[Pontiaco]

Got a 70 455 stroke to 496 eagle forged Bottom assembly balanced, Milondon 4bolt caps , Kauffman high ports 80cc ,solid roller on a 68 firebird.

Got twins gt45s turbos, question is would the motor stay together to 1200hp??

Th400 w/3.25 9in

[padgett]

A stroked 455. Oh my.

[JSPONT]

FWIW: I feel there is things you can do to help the block. I feel the stock side mounts and that much power even if they are strapped, can cause block flex. With out a real long winded post, once I put a mid plate on my car, I do not see cap walk. same everything in the motor. I also have the car lifting dead straight on launch with a drag bar. This is my opinion, from my personal experience.

[Tom Vaught]

Originally Posted by JSPONT

FWIW: I feel there is things you can do to help the block. I feel the stock side mounts and that much power even if they are strapped, can cause block flex. With out a real long winded post, once I put a mid plate on my car, I do not see cap walk. same everything in the motor. I also have the car lifting dead straight on launch with a drag bar. This is my opinion, from my personal experience.

TRUTH

Which is why some use a chain and turnbuckle on the left FRONT of the block, or just a strap with a SLIGHT clearance slot in the strap.

There are times when a midplate cannot be packaged with all of the other
items the owner wants to keep. Ok for a race car/TOY. Not so good for a daily driver (but even a daily driver can rip apart the drivers side mount).

Tom V.

[turbo69bird]

Originally Posted by Pontiaco

Got a 70 455 stroke to 496 eagle forged Bottom assembly balanced, Milondon 4bolt caps , Kauffman high ports 80cc ,solid roller on a 68 firebird.

Got twins gt45s turbos, question is would the motor stay together to 1200hp??

Th400 w/3.25 9in

If it’s put together correctly there’s no reason it wouldn’t

The biggest killer of an engine is going to be detonation from a poorly tuned engine , properly / safely tuned for a turbo engine would be a very fat and lazy tune for a naturally aspirated engine.

When I’m
Under full boost I want 10-1 afr. I know I’m safe if there’s any fluctuation or mistakes. It’s a very conservative tune but it keeps it alive . It leaves a little power on the table but your gonna keep it together .

[er455]

Originally Posted by turbo69bird

If it’s put together correctly there’s no reason it wouldn’t

The biggest killer of an engine is going to be detonation from a poorly tuned engine , properly / safely tuned for a turbo engine would be a very fat and lazy tune for a naturally aspirated engine.

When I’m
Under full boost I want 10-1 afr. I know I’m safe if there’s any fluctuation or mistakes. It’s a very conservative tune but it keeps it alive . It leaves a little power on the table but your gonna keep it together .

Hey Jeff I bought my turbo S475 from you over 6 years ago , finally getting to drive the car and do some tuning , can you tell me what your timing is set as ? Locked out or are you pulling timing as it makes boost ? Thanks bud

[Don Keefe]

That 700 horsepower threshold for a production block had always been a bit of a headscratcher for me as well. The question I would always have is "How are you getting to that level? Was it a NA stroker with a 4.5-inch arm and spinning to 7,500 rpm with 13:1 compression and an .800-inch lift cam? That's going to be a very problematic combo for a stock block. Failed cylinder walls, lifter bores, the chance of splitting the whole thing is very present.

Another problem combo is an overdriven 6-71 or 8-71 combo. Blowers will put enormous stress on the end of the crank and in turn will encourage block flexing. It's not a huge problem for a mild, low-boost street combo but things get very questionable as the rpms and boost go up.

A far friendlier setup would be a turbocharged short-stroke setup using a max of 3.75 inches. A combination like that will not put nearly as much stress on the block for a few reasons. One, the stroke will keep the stress on the cylinder walls down and will be less prone to cracking down the middle. There is also nothing on the end of the crank to cause stress and the cam can be relatively mild, so the lifter bores are not under the stress caused by a radical profile.

I have been a fan of turbos since I saw an 1800 cc VW make 460 horsepower in 1979 and lay down nine-second runs. Look up "Little Leroy." Then in 1996, I saw Marty Palbykin take everything I ever believed about turbos and make it come to life in Norwalk. He made 1,600 horsepower with a stock 1967 400 block without filling or block bracing, street-ported 670 heads and a 400 RAV crank. I will never forget that.

If you're looking for a street/strip stock block combo that would live, I would look to the 350. The smaller bore helps with block sealing, they tend to be a little beefier where it's needed and valve shrouding isn't an issue when under boost. Remember, Mopar went to a smaller bore for their supercharged Hemis. And GM didn't use the 427 LS7 as the basis for their supercharged engines. They stuck with the 6.2's smaller bore size for sealing and thicker cylinder walls.

[opeliac]

I dont have anything against KRE, but I also dont think they can walk on water...

There are numerous shops that can handle the job that the OP is asking about...It shouldnt be turned into who can charge the most for the job either...

Too many people will take the fun right out of their project by getting in way over their head with high cost engine builders...

[GTOGEORGE]

Originally Posted by opeliac

I dont have anything against KRE, but I also dont think they can walk on water...

There are numerous shops that can handle the job that the OP is asking about...It shouldnt be turned into who can charge the most for the job either...

Too many people will take the fun right out of their project by getting in way over their head with high cost engine builders...

KRE like Butler and DCI have built PA engine, hell any reputable place that has PA experience would work! I always ask experience people for their opinions and do a lot of other research then I make my own decisions and so far it’s worked pretty good.


GTO George

[turbo69bird]

Also size the turbo or turbos correctly too small= too much heat and your toast

[Tom Vaught]

Listen to turbo69bird, pontiaco.

This is not his first Rodeo as they say in the west.

Years ago Mark, (at Luhn Performance), boosted a 462 Pontiac (13 psi boost using a single belt driven Vortech Supercharger) and made 863 HP at 5300 rpm.

Nice low rpm, nice low boost level, almost 2 hp per cid at only 13 psi.

With a 455/462 engine you need to keep the rpm low and let the boost (mass flow) make the HP.

Been there done that.

Tom V.

ps a 455/462 will start fretting the main caps at about 5300-5500 rpm. Your 496 (larger stroke) engine will probably have a hard time
with bearing life at the hp numbers you want. Aftermarket block and crank helps.

[Pontiaco]

so are the gt45 t4 turbos are ok?

[charlie66]

Originally Posted by Pontiaco

so are the gt45 t4 turbos are ok?

For twins Yes

[Curtis Slowe]

Originally Posted by Pontiaco

Got a 70 455 stroke to 496 eagle forged Bottom assembly balanced, Milondon 4bolt caps , Kauffman high ports 80cc ,solid roller on a 68 firebird.

Got twins gt45s turbos, question is would the motor stay together to 1200hp??

Th400 w/3.25 9in

What is the compression on this engine?

[Pontiaco]

9.5cr

[Curtis Slowe]

Originally Posted by Pontiaco

9.5cr

Ok. Thought it was going to be higher. You should be fine.

[ta man]

The mention of a 350 for a turbo application has always been my thought.

[AIR RAM]

A while back I started asking questions about limitations of the factory iron block looking to find ways to give it the best chance to survival.

https://forums.maxperformanceinc.com...d.php?t=830317
http://www.pontiaczone.com/forum/showthread.php?t=31850

I was very interested in finding learning if there was a coloration between the rotational weights and mean piston speeds of failed blocks... because I just find it hard to believe 750hp is the magic limitation... The block must contain the Rotational weights @ RPM... So for the best chance at longevity... keep both those numbers low and cross your fingers.

The old school Pontiac guys on PY and other forums shared their experience and predictions to the point I started to doubt the long term reliability over the 750hp threshold. Could it be done, YES, but for how long was always the question with no real answers pertaining to rotational weights @ RPM. Simply questioning that 750hp threshold sparked anger in a great many people... This is how passionate some are on the topic...while I never said they where wrong, I just questioned the what, why how... which they where unable to fully articulate other than it just is. This made asking the questions on this very topic a bit aggravating to me because I thought there would be more specific answers.

In the end, what I got was that the factory iron blocks are inconsistent in their strength... So even trying to collect information on rotational weights and RPMs would lead to no usable data. So while some blocks will survive at 1000hp, others will crack down the middle at 600hp.

With all that said, most of these people who have responded have MUCH MUCH more experience than I have with 455 blocks so I ended up heeding their collective advice and just sacrificed my first born for an MR1/ 3.25" mains. Now instead of the original 10-15psi goal, its now 15-20psi.

Sorry the long winded response.... basically I asked the same question and left with no real answers except Keep the RPMs down... 5500 seemed to be as high as you should go as far as RPMs are concerned... Lower will be better... it will last forever at idle.

SPEED SAFE, NICK

[73 TRANSAM]

For street driving and if you already have the parts. It will okay but not ideal. If Going to the track is your plan then don't rev past 6000 rpm for sure. It will also wear your piston skirt faster. GL with your build. Two GT45 would work. I like a big single myself, but twins make less back pressure.

[JSPONT]

If it is a street car, with trips to the track it will hold up for years if the tune and chassis is right. To be honest. 1200 hp on the street with a small tire car is a waste. it gets real tricky after 750 on the street. You can never leave on a psi on the street like on a prepped track. On the street with my 461 I leave on 5-6 psi and at 11-12 on the top end and still can come loose in 3rd gear. I put about 30 passes on it this year and 3000 street miles. Just about the same for the last 5 years with no issues. I have had friends blow up better built engines than mine with less power. Greedy tunes and lack of reading plugs will get ya. If you can swing the a/market block go for it. They are no picnic. A ton of machining and then oil pans never fit amount other issues. JMO