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Author Topic: 455 Pontiac: Supercharger low & compression/or high compression rebuild  (Read 2148 times)
battlegroundtransam
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« on: December 23, 2011, 02:10:07 AM »

  Hi!,   

     So I picked up a relatively rust free 1977 trans am last year, and I'm starting the restoration right after Christmas. The build sheet says it is original black on black. Also, its t-top and automatic. And this past summer I picked up a 455 that came out of a '71 grand prix, I think, I'd have to look at it again, but at least '71. And I'll need heads.

     So I have this mechanic who is going to help me build this, I've got 5-6k to work with, and I'm wondering if I should build a low compression engine with a supercharger, or just a high compression engine.  I was reading around that there are passive switches that bypass a supercharger and let air come in from an alternate duct when driving casually, and flipping the switch closes this duct and the supercharger becomes the main air intake again. I've heard the switch can be built into the accelerator pedal so when stepping harder on the gas, it closes the alternate air intake. Would this lead to significant increase in mpg for city driving? And I do realize even the new cadillac ctv 550 hp gets only 12-18 mpg, but would what I'm thinking of building get much lower than that?
     And if I built the car without the supercharger, I would obviously be spending less money, and it would be a higher compression engine; possibly 10:1, 425-450 hp for 5-6k. I might have to use a fuel additive if it gets up to 425-450 hp, but I can live with 3 extra bucks per fill up.
     Maybe I am being a little unrealistic, but I would want the most hp for 5-6k, the most low end speed(lower gears?), and the best mpg I can get. So with this combination of expectations, is there anyone who might have a suggestion as to how I should build the engine? Thanks for your time!-Chris
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LeighP
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« Reply #1 on: December 23, 2011, 04:00:18 AM »

My thoughts....just an opinion....
For your budget, forget all together about a supercharger, that'll eat most of the budget right there. If you were going to supercharge an engine, its more expensive to build to suit the supercharger anyway.
You should have no problem getting a 455 to deliver 450hp on pump gas....but you may push the budget you've got doing it. A decent set of heads will cost you 2-2.5K alone.

Find a copy of "How to Build Performance Pontiac V8s" by Jim Hand....it has a ton of information, and some recommended build combos in the back of the book to follow.
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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

Thomasmoto
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« Reply #2 on: December 26, 2011, 05:50:34 PM »

My thoughts....just an opinion....
For your budget, forget all together about a supercharger, that'll eat most of the budget right there. If you were going to supercharge an engine, its more expensive to build to suit the supercharger anyway.
You should have no problem getting a 455 to deliver 450hp on pump gas....but you may push the budget you've got doing it. A decent set of heads will cost you 2-2.5K alone.

Find a copy of "How to Build Performance Pontiac V8s" by Jim Hand....it has a ton of information, and some recommended build combos in the back of the book to follow.
I totally agree with Leigh. A blower of any kind is gonna crash your budget, not to mention what it would cost to get the bottom end up to live with it. A warmed over street engine will get to 5k pretty quickly anyway. There are Pontiac specific machine shops and builders that are on this forum. Get in touch with one of them and get the most bang for your buck that way.
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David Thomas
MikeS
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« Reply #3 on: December 26, 2011, 09:17:41 PM »

X3....my 400 build is rapidly approaching $5500....not to hard to get there fast!

Compression ratio, heads, and camshaft....Your dynamic compression ratio is the important one, not the static compression ratio...if you want to run pump gas you need to be around 8:1 dynamic.  Much over this you'll run into detonation problems.  You'll want to achieve this dynamic ratio by matching your heads, pistons, and camshaft together.  Make sure you use a calculator that takes into account your altitude when figuring your dynamic ratio...You can get away with a higher static compression ratio at higher altitude....my static in my 400 is 10.7:1 ! My dynamic ratio based on my static ratio, camshaft profile, and altitude is 7.8:1...right in the sweet spot for max power on pump gas...

here is a good calc for altitude and cam effects on comp ratio... http://www.wallaceracing.com/dynamic-cr.php

You'll need to know your static ratio upfront to use that calc...you can figure that here...http://www.gtsparkplugs.com/CompRatioCalc.html  or here... http://www.projectpontiac.com/ppsite15/compression-ratio-calculator

You'll probably want to run flat top pistons...

Heads to keep an eye open for would be #64's...they have the bigger 2.11/1.77 valves to feed that big 455 and at 87cc's will give you around a 10:1 comp ratio...you don't even have to go too radical with the cam to get it into a good dynamic ratio, but you want to make sure your hitting the 7.5-8 ratio...


6X-4's would be a good choice as well...they will be easier to find, they also have the big valves, and you can mill them down a bit to get the right comp ratio...

With a dynamic comp ratio around 8:1, good cam, carb, intake, headers...that 455 should make 400 hp on accident... Very Happy
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72blackbird
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« Reply #4 on: December 26, 2011, 11:05:11 PM »

Iron- headed Pontiac V-8's don't like alot of static compression- 9.5:1 is about the max you want to run on pump gas, preferably 93 or 94. 450 hp from a 9-9.5:1 455 that runs on pump gas is definitely possible, but there's alot of head prep required to keep the pre-ignition and detonation at bay- you'll need to smooth all sharp edges in the combustion chamber, and a street port job with some bowl work will help flow as well. I would also recommend forged rods and pistons at that hp level, as cast rods can shatter like glass when they let go and cast pistons will crack if hammered by detonation.

A customer of mine recently lost a good running 389 I built for him- the two cracked hypereutectic pistons and damaged cylinder wall were a result of running too low an octane fuel for his static compression ratio. An 8.8:1 SCR combined w/ 89 octane and a  split duration cam (210/221@.050) still lead to an engine that experienced detonation and an engine failure- there were probably a few other conditions that contributed to the failure, but one tank of poor quality gas could have done it.

A solid 455 2-bolt bolt w/ ARP main studs, forged pistons and rods and all machine work will cost you around $1500-2500 depending on rod/piston choice- this combo should be able to support around 600 hp. Stock iron heads with 2.11/1.77 valves and a split duration cam around 224/232@.050 with an SCR around 9:1 should make at least 400 hp. The same heads w/ porting and combustion chamber prep will make around 450 hp- I would increase the cam duration to around 236/242@.050 to take advantage of increased airflow capacity. Fully machined iron heads (stainless valves, bronze guides, pc seals, surfaced) will cost at least $1000- add another $600+ for porting and you can see why $2000/pr for stock aluminum heads that make 500 hp are a good option.

Geno
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tajoe
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« Reply #5 on: December 26, 2011, 11:48:44 PM »

A blower motor with relief ports for low speed driving? (You've been watching too many Mad Max movies.) That set-up alone would eat up your budget.  Confused
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LeighP
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« Reply #6 on: December 27, 2011, 04:53:29 AM »

Only engine I've personally seen set up with an "on demand" blower was a Japanese limo car's engine (can't recall if it was Toyota or Nissan) that was a combo turbo/supercharged system. The supercharger was a low pressure job on an electric clutch like an AC compressor.....as the engine revved, the supercharger was engaged and supplying boost, as the turbo spooled up, a pressure switch disengaged the clutch on the supercharger as the turbo boost built up past the supercharger's output.
The idea was to remove the turbo lag from the engine.
Modern turbo design, and improvements in engine management have made that complicated system redundant.

A Pontiac's big advantage is huge torque and simplicity.....best to play to the advantages of old school V8's and build accordingly.
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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

SavingTheBird76
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« Reply #7 on: December 27, 2011, 06:57:20 AM »

Just Build your motor with a decent compression ratio of 9:1 and add the blower at a later date.
Nominal increase in cost adding forged pistons and crank..figure $600 for the crank and another $600 for pistons..everything else can stay the same...except for the blower cam added later.
The heads,machine work and valve train will cost nearly the same.
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MikeS
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« Reply #8 on: December 27, 2011, 12:45:37 PM »

X2 on the forged piston recommendation....avoid the hypereutectics.  I know the price makes them tempting, but the few extra couple hundred dollars spent to get forged is well worth it.  Hypereutectics apparently have a nasty habit of shattering their ring skirts under certain cirumstances....many shops won't even use them...even if it's not too common, the extra piece of mind that money buys using forged pistons is worth it in my book...

On the static compression ratio...yes, at sea level 9-9.5:1 is a good rule of thumb...but there is a lot more that goes into detonation than just your static comp ratio.  Elevation, camshaft profile, ignition advance, cooling capacity, piston shape, proper head gasket quench, air/fuel mixture, etc all come into play here.  A properly matched and tuned high compression engine is less likely to have detonation issues than a poorly matched and tuned engine with a lower compression ratio...it's important to do your homework on your build...little things make a big difference!

Is this car going to have an automatic or a manual transmission?
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ILLTA77
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« Reply #9 on: December 27, 2011, 01:12:29 PM »

I think a Pontiac engine with a supercharger in a TA would be awsome..
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LeighP
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« Reply #10 on: December 27, 2011, 10:51:46 PM »

I think a Pontiac engine with a supercharger in a TA would be awsome..

Very true...I'd go the Vortec style myself.......but I guess our replies were aimed at staying within the original budget and HP targets...which really would preclude using a blower, just on budget alone......why is everything so expensive!!!!!!!!  Laughing

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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

ryeguy2006a
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« Reply #11 on: December 28, 2011, 08:33:22 AM »

Unless you were planning on buying the supercharger brand new, you have a few options. If look around you can find some very good deals on Vortech superchargers off of newer mustangs. If you have some fabrications skills you could make your own brackets and you could build a supercharged motor for the budget you have. On a local for sale thread, there is a complete Vortech kit for a GT mustang for around 2k. Now that came with every, the head unit, injectors, intercooler, etc. You could sell the other parts not needed to add to the budget. Also I have seen just the head unit on Ebay for about 800 bucks. If you would be willing to do a lot of the work yourself it would be definitely possible.

800 head unit
200 Fabricating brackets
2000 Butler forged rotating assembly
500 Holley Carb (Holley because they are easy to modify for Blow-through)
500 Street port stock heads
500 Piping, clamps, BOV
100 Carb hat
300 Better Fuel pump (A1000)
200 Wideband O2 Sensor (for tuning)

I might be missing some stuff but all that’s listed comes below your budget, and would leave about 400 bucks for the little things.
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firebirdparts
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« Reply #12 on: December 28, 2011, 09:07:35 AM »

It seems to me like your interest in fuel economy makes the decision for you.  High compression will increase fuel economy, but the blower will reduce it.
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Doug
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« Reply #13 on: December 30, 2011, 08:49:50 AM »

I looked into this extensively on the Triple Threat car.  Even with some pretty heavy discounts, about the lowest I could come in with something that would stay together was over 5 to 6 times your budget.  You might piece something together but I would not count on it staying together very long.  These motors make a lot of torque already, you can get a lot more bang for your buck otherwise.

Follow all the guys advice on this and use the $5k to go aluminum heads, good cam and quality internals for the bottom end. That will eat up $5K  pretty quickly but you will have a 500+ hp motor.
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battlegroundtransam
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« Reply #14 on: January 05, 2012, 06:42:03 PM »

Hey thanks for all the helpful posts! I'm bringing the engine to the machinist this week. I might post the restoration on that particular thread-Chris
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critter
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« Reply #15 on: January 05, 2012, 08:57:13 PM »

The great thing about a Pontiac motor is that you can build a mid-400ci displacement motor and make 400hp pretty easily. Busting that 500hp mark means buying good heads. After that, it gets interesting. Good luck on your build.
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