Small Bore = Big Power Cheap?
 

I have been thinking about this combo for a while and I think that there is a lot of power to be had cheap with a turbocharged 350 Pontiac. Here is my thought: the early blocks have a lot of cylinder wall thickness and the small bore will greatly reduced head gasket issues. They are also as cheap as landfill.

Forged pistons for these engines are now readily available and the valve shrouding issue shouldn't be a significant problem in a forced-induction situation. You could mess around with valve chamfers but I doubt you'd even need to.

I think a '72 350 with the 1.96/1.77 valve combo would be a great start. Add the aforementioned forged pistons with some cheapo forged rods, stock crank and an 067 or 068 cam you'd have a pretty stout foundation. Round it out with a Tomahawk intake, Holley carb and a set of Ram Air III exhaust manifolds and I think that you'd be well on your way to 600+ horses with the right turbo. I think a BW S475 would be a good choice, provided the exhaust turbine wasn't too big.

Has anyone tried anything like this?

I have not tried it but have thought of it many times... specially after looking at the 350 deck next to a 455 block. Massive amount of sealing surface along with very beefy casting everywhere.

Locating stock logs that you could flip forward like I did on my S15 would be a smart move.

600 horses on low boost setting...

350 under boost!
 

I think Jeff -aka-- 69turbobird---was running a 350 stock and got it to run 11. e/t ---1/4 mile, but i am not 100% sure, I am too lazy to look for his post--look for him and I am pretty sure you will find more info...he sells turbos, turbo headers and relate items...

I think you could get 700 hp out of it on pump gas if you intercool it and maybe add a water/meth kit... just be sure you got strong pistons/rods and maybe better main caps. (splayed 4 bolt)

An s475 would work great. I have one on a 351w it starts to spool around 2200 and about 10psi at 4000.

Sounds like a very workable combo to me, but turbo and cheap don't really go together. LOL
Once a turbo spools you have huge torque so a 600 HP turbo engine is going to do a lot of work.
I think it was Firechicken that had a 068 cam and went mid 10's, but don't remember at what C.I.

I'd prefer two smaller turbos so you have boost just off idle.

I thought the same thing but unfortunately the bolt pattern is asymmetrical. Needs to be fabbed.

Sorry for the confusion..... Use a RH log on the left side and the LH on the right side... If you have a big pile of Pontiac logs and big chassis chances are that you might get lucky with some manifolds.

Some Pontiac exhaust manifolds are center and/or near center outlet. No big deal makin a u and going back up or if goin fwd meetin under the pan somewhere(ala single exhaust crossover or if twin turbo makin an x under the pan) If motor mounts werent in the way long branch manifolds could be swapped side to side(fwd facing vs rear facing) Ram air logs arent bad either.

subscribbing

Don, you could always go twin turbo and make some power.

Twin turbos

:D

Would have been neat to see you use them John... Not a bad deal either. 1200+ in your dragster is serious fast... Sub 7's at 2000 lbs... Heck a 3200 lb door car could go bottom 8's with them.

I'm not so sure I would want boost down that low as the engine will be going in a mostly stock '66 A-body chassis. I would like to make sure the tires are firmly planted before the boost comes on. This will be a street car that will see a few trips to the track per year.

While it will certainly be easy to make more power with a larger bore engine, I am looking for a durable stock block combination that won't have an appetite for head gaskets, yet will have enough power to get a full-bodied car into the 10s. I think it is doable.

The problem is (other than getting it to the ground) going into boost kills your MPG. I know this isn't a high mpg build but...

You want it to start building boost just above your normal cruising rpm.

That is exactly what I was thinking of perhaps getting a converter that is just loose enough to build boost against while power braking at the starting line. Being in boost all of the time would also make for a very difficult car to manage on the street.

Took the first test drive tonight in my 1970 turbocharged 350 Lemans wagon. It is going to be fun!(once I finish installing body panels) Pulled really hard for a completely stock 350, buying up parts to build the replacement engine currently :) Forgive my horrible video editing skills.

http://www.youtube.com/watch?v=MXUd1TmB2Vk

LOL.. all stripped down and hammering the country roads.... I like your style!!

Love it- please send more photos/videos!

Thanks! I won't have anymore videos until later this fall when I get paint and some body panels on it. I could not resist taking it out for one blast down the road :). I will start my own thread when I get some better pictures and have time to write down more details of the build. Highlights of the build are cheap Chinese gt45 turbo, completely stock 350(for now), lots and lots of fabrication and using parts the way they were never intended!

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A nice, clean, simple installation. Would love to see what the hot side piping looks like.

Do you have a source for 350 forged pistons? I can't find them.

I am also interested in this thread because I have (3) 350 motors, and I've always wanted to do a boost motor - nothing crazy, also mostly street motor with the ability to get a little nuts.

Nice build, Alex. I will stay tuned.

I purchased a set of Probe forged pistons from Ace Brewer, formerly of Pacific Performance Racing. He closed up shop but has a few sets left over. I got in touch with him through Facebook.

Failing that, Probe could make a set but I don't know what they would cost, as they aren't currently listed on their web site. Actually, Ross can also make them as well but again, have no idea about the cost.

Now it is time to find a rebuildable engine locally.

DJK

i have it all worked out in my head i just need to find a bare 350 block and its on.

I think I remember seeing that, but they were set up for a 4" stroke IIRC. I can't remember if they used stock rod length or 6.8's. Hmmm...

Pontiac Dude can have any size piston made.
1-352-769-8800

I had a set of custom BRC pistons off PDude,very nice pistons for the money. Good thing is you can have the ring lands set where you want them,specify ring thickness etc.

The pistons I bought were for a stock rod and stroke length. They just showed up today and they really are beautiful.

Just closed the deal on my set of forged slugs from Ace's "secret vault";)

And so begins our journey.:D

Squidward. I see you are down here in Mesa (Phoenix area). Are you a member of the Pontiac Power Group down here? Just wondering if I might know you. I building a twin turbo '60 block 389/406 for my '63 Catalina.

Mark L in Glendale.

I can't say directly. We might have talked at a Pontiac Heaven event over the years. 40-something, 6'5" white dude, with 73 Formula (up until 07) and currently a 67 FB - that's me. I was at the Marriot event back in May.

The PPG is on my list of things to do. I want to get more involved locally with car stuff, and meet some like minded folks.

Good to meet you!

-Sean E.

I look forward to talking to you some day.

Mark L

I did a 350 block sometime back (side tracked and put aside) and sleeved all the cyls to 326 bore size. Foundation for a really stout piece with really thick cyl walls and a lot of meat for sealing on the deck.

I'm glad to see some folks looking at doing the "inexpensive turbo" conversion on a Pontiac. You will undoubtedly end up with a relatively inexpensive, high torque engine that will be tons of fun on the street. Totally unusable torque that will turn the rear tires into smoldering gobs of black goo at nearly any speed!

That sounds like a great use of torque!;)

I have to do some reading/research on how to put together a single turbo setup with external wastegate and a blow-thru carb. Gonna get new forged rods next week, and get a 350 block or two down to the machine shop for some work. I have two candidates, and will have to see which one is up to the task - a 69 350 or a 72 350.

Interesting thread, low-buck home-built single turbo setup using stock log exhaust manifolds:

http://forums.maxperformanceinc.com/...d.php?t=572528

I tried to get a few pictures of my hot side, will get better pictures when I pull it apart to drop in the new engine I am working on for it. The new engine is getting a set of the Probe pistons from Ace I picked up awhile back. The headers are mostly constructed of an old set of headers that I cut up and modified, they actually turned out pretty nice. I used 2-1/2" bends and tubing from Summit for the crossover and 3" from the merge to the the t4 flange. I drew up the t4 flange and turbo mounting brackets quickly during my lunch break one day and had a few sets made, I have a spare set of the brackets I would be willing to cut someone a deal on if anyone is interested. This was a very budget build done during my last semester at college. Probably ended up doing the complete turbo setup for around $1500. Working on my second (not so budget) turbo project now!

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Travis- I am planning on using an 068 cam for its wide lobe separation, availability and smooth operation. Do you have a suggestion for something better? I am planning on using log manifolds, a Holley Street Dominator intake and 750 Holley. I haven't finalized the choice of a turbo but am leaning toward a BW S475. Also, what suggestions would you have for valve springs for a 12-15 psi boost level? This should be a fun combination!

Don -

I like your choice of camshafts! Cams in street cars need to be small. Overlap needs to be kept to a minimum, because you'll probably have a fair amount of backpressure. But don't worry about the backpressure, it doesn't amount to a hill of beans. Anything in the 220 to 230 @ .050 will work great.

The S475 is darn near impossible to beat for the money. They are pretty heavy, and they don't make as much power as other turbochargers with similar wheel dimensions, but they are durable, and above all, they are CHEAP. And AVAILABLE.

Don't lose a lot of sleep over the exhaust side of things, either. The most important detail of a turbocharged exhaust system is that the exhaust gases go from the exhaust valve to the turbo with as few leaks as possible! In all seriousness, smaller is better in this regard. A two inch pipe from each manifold to the turbo is way more than enough for this power level. Log manifolds are fine. Durability and good packaging are the keys.

Valve springs will be dictated by the cam and by the rpm you want to spin, as well as boost level. I would think that something like this would be just fine with 130-140 on the seat, if the lifters will tolerate that much. Break-in will be critical.

I have been wondering about cams, too. I read some articles in Car Craft & Hot Rod that were suggesting maybe a single pattern grind would be better versus the usual dual pattern that is heavy on the exhaust duration for a NA setup. I was thinking about maybe an 068 for the wide LSA, but they were saying the big LSA is more old school when compared to the design of today's turbos. I thought about a 2801, which is the cam I would go with for a NA build, and it still has a 112 LSA.

IDK... Much to learn still. I might have to do some engine analyzer sims with some single pattern grinds and see what goes. Maybe a 218/218, 450 lift, and a 112 LSA? So far I am thinking of a single turbo somewhere around 68-70mm, and AR of around .7 to .8 so I can spool quickly and keep my power down in the midrange.

Time to run some sims in the morning when I get home from work!;)

That was a great build. I learned some good real world lessons from that thread.

Thanks for the advice, Travis- you confirmed a lot of what I suspected. I was initially leaning toward a 744 cam but they tend to be a little rough in a 350 and I want this thing to be as easy-going as possible, as it will be running most of the time out of boost.

anyone have any 350 bare blocks cheap?

I thought there was a guy with a thread on the street section a while back who was wondering what to do with one, and what to keep from it. Didn't know if he should sink it in the swamp or keep it.

If memory serves correct, he was in either SC or GA.

Back when the rules for some racing was 366 cid, several of the low buck Pontiac guys ran stroked 350 pontiac blocks and a .030" overbore with Ram Air IV heads.

RA-IV camshaft in a 350-366 size engine does thump pretty good, ;)

Tom Vaught

Subscribing. I want to do this to my 67 Tempest Wagon and a 326...

If an off-the-shelf forged piston could be obtained, I think a 326 would also respond very well to some boost. It definitely would be something a little different!