Mix Matched Lemans

[DustinMitchell]

Hi all. New here and I will complete my profile as soon as I can. I am completely outside my wheel house here and have spent most of my time tinkering with newer sports cars. Recently I came across a 66 Lemans for a great deal and decided to pick it up. This car is completely a mismatch of Pontiac parts and I will do my best to lay it all out for ya in the hopes of getting a solid answer as to why I seem to be lacking in the power department. The car is a 2 door Montereo red Lemans that has been dressed like a GTO.

What I have

1- Pontiac 400 motor code YD and from what I can see this was a 290HP variant from a Pontiac executive. I had this motor completely stripped down and reassembled with the following:

2). Stock pistons (motor has never been bored. New bearings bla bla bla

3) the CAM springs and lifters were all changed to comp gear with the cam being:

Comp xtreme energy with
268/280. 477/480

4) the intake manifold is a Holley street dominator

5) the carb is a Holley 750 double pumper with mechanical secondaries that’s do indeed work as they should. I verified this morning along with the throttle linkage

6) msd dizzy with built in coil. 10 degrees of timing
7) long tube headers not sure what model magnaflow mufflers
8) good spark plugs and wires
9) the heads I’m unsure but I will post some pics of the numbers on the sides
10) the tranny is a 4 speed saganaw. Completely rebuilt but still a weak point
11) the gearing I’m not sure but I found a receipt for 373 gears from the previous owner

She sounds great and drives real nice. It just seems to be lacking a lot of get up and go. I can’t even spin the tires without dumping the clutch. I’m guessing the problem is to do with the cam being a bad pairing with the heads ? Maybe over carbed? Any help on which direction I should go would be helpful. One last thing, it seems like fuel supply is not the issue

 

[92 Sunbird LE]

Cam is good for the street , intake is a race intake so no good for the street, you need a dual plane or a stealth for the street.

Friend in the late 70's had a 68 GTO with a stock 400 and a 4 speed, would light the tires at will in second gear barely warmed up.


Maybe your intake is keeping the torque back, cam is rated at 1500-5500 rpm .

Need a pic of the head with the middle port showing, only half shown in the one pic .

Doug in P.R.

 

[DustinMitchell]

Cam is good for the street , intake is a race intake so no good for the street, you need a dual plane or a stealth for the street.

Friend in the late 70's had a 68 GTO with a stock 400 and a 4 speed, would light the tires at will in second gear barely warmed up.


Maybe your intake is keeping the torque back, cam is rated at 1500-5500 rpm .

Need a pic of the head with the middle port showing, only half shown in the one pic .

Doug in P.R.

I’ll attach a pic, it almost looks like a 1 and 6 ??

 

[92 Sunbird LE]

16 =290 hp 1970 motor, 10:1 compression,1.96 intake 1.66 exhaust valves cylinder heads.

Small valve heads, you are probably only making 300 gross hp or so which equals only 210 net hp with the accessories spinning.

That's about the same as my 1990 Silverado 350 TBI.


Doug in P.R.

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[DustinMitchell]

Okay. Are there better heads I could get without having to dig into changing out pistons and such? I’m just looking at different intake manifolds as well. Not much available locally up here in the prairies!

 

[melsg5]

agree with poor intake choice for a street car.
cylinder heads are also weak for a performance engine.
you state 10 degrees of initial with vacuum advance disconnected?
what is the total mechanical advance and at what rpm do you achieve it.
ideally you should have 36 degrees of mechanical advance at about 2,800 rpm.

 

[melsg5]

heads are based on your budget.
if you can afford them Edelbrock aluminum heads are a good choice.
If not you need to look for large valve OE Pontiac heads.

 

[DustinMitchell]

heads are based on your budget.
if you can afford them Edelbrock aluminum heads are a good choice.
If not you need to look for large valve OE Pontiac heads.

Okay I’ll look into the Edelbrock heads and try to get an answer on the timing. This is a learning curve for me
I was told to get 6X heads but then I read I would need dished pistons. I sunk my money into the wrong place for sure. I had limited parts locally but I’ll check out eBay!

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[DustinMitchell]

heads are based on your budget.
if you can afford them Edelbrock aluminum heads are a good choice.
If not you need to look for large valve OE Pontiac heads.

Ya looks like Edelbrock heads are not quite in my budget
I did see locally 1973 4x heads and 1969 #62 heads. Both need to be rebuilt but are only $70.

 

[melsg5]

Look at the www.wallaceracing.com site. I dont think you need different pistons and the 69 heads would be better if large valves and you are willing to run premium gas.

Pontiac Cylinder Head Search

Wallace Racing Home of Pontiac Powered Firebirds,Trans Ams,Pontiac Powered Dragsters,Pontiac Power Rules!

www.wallaceracing.com

Pontiac V8 Cylinder Heads

The Ultimate Pontiac Head

 

[92 Sunbird LE]

Don't forget to add more $ for the hardened exhaust seats for the 69 heads being rebuilt if you choose them.

Need them if you run unleaded fuel.

Buyer beware on EBay on used parts also.


Doug in P.R.

 

[DustinMitchell]

Thanks a lot! I will pick up the 69 heads and have them rebuilt. I’ll look into a different intake as well and hopefully this will net me a little bit of power.

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[cammerjeff]

Anouther thing to consider is rear end gearing, do you know what the ratio is? If the car originally had A/C your rear end ratio would be around 3.08. Just a rear gear swap could very well get you the acceleration you are looking for. A set of 3.55 or 3.73 gears would really help the car from a standing start.

I agree on the poor intake manifold choice on the engine, just a stock 65-79 4bbl intake would really help the car. You are describing exactly what a single plane intake is designed to do. Not low end torque below 2500-3000 rpm, and better high end HP, the trouble is your heads are designed for low rpm torque.

I would not change the heads personally, they are not great performance heads but would be OK with a duel plane intake & a properly set up Carb. It may surprise you with that camshaft. If you are looking for more HP after swapping the intake, them heads would be my next addition. you still should be able to use the new intake and carb on the next set of heads.

 

[G-985309]

Thanks for the reply. I believe I have 373 gears but can only base that off of an envelope full of receipts that came with the car. Can you recommend a good square bore intake that would match up nice with my Holley double pumper ? I’m just taking a look around on eBay but not a lot of buyers who want to ship to Canada. I see a lot of Edelbrock ones and one or two OE ones

 

[melsg5]

Assuming you have a positraction rear, raise the rear of the car, transmission in neutral, parking brake off, chalk mark on drive shaft, rotate one of the rear tires one revolution. If you have a 3.73 the driveshaft will turn approximately 3 3/4 turns.
An OE intake will not take a Holley square bore carburetor without an adapter and that is not recommended. You will need one of the aftermarket intakes, Edelbrock, Holley, Weiand, etc. Look at www.summitacing.com and www.jegs.com to see what is available.

 

[G-679388]

Okay so I have confirmed that I have 373 gears. I also have a new Edelbrock performer 2156 intake ordered, hopefully be here by the end of be week. I understand the terrible mismatch with the cam now and it explains a lot. My only other question is again with the heads, the date code on them is G309. Would that not make them July 30th 1969? Which would be the bigger valve compared to 1970? The motor is definitely a 1970 YD block which I guess isnt great. Thanks again for all the help, there is a lot of info out there it’s just hard to sift through all of it!
I hope this intake pairs better with the cam, I didn’t realize the street dominator was essentially ineffective until 4500 RPM! Which gave me like 1000rpm of usable power

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[DustinMitchell]

Good morning, I have confirmed I have 373 gears so at least I have that going for me. I understand the intake and cam mismatch now and ordered a new Edelbrock 2156 intake. I went new this time to avoid any hassle, hopefully this is a better match. Again I just have one quick question about my heads, the date code is G309, would that not make them July 30th 1969? The bigger valve? I know my block is a YD 1970. Thanks again for all the help, there is a wealth of knowledge here

 

[melsg5]

go back up to the previous post I gave you for Wallace Racing cylinder heads. You need the two character number on the center of the exhaust ports to determine which heads you have. A july 1969 date could be 1970 production.

 

[92 Sunbird LE]

Correct, that's the casting date, alot more has to happen for that engine to get in a chassis , maybe a couple of months.

70's we're not kind to car manufacturers , young ,lazy , pissed off and hippie workers missed alot of time on the assembly line. ( Not to forget strikes also)

Doug in P.R.