Budget high performance build... Can I get 400-450 HP?

Hi all,

I'm working on a hot rod build, and I'm at a stand-still in the frame dept for a while, so I thought I'd put some time in on the power plant. I was thinking about using a Pontiac OHC-6, but it's looking like getting 250 HP out of it might cost more than getting 400 HP out of a V8.

I've never rebuilt an engine to anything other than back to stock specs, so I have lots of questions, and I know there is tons of knowledge and experience here. I'd hate to do anything wrong or miss something.

This will be a street engine in a car that might weigh 2000 lbs. It might see the occasional run-what-you-brung parking lot cone race.

Here's what I have in the shed out back:

Two Pontiac V8 blocks with cranks, rods, & pistons... one 389, one 400. They are currently buried under the OHC6, so I don't know the casting numbers on either of them. I'll try to get them out from under the 6 tomorrow.

One 0.010 under stock Pontiac cast crank (#97954). According to a couple charts, it's from a '69 to '70 (or '74) 400ci. Whomever used it after the re-machining put it together dirty, so all of the journals are a little scratched. You can see the wear, but you can't feel it. 0.001 off of it would shine it right up. Can you get 0.011 under bearings? haha


One set of 4X-4H heads from a 2 bbl 400ci. 1.960 intakes - 1.660 exhaust - 98 cc chambers - 8:1 compression ratio, pressed in rocker arm studs. I read an article here that says some 4X heads were not that hard to get up to 6X performance. Looks like the 4X-4H heads I have are not that kind, but the 4X-3H or 4H-7H are. I'd post the link to the article, but I read something above that says html is not permitted, and I don't want to get in trouble! haha

My first questions are:

How much power can I make with one of the stock cranks? 400? 450? How much torque? I'd hate to have to buy a new crank.

What diameter can the cylinders be bored to, while still using the 400 crank, and still have a good running engine? Can a 400 be bored out to a 455's bore? or maybe 455 plus .030 or .060 or more? There's no cheap substitute for cubic inches!

What about stock connecting rods? Are they good to 400-450 HP? I've heard that the "regular" Pontiac rods are a weak link. Forged rods aren't as pricey as I thought they'd be, though... but still plenty.

My 4X-4H 2 bbl heads have pressed-in rocker studs and smaller valves. The 4X-3H and 4X-7H 4 bbl heads have screwed-in rocker studs and bigger valves. Can they be machined to accept bigger valves and screw-in rocker studs cheaper than I can get bigger valve heads? What about porting and flow... do the 4X-3H and 4X-7H heads have bigger, different, better porting and/or flow?

Is there anything I can do with my 4X-4H heads to meet my performance goals? Will I need to find a set of the 4X-3H or 7H heads that are relatively easy to get to 6X performance? I'd hate to have to spend a ton on heads.

I know... It's a big long post... sorry about that, but it's all related, so I thought it would be better in one spot.

Thanks!
Chris  

Do the 400, plentiful parts.
If the crank has to be turned .020/.020 no biggie.
I personally don't like the stock cast Pontiac rods but you can use them for this build if you want. I think a set of aftermarket forged rods are a good investment however, they're better from start to finish and use slip fit pins. There are plenty of aftermarket pistons available for those rods.
Being such a light car, just shoot for enough compression (9.0:1 or so) to be able to use a cam with some noise if you like, that will be an easy choice. Use an RPM intake if you like or if you can score a Torker that'll work fine, again it's a light car. Opt for some better heads if possible or install bigger valves in the ones you have and you'll hit your 400hp goal with little difficulty. Let me know if I can help any further.

By the way, the major difference between the 400 and 455 is in the stroke not the bore. The strokes are 3.75 for the 400 and 4.210 for the 455.

Don't skimp on the machine work, ever. You'll regret it if you do.

Good luck and keep us posted.  
Mark
Engine builder, located in Central Florida

Thanks for the reply,

I'll get both blocks all cleaned up and the parts all checked out this weekend. That'll tell me which block to use.

The 400 block is drilled and tapped for 4-bolt mains, but has 2-bolt caps.

There's a curiosity with the 389 block. It's a 38P block, June 28, 1962, 303 horsepower, used in '62 & '63. The curious part is that, according to Pete McCarthy's book, there are some things that only 389SD and 421SD blocks have, though. Square machined passenger side deck surfsce, "special ribs on both sides of the block", and a couple other things. Who'd know what this block is? I have pictures.

I found a set of Keith Black pistons on close-out for 1/2 the price of new regular cast pistons... so those are on the way. I think I'll use PPR's Tomahawk 5140  forged rods. They're only $240 for a set, and good to 550 horsepower.

I think it would be cheaper and better to find some better heads to start with than to machine bigger valves into the heads I have. Turns out I have a friend with a stock pile of Pontiac heads. I need to go see what he has. I also spotted a Craigslist ad for a guy with lots of Pontiac heads. It's a couple hours away, so I hope he feels like sending casting numbers back to me.

Thanks for the help, and I will keep you updated. I'm sure I will have about a million more questions!

Chris  

Hey Chris- Matt here. Fastone told you right.

I'm gonna go out on a limb and just kinda discuss things you mentioned, I'm kinda the same way with the pile. I am a non-engine-building bodyman but I have played with the externals on 400s in the past.

That OHC6 ... man don't break anything when you move it! My first car was powered by a Sprint one and I loved it.

I'd say if the whole car (no engine/trans) weighs only a ton, the six would be plenty but yes as far as power to weight ratio and size it leaves a lot to be desired.

A plain ol 400 will probably outmuscle the available traction on a rig like that, so I say you have what you need already.

I have a set of those 4X-4H  heads, unported with maybe five thousand miles on them sitting in the garage. I hosed myself and put screw-in studs, hardened exhaust seats, 2.11/1.77 valves, #995 springs, back-cut on the valve stems, etc. The works- they saw me coming! Learned a lot since then. But uncracked iron head cores were scarce, aluminum heads hadn't been available very long at that time. Just saying theres no reason you can't totally soup up those heads if you want, the 4X ain't a bad iron head choice. Not very different from 6X, from what I've gathered.

In my humble opinion, you should stop at .030 or .040 over on boring the cylinders and sleeve the rest. The tired ol iron gets pretty thin at .060. I had a 400 that bore size and after a round or two of overheating, it cracked three holes on the right bank. I had another that was .040 over and I punished it just as hard but it never cracked.

So- can you show us the project? Curious now, sounds fun like a barrel of monkeys! If you can post some pics of the parts you want to use, I bet more engine oriented helpers will speak up. Good luck with the build.  

A 2000# car should go great with a stock 400, so anything better than stock will fly.  
Drive it before your dead!

Pontiac not cheap to build, plan to spend about 2 to 3k on a stock reliable rebuild, anything less will leave you stranded or rebuild in the future.  
Carlos
70 Lemans(GTO Clone),406,Solid Cam 218 single pattern, 105 LSA
Serious Hobbyist

Hello there ,im glad to be apart of this site with you guys, and im new to hp in engines etc, but i purchased a 1979 trans am with a 400 in it. what must i do in order to make it run with todays new cars . I would like to get a least 400 hp from it as well, can you guys help?  

hello mishoe89g

Welcome to the site. The first thing I can suggest to you is to post your question as a new topic. You will get a lot more replies this way because many more people will see it. Don't worry, that's what the new topics are for.

You will probably need at least $6k and a lot of your own labor to run close to a new high perf car.

As far as your motor goes everyone will ask the same questions.

What is your max budget for the engine only? If you increase the hp enough you will need money for traction bars at the very least and maybe a posi unit.

Are you willing to sacrafice some fwy driveability due to a gear change or are you a fwy flier.

Do you want a nasty lope?

A Big cam might cause your power brakes to work poorly at low speeds and you might have to add an aftermarket vacuum chamber for them. Is this a problem for you?  

Hello

Your 2000 lb body project sounds very cool. What are you putting it in? Anyway you will get a lot of good suggestions from people more knowledgeable from me on Pontiacs specifically so I can only offer what I know about engine building in general and what I have read about Pontiacs so if I’m wrong I’m off the hook.

Crank – I don’t think there is any problem using a stock crank up to around 450 hp especially since you won’t be subjecting it to heavy load in your light car like you would in a 3500lb car. They actually do make thicker bearings for cranks in plus .001, .002, and .003 for some models. I had to build an engine with them once but don’t do that.

Cylinder bore – I would not go over .040 otherwise you greatly increase the risk of overheating. Some others say boring a motor does not contribute to overheating so ask an experienced engine builder if you have uncertainties regarding this. You will never notice a difference in displacement with the additional displacement ovSince you already bought

Connecting rods – You may get lot’s of varying opinions here so here is my opinion only based on my level of experience. I think I have read that some factory pontiac rods like ra rods or similar are better than a base 400 rod and should be good to 450 hp but may not work with your pistons if they are floating pins so the point could be moot. Someone here will know better. As far as any of the inexpensive rods you are considering, they are all cast in China. Most if not all the Eagle rods are machined in the US on a fancy new german made machine. No matter which brand you buy, you must have the size and rod bolts strength inspected. I personally would not run the run the prr tomahawk rods. I know nothing about them but logic tells me that if Chinese Eagles and Chinese Scat rods are $400.00 and you say the prr’s are $240 the price difference should speak for itself. Here's the problem, the EXACT arp bolts they claim to use cost $100.00 at summit racing p/n ARP-190-6003. China can't buy these bolts from arp for much less than this so if you subtract even $80.00 from $240.00 you now have a set of high perf 5140 "precision machined" steel rods for $160.00. OK, this just sounds unreasonably cheap to me and makes me highly suspect.  

Block – You yourself said “there is no substitute for ci”. Use the 400 there will be a big difference. I personally like the 4 bolt main idea however since you are on what sounds like a very tight budget I would say don’t worry about you will not have a problem in your application.

Main caps - You might be able to buy 2 bolt steel main caps and have them machined to the block if you like.

Heads – Here's where 30% of your money will go. I’ll get back to you on that shortly but others will know more than I do here.

a. Flow difference - My guess is that the exhaust flow is the same because the exhaust valve is the same size. However the intake flow would be greater on the 211 valve head simply because the valve is bigger. The intake bowl and port on the 196 valve head should be able to be ported to closely match a stock or ported 211 valve head. Tuffnuff will know better.

b. Enlarge valve size - Yes  I used to install seats in heads etc so even though I have never oversized the valves on a small valve pontiac head I see no reason why you couldn't. The main concern is with running into a water passage however this possibility is significantly reduced by using a "thin wall" and/or "shallow" seat.

C. Cost to enlarge valves and install screw in studs - Labor only might be around $80.00 for intake seats only, $120 for studs. Seat cost $35.00, stud cost $40.00

d. 2.11 intake valve cost - I suggest using stainless. I would use manley race series. They are inexpensive and flow more than ferrea but heavier, who cares at 6000 rpm. summit p/n 11352-8, price $137.00

c Head upgrade cost with parts -  $412.00

d. Porting - The cheapest biggest bang for your buck you can get is to “pocket port” them only. You need to specify to the person doing the work that you want the valves unshrouded, valve guides blended and bowls cleaned up. You do not need any port work if you don’t have the money.

The porting should vary from $250.00 a head to around $400.00 a head. This price is for porting by hand. CNC porting is nice but costs substantially more.

The next porting upgrade would be to match the head ports to the intake ports. Again if you are on a budget this is not necessary. The main reason to do the head only and not the intake is to remove any part of the head intake port that obstructs any part of the flow from the intake manifold.

Matching the intake manifold ports to the cylinder head ports is just the opposite process and is just frosting on the cake. It will not net you much gain in air flow especially for the additional cost.

You can also have your stock valves “back cut” if you don’t want to buy new high flow valves. This will also improve air flow. Back cutting is cheap and easy.  

d. I have no idea what a set the used heads you are referring to cost. My random guess is they won't be cheap. Maybe at least $500.00 a pair or more.  


Compression - I'm guessing by your parking lot cone comment that you are referring to auto cross and you will not be taking long fwy drives in it so it will be geared low like 323-391 etc. Increasing the dear ratio helps reduce detonation a little. Is this correct? Either way, simply because your car is so lite I think you can safely do 9.5:1 max compression with no ping on 91 pump gas. 9.0:1 min for what you are looking for in performance.

8.0:1 vs 9.0:1 Compression - In your particular case you will gain around 23 hp and and 18 lb torque by increasing your compression by 1.0 point. If you mill them .025 from orig it will buump your comp slightly. If you 0 deck your block you will gain a bit more. Your compression also limits putting a "massive cam in it". The biggest I would use is around a 274 advertised duration like comp xe274h which is a decent size anyway.

Boring align bore etc – It is nice to align bore the crank then cnc the rest of it and 0 deck it however again since you are on a budget and your car will not see heavy load because it is super light I would say just check the align bore and check deck for flatness but bore with torque plates at least.  

if i remember wright in 64 or 65 the bolt pattern changed for the trans so the older block will not except the newer trans. if it is a 389sd block sell it to help pay for your project.

i would use the # 46/4x/5c/6x 350 91cc heads on a 400. 82cc will net around 9to1.  
76 455/4spd TRANS AM
69 GRAND PRIX 406/5SPD