New to the forum, building a 1970 GTO tribute.

Hello everyone, I have a 1972 lemans that i am building and would like to pick brains on some advice for the build. The car was pretty straight when I got her, no major problems beside some rust in the usual places. The current set up consists of an a/c 400, 7J2 heads, stock intake, quadrajet, Hei distributer, TH400, 2.73 rear, and discs up front .

All my buddies are telling me to yank out the poncho and drop in a 383  stroker but I refuse!  To shut them up I'm leaning towards a 462 stroker for this project if possible.

1. I Know the 7J2 heads have to go. They are low compression, small valve, and are missing the end holes, so no real header options. I have a set of #17 heads I was thinking of using for the build after some modifications. I was thinking of having the bowls enlarged, installing 2.11 intake/ 1.77 exhaust, port & polish, screw in studs, new springs, rollers, and mill a bit off for flatness. Brand new heads are not in the budget. Your thoughts...

2. I have an Offenhauser 360  Intake I found in a scrap yard, don't know anything about its flow pattern, anybody have any info on this one? From what I gather the stock intake flows pretty well and can be polished as well. Maybe a 1" spacer to increase runner length and thermal isolate carb.  

3. Can I and should I keep the quadrajet? I hear it's not bad, but will it be enough to feed my 462 or does it need modification.

4. Cam selection. This will mainly be a street car, however I wan't as nasty an idle as I can possibly get away with and still have use of the power brakes with an additional vacuum canister.

5. Transmission. Bone stock at the moment, Shift kit? Remove valve spring?

6. Rear end. As i said this will be a daily driver so I'm not too sure about ratios. Posi is great for drag racing not so much for every day driving. Your thoughts....

I know this is a HUGE post but I thought it might   get interesting.  

Hello Welcome


What is your max budget?

What is your intended use of the vehicle ie mild street, street/strip, all out tire burner or auto cross etc.

What power options do you have and want to KEEP.



HEADS – You need to cc your heads to determine exactly what they are but kens perf says they are 75 cc and Wallace racings free online comp calculator says you will have 10.93 compression with a 462 ci motor which is way too high.It says 92 cc = 9.43 comp which I think is as high as you want to be as long as you stuff a large cam in it and 98 cc = 9.0 comp which is a bit safer margin. You  



VALVES – Back cut to increase flow. Stock valves are fine for your app.



INTAKE MANIFOLD – What does your current one say on it exactly. You can only polish an aluminum intake to be practical and I have only seen factory aluminum ones on ra cars and 71 455 buick X cars. An edelbrock performer and performer rpm is a known quantity however if you are trying to save a few bucks the offy will work. The offy is a single plane, the eddy’s are dual plane and theoretically should perform better overall in most street apps as shown on comps computer dyno.

The offy should be designed for a square bore Holley, a quadrajet should not fit the rear butterflies should hit the intake. Set it on and see if you can open the rear butterflies.Either way a larger carb is better and a holley is my preference and it will fit a square bore offy and any new eddy performer. I would buy a new eddy performer rpm.

CARBURETOR – Your carb cfm is probably a bit low for a 462 especially cam, intake headers big valve heads etc. It will also require what I consider complicated mods including possibly drilling out the isle circuit air bleeds. I prefer a mechanical square bore holley and would use a 750 mechanical. It is easy to tune and I prefer the "type" of perf they give. A mechanical secondary uses more gas than a vacuum secondary. Any q jet or edelbrock carb of equal size to any holley will provide better gas mileage.

GEARS – I would install 323 for partial street but mostly fwy or 350 max for better street perf and short fwy trips or slower fwy trips.

POSI – I personally wouldn’t waste a dime on performance upgrades like you desire if I'm not going to accelerate from point a to point b any faster. A posi has 0 negative effect as long as you use friction modifier oil and have it set up loose for the street.


EXHAUST – You will need headers or ra cast manifolds and at least 2 1/2” pipes all the way back. Exhaust - 2 1/2 - 3" kits available from summit 2 1/2 is big enough. If yours are smaller than 2 1/2 they won't cut it. I would use hooker super comp hkr headers. They supposedly fit the better than other headers also.


RA MANIFOLDS VS LARGE TUBE HEADERS – In your particular case you will gain approximately 15-20% hp by replacing stock manifolds with ra manifolds and approx 30% with large tube headers over stock. In lower ci motors with smaller improvements it might be around 15% with the ra’s and 22% with headers.





Mufflers - Flowmasters sound cool but magnaflows and cheap cherry bombs show a little more hp on a real dyno on a couple different high perf v8's.  


ENGINE BALANCE – Any rebuild should be balanced.



TRANSMISSION – If your trans is stock and old, worn etc your new high horse motor will soon send it to it’s demise no matter what you do but your shift kit may stave it off temporarily. It will eventually need a high perf rebuild with high perf clutches and other improved internals etc. See Art Carr, B and M or other for trans stuff.


TORQUE CONVERTER – You will need a 2200 rpm stall converter with a 284 duration cam.
450 at 5000 498 at 4000   386 443  334 411  340 419

TRACTION BARS – Y ou will need a set.  

Welcome to the forum!.
Your friends will be eating thier words when you get this motor together..
For the intake, Offenhauser made both square bore and spread bore so check to see which one you have. They are a great manifold (I'm running the 360 dual quad low rise) and with a judicious and light touch of an air grinder they can be made to flow far better than stock and for my money, the Eddys too. What really helps wake them up is a 3/4 spacer under the carb. BUT.. It is a high RPM manifold, so unless you have the heads and exhaust system to match the flow characteristics and if you're wanting street application, it's probably not the manifold you want.
70bird has some good points through out his post..  
Jim,

Howdy, CI. Welcome. Cool ride you scored! If you need help with the rusty parts, holler at me.

I ain't messed up about putting Chevys in Pontiacs and vice versa, GM did it. But today your HP will cost about double if you use the Pontiac engine. Fair warning!

Stroking isn't necessary. Unless you need braggin rights on 454s. An overbored 400 is in my opinion potentially the most efficient stock block Pontiac V8 configuration available.

Those stock head mods are gonna bite you in the wallet, at least they did me. Seriously consider aluminum heads. On your stockers, the end bolt holes can be added. Enlarging just the intake valve may be prudent in your case. I am no cylinder head expert though.

Use the Offy if its correct for the build. Use the Q-Jet if it fits. I think you would have less tuning headaches with a more readily adjustable aftermarket carb.

Cam- Pick whats right for the setup and let the idle fall where it may. Carb spacers and vac cans can help a chunky-style idle but I've had one that was super lopey and ran brakes fine without a can once I discovered the right tune and with a tall carb spacer.

Shift kit? Stay away from the cheapest ones. A nice reprogramming kit with shift feel options is what I recommend. Mine has the TCI Trans-Scat kit and heavy duty sprag.

Rearend? Posi is always good, don't leave home without it. I prefer a gear ratio around 3.3:1 for all around usage. Tall tires on the highway, short ones for the strip.

Just my thoughts ...  

Thanks 70bird,

Mild street, tire burner...
Max budget?   Hmmm...  We always spend more than we plan, but here goes...

$1500 bottom end + $300 machine work
$300 cam
$400 valve train parts + 500 machine work
$500 headers
$500 exhaust
$300 transmission work ( convertor/ shift kit)
$200 new HEI coil/ wires/ cap/ rotor

Rear end... I guess I'll have to find a posi unit in the scrap yard and clean it up.
$500 wheels
$600 tires



Already done,
Hotchkis tvs sport sytem.


Parts on order,
VFN fiberglass 1970 gto Hood & 1 piece fender bumper combo
rear wing  

Thanks my71 & idrivejunk,  would a pair of 6x heads be a better on the cheap choice?  Three grand on heads at this time is really not in the budget. Could I or should I swap out the 7j2 for the 17's  only freshened up on the stock motor with no other mods at this time to bump up the compression. That might get me to 1969 specs 270hp? 10.5-1cr  a little high? When I have sorted all the parts that will perform well together I will do a complete tear down.  

Custom,
Your 1972 front end is a good deal different than a 1970 front end. Not that you can't make it work, but you may end up scouring high and low for front end bracket and frame pieces to make it work on your 72'.  
Jim,

Yep, I thought about that... That's why I went with the fiberglass front end. I won't need any brackets or try to find fenders or lower valance parts. The 1970 endura style gto bumper, lower valance, and fenders are all molded together as one piece and only uses the radiator support. The hood is a pin on type. It will also shave about  300lbs off the front end.  

I have a glass one piece on my 71 and the body man used some of the front brackets to help mount the front end piece and make it tilt as one unit. I had a fellow want to clone his lemans into a GTO. he had a 70 lemans and once i showed him the pictures that showed the differences, he realized the front end mounting brackets were completely different. Good luck with it! let us know how it comes out!  
Jim,

Hello

Thanks for the expense info this helps greatly.

I see quite a few  great and  reasonable suggestions for you to mull over, now everyone can start making more cost wise suggestions for you. I will attach some head work prices. Labor and parts prices are  what I have currently found. As far as the q jet pattern offy goes  if you have this tye you probably need an inexpensive old school thin adapter plate if your holly butterflies hit  then you need an $10.00 3/4 inch adapter, no problem.  

I’m a bit confused about a couple things now so all I can do without more info is guess about your new reduced performance expectations due to financial constraints. We all have those now.

COMPRESSION – I answered this question in my previous post but perhaps you missed it or it wasn’t clear enough which what I think the case is so here it is again with a clarification.

“HEADS – You need to cc your heads to determine exactly what they are but kens perf says they are 75 cc and Wallace racings free online comp calculator says you will have 10.93 compression with a 462 ci motor which is way too high. It says 92 cc = 9.43 comp which I think is as high as you want to be as long as you stuff a large cam in it and 98 cc = 9.0 comp which is a bit safer margin. You  

VALVES – Back cut to increase flow. Stock valves are fine for your app.”

COMPRESSION CLARIFICATION – You should not run compression over 9.5 any v8 motor in any make of car because it is the general threshold of detonation.

This means you can’t use more in your 400 ci build either.

270 HP – I could be wrong but I’m just guessing that any stock 4v 400 pontiac should easily have 270 hp at the crank with just 8.3 compression. Either way you certainly do not need compression over 9.0 to get there in any case and this would be a slow motor.

462 CI STROKER – It sounds like you are abandoning this idea, is this right? This info will help others to focus on your new target if that’s the case.

$3000.00 FOR HEADS – I don’t know where you got that number perhaps I missed it, either way they will not cost anywhere near that for modified stockers.

HEAD VS COMPRESSION HORSEPOWER INCREASE – T his a misunderstood area by inexperienced engine buikders so I hopoe this will clarify things a bit. Although compression is a significant contributor to hp and torque increases the single most important is air flow. No matter what you do if you do not match increase air flow accordingly you will not be optimizing your other performance upgrades.

You can install a massive cam but your hp will not increase after a certain threshold due to flow restrictions caused by the intake and heads. Often once people see the high cost incurred when getting heads to flow decent for a performance build they throw that idea out the window and try to compensate for the loss of hp from restricted head flow by adding compression and bigger cams unfortunately it doesn’t work that way. Believe me, we all wish it did. Just remember, no flow no go!  

Thanks 70 Bird,   I'm by no means abandoning the 462 stroker.  I't's a definite go.. Just a little budget constraint at the moment. First on the agenda was to get the chassis in order which is pretty good for now. I am currently addressing the minor rust spots in the lower quarters. I epoxy primed the whole car and will be block sanding it until my new front end arrives in the following weeks. I'm now on the hunt for a posi rear end as you all have suggested. I plan to have all the bodywork done and the car painted before I drop in the stroker. She runs perfect at the moment in stock form. I think you misunderstood what I was saying about the heads. I get what you mean about the 462 and the the ultra high CR. That makes perfect sense. What I was thinking of was trying the 17 heads on the stock 400 for a few weeks to play around while I'm waiting for parts. The 17 heads are in fact 75cc. I was under the impression that 10-1 was fine to run on 93 at the pump and that's exactly what those heads would give me correct?  they are almost identical to the #16 small valve I'm told.  
The $3000 number for heads was to buy new ones, which I am kinda leaning towards after the great information that everyone is providing here in the forum. For reworked 6x stockers I was thinking $1000 would get me by fine for the heads and all the modifications. How do I post pics?  

Hey Jim, I'll be posting build picks soon. I spoke with VFN and they said there would be no issues but I guess we'll see when it gets here. I do custom fiberglass work and metal fabrication so I can pretty much address anything that comes up. Thanks for the heads up.  

Your pics will need to be uploaded somewhere on the web. You can't attach them here, only link to them. I like bodywork pics, its what I do! Click on the image icon to the right of the B I U above where you type, then paste the web address of your image in the window that pops up. Preview to see if it worked, before posting. If your photo hosting site offers you an "IMG" code, you can just paste that here and it works. Just don't use "quick reply", it doesn't work there.  

Hello

I posted my compression comments for you again below. I don't know who told you 10.0 is ok but it doesn't matter as you will be very hard pressed to find anyone to make that comment here so I suggest to do what you want in this matter.

If you are only going to run it with high compression for a few weeks it is not a big deal but here's the potential problem. If it does detonate then you will have to reduce your timing to compensate for it. If you reduce your timing you will be reducing your hp by about the same amount you just gained by increasing your compression thereby rendering the performance gained by your increased compression a moot point.

You must cc your heads as I also mentioned if you haven't yet. Never, ever, assume the book is correct or your heads have not been milled beyond practicality.

I suggest you have 17 heads cc'd and also checked to see how much they have been milled from stock if any. If they have been milled more than .025 from orig, then your intake may need to be machined to fit!

The calculator says 75 cc heads on a stock bore 400 is 9.60 and 9.72 at .030 over bore. These numbers combined with your heavy car and 273 gear ratio should most definitely detonate.


COMPRESSION CLARIFICATION – You should not run compression over 9.5 any v8 motor in any make of car because it is the general threshold of detonation.  

Point well taken, 17 heads are out. How about the 6x or just save my money for something better?http://i437.photobucket.com/albums/qq100/custominstaller2/gto%20project/IMAG0827_zps05145f97.jpg