# Engine build



## hyfye (Jul 15, 2013)

Gentlemen I need some help,
I have a 67 GTO that has no balls. The motor dyno'd at 180 hp and went flat at 3000 rpms. I know nothing about the motor or what had been done to it prior to me buying it. The engine is stamped XM and has 46 heads, 750 quadra jet with and edelbrock intake , headman headers and an HEI ignition. It sounds like it has a big cam in it and it's not matched to the heads. Runs on 86 octane without pinging. My plan this winter is to tear it apart change the heads to edelbrock with 72cc, change the pistons and lifters and match up the cam to make 10 to 1 compression. The question I have is the low compression 400 block and crank the same as the HO motors or am I wasting my time with this motor?
John


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## PontiacJim (Dec 29, 2012)

And it ain't going to have any balls either. The XM 400CI for 1967 is a base 255 HP engine with 8.6 compression, thus it runs on unleaded regular. The correct heads should be 142, but someone installed the 46's which could be the 1969 head having 10.5 compression OR the 1973 350CI 150HP head that had 7.6 compression.

At 180 HP and done at 3,000 RPM's, you have some problems. A compression check will give you more knowledge on what compression you actually have. Its possible the 1973 46 heads are on your engine if I had to guess. Pontiac has used the same numbers on their heads for "good" heads as well as low performance heads, so you have to know what you are getting.

The engine is a keeper as you can very easily bring it back up to big horsepower standards if you are planning a rebuild. The block and crank are the same as any 400, so no worries. You might consider a 461CI kit from Butler that will most likely be your best cost effective way to build the short block once you start pricing the individual pieces- pistons, forged rods, rings, bearings, balancing, etc., and you get a new crank. So all you really need is the block and go from there.:thumbsup:


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## hyfye (Jul 15, 2013)

*engine build*

Thanks for the advice. I'm not Chip Foose who has unlimited resources. Would you still use the edelbrock heads of can I get by with the 46 heads or maybe even 6x heads? You put the name Pontiac on anything and the price doubles.


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## Chris-Austria (Dec 23, 2010)

Edelbrock heads are pretty expensive.. for the same money you can get a stroker kit, matching camshaft and maybe rebuild your old heads if they match the stroker-combo or get a set of iron heads that give a good CR with the new cui 

But first I'd remove the engine, check the block and the parts and after that decide what to do. A stroker kit includes almost everything for a short block rebuild and is about... 1500?!


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## PontiacJim (Dec 29, 2012)

hyfye said:


> Thanks for the advice. I'm not Chip Foose who has unlimited resources. Would you still use the edelbrock heads of can I get by with the 46 heads or maybe even 6x heads? You put the name Pontiac on anything and the price doubles.


Agreed, Pontiacs are not cheap to build. That's why some choose to go with the LS swap and weenie out of it.

Your heads should have a build date cast into them. You should find a Letter followed by 3 digits. The letter corresponds to Month, ie Jan=A, Feb+B, etc., then day, and the last number is year. The last number is your identifier on the 46 heads that will tell you what you have. Should be located to the right side of the center exhaust port just below the valve cover. Also, check to see if you have screw-in rocker studs or pressed-in studs. The good heads have screw-in rocker arm studs.

Head choice is all about $ and performance level. Pontiac heads come in a flavor of combustion cc's which are used to adjust your compression ratio -this is what the factory did. Additionally, pistons are also cast in an assortment of cc's at the crown or valve relief's to provide differing compression ratios based on the head used. You can mix and match heads/pistons to get the preferred/typical street 9-9.5 compression on iron heads or 10-10.5 on aluminum heads.:thumbsup:


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## hyfye (Jul 15, 2013)

Thanks I have really thought about the swap. Though the LS motors are more efficient and cost effective, It's like dating your sister, it feels good but just isn't right.


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## geeteeohguy (Feb 2, 2008)

hyfye, you've been given solid information here. You need to go onto the Wallace Racing site and figure out which head and piston you want to use. You want about 9:1 or a little more CR with iron heads, and at least 10:1 with aluminum. From the research I've done, KRE heads offer more 'bang for the buck' if you want to stay with "D" ports. (and run your Pontiac manifolds). Check out the pyforums, and you'll get all the information you need on how to build a solid, 400-450HP engine on the cheap....or at least as cost effectively as possible. Kudos to you for keeping your Pontiac real. LS engines in these cars suck, IMO.


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## hyfye (Jul 15, 2013)

Thanks for the information. I'm still unsure with the way to go. I've been to Wallace racing and Butler's. A lot of ideas out there. If I had unlimited funds and a wife that didn't keep and eye on spending, this would be an easy decision. I am going to take your advice; pull the motor, freshen the block, find out what I have and go from there. I am hesitant to stroke the motor since I have heard so many stories about engines tearing themselves up after the build. I have built several GM motors but I find pontiac is the most difficult to plan for. Again thank for the ideas.
John


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## BearGFR (Aug 25, 2008)

Ignore the "stories". I built my numbers matching original 400 into a 461 stroker. The car has balls  So far, a best quarter-mile time slip of 11.86 @ 113, that was leaving off the foot brake, transmission in "D", auto upshifts happening at about 4800 rpm. I think there's more left in the car still. It has a functioning a/c, functioning power steering, and we drove it comfortably on the complete Hot Rod Power Tour in 2013 (Arlington Texas so Concord, NC and back). I'm running a 3.50 rear gear.

It wasn't cheap to build by any means, but it's sure an example of what can be done with these engines. 

The advice you've gotten already about takiing inventory of what you've got, finding out "where you're at" with it (measure and inspect everything), and starting from there is good solid advice. There's a lot that depends on your budget but there are some principles that apply regardless.

Pontiacs are torque engines. They make mountains of it and they make it low in the rpm band. Trying to build one of these like a garden varieity high rpm small block is about as wrong as you can get (and besides, it's beyond boring).

Longevity and pump gas. Shoot for 9.3:1 - MAYBE 9.5:1 if you're running iron heads, 10.3-10.5:1 if you're running aluminum. At the torque and power levels these engines make, the difference between 9.3:1 and 9.5:1 is going to be less that 5-7 HP. Moral: pushing the limit on compression usually is just not worth the risk.

Rods. If you do nothing else, invest in a good set of quality forged rods. The weak link in these engines has always been the factory cast rods, and once you factor in the cost of quality reconditioning on a set of factory rods, you've very nearly paid for a set of good rods anyway. No brainer on this one.

Crank. Pontiac cranks are strong. Factory (and aftermarket) cast cranks are good up to 600 HP or so. I'm running an Eagle cast 4.25" stroke crank in my engine.

Pistons. I like forged (I'm running KB-Icon's). Set up right, they're not going to be noisy once the engine is warm. (Besides, if you're building one of these cars because you care about "quiet" you might be in the wrong business...


Heads. If you want to run factory iron heads, be picky on chamber volume and be sure to measure them yourself and not rely on published factory specs. These heads can vary quite a bit, may have been machined at some point in their past, and a small variance in chamber volume makes a significant difference in compression.
If you opt for aluminum heads (can be pricey) don't buy them "complete" with valves and springs included. The ones you get usually aren't the best parts. Instead buy them bare and then have them completed by a head builder you trust. I got my 72cc Edelbrocks from Dave Wilcox at Central Virgina Machine, and they are works of art - and they're a big part of the reason my car runs the way it does. These too are not cheap.

Valve-train. Another opportunity to spend money. Critical that you pick a cam that's suited to what you need the car to do and the rpm range where it's going to spend most of its time. You also have to think about the rest of the drive train. What rear gear are you going to run... or will you NEED to run? Transmission... if it's an auto, what sort of converter will you need to let the engine flash up into its torque band and can you live with that? Or should you cut back on the cam "some" in the interest of imrpoved manners? If you've got the budget (again) running a roller system sort of gives you the best of both worlds because you can get more aggressive on duration without having as much of a negative impact on overlap as you would with a comparable flat tappet cam (overlap is what kills low end torque and also idle vacuum - which you should care about if you're running factory power brakes). Rollers also have the advantage of not being nearly as sensitive to the ZDDP content (or lack thereof) in the oil you run.

Carb/Intake. Unless you're building a pretty "serious" engine, the plain truth is that there's not really anything out there that will perform as well as the factory iron dual plane intake and a _properly_ set-up 800cfm QJet. I'm running an 800cfm QJet on my car, and the only reason I'm not running a factory intake is because my factory intake doesn't match up with my head ports and there's not enough meat left in the manifold to match them --- otherwise, that's what I'd be running.
(I'm currently running a first generation Edelbrock Torker intake - single plane aluminum - the one that lots of people say is crap  )

If I was in your position and I wanted to build (as much as possible) a budget Pontiac, I'd start with the block you have - strip it and clean it - have it checked out. I'd start hunting for a good set of iron 6x-4 heads and measure them to make sure that they really do have 94cc chambers. I'd buy a 461 stroker kit with good forged rods, forged pistons, pistons with a total dish and valve relief volume of 9 cc's (make sure the dishes are D-shaped, not round). Then I'd have the block zero decked and bored to fit those rods and pistons.

Cam and valve train: If you're running power brakes and want to keep them without having to convert to a vacuum pump assist or hydro-boost system, then you want to keep idle vacuum at least around 15 inches or more. Manual brakes and manual transmission (or if you're willing to go the pump/hydroboost route on brakes and also go with a more "loose" converter), you can get a little more rowdy on the cam. I'm running a solid roller in my car that has duration figures of 236/242 @ 0.050 on 110 degree lobe centers, and it's just over the line on brakes (I'm running hydroboost) and I've got a 3200 rpm stall converter in it. I could get away with "more" because the rest of the car is set up for it. On a budget build I'd go slightly less agressive than that on a roller, and slightly less still on a flat tappet. 

I promise - an engine built to those specs will definitely plant a smile on your face whenever you touch the loud pedal and will also surprise the majority of folks who might try you on for size. It'll also live on pump gas and be something you could drive anywhere.

I've attached a spreadsheet I wrote and use (embedded in a Word document) you might find handy in calculating/planning for compression ratio.

Bear


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## hyfye (Jul 15, 2013)

Thanks, I really appreciate the advice. It is so much easier following someone who has already made the transition rather than someone making all of the mistakes.
John


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## PontiacJim (Dec 29, 2012)

hyfye said:


> Thanks, I really appreciate the advice. It is so much easier following someone who has already made the transition rather than someone making all of the mistakes.
> John


Yeah, but, you don't learn much when things go right. Break a few engines and you learn so much more.:lol:


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