# 66 GTO Engine rebuild



## DirtyD (Aug 29, 2015)

Hey everyone I am looking for a little advice. I have a 66 GTO and I have having the engine rebuild. Still runs just was leaking oil bad and the valves were sticking bad. The engine is a 67 400 out of a Firebird. 

My mechanic gave me the following options below.....

First one I wouldn’t even consider, but here it is. Stock everything and you would most likely loose a ton of HP.
About $1800 for the engine

2nd option, is a good one. Forged Speed Pro pistons with a Comp Cam’s camshaft. Most likely a small gain over stock.
About $2100 for the engine.

Other options are available to increase the HP, some are pricey, some not so much. If you know anything about camshafts you might know the new roller cam set up is far superior to the stock flat tappet hyd. To convert yours over to hyd roller would probably cost a $1000 but you would never have to worry about the cam again, where as with the flat tappet you might have to replace the cam every few years due to lack of additives in the oil.

Anyone have any advice on the subject?


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## Goat Roper (Oct 28, 2014)

Put the additives back in the oil.

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## oldskool (Apr 26, 2015)

"... I have a 66 GTO and I have having the engine rebuild...2nd option, is a good one. Forged Speed Pro pistons with a Comp Cam’s camshaft. Most likely a small gain over stock..."


If your '66 GTO engine is a 389, with #093 389 heads, you can't use the Speed-Pro forged pistons. The valve reliefs are in the wrong place, and the compression will be too high for pump gas. Some of the head charts show the 093 heads to have 68cc chambers, producing 10.75:1 compression. 

You can use the SP L2262F 400 std bore pistons, and bore the 389 block to fit. But then you'd have to use some '67 and later heads, to match the valve reliefs. At least that's what I've read. But I never fooled with any 389 stuff--mostly '67 & up 400 & up. So, I could be wrong.

Now you can use the "8-eyebrow" cast pistons that everybody hates. But that is not advisable.

The cheapest way I know of to do it, with forged pistons, is with Auto-Tec/Race-Tec brand custom pistons. They will cost about $500, with the valve reliefs and dish in the correct place, the popular thin metric rings, and the compression distance increased slightly, in order to get near zero deck height, without milling a lot off the block. Most engine builders recommend from .005 to .000 deck height and between 9:1 & 9.5:1 static compression ratio, for pump gas. With 72cc or smaller combustion chambers, you'll need dish pistons, to get below 9.5. 

Now, Icon makes a forged 8-eyebrow 400 std bore piston, that might work. The valve reliefs are 10.8cc. They have the thick 5/64 rings, and the pin height is 1.714, which will raise the top of the piston .014 in the hole, over stock. Looks like these will still make a hair over 10:1 static comp. But, with the correct cam, to bleed off some of the pressure, and the correct timing and carb tuning, you might be able to get by with 93 octane pump gas ? I've never read of anybody using these pistons, but there may be some who post on this site who know if these are good for a 389 build or not ???

http://www.summitracing.com/parts/uem-ic9946-std/overview/make/pontiac

The RPM brand 5140 rods are the cheapest forged rods @ $288 shipped direct. Or, the RPM H-beams are $400 shipped direct.

"...About $2100 for the engine..."

I'd be leery of a rebuilt Pontiac engine, with forged pistons and a new CC cam set-up, that would only cost $2100. Don't know anybody who can do it for that, CORRECTLY, and still make a profit. Parts and correct quality machine work, for a Pontiac engine, is not cheap. 

I'd like to see some more specs on your engine. Like block casting number, what heads, what rods will be used, what will be done to the heads, etc, etc--details.


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## PontiacJim (Dec 29, 2012)

Like oldskool, I'm a little leery on the price you have been quoted. I suppose your mechanic will be using as many of the old parts as possible to get you near that price. 

I posted this in another recent post with regards to re-building an engine on a budget *IF* you can do the rebuild/assembly yourself. You can get the engine in the $2500-$3000 range and you would be using an inexpensive rebuild kit, cast pistons, basic head rebuild, etc..

I see you are in Charlotte. I had my engine work done at Greg's Machine Shop in Kings Mountain. They are off of Hwy 74 heading towards Shelby, Moss Lake exit. Two older brothers in their 60's who have been building engines of all types (stock to blown) for 40 years and KNOW their engines. You may pay a little more, but they will do it right and help you with what you need and will tell you what you don't. You could build your engine in stages as most of us do.

If you plan on keeping the car, do it right once. If you are going to flip the car, then go cheap I suppose. :thumbsup:


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## geeteeohguy (Feb 2, 2008)

I used the forged speed pro 400 pistons in a 389 back in the '80's. It had to be bored .060", so not ideal. I ran the stock 093 heads, no issues. Had a Sig Erson High Flow 2 cam in it, ran fine, no clearance issues. Needed about 100 octane fuel to run, though. Today, the only correct way to rebuild a 389 so it will last is to have a set of dished pistons made so you can run today's poor gas with the stock cylinder heads The other option is to spend the $2500 on some 72cc aluminum heads and run stock style (but hard to find) flat top pistons. No matter what, a decent rebuild is going to cost more than $2100....probably 4-5k or thereabouts. There are MANY threads on exactly this topic if you search, and a ton of information. All due respect, the impression I'm getting from 'your mechanic' is that he's not familiar with old Pontiacs. That can get both costly and very, very, disappointing. Do your homework, and you should do just fine. Congrats on keeping the 389....great engines. I've been running the 389 with a flat tappet cam in it in my '65 GTO since I rebuilt it in 1981 (for about $2700 then). My cam hasn't gone flat in 35 years.....hmmmmm.....


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## oldskool (Apr 26, 2015)

"...The other option is to spend the $2500 on some 72cc aluminum heads and run stock style (but hard to find) flat top pistons..."

I don't think cast 389 pistons are that hard to find. ?

http://www.summitracing.com/parts/s...np_6_M_LqjV1wyflufXWP4uMY4z-6rEEhhBoCsW7w_wcB


If you decide to go with the alum heads, then the SP std bore 400 forged pistons will work just fine. 

BUT, if I had an extra $2500 to spend on the engine, I'd go with a forged crank stroker assembly and the iron heads of your choice. You can have the pistons matched to the heads and compression you wanna run. Could probably choose a 4", 4.21", or 4.25" stroke. The Ross pistons are HIGH, but can be ordered any way you want 'em.

This engine COULD look correct, AND have more power and LOTS more low end torque, than any stock 389 ! 

http://www.jbp-pontiac.com/products/engines_assemblies/rotating_assemblies.html#447_453

Butler Performance - Pontiac Engine & Rotating Assembly Combinations - Featuring Eagle Pontiac Kits


"I used the forged speed pro 400 pistons in a 389 back in the '80's. It had to be bored .060", so not ideal. I ran the stock 093 heads, no issues. Had a Sig Erson High Flow 2 cam in it, ran fine, no clearance issues..."

I like this idea. But, I'd like to know more about it. Specifically, I'd like to know exactly how much cam you could safely use, if you use a deck height/gasket thickness that would have no more than .045 quench distance.

For example: could you go with .005 deck height, the .039 x 4.3 Fel-Pro head gaskets, and a Summit 2801 cam ? If not, how about the "068" clone Melling SPC-7 ?

http://www.summitracing.com/parts/sum-2801

http://www.summitracing.com/parts/m...lwu6AYDds6KeKlV_MflssDLVECxkUbjekUhoCpNrw_wcB


"...Had a Sig Erson High Flow 2 cam in it, ran fine, no clearance issues...I installed a Sig Erson High Flow I in my '65 389 when I built the engine in '81. It's a primitive, single profile, high lift, big duration hydraulic cam with a ton of lope. It stings your eyes, and pulls about 12" vacuum..."

Couldn't find a cam listed as "high flow 2". But I found several with between 220 & 235 duration @ .050 lift. They all had .472 lift. 

The E310421 is listed with 228 dur @ .050 lift--listed as a Hi Flo 1H

The E310321 is listed with 240 dur @ .050 lift--listed as a Hi Flo III

http://ronspontiacpage.com/reference-pages/erson.htm

So, exactly what were the specs on the cam you ran ? Do you know what your deck height and gasket thickness was ? 

If you got by with the 228 duration cam, then the Summit 2801 should clear--unless maybe you had .020+ deck height and .040+ thick gaskets. In that case, I assume that the valves could possibly come real close to the pistons ??? If not, then it appears that the 389 pistons didn't even need valve reliefs ???

That brings the question to my mind--how many Pontiac pistons had valve reliefs, in engines that didn't really NEED 'em ? Even the 068 cam only had barely over .400 lift. So, did all the engines that came with this cam NEED valve reliefs ?

I know that the 350's did not have any reliefs, for the last few years they were made. But, I assumed that was because of the big chambers, which placed the valves farther away from the block. But maybe there were quite a few earlier 350's and other size engines that didn't really NEED reliefs ? The 455's with 114cc and larger chambers, come to mind. Except for the SD455, the 068 was the biggest cam used.


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## DirtyD (Aug 29, 2015)

Thank you everyone for your input. Gives me good info to think about.

I forgot to include an important fact. The engine is not a 66 389 but a 67 400 out of a Firebird. Sorry I forgot that detail in my rush to post.


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## oldskool (Apr 26, 2015)

"...I forgot to include an important fact. The engine is not a 66 389 but a 67 400 out of a Firebird..."


LOL ! Yeah, I think that might be a VERY important fact !!! :lol:

OK, NOW, in order for any of us to help you, you must 1st help us make an ABSOLUTE POSITIVE ID of what you have. Just because you say it is "a 67 400 out of a Firebird", that does not mean that it originally came in a new '67 Bird. Hey, it could have come in a '74 TA, a 71 GP, a full size B-Body, a wagon, or ?--then somebody swapped it into the '67 Bird. 

So, here's the info we need:

The block casting number, which is cast into the block, on a pad which is below the rear end of the passenger side head. 

The 2 or 3 digit number of the heads, which is usually cast above the center exhaust ports. Could be something like 670, 16, 62, 96, 7K3, 4X, 5C, 6X, or lots of other numbers.

What intake is on the engine ? Stock iron ? If so, what is the casting number ? It's found on the top just in front of the carb.

What carb is on it ? What carb would you prefer to run ?

You mentioned a roller cam, and the fact that they are about $1000 more than a HFT. So, do you want to pay that much to have a roller cam ?

This info will give us more to go on.


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## geeteeohguy (Feb 2, 2008)

Oldskool, I'll try to clear this up a bit. I built 2 389 engines. The first, built in '81 is the more 'radical' and has the Sig Erson Hi Flow 1. The cam card is long gone. I remember the max lift at right around .480 with a lot of duration...your e310421 looks close. This was a '65 WT block punched .030 with forged Sealed power pistons, shot-peened rods, and chamfered oil holes in the crank. Balanced and blueprinted at extra cost. I was a kid, but assembled it in the basement garage, and all the clearances were dead on when it came back to assemble. I did NOTHING with the heads other than the standard HP valve job of the day, with bronze guides, I think. Standard Victor-Reinz gaskets, I think.....or Felpro. Cloyes chain. This engine went into my then daily driver '66 GTO, which I drove the wheels off of for the next 7 years. It ran really strong, but very lopey idle. Still, 3rd gear starts with a 3.55 rear end were not an issue.....plenty of low end. In 1987, the 428 in my '65 GTO went south. I managed to find a '66WW 389, and rebuilt this engine with the standard 400 pistons, .060" over, and the 'High Flow 2" cam, which was milder than the one in my WT 389. This engine did not get the shot peening, balancing, polishing, etc. It was a budget rebuild with a cam and headers. Both of these engines were tripower equipped, and both cars were 4 speeds. In 1988, I thought it would be a great Idea to swap engines: put the hell-bent-for-leather 1965 WT 389 in my '65, and the milder '66 WW 389 in my '66 GTO. So one rainy weekend, under tarps and in the backyard by myself, I did just that. So, since 1988, my '65 GTO has the engine I built in 1981 in place. No screw in studs on either engine...I guess I've gotten lucky. I sold the '66 in 1990 to buy a house, and that engine ran well with a ton of power. The trick was to get good enough gas and keep it running cool. I did a compression test on the old WT block in my '65 this past summer, and it is 175PSI in every hole.....not bad for an engine that makes 12"hg and has 34 years and 60,000 miles on it. The asbestos rear main seal is still bone dry, too. Both these engines were built back in the day, when I knew very little, other than how to measure clearances and check to make sure parts went together correctly. I didn't degree cams, I didn't know about zero decking, quench, deck height, or any of that. I just bolted them together and ran them. It's ironic that the only screw-in-stud Pontiac I have is my super mild, de-tuned '67 ragtop, which has a mild 068 cam. In closing, I have to say that I have never even adjusted the valves on the '65 WT engine since 1981. Not even once. And I'm still driving the car. Hope this clears things up a bit. Many engines, many cars, some knowledge but not a lot!


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## oldskool (Apr 26, 2015)

"... a '66WW 389...rebuilt this engine with the standard 400 pistons, .060" over, and the 'High Flow 2" cam...I didn't know about zero decking, quench, deck height, or any of that. I just bolted them together and ran them..."


OK, so for this discussion, you ran 400 pistons, 389 heads, the "High Flow 2" cam, and don't know the EXACT deck height, quench distance, cam specs, or how close the valves came to kissing the pistons. But, you are fairly sure they never touched. Is this a correct assessment ?

Therefore, according to your experience, would you feel safe building a 389, with the SP L2262F std bore 400 pistons in a 389, using the 389 heads and something like the Summit 2801 cam ? If so, what is the smallest quench distance you would feel safe with, without checking the valve to piston clearance ?

This info won't help the OP, now that we know he has a 400. But, it might help somebody else who reads this, who would like to rebuild their 389, with the forged SP 400 pistons. 

If anybody else who reads this, has had experience using the 400 pistons, with 389 heads, please post any info which might help us determine how much cam can be used, without valve reliefs, in the correct location.

Even if the block is not decked at all, the SP piston tops will be .014 higher in the hole, because of the increased pin height. If just a few thousandths extra clearance is needed, you could use the Butler head gaskets, which are .045 thick. But, if you have over .010 deck height, that makes the quench distance .055+. Many engine builders today recommend closer to .040, and not over .050. But, I suppose the safe quench distance could be affected by a lot of different things, and may or may not be safe at, say .060.

Butler Performance - Pontiac Head Gaskets

If valve to piston clearance will allow, closer to .040 quench dist is best. .027 & .036 Cometic gaskets are made, if needed. BUT, they cost about $100 each. So, that $200 would be better spent on the extra cost of custom dish pistons. These would solve the valve clearance, compression, and quench issues, for less than $200 extra. Plus, the pistons are lighter and can have the thinner rings. They offer lots of advantages.


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## geeteeohguy (Feb 2, 2008)

Oldskool, correct. I would never put an engine together today knowing what I now know. No measurements were made and the different valve angle of pre-67 heads wasn't even a thought. The only consideration at that time was that .060" 400 std. forged pistons were cheap, would fit, and that the block needed .060" to clean up. I count myself lucky. That engine ran for years and many tens of thousands of miles, and is still out there running strong, for all I know. The consensus among most Pontiac guys these days is that with a mild cam, no bigger than the 068, and stock rocker arm ratios of 1.5-ish, it is safe to run the 400 pistons with the old style heads. Today, I would check the clearance, valve to piston, no matter what. And I know I've gotten lucky with the high lift cam in my '65 GTO, with the pressed-stud heads holding up after all these years. If I were to do this engine today, I'd probably go with newer tech pistons, aftermarket rods, and KRE cylinder heads. I am still a flat tappet cam lover, so I'd try to source an NOS cam and lifters that were quality, USA made items with the proper machining and hardening. The only cams I've seen go flat in a hurry are the newer aftermarket ones, in the past 10 years or so. I have seen worn out cams and lifters in these engines that were oem equipment, but only after 200,000 miles or years of poor maintenance. So, if using the old style 400 pistons, ALWAYS check the piston to valve clearance in a 389 with the early heads. I think that most folks would not rebuild one of these engines today using 35 year old technology, but you never know.


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