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Author Topic: 455 rebuild  (Read 630 times)

Jeremy

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455 rebuild
« on: November 08, 2019, 07:27:37 PM »
It looks like the 455 in my trans am is going to have to come out to find the source of a knock.  I'm hoping that it will be the last time it comes out.

Current combo is a stock 455 block bored out to a I think a 468.  6x-8 heads with an 041 cam and Rhoads lifters.  FITECH with timing control.  Performer intake with 1 inch spacer.  Factory exhaust manifolds cleaned up internally as much as I could feeding pypes exhaust necked up to 3 inch as soon as it turns with an X pipe.  Motor is hooked to a tremec 3550 baced by 3.08 gears.

Currently it runs fine, other than the knock, but seems to run out of breath at 5000-5200.  My goal is strictly street performance and boring reliability. 

The two upgrades I am considering are a different intake and or Ram Air exhaust headers. 

My question is will I really see any difference on the street for either or both modifications?  I'd guess any difference would show up on the upper end which I wouldn't see very often realistically.

oldskool

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Re: 455 rebuild
« Reply #1 on: November 08, 2019, 08:44:08 PM »
"...My question is will I really see any difference on the street for either or both modifications?  I'd guess any difference would show up on the upper end which I wouldn't see very often realistically."

You answered your own question.

Even a stock Q-jet manifold is better than a Performer, on a big inch Pontiac. A Performer is the choke point. Just won't flow enuff. With the FITECH, a single plane might work better than a Q-jet intake. A Torker 2 should work. If you don't need the exhaust heat crossover, for cold weather operation, one of the Chinese single planes might work OK, & are cheaper. 

And, log manifolds also choke a big inch Pontiac down. The RA manifolds with the 2 1/2" outlet will make quite a difference in flow.

BUT, under 4500 rpm, there probably wouldn't be a huge improvement. The 455 gets all it's low rpm power from it's long stroke. So, up thru 3500 rpm, the Performer & logs do OK. But, to make more above 4000, it needs to flow more air. I've read that an engine is a big air pump. So, to make more power above 5000 rpm, it'll have to flow more air above 5000 rpm.   

Back in the '70's, I ran the 041/Rhodes in all my 455 bracket engines. But, they all had the small chamber, big valve heads, like 16, 48 & 62. So, those engines had more compression. All those engines had cast rods. So, I set the rev limiter at 5500 rpm. Since we were bracket racing, on a normal run, we shifted at 5000 rpm. But, the cars would go just a little quicker when shifting just below 5500. I suppose that means that shifting higher kept the engine within it's peak power band longer, than shifting at 5000 did.

I've read that, for max ET, you need to shift slightly ABOVE your peak hp rpm. So, for the engines in my cars, that means that the peak hp was probably somewhere in the 4800-5200 range. Never had any of 'em on a dyno. So, it's only a guess. But, with unported iron heads, they're not supposed to make peak hp any higher than about 5000 rpm.

Don't mean they won't rev higher, or run quicker when shifting a little higher. Just means that, on a dyno, the hp would BEGIN to fall off. But, it doesn't just drop off completely. Lets say it made a peak of 400hp @ 5000 rpm. At 5200, it might make 390hp. At 5400, it might make 380hp. Well, 380hp will still maintain a high speed. It's just that you're past the rpm at which the engine makes it's peak dyno hp.

Now, exactly how quickly the power falls off, above 5000 rpm, is dependent on several things. Obviously, the engine will have to be supplied with enuff fuel & correctly timed spark. The cam will have to open & close the valves at the right time, and to the necessary height. The heads & exhaust system will have to flow enuff.

As you probably know, the 041 cam only came in high compression 400 engines, with round port heads & RA manifolds. I think the peak hp was rated above 5000 rpm, maybe 5200. Now real sure. The RAIV engines also used 1.65 rockers, which probably raised the peak hp rpm. So, the RA4 engines probably made peak hp at a higher rpm than the RA2 engines. Anyhow, that same cam, in a 455, would make it's peak hp at a lower rpm, say somewhere in the 4800-5000 rpm range.  There are a LOT of variables which can affect power numbers. The only way to know, for sure, is actual, and ACCURATE, dyno numbers. And the ONLY way to know exactly what ET numbers different combination of parts & tune will produce is actual drag strip testing. And, I suppose the only way you'll know "seat of the pants' feel, is to do street testing, with different parts & tune combos.

People can tell you what THEIR results were. But, there are so many variables that could make your results different from their results, that you can't possibly be absolutely sure you'll get the same results somebody else got. For example: There are 400 Pontiac drag cars running mid 10's & turning 8000 rpm, with iron heads, intakes, a 750 Q-jet, and a flat tappet cam. But, on most of these Pontiac street forums, they'll say that's not possible. Most don't think an iron D-port head will flow enuff to go 8000 rpm. And the heads those Stockers are running can't show any obvious signs of porting.

So, when guys on these forums tell you something CAN'T or WON'T, remember that you can't believe EVERYTHING you read on the internet. You just have to weigh what everybody says, & decide what you wanna try. Only AFTER trying something will you know exactly how it will affect the performance of your engine. Some enjoy the process of testing different parts, to see what helps & what hurts performance. Some just want somebody else to tell 'em what will work best in their car, without doing any testing themselves. My question is, without testing different parts/tuning, how will you know what's best for your car ?
« Last Edit: November 09, 2019, 07:12:13 AM by oldskool »

gm muscle

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Re: 455 rebuild
« Reply #2 on: November 10, 2019, 07:39:16 AM »
Absolutely right but for your average guy, buying different cams, intakes, lifters, rockers and heads is an expensive and time consuming proposition. Therefore, we turn to guys like you, Geno and Critter with years of been-there-done-that experience who can guide us in the right direction.
« Last Edit: November 10, 2019, 07:52:31 AM by gm muscle »
1977 Trans Am stroked 400 (468)
1989 Iroc-Z28 5.7 TPI 90K original miles
1987 Monte Carlo SS LS 2/4L65e
1997 Silverado 5.7 Z71 Single Cab, Short box (daily driver)

Fbird

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Re: 455 rebuild
« Reply #3 on: November 10, 2019, 08:35:56 AM »
as already noted about the performer intake....and lack of exhaust..... You could probably lower some et's by gaining TRACTION! as I'm sure that with those cubes and  (assuming your running 1.5 rockers) soft camshaft you have monsterous torque in the 1800 rpm range.....probably shred the tires at will if you really hammer it AFTER coming out of the clutch.
You have s decent combo just need some more support peripheral components to maximize where your at.
more air in...more air out. Once you look to add air movement you could look to add some 1.65 rockers (MUST CHECK PUSHROD CLEARANCE) to feed that 468.
67 Firebird
1981 Turbo TA (injected 400 now :) )

gm muscle

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Re: 455 rebuild
« Reply #4 on: November 10, 2019, 11:27:30 AM »
What about the performer RPM, is it also a choke point...not flowing enough air?
1977 Trans Am stroked 400 (468)
1989 Iroc-Z28 5.7 TPI 90K original miles
1987 Monte Carlo SS LS 2/4L65e
1997 Silverado 5.7 Z71 Single Cab, Short box (daily driver)

oldskool

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Re: 455 rebuild
« Reply #5 on: November 10, 2019, 04:59:24 PM »
What about the performer RPM, is it also a choke point...not flowing enough air?

No. It's completely different & quite a bit taller.

Again, some say the FITECH works better with a single plane intake. Can't confirm, since I've never used FITECH.
« Last Edit: November 10, 2019, 05:01:45 PM by oldskool »

Jeremy

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Re: 455 rebuild
« Reply #6 on: November 11, 2019, 12:57:10 PM »
I am running 1.50 rockers.  The compression ratio is listed at 9.25:1.

It sounds like I should save up for the exhaust manifolds first thing as they will be much easier to swap while the motor is out.  Looks like it is going to require new down pipes as well.

The manifold I can change a whole lot easier as time and budget catch up.  I was curious how a single plane might work since I am running fuel injection.  I was worried about it being less efficient at 1500 to 2500 rpms as this is where I spend a lot of time steady state cruising.

When I get to doing the intake, I'd like to remove the exhaust crossover as the car won't get driven below 40 and I'd like to keep the intake cooler during the summer months.

I do have a cast iron intake but it is a mid to late 70's EGR intake.  Not sure how it compares to the pre 72 intakes.

I don't think I could fit the performer RPM under the shaker assembly.  I fit the performer with a 1 inch spacer and its as tight as I can go.

Thanks to all that have chimed in.  I don't have the time or desire to change parts looking to optimize everything.  Trying to sort through everything one last time and get it as close as possible for a fun street car.

Surprisingly, street traction is not too hard to maintain.  I can break the tires loose when I want, but I can get the car to stick when I want it to as well.

gm muscle

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Re: 455 rebuild
« Reply #7 on: November 11, 2019, 02:36:41 PM »

I don't think I could fit the performer RPM under the shaker assembly.  I fit the performer with a 1 inch spacer and its as tight as I can go.


http://www.pro-touringf-body.com/engine.html

This is the one I bought from Dave. I previously purchased one from Butler Performance that did not work. The one from Pro Touring FBody is clearly superior. I have a Performer RPM with the original Q-jet carb and hood closes just fine with the shaker on. Are the physical dimensions of the FiTech throttle body similar to that of a Q-jet?
« Last Edit: November 11, 2019, 02:46:11 PM by gm muscle »
1977 Trans Am stroked 400 (468)
1989 Iroc-Z28 5.7 TPI 90K original miles
1987 Monte Carlo SS LS 2/4L65e
1997 Silverado 5.7 Z71 Single Cab, Short box (daily driver)

Fbird

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Re: 455 rebuild
« Reply #8 on: November 13, 2019, 06:09:16 AM »
you are correct on the do as you go idea. If you have the motor out....definitely swap the exhaust!!!! doing an intake manifold is easy peezy on the car... doing exhaust uhmmm...lets just say NOT so easy peezy on these ..
The shaker nightmare! Many different issues come up trying to get these things RIGHT. I have yet to see a composed list of combos that WORK.....but sometimes one must be creative (and that does NOT mean BOLT THE SHAKER TO THE HOOD!!!!) Shakers are meant to SHAKE...
67 Firebird
1981 Turbo TA (injected 400 now :) )

79T/Aman

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Re: 455 rebuild
« Reply #9 on: November 14, 2019, 08:12:23 PM »
you are correct on the do as you go idea. If you have the motor out....definitely swap the exhaust!!!! doing an intake manifold is easy peezy on the car... doing exhaust uhmmm...lets just say NOT so easy peezy on these ..
The shaker nightmare! Many different issues come up trying to get these things RIGHT. I have yet to see a composed list of combos that WORK.....but sometimes one must be creative (and that does NOT mean BOLT THE SHAKER TO THE HOOD!!!!) Shakers are meant to SHAKE...

The PTFB air cleaner is over 90% effective solution to fitting a Performer RPM under a shaker.
www.pro-touringf-body.com  your source for making your Trans am do what it does best!......SHOW OFF!

Fbird

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Re: 455 rebuild
« Reply #10 on: November 19, 2019, 07:24:48 AM »
good to know  ;)
always a PITA when setting up an intake/induction on a bird.
67 Firebird
1981 Turbo TA (injected 400 now :) )

glenn911

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Re: 455 rebuild
« Reply #11 on: November 19, 2019, 09:24:48 AM »
Any body have any numbers showing gains from going from performer to performer rpm on a iron head 455?  Hopefully, I will be one of the 90% that the drop base works for.
'79 400 4 spd esprit
'78 455 WS6 auto
'74 461 4 spd T/A

Re: 455 rebuild
« Reply #11 on: November 19, 2019, 09:24:48 AM »
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