM
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Quote:
Originally Posted by MarkS57 View Post
Regarding the OHC in a gen 2 Firebird, I believe there might be a hood clearance problem. Seem to remember that being one of the reasons why they went back to the Chebby I6.
Maybe it depends on the hood? Seems like 70-76 hood would have less clearance than 77-81 just looking at the shape.

Anyway...good topic. I have a 70 with original I6 and was also thinking a turbo would be fun, but with all the spare V8 parts I have it would be much easier to just swap a traditional Pontiac into it.

  #7  
Old 08-13-2021, 03:05 AM
LM93 LM93 is offline
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Quote:
Originally Posted by charlie66 View Post
I found this online and copy an pasted it .

The ohc6 was based off of Chevrolet’s 230 cubic inch L-head six-cylinder engine but nearly all components were either modified or of a completely new design. The ohc6 had a bore of 3.875 inches and a stroke of 3.250 inches with a 9.0:1 compression ratio. The crankshaft was a cast nodular-iron design supported by seven main bearings and the block was extended well below the crankshaft centerline to provide greater stiffness, improve bearing life, and minimize vibration. The steel forged connecting rods were conventional in design and attached to cast aluminum flat-headed pistons of a slipper skirt design that contained deep recesses for the valve heads. The pistons did not include any expansion control devices which differed from those found in other engines.




Looks like these engines all came with forged rods ..

If so it think this engine would definitely hold some power.

I've been looking for what rod length they have because the stroke is a half inch less then a 8cyl . But i cant seem to find any information .


The fact that it has a short stroke really gets my interest..

My question would be, can you get a cam ground for this . If not , then you're stuck with the factory spec's. Which im sure will work but not what i would want to go off of. It does have a decent amount of duration right off the bat though.. .228 degrees is not bad..

I think if you got a low compression version like the 9.0:1 which makes around 175hp you could make 500hp with 25 to 30 psi. That would be with a stock motor right out of a car with no mods..
If the pistons were a unique design, could pistons from a different engine with the same dimensions be made to work? Those Jeep I6 ones have close numbers and are forged.

Forged rods for the Chevy 250 are available in 5.700" and 6.000." I'm sure I saw on SpeedTalk.com a comparison of the Pontiac and Chevy rods. They were the same length but the Pontiac's were much beefier. Can't find it right now. Are the crank journals for the rods the same for the Chevy and Pontiac?

A new cam would be cut from a blank, right? Would the new cam be too hard a metal for the original followers? I wonder if roller followers could adapted or specially made. Would probably need to order more than just one set if so.
https://www.ebay.com/itm/142992244403
I messaged the seller of these to see what info I could get about them. I'll follow up if I get a response.

The short stroke like you say is good for turbocharging. Shorter stroke=higher redline. More rpms=more boost. The valvetrain has to live at that speed, though.

About compression, rule of thumb for V8s is 9.5:1 for N/A, 8.0:1 for boost on pump gas. But it's cylinder pressure under load that really determines preignition threshold. Are the combustion chambers on the I6 similar to the V8s? If they are, wouldn't they have the same cranking pressure tolerance? I've read that 160psi is the limit for iron heads. Wouldn't you need a considerable piston dish to run 25lbs of boost and not blow your engine?
https://forums.maxperformanceinc.com...d.php?t=852412. Asked about block strength in the boost section. Mr. Jack Gifford said he was told by Mickey Thompson's crew chief that the OHC heads would crack between the valves when they tried to run them. Races push their engines to the absolute limit, so I wonder how hard their engines went before failure.

So many unknowns, so many new things to learn!

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1979 Esprit, Starting the Resto-Mod Process with a 350 and a TKO 600.

"And the one thing you can say about Capitalism is that, although it produces inequality-which it absolutely does-it also produces wealth, and all the other systems DON’T. They just produce inequality." Dr. Jordan Peterson
  #8  
Old 08-13-2021, 06:45 AM
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Quote:
Originally Posted by LM93 View Post
If the pistons were a unique design, could pistons from a different engine with the same dimensions be made to work? Those Jeep I6 ones have close numbers and are forged.

Forged rods for the Chevy 250 are available in 5.700" and 6.000." I'm sure I saw on SpeedTalk.com a comparison of the Pontiac and Chevy rods. They were the same length but the Pontiac's were much beefier. Can't find it right now. Are the crank journals for the rods the same for the Chevy and Pontiac?

A new cam would be cut from a blank, right? Would the new cam be too hard a metal for the original followers? I wonder if roller followers could adapted or specially made. Would probably need to order more than just one set if so.
https://www.ebay.com/itm/142992244403
I messaged the seller of these to see what info I could get about them. I'll follow up if I get a response.

The short stroke like you say is good for turbocharging. Shorter stroke=higher redline. More rpms=more boost. The valvetrain has to live at that speed, though.

About compression, rule of thumb for V8s is 9.5:1 for N/A, 8.0:1 for boost on pump gas. But it's cylinder pressure under load that really determines preignition threshold. Are the combustion chambers on the I6 similar to the V8s? If they are, wouldn't they have the same cranking pressure tolerance? I've read that 160psi is the limit for iron heads. Wouldn't you need a considerable piston dish to run 25lbs of boost and not blow your engine?
https://forums.maxperformanceinc.com...d.php?t=852412. Asked about block strength in the boost section. Mr. Jack Gifford said he was told by Mickey Thompson's crew chief that the OHC heads would crack between the valves when they tried to run them. Races push their engines to the absolute limit, so I wonder how hard their engines went before failure.

So many unknowns, so many new things to learn!
Being you do have a lot of unknowns regarding this engine being boosted which is leaving you with a lot of questions that you're asking, you're going to get a lot of opinions from most that never did it and are just speculating . With that said its not going to be first hand information from someone who has done it before. So all you can do is make a list of what you're going to need and see how much of it is available . From there you will decide if you want to take the chance.
I've been there before. I wouldn't worry about the head cracking . To me that was back in the 60's when things were different . Technology has come along way since then . Im not saying that it still wouldn't happen. Just that you have a good chance that it wont. I was told that if i put 15 psi to my 4cyl it would explode . Well ive been as high as 44psi now and i'm still going for more . That's all i heard when i was building that engine and i,m glad i didn't listen because i run 22 psi on a daily bases and when i race with the faster guys its set higher like 35 to 40 psi.. No matter what engine you build it can come apart.

So the way i see it, you can call and have parts made and spend a lot of money or just get a motor re-gap the rings and put it in the car with a turbo and tune it to see how it holds up . That would be what i would do.. Because now you have real world information that tells you if its worth spending money on good parts.

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Old 08-13-2021, 06:53 AM
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If you go the re-gap rout i'm not saying with 25 psi just to be clear. Lower psi and if it works out creep up..

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Old 08-14-2021, 06:21 AM
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Quote:
Originally Posted by charlie66 View Post
If you go the re-gap rout i'm not saying with 25 psi just to be clear. Lower psi and if it works out creep up..
Boost 'till it breaks?

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"And the one thing you can say about Capitalism is that, although it produces inequality-which it absolutely does-it also produces wealth, and all the other systems DON’T. They just produce inequality." Dr. Jordan Peterson
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Old 08-14-2021, 09:50 AM
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Boost 'till it breaks?
Lol well yeah is there any other way! No...

I think what you're thinking about doing is cool. Besides breaking it (which im not saying to do) you will be getting information on lots of things. Then when you're all done and some what figured out you will have established a working turbo system which is a huge leap into the success of this whole idea. The other side is the tuning..

I think in stock form you could have fun with this as well as pave your way to what you want.

It wont be a 500hp setup at first but once you get it all together and working on 5 to 10 psi which im confident would be no problem in stock form . At this point you will know more if you want to dive in and buy good parts. I bet 300 to maybe 400hp you could get away with for awhile. At that level you might start cracking the pistons . Maybe.. But you will have all the knowledge you need... JMO...

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Old 08-25-2021, 01:41 PM
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Quote:
Originally Posted by Jeff Hamlin View Post
It's been posted before but worth a re-post.
Jon Peters Turbo engine.
I need the local track to open so I can provide an update.

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Turbocharged OHC 6, TH350
1/8 mile stats 8.4813 ET / 82.07 MPH
  #13  
Old 10-25-2021, 06:17 AM
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Exclamation Found this in my files

Sorry no info;
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  #14  
Old 10-25-2021, 08:57 AM
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That turbo unit is massive. Wonder how it runs (ran)?
Without an intercooler I am curious if they might be running it on ethanol.

  #15  
Old 11-03-2021, 01:22 PM
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A guy named Randall did one hell of a turbo build on his OHC 6 in a Firebird. Here are some links to his build threads. Sorry, most of the pics are gone, but there is a TON of info in them.

https://www.tapatalk.com/groups/sohc...ous-t2700.html

https://bangshift.com/forum/forum/ba...ontiac-ohc-six

https://www.v8buick.com/index.php?th...ne-six.219250/

https://bangshift.com/general-news/p...-turbocharger/


Last edited by 63 bomb; 11-03-2021 at 01:28 PM.
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