496 turbo 1200 hp, yes, no or maybe so??
 

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

A stroked 455. Oh my.

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 .

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

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.

so are the gt45 t4 turbos are ok?

For twins Yes

What is the compression on this engine?

9.5cr

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

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

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.

No one could ever know what any stock block will handle . No 1 block is made equal to the other. Its a crap shoot. That's the only real answer .....

We were making about 1100hp in the Bandit, 462 stock block, crower crank 4.25" stroke, 90cc E heads, 9.2:1 compression, before a cheap ass crane HYD roller lifter broke. Twin 78/75 turbos @ 18 psi. It'll be back together soon.

You had a bunch of good parts, Heads and Crank.
What rods were you running? And Pistons?

Tom V.

Eagle forged crank, Eagle rods , mahle forged pistons, mahle piston rings gap at .028

496ci rotating assembly

Oliver rods, Ross pistons with thermal coating and LS ring pack (1.2, 1.2, 3.0 mm)

Our experience was with 1972-1973 455 castings. Running Nitrous Oxide with total running HP around 1200 and maximum RPM's of 7000. We had consistent block failure in the same place on all three blocks. All 3 cracked the block up the #2 main oil feed from that feed hole to the cam bearing bore. Nothing dramatic, it just happened after quite a bit of racing time on the track. Several years worth of racing. One of them cracked up the #2 main and the #4 main oil feed as well. We ran aluminum rods in all of them. As mentioned, tune-up and detonation is the block killer, especially stock blocks. I would build the best engine you can and not pay too much attention to those old timers who insist a stock block Pontiac is a throw away at 700 HP like we had been hearing for decades. That kind of talk comes mostly from people who haven't done anything and believe everything they read. That said, an aftermarket block gives you to a whole different level of performance potential and abuse they can withstand. Good luck with the build.

Thank you guys, I will keep u posted