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Author Topic: 400 hp out of 73 pontiac 400  (Read 6510 times)
ddman
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« on: February 28, 2010, 10:09:41 AM »

what are some good builds to get 400 hp from this engine? he has 2500 to do it with.
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ronj1977
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« Reply #1 on: February 28, 2010, 03:35:45 PM »

Cam and heads  done !!  get a pair of 1969 #62 heads along with a decent cam and headers a little tuneing and your there or juice it
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rumble412
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« Reply #2 on: March 05, 2010, 01:08:09 PM »

I have a 1973 trans am 400 engine in my 1981 trans am.  I'm pushing 400hp with a howard racing cam at .472 lift, bored out to .60 over with 10 to 1 compression.  I believe my heads are from a 68 GTO, pertronic's flame thrower distributor, edelbrock cast aluminum intake manifold, 2 1/2 inch exhaust manifolds with flowmaster 40's out the rear.  Oh, don't forget the holley 650cfm dual line feed carburetor.
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72blackbird
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« Reply #3 on: March 05, 2010, 03:00:27 PM »

The 72cc D-port heads (no.12,13,16,48,62,670) are good heads, but with your SCR at around 10:1 you need to mix race gas w/ 93 to run it w/ flattops. And if you're only running pump gas in this configuration your motor is detonating even if you don't hear it- your bearings will be pounded out and you know what happens next.

You have to build the motor for the gas you're going to run it with-if that's pump gas and 72cc D-ports, that means you need dished pistons.

Geno
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1977 SE T/A (sold Sad )
1974 455 T/A (sold Sad )
1972 Esprit restomod
1976 T/A restomod
1975 Formula 400 4-speed
Rick
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« Reply #4 on: March 05, 2010, 04:38:49 PM »

X2 on Geno's comments.  The limit for available 92-93 octane pump gas these days is in the area of 9.3:1 with cast iron heads -- maybe 10:1 if you are using aluminum heads.
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badmonkey
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« Reply #5 on: March 06, 2010, 05:02:05 PM »

X2 on Geno's comments.  The limit for available 92-93 octane pump gas these days is in the area of 9.3:1 with cast iron heads -- maybe 10:1 if you are using aluminum heads.

That depends on your elevation. In Denver, 10:1 on iron heads is actually a wise move, just don't forget the de-burring of any sharp edges before final cleaning and assembly.
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ddman
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« Reply #6 on: March 08, 2010, 01:17:25 PM »

he is looking to rebuild with some macjine work on the block and heads. thinking of going .030 over on the block,porting the heads, and a cam around 484 lift. just wondering where that will put him. he has a set of 6x heads, not sure what his compression ratio is, or will be. it will be fed by a holley 650 atleast. crank will remain stock as will rods, pistons are up in the air at this point. trying to find a cost for this build and compare it to his budget.
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72blackbird
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« Reply #7 on: March 08, 2010, 02:18:57 PM »

You're fine with flattops if you're running 6x heads- depends if they're 6x-4's or 6x-8's how much you'll need to mill them down to get 9.2-9.3:1. We need the complete cam specs to determine whether it's a good choice or not- lift alone won't tell us that. The stock cast crank is a strong piece as long as it's properly prepped- the stock cast rods, otoh, are like pouring gasoline on your $2500 and lighting it- a good way to waste your time and money.

Geno
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1977 SE T/A (sold Sad )
1974 455 T/A (sold Sad )
1972 Esprit restomod
1976 T/A restomod
1975 Formula 400 4-speed
PMDMAN80
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« Reply #8 on: March 08, 2010, 04:24:50 PM »

Stock rods are good strong pieces up to 7k r.p.m.Have them checked for cracks first. The rod bolts are weak and need to be replaced with A.R.P. or equivelant. A small expense for piece of mind.
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77 LE MANS SPORT
80 T/A
91 GRAND PRIX G.T.P.
01 AZTEK SPORT
O7 TORRENT
07 Caliber R/T
LIFE IS GOOD!!!!!!!!!!!!!!!!!
FLYNLOW
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« Reply #9 on: March 08, 2010, 04:36:45 PM »

Stock rods are good strong pieces up to 7k r.p.m.Have them checked for cracks first. The rod bolts are weak and need to be replaced with A.R.P. or equivelant. A small expense for piece of mind.

Now this I wouldn't agree with. I'd install ARPs for piece of mind and obvious strength, but asking for 7K is a bit much on a regular reliable basis. I have my disagreements on 5200rpm, I have no problem revving a 400 to 5700, and with bolts to 6000 or so, but 7K? It may survive a misshift and a quick rev to 7K - heck, I've done it. But as a rule of thumb, this is probably not a good idea.
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1973 Formula 400
Now with LS1/T56
Formerly...
2001 LS1/4L60E/3.08's
Headers and a K&N, no tune.
12.920@106.041 2.03 60 foot.
lfdsteve
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« Reply #10 on: March 08, 2010, 04:54:11 PM »

I think what you will find is that for the cost of the upgrade to ARP hardware, checking and reconditioning your dang close to a good set of forge rods...
Thats the way I'm going and I think you will see that many of the guys in the know will say similar.

Steve
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72blackbird
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« Reply #11 on: March 08, 2010, 05:48:15 PM »

Stock rods are good strong pieces up to 7k r.p.m.Have them checked for cracks first. The rod bolts are weak and need to be replaced with A.R.P. or equivelant. A small expense for piece of mind.

Piece of mind w/ cast rods?! Obviously you haven't run a Pontiac motor w/ cast rods hard enough to blow one up.

Geno
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1977 SE T/A (sold Sad )
1974 455 T/A (sold Sad )
1972 Esprit restomod
1976 T/A restomod
1975 Formula 400 4-speed
Mr. P-Body
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« Reply #12 on: March 09, 2010, 07:49:19 AM »



   It seems every time forged rods "come up" in the conversation, at least one individual will "defend" the original cast rods. 

   The plain truth is, the cast rods were inadequate when new. They are now at least 35 years old and have a bazillion "cycles" on them. For a low-revving "long distance" engine (Bonneville, Grandville...), they're fine. For a performance engine, they are not.  For every "success" story using them, there are 100 Pontiac V8s in scrap heaps with cast rods "hanging out of them".  For $260 or so, why take a chance? It costs about $200 to "rebuild" the cast rods with new bolts. For a part that is no less than 10x stronger, it's foolish to even CONSIDER not replacing them.  7,000 RPM? I don't THINK SO...  At least more than "once". (:- For under $500, you can have the Eagle H-beam, a PREMIUM rod, capable of withstanding 7,500 AND 700-plus HP.

Jim
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LeighP
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« Reply #13 on: March 09, 2010, 07:59:25 AM »

As I've pointed out a few times...I've personally had two engine come into my possession from people who thought you could rev a Pontiac (stock rods) like a small block chevy.....both engines destroyed by broken cast rods.
At the price you can get decent rods for these days....don't even think about cast rods.
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Regards,
Leigh

Sydney, Australia
Former Firebirds -
1971 Pontiac Firebird 455
1977 Pontiac Trans Am
1976 Pontiac Trans Am
1967 Pontiac Firebird 400 convertible
1967 Pontiac Firebird 400 coupe

72blackbird
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« Reply #14 on: March 09, 2010, 11:38:53 AM »

I don't build any more Detroit V-8's with cast rods anymore simply because the forged rods now are reasonably priced and far better than any factory cast rods- there's also no point in building any engine with an inherent weakness like a cast rod when better rods are available and cheap. I've already turned away a few customers who wanted a stock rebuild and didn't want to pay for forged rods, yet these people gladly paid to have their stock rods reconditioned- close to what it costs for a set of RTR forged replacement rods.

I'm sure not everyone thinks they need forged rods, but as more engines fail in regular use to connecting rod metal fatigue it will become regular practice to use them in even standard performance rebuilds.

Geno
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1977 SE T/A (sold Sad )
1974 455 T/A (sold Sad )
1972 Esprit restomod
1976 T/A restomod
1975 Formula 400 4-speed
Mr. P-Body
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« Reply #15 on: March 09, 2010, 12:39:07 PM »

Geno,

   For the most part, we've had "co-operative" customers regarding this.  Once in a great while someone will "challenge".  We'll build the engine any way the customer wants. We'll only "warrant" it OUR WAY.  I was recently "bit" by a customer that INSISTED I use Scat rods instead of Eagle, "saving" him $100.  For a "floating pin" application, Scats might be fine. This one was press-fit.  I recommended against it simply because we've seen this before. Sure enough, the pin "walked" in the rod, grooving the bore. Of course, this was "the shop's" fault... So we bit the bullet and shipped it back, replaced the rods with Eagles, sleeved the cylinder and sent it back.   The rest is a "long story", but he lost "faith" in the engine and sold it to another.  That guy is happy as a clam!

   This incident is also why we never recommend Scat products. When I spoke to the main guy (he'll remain nameless here), he argued that we "did it wrong", that heating the rod is NOT the "correct" way to hang the pistons.  He said we should "press" the pins. Piston makers and SAE VEHEMENTLY disagree. Yah, his rods would maybe have "served" better, but the odds of the pins being completely "free" and no damage to the pistons are VERY HIGH.

  I guess the point here is to listen to the engineers that design this stuff and NOT the guys selling them.

Jim
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72blackbird
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« Reply #16 on: March 09, 2010, 01:00:37 PM »

Jim,
I totally know where you're coming from on this- why I do it my way or tell the customer to go find some other shop to build their engine. I have too much at stake to have an engine fail and have that customer bad-mouth me on the internet or at the Pontiac car-club scene here in SoCal. I think it's better to be known as kind of ornery but a builder of strong, reliable engines, than a guy who gives the customer whatever they want and fixes their mistakes for free.

I used to build stock engines, but quickly found out my customers were racing them and still thinking I'd give them a 100% warranty when they blew them up. I even had one take me to civil court, but my invoicing saved me from having to shell out a wad of cash and vindicated me. It's much easier to turn them away now instead of seeing them in court later, and far better to spend time on customers who can heed the advice of knowledgeable engine builders over what they read on the internet or hear at the local speed shop.

Geno
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1977 SE T/A (sold Sad )
1974 455 T/A (sold Sad )
1972 Esprit restomod
1976 T/A restomod
1975 Formula 400 4-speed
428 78T/A
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« Reply #17 on: March 09, 2010, 03:15:07 PM »

Geno,

   
   This incident is also why we never recommend Scat products.

Wish I had known this^. Got 8 brand new ones for my 428 sitting in the garage.
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PMDMAN80
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« Reply #18 on: March 09, 2010, 04:28:41 PM »

I HAVE BUILT MANY PONTIAC ENGINES WITH STOCK RODS,AND IF PROPERLY PREPPED WILL SURVIVE.I PERSONALLY RUN MY 400 IN MY L.M.S. UP TO 6500 R.P.M. WITH NO PROBLEMS. ALSO ACCORDING TO JIM HAND (WHO HAS BEEN BUILDING AND RACING PONTIACS SINCE MOST OF US WERE BORN, 1955) I QUOTE HIM "MANY BELIEVE THE STOCK PONTIAC RODS ARE INHERENTLY WEAK,THIS IS NOT TRUE. STOCK RODS ARE ENTIRELY ADEQUITE AND WILL HAVE A LONG LIFE IF RUN IN THE R.P.M. RANGE THEY WERE DESIGNED FOR" I CAN GO ON BUT NO NEED. UNLESS SOMEONE ELSE HAS MORE EXPERIENCE THAN HIM, I'LL STICK WITH HIS,AND MY OPINION. 
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77 LE MANS SPORT
80 T/A
91 GRAND PRIX G.T.P.
01 AZTEK SPORT
O7 TORRENT
07 Caliber R/T
LIFE IS GOOD!!!!!!!!!!!!!!!!!
Rick
Jedi Council
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Posts: 13130



« Reply #19 on: March 09, 2010, 09:37:10 PM »

As I said in another thread about this:

My 75 400 tach has the 5700 RPM redline on it, and I've had the engine up to nearly 6,000 RPM before.  That was when the cast rods were new.  Today I wouldn't do that unless I had the next engine ready to go.  Old cast rods (by definition, they're all old in 2010 since production ceased in 1978) + high RPM = high probability of coming home on a rollback.

There are 2 theoretical limits to engine RPM.  One is related to the piston speed that the short block can handle.  For continuous duty that limit for factory cast rods and cast pistons that maximum is 2500 feet per minute (fpm).  For maximum RPM, that maximum is 4000 fpm.  That works out to 4000 RPM and 6400 RPM (respectively) for the Pontiac 400.  The second RPM limit is related to the speed that the main bearings will handle safely and still retain sufficient lubrication ability.  That number is 60,000 inches per min for a street engine.  Given the 3.000" main bearing size of the 400 CID engine, that works out to 6400 RPM.  (Note that the 455 factory crank is the larger 3.250" size, and thus that same limit is reached at 5900 RPM -- lower than the 400 crank.)

Bottom line is that even with all-new guaranteed good pieces, 6400 RPM is the theoretical upper limit for peak RPM on a street engine if you are using cast rods and pistons.  ANYTHING less than "perfect" pieces and preparation degrades that limit downward significantly.  If you fully race-prep the engine (much stronger forged rods + pistons, oil system enhancements, etc.) you can stretch these limits upward.  But doing that will get MUCH more expensive VERY quickly, and your overall long-term reliability will drop significantly.

Before anybody jumps in with the protestation that drag cars are different -- drag race engines are a different animal all together.  Running an engine all-out for 6-10 seconds, then doing a complete tear down and replacement of many parts, is a LOT different that bolting an engine together that's going to run for even 5,000 miles.  The presupposition here is that "street use" implies that your engine will hold together for several years and many thousand miles.  Winding it up into the 6,000+ RPM range isn't conducive to accomplishing that goal.

One additional observation:  Many (not all, but many) of the latent defects in cast rods can be alleviated by properly preparing them.  Generally, that consists of polishing them to remove the part lines and then shot peening them to stress relieve them, and then balancing them to be sure they're all very close in weight.  You have to do all of that to eliminate the stress riser points hidden all along the part lines, because that's where the stress put on the rod is concentrated and it facilitates them shattering when the limit is reached.  Doing all of that isn't cheap, and it still won't cure the fact that the cast parts fail catastrophically when they DO fail.  Given the cost of forged rods today, there's no economic justification for NOT using a forged rod.  Yes, cast rods CAN be improved, but WHY?
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