Turbo shortblock combos
 

I've been thinking about building a small ci turboed street motor. Something like a 400ci with a 3.40 or 3.30 stroke. I always have liked the idea of a small stroke big bore for a street driven setup to get rid of some of that unwanted torque that kills a street cars performance . But then the other day I saw a 1967 326 for sale and thought to my self, this motor would have a really small bore ,still being bigger then the stroke. The bore would be .339 smaller the 400ci which I know is not that much smaller but I thought it might give the piston more stability in the bore. Is the 326 block as strong as the 400 . I would think it would be stronger with maybe having more meat in the cylinder bore but not sure about the webbing area . Now after having built a 4 cylinder I know from my own experience that ci doesn't make or break you with a turbo in making more power then a street car really needs. My guess with building a short stroked 326 will be , it will make more power with less boost then the 4 cylinder and have more reliability in the end. It will still have some cool factor like to 4 cyl because who really does these motors like this..

Please let me know what you guys think...

I've always wanted to do this!

the issue will be the crank!You will need a custom crank unless you go back to a 57-58 block,they had smaller mains,shorter stroke and were very strong.Down side is hooking a trans to them.Its like everyting else in our sport,just numbers in a check book.Many 57-58 engines also had forged cranks.Tom

It sounds like a very interesting combo and I spec'ed out a similar treatment for a Bonneville application. It used a 326 block and a 303 crank for 255 cubic inches with a 3.78-inch bore. It was never built but in a situation where the weight of the engine was not a factor, like in land speed competition, this would have been an interesting alternative to the 255 Chevys that were dominating the class.

I would just do a 3.75 stroke 400 and boost the snot out of it! Less headaches and B.S. and will make 700+ all day long with a turbo.:)

Perhaps a Turbo 250 CID OHC6 ?

Modern ignition & pistons will wake that motor up.

A 350 combo is still oversquare and some of the earlier 350 blocks are very thick in the areas where it matters,in the main webbing,the pan rails, main bolt holes not drilled all the way through etc. I was moving a couple of blocks around the workshop one time and the 350 block was quite a bit heavier than the 400 blocks.
A short stroke crank out of a 370/347/317 could be used but you're back to fabricating main bearing spacers

I am a firm believer that a 350 would be the best overall stock-block turbo combination, by virtue of the block's beefiness, the smaller bore giving more surface area for head gasket effectiveness and the fact that they are still as cheap as landfill. While the combo might not make as much total power as a larger bore Pontiac, I think you will still be way past the point of being able to get it all to the ground without some serious traction aids. I am collecting parts to build one right now.

Hey guys, thanks for all your reply's! The 350 sounds like a good idea. I was thinking earlier about the idea of using such a small bore if there would be any valve shrouding issues. What do you think? I really want to stick with the small stroke though. I've never built one and I really think it will change the characteristics of the way the power will be put down. I have a friend that's a real street racer. I know some of you frown on this but there is NO tracks around here anymore. He always wins to the point of no one will race him because his car works so good that he pulls the wheels. Well he always builds his engines with the smallest stoke and the biggest bores. He tells me all the time that Pontiac has way too much stroke for the street... I would like to try it now and see if it will work for me. I'm not worried about finding the right crank because I will just call Moldex or one of those company's and get a steel one made. I might even try with a even smaller stroke then I mentioned . I guess it will all play on what rod is available..

When spinning a motor higher , does it make the turbo work any better? I wouldn't be against building one for 8000 rpm's...

700 is not enough for Charlie!

A larger engine will spool a turbo faster, getting the turbine sized right will make boost control easier.
A boost over time, boost control can get you out of the hole.

I never thought of that. Thanks

lol!

How can you build a v8 for 700 h.p. when that little 4 banger is making more than that!

There is no replacement for displacement!! (But a turbo is the equalizer) :D

Around 93 Marty P was making over 1600 hp with turbos on a 406 stock block... Block held thru 3 seasons... end of season teardown a crack was found. Methanol fuel, turning @ 7800 rpm at 38 psi iirc.

Todays turbos and cylinder heads should be able to meet or exceed that number at lower rpm and boost psi... but it would still be alot to ask from a stock block. Maybe a bit more life from less rpm stress... Near impossible to predict due to block and build variables.

That said... a good well prepped block with strong light rotating parts(Like BME rods and pistons up to the task) with lots of attention to harmonics, safe tuning, (efi safer than blow-thru at high boost or power levels) intercooling (good gas or e85) could make a hell of alot more than 700 hp and live. The shorter 3.75" stroke is a lot less stress than 4" stroke or greater. (BTW the BME rods will live a long time on the street if you dont run it hard til oil is up to temp)

Alternately a 350 wouldnt be far off in power capability and as Don pointed out has better sealing possibilities with the smaller bore. 1000 HP at 360 ci (.030 over) under 7000 rpm should be doable and give reasonable life if done right.(lots more power could easily be made) BTW newer than 75 350 blocks are built just as weak as 400 "557" blocks... check me on this but I think those castings end in "558"

Hi Bruce. Are you against a smaller stroke then 3.75?I'm only looking for 8-900 hp. My turbo is only good for just under 1000...

I got a 347 steel crank for ya Charlie.
I got a complete 57-motor if interested. (Apart)

GT.

What ci motor did that crank come in.

If you use a 57-58 crank outside of a 57-58 block you will need bearing spacers.Tom

What is that? Do you have a picture so I can see......