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SPRINT 6's 1966 LEMANS 2DR HT

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Hey I have come across a '76 Trans AM I am going to "restore" I'm not completely worried about keeping it original although I am keeping any original parts I would replace; heads, cams, etc....



Well I have the original 455 engine I need to have some work done on it, and I want to beef it up some as I know in '76 it took a huge power dive to about a 200hp engine. I was wondering if anyone had any ideas or information on what kind of upgrades I could get on the engine (like aluminum heads possibly, or a better cam) and what kind of compression ratio I should get it set to. I'm under the idea that the original compression ratio is 7.6:1 which is pretty low, so what might be an ideal compression ratio? If anyone has any information that would be helpful to me that would be great.



Thanks



Nick


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The 455s that I have seen really like about 9:1 compression for it. That would make a nice street motor for it. Edelbrock makes some nice heads for it and a comp cam 270H cam for the bump stick would help matters alot. Aluminum intake from Edelbrock but a carb from Holley that is rated in about 800 cfm. Just remember those 455s had a ton of torque and even tho your 200 hp does not sound impressive the torque number is probably close to 300.


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moved into performance


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:welcomeFP: sinister poet.




I have a 455 that has been bored out to a 462 (.030 over) in my '72 Lemans Sport convertible. So I can give you some tips. Based on what you've written, I am going to make some assumptions here. First, the car is going to be street driven. You'd like to have performance but have has to be able to run on pump gas. Your engine has to produce enough vacuum to support your power accessories so a race cam/heads is out of the question.



Stratman and notallthere are correct in their recommendations. Butler is the premiere Pontiac engine builders in the country. Edelbrock makes a great performance aluminium head for Pontiacs.



Short Block: Eagle crank, stock rods, JRE pistons, Melling oil pump, a hydraulic McKellar #10 cam profile from Melling, Clevite bearings, ARP studs and rod bolts everywhere, factory windage tray, BOP Engineering Vlitron rear main seal (not a factory style rope seal), stock oil pan (Melling reproduction if necessary). double timing chain/cam & crank sprocket, stock timing chain cover and water pump. block and rods shot peened and magnafluxed, block align honed




Top end is a different animal since you have choices: Edelbrock, Kaufman, allpontiac.com produce aftermarket heads for Pontiacs. Even certain stock heads are desirable based on their cc's, intake and exhaust sizes. You have to do your homework on the stock heads to know which ones to get. Assuming your 455 has the original 6S or 6H heads, they quite good - they have with 2.11" intake and 1.66" exhaust valve. The 7M5 heads on my Lemans run 2.11/1.77. So some gasket matching/port/polishing and a triple angle valvel job is all I did to mine. My intake is an Edelbrock Performer RPM. I run a stock QJet carb. My compression is about 9.6:1 on 94 octane gas (no octane boost). The original factory intake 4-bbl manifolds are really quite good other than for weight. So unless you want to see a shiny aluminium manifold under the hood, you don't have to swap it out. I run a stock distributor with a Pertronix II Ignitor to replace the points and condensor. In your case, an re-built HEI is fine. I tun Comp Cam springs, push rods, and stamp steel roller rockers. Again, ARP studs and bolts all around.



Exhaust: Doug's Headers, or factory re-production performance manifolds from Ram Air Restoration. Mandrel bent exhaust tubing. Your choice of mufflers - Pypes, Magnaflow, Flowmaster, Cherry Bomb, Thrush, Heart Throb, etc.





There is a video series in another thread on this sight where another member has his 455 professionally built to run on E-85 fuel. I think the build tips are valid regardless of what you plan to do with your motor.



http://foreverpontiac.com/topic/4211-pontiac-v8-engine-building-series-in-1080hd-on-vimeo/


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I beg to differ. The 6X-8 heads were on the 180 HP 400 motors, the 6X-4 heads were on the 200 HP 400 motors, starting in '77. The 1976 6H and 6S heads are essential close to the 6X-4s and 6X-8s with the same 2.11/1.66 intake and exhaust valves. The 6H, 6S, and 6X-8 heads were designed for motors with 7.6:1 compression ratios. The 6X-4 motors had a compression ratio of 8.0:1. Not statistically significant if you are moving up to 9.5:1 compression in the first place.



I will say that given the number of Trans Ams and Formulas built in '77 and '78, the 6X heads should be plentiful and cheap....assuming the 455s original heads are gone or junk to begin with.


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Hey I have come across a '76 Trans AM I am going to "restore" I'm not completely worried about keeping it original although I am keeping any original parts I would replace; heads, cams, etc....

Well I have the original 455 engine I need to have some work done on it, and I want to beef it up some as I know in '76 it took a huge power dive to about a 200hp engine. I was wondering if anyone had any ideas or information on what kind of upgrades I could get on the engine (like aluminum heads possibly, or a better cam) and what kind of compression ratio I should get it set to. I'm under the idea that the original compression ratio is 7.6:1 which is pretty low, so what might be an ideal compression ratio? If anyone has any information that would be helpful to me that would be great.

Thanks

Nick

7:6 to one is the perfect starting point for a blower!!!!

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7:6 to one is the perfect starting point for a blower!!!!

True JUSTA - you would be the one guy to suggest that on this forum ! I like that idea BTW.

However, sinister poet, be sure to blueprint the entire motor with most of the parts and suggestions from above. Forced induction will require smaller compression pistons, but the added power will put stress on the rest of the engine - if you don't take precautions to handle that power correctly. As I often say through out this forum - do your homework. Talk to expert engine builders, pick their brain on what the best combination they think will work for your car, wants, needs, and most importantly, budget.

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Might add that blower and budget do not work together.


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From the way it sounds you have the right ideas for this ride. Remember the hp you add will also add torque, so just remember the more torque the pressure on the chassis to.

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I beg to differ. The 6X-8 heads were on the 180 HP 400 motors, the 6X-4 heads were on the 200 HP 400 motors, starting in '77. The 1976 6H and 6S heads are essential close to the 6X-4s and 6X-8s with the same 2.11/1.66 intake and exhaust valves. The 6H, 6S, and 6X-8 heads were designed for motors with 7.6:1 compression ratios. The 6X-4 motors had a compression ratio of 8.0:1. Not statistically significant if you are moving up to 9.5:1 compression in the first place.

I will say that given the number of Trans Ams and Formulas built in '77 and '78, the 6X heads should be plentiful and cheap....assuming the 455s original heads are gone or junk to begin with.

When you look at the cc difference of the 6H at 124cc and the 6X-8 at 101cc, a simple head swap will make a difference.

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i had a set of 6x8's measured at 112cc's.Look for a set of 71 96's.after milling mine came in at 94cc's.my 469 with 96's is about 9.5 compression.still have some tuning to do so..time will tell.fwiw the low compression 8ish 400 i had in the car was a lot of fun to drive with no pinging to worry about and i could gas up anywhere,no premium needed.


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Joe....He is ALIVE. LOL How about an update?? You can try dropping your plugs a heat range too.

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Some pretty good tips so far, however I'm going to politely disagree with Frosty on some things. 

One is connecting rods.  Factory rods are the weak link in Pontiac engines, and by the time you pay to have a set of factory rods reconditioned and prepped for an overhaul, you're going to be very close to the cost of a new set of good forged H-beams.  Considering that long stroke and larger main journal size of the 455 (with attendant oiling difficulties), putting a set of good rods in it is one of the better investments you can make.

 

Rear main seal: I've got the 2-piece Viton from BOP in my 461 (stroked 400) and even though I *know* I followed the directions explicitly and to the letter, it leaks. I think the reason is because I had my block align honed, and that process leaves the seal groove out of round.  Up until about a year ago if I'd redone it, I would have gone with the Graphtite rope seal for that reason.  NOW whenever I get around to pulling the motor and resealing it, I'll be going with one of these:
http://www.bopengineering.com/beltdrive_acc_topend.shtml

It's a double lip seal, and the from the instructions it's pretty clear that this thing just HAS to work.

 

Cam:  I'm running a solid roller in my car.  These days if I were building a fresh street engine I probably wouldn't even consider a flat tappet cam because of the difficulty of making one live with modern oil that has had most if not all of the ZDDP content eliminated.  You can add it back, or buy specialty oils that have it, but it's one more thing you have to remember to do.  There's also been some discussion that adding ZDDP may not be as effective as having oil that is "made" with it due to molecular bonding, but I have no direct experience or knowledge about that - just passing it along for what it may be worth.  At any rate, even thought they're more expensive i wouldn't consider anything other than a roller cam and valve train - hydarulic or mechanical as is your preference.

 

'Rule of thumb' on compression.  For a street engine, shoot for a ratio that's "the same as" whatever octane fuel you plan ro run. i.e. 9.3:1 on 93 octane, 9.1:1 on 91 octane, etc.  I said 'rule of thumb' because there are a lot of factors involved here.  Combusion chamber shape, head material (cast iron or aluminum), piston deck clearance, piston dome shape, altitude, fuel mixture, cooling system efficiency and more all have an effect on how much compression you can 'get away with'.  Some people can and do push the limit successfully with no issues.  Others aren't so lucky.  However, consider this: on a relatively 'stout' 455 build, the difference between 9:1 and 10:1 compression is only going to amount to about 6-8 HP in an engine that's already over 400hp.  Is it really work trying to push the limit to the max for that much power?  That's a question you have to answer for  yourself.  I'm new to this forum so haven't learned all the ins and outs of dealing with the software yet. but I'm going to attempt to attach a word document to this post that has an embedded excel spreadsheet in it.  You can use it to play 'what if' games with various engine measurements and cylinder heads/chamber sizes, piston dish volumes, etc to see where various combinations would wind up, compression ratio wise.  If you dig into the topic (and this one is "popular") you'll eventually run into a discussion of "static compression ratio" vs. "dynamic compression ratio".  The working theory on the dynamic side is that you use a cam profile (or install the cam retarded) such that the intake valve closing event is delayied, the idea being that the compression can't begin until the valve closes.  This notion is false simply because it ignores the fact that rapidly flowing air has mass, and therefore inertia, and therefore can flow into a cylinder (with the exhaust valve closed) and start pressurizing it even before the intake valve closes.   However this effect is going to be more pronounced at higher rpm as air flow velocty in the intake tract increases, and at higher rpm there is simply less time for detonation to develop (which is probably the real reason why the whole 'dynamic compression' approach appears to work).  Ths whole area though is one where folks tend to polarize on both sides.  Personally, I'm not sure which if either side is the right one, but I decided a long time ago that for a street engine, dancing with the devil to try to milk every last scrap of comression out of it for less than 10 hp difference just wasn't worth the associated risk.  This is another "make up your own mind" thing.

 

Regardless of which heads you go with, ALWAYS measure the combustion chamber volumes yourself.  Pontiac heads are known to vary from the published factory specs to begin with, and also you never know whether a set of used heads might have been milled in the past.  Even a few cc's difference in volume has a significant effect on compression ratio.

 

Lastly, yes Butler is very good, but for my money the best Pontiac engine builder in the country is Jim Lehart at Central Virginia Machine. 

Give  him a call and talk things over.  He'll tell you the truth and won't try to milk you for business.

 

Good luck and please remember to post up some video of it running :)

 

Bear

CompressionRatioTool.doc

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The 70's affected all cars....


 


A 455 surely has the foundation to make some power, you just have to coerce it out.  A cylinder head swap and a modern camshaft would help tremendously. 


 


A compression ratio bump will also help.  I do agree with Bear though, the difference in horsepower between a 9:1 engine and a 10:1 engine is negligible and if you live in an area that has poor quality gasoline or only low octane gas available, it's best to err on the side of safety.


 


Flat tappet cams are more difficult to mess with these days and I generally try to talk my customers into hydraulic or solid rollers.  However, when the need arises, I will do them with a nitrided core, EDM lifters, and break in the camshaft with Brad Penn oil and reduced spring pressures.  I'm building a 400 for myself right now and I'm using a custom Comp solid flat tappet...with some Crower EDM lifters.  It will get beehive valve springs but will be broken in with some low pressure outer springs from a dual spring package. 


 


To the OP, an aluminum cylinder head swap can get pricey, but when you look at it in relation to R&R'ing your factory heads (and some port work), then it's very cost effective.  With any engine, the heads and camshaft make the power and there's no reason why you can't make 1 hp/ci with a little bit of work.


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On 10/26/2015, 4:08:09, BearGFR said:

Some pretty good tips so far, however I'm going to politely disagree with Frosty on some things. 

One is connecting rods.  Factory rods are the weak link in Pontiac engines, and by the time you pay to have a set of factory rods reconditioned and prepped for an overhaul, you're going to be very close to the cost of a new set of good forged H-beams.  Considering that long stroke and larger main journal size of the 455 (with attendant oiling difficulties), putting a set of good rods in it is one of the better investments you can make.

 

 

I do like the idea of running H-beam rods Bear. I guess our difference of opinion lies in what we consider the operating perimeters to be. For me, stock rods for engines producing 400 HP or less are fine, naturally aspirated. The ability to re-use existing parts in order to save some moeny is the key to my thinking here. Now if you added a power adder like nitrous or forced induction that requires strengthening the bottom end, then I would spring for H-beam rods. 

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I  have a .030 over 455 with '71 96 heads off a 400.  My compression is 9.6.  6X-4 heads originally came on the 76 (I believe)  350 engine as I have two sets which I physically pulled off of 350's.  They are as good as the 71 96 heads (smaller exhaust valve) and their CC's are close to 90 and the 96's are guess what?  About 96 CC's.  If you know of a competent machine shop talk to them about  doing the machine work and you assemble the engine.  There are a couple good books of info on building Pontiac engines by Rocky Rotella and way back was Pete McCarthy.  Take your time with building the bottom end (double check your clearances) and follow the instructions/guidelines  and you will have the self satisfaction of building your motor!  A dual pattern cam --hydraulic or solid-(220's intake--230's exhaust) will work fine with a descent rear axle gearing.  Enjoy the build!

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