Ad Radar
High Performance Pontiac
Click here to find out more!

New to the forum looking for a little advice for my lemans conv.

High Performance Pontiac
1 |  2 |  Next   | Last 
Item Posts    Sort Order

New to the forum looking for a little advice for my lemans conv.

terrenceo terrenceo
New User | Posts: 3 | Joined: 10/13
Posted: 10/29/13
05:19 AM

Hello i have a 69 lemans conv, i put a saginaw 4 speed in it. It should have 2.56 rears. Right now it is geared perfect, but the abuse to the old 350 finally cost it its life. I have a 68 yh code 428 ready to get rebuilt. I know the true answer is drop the heads and put on eldebrock heads, but i feel like the 2 grand can be used better elsewhere. I have a set of 4x heads, i also thought about dished pistons to use the original heads on the 428. Also i want it to be a stump puller on the road a real gear rower 1st and 2nd and 3rd i could care less about making high rpm hp and tq so what cam should i look for? Sorry for the long post looking forward to hearing from you guys.
1. What to do about the high compression, use the 4x? aluminum heads? dished pistons?
2.  What cam to use? roller rockers? 1.65 ratio?

Thanks again guys

Terrence OBrien  

Mr.Milt Mr.Milt
Guru | Posts: 1135 | Joined: 08/08
Posted: 10/29/13
06:34 PM

This is not an answer to your question; however, I do have a suggestion.  Before you plan on using an engine that old I would disassemble it, have it boiled out and manga-fluxed it to make sure it is a solid platform. Plan your build from the bottom up.  Put money into making it a reliable sound motor. From this point I will let the engine people chime in.  

Guru | Posts: 1016 | Joined: 07/11
Posted: 10/29/13
09:24 PM

welcome to the forum. 68 yh 428 4 bolt main 375 hp 067 cam and 16 or 62 heads.

you will need to determine witch 4x heads you have by the secondary number on a boss just below the valve cover to the front of the head.

the best you could hope for would be 3h or 7h at 98cc. 8.3 to 1

The following are 73-74 heads

4X-1H uses 4.881/4.870" valves
4X-1H are 455 head with 114cc, 2.11/1.66" valves and pressed studs.
4X-3H are 400 4bbl head with manual transmission, 98cc, 2.11/1.66" valves and screw-in studs.
4X-4H are 400 2bbl head, 1.96/1.66" valves and pressed studs.
4X-7H are 400 4bbl with auto trans, 98cc, 2.11/1.66" and screw-in studs.
46 are 350 2bbl/4bbl heads with about 86cc, 1.96/1.66" valves and pressed studs.
4C-5 are 350 with AIR, 1.96/1.66" 86cc, pressed stud.
4C-9 are 400 with AIR, 1.96/1.66", 98 cc, pressed stud.

*All heads cast on or about April, 1973 received threaded studs.
So, take the head above and if they were cast after or about April 73,
the "pressed" applications will be "screw-in".

info from wallace racing.

you can also have hardened exhaust seats put in your 68 heads and use a good set of dished pistons to lower the compression to around 9 to 1 and a cam with .218/224 duration at .050 with 1.5 rockers. imo this will be the cheapest route.  
76 455/4spd TRANS AM

terrenceo terrenceo
New User | Posts: 3 | Joined: 10/13
Posted: 10/30/13
05:07 AM

hello guys thanks for the replies. I plan on getting the block boiled and magged, It has never been apart so we are going to send it out to be checked. I believe i will go the dished piston route as i would like to keep the big valve heads and stay as close to the magic 9:5 to 1 as i can. Does anyone have a suggestion on which pistons to use and where i could source them from? Again thanks in advance.  

Poncho462 Poncho462
User | Posts: 103 | Joined: 01/12
Posted: 10/30/13
07:40 PM

Hi Terrence, and welcome!

I have a set of 4X 7H heads, 98cc chambers, on my flat top piston '70 455.  I am in California and live with 91 octane gas pretty good, and my compression would be a tenth of a point or so more than even an overbored 428.  The 455 is .030 over for 462 ci.  My dynamic compression is on the high side due to the small cam, which you could also compensate for by more duration and overlap if you felt it was needed, though you would sacrifice some mileage economy if you went that way.
I coincidentally run a Richmond 5 speed, which like the Saginaw has a 1:1 top gear, and high numerical 1st gear.  Many of the Sag's have either 3.11 or 3.50 low gears, and my Richmond has 3.27 low.  I run a 2.75 rear axle, which gives me excellent economy acting as a "virtual" over-drive, along with a very mild Comp Extreme Energy 256 cam.  With my ratio's, I can reach 47 mph in low, 72 in 2nd, 97 3rd, 119 4th, and 149 5th @ 5200 rpm.  As you can tell, I set this up to go through quarter mile lights just under redline in 4th gear.  The Sag's 4 gears would be wider spaced overall, but with a 428 or 455 Pontiac's torque, It should not make much difference in a street car.  It will burn rubber and GO any time you punch it.  My car is an excellent street car and I basically have too much torque in the lower gears, not too little.  Street tires act as mechanical "fuses", and let go normally before any real stress reaches the drive train.  Make sure you have a good clutch too.  I have a dual friction Centerforce, and it has been great so far, just had it out and inspected it at 10,000 miles and it looked new to me.  It has very smooth engagement for the street, but when engaged, has never slipped.  It is installed on a steel Hayes flywheel I bought new when I converted the car from a turbo 400(M400) to the 5 speed.
My cam is one or two sizes too small for my Firebird's light weight, and I would go just a bit bigger next time to raise the torque peak and HP peaks a little higher up the rpm band.
A couple words of caution..You will have much more torque in the new motor compared to a 350, and both the Saginaw and the stock rear will be marginal in strength, so if you keep them initially, go easy on the starts especially.  My Richmond is a very strong transmission, and I converted to a F*rd 9 inch from my original 8.2 rear to gain the strength needed to stand up to the big torque, should I be unfortunate enough to get some unexpected traction.  I was passenger in a pretty mild chevy one time that hit a patch of rough concrete paving and really grabbed unexpected traction and tore out the differential BANG!  Not something you want to contemplate in your car.

Sounds like you have a pretty good idea what you want, so stick to making it the best for your desires and needs, not necessarily the biggest cam etc.  Best of luck!

Larry Noble  
"Wherever you go, there you are."..Buckaroo Banzai, 1984

70bird 70bird
Guru | Posts: 1064 | Joined: 02/13
Posted: 10/30/13
08:25 PM

i might do this

comp 275deh  275/277  219/225  462/480 lsa 110  ivc 63 bbdc  rpm 1500 - 5800

HEADS - pocket port and back cut intake valves.

INTAKE - Either stock, eddy std [similar to stock] or eddy rpm. tough call for a stump puller.

CARB - An annular boost venturi type will give the most hp below 6000 rpm. holley 770 vacuum secondary street avenger, quick fuel 750. 650 cfm is the smallest i would use.

EXHAUST - I would run the ram air cast ex.


GEARS - i CAN'T BELIEVE YOUR GEARS ARE 256 AND YOU LIKE THEM. YOU CAR WILL GO AROUND 200 MILLION MILES AN HOUR AT 5000 ENG RPM. i would run at least 2.80 - 3.00 on a big heavy car like that.

ROCKERS - Scorpion std ratio race model. us made, forged, full roller, aluminum. see at summit racing or scorpion online.

this based on a 26.5 tall tire.

(RPM)     2.56 Gear       2.80 Gear   3.00 Gear  
8000 RPM 246.37 MPH 225.25 MPH 210.23 MPH
7500 RPM 230.97 MPH 211.17 MPH 197.09 MPH
7000 RPM 215.57 MPH 197.09 MPH 183.95 MPH
6500 RPM 200.17 MPH 183.02 MPH 170.81 MPH
6000 RPM 184.78 MPH 168.94 MPH 157.68 MPH
5500 RPM 169.38 MPH 154.86 MPH 144.54 MPH
5000 RPM 153.98 MPH 140.78 MPH 131.40 MPH
4500 RPM 138.58 MPH 126.70 MPH 118.26 MPH
4000 RPM 123.18 MPH 112.63 MPH 105.12 MPH
3500 RPM 107.79 MPH 98.55 MPH 91.98 MPH
3000 RPM 92.39 MPH 84.47 MPH 78.84 MPH
2500 RPM 76.99 MPH 70.39 MPH 65.70 MPH
2000 RPM 61.59 MPH 56.31 MPH 52.56 MPH
1500 RPM 46.19 MPH 42.23 MPH 39.42 MPH
1000 RPM 30.80 MPH 28.16 MPH 26.28 MPH  

Guru | Posts: 1016 | Joined: 07/11
Posted: 10/30/13
10:47 PM

70 bird he may have the 3.50 low gear 4 speed. in the 1st 3 gears it would feel more like having 3.55 or 3.73 in the rear end!  
76 455/4spd TRANS AM

4zpeed 4zpeed
Enthusiast | Posts: 369 | Joined: 04/13
Posted: 10/31/13
01:43 AM

+1 Row
I believe he is saying that he's using a Saginaw 4 speed manual  transmission with a 2.56 1st gear but that ratio is for a 1963-1965 Muncie M20 wide ratio transmission.

Welcome to the HPP forums Terrence, here are the different ratios for the Saginaw. If the trany is still in the car and you want to roughly figure the ratio you can put the trany in 1st gear, jack the rear, mark the engine balancer at 12:00 high, mark the drive shaft and have a buddy watch it for the number of rotations as you spin the motor by hand.

Also it would help to know what rear end gears you have, you can also check this by jacking the car and checking the rotation of the driveshaft compared to the rear tires. This will help with cam recommendations as well.

By the way just curious, are your heads #16 or #62?

Saginaw 4 speed
1st     2nd     3rd     4th
3.50 - 2.48 - 1.65 - 1.00
3.11 - 2.20 - 1.47 - 1.00
2.85 - 2.01 - 1.47 - 1.00
2.54 - 1.80 - 1.44 - 1.oo

If you have the trany out and provided the input shaft has not been changed you can check the grooves on the shaft to identify the ratio.

No grooves 2.84, 2.01, 1.35, 1.00
    1 groove 2.54, 1.80, 1.44, 1.00
    2 groove 3.11, 2.20, 1.47, 1.00
    3 groove 3.50, 2.47, 1.65, 1.00

Poncho huggen gear snatchen posi piro.

70bird 70bird
Guru | Posts: 1064 | Joined: 02/13
Posted: 10/31/13
04:16 AM

70 bird he may have the 3.50 low gear 4 speed. in the 1st 3 gears it would feel more like having 3.55 or 3.73 in the rear end!  

well if he has 355 first gear then hey terrenceo maybe buy another trans, lol.  

Poncho462 Poncho462
User | Posts: 103 | Joined: 01/12
Posted: 10/31/13
10:06 AM

How about it Terrence?  It was not crystal clear to me about the rear gear ratio either, but I believe 2.56 was standard for quite a few of the A and F body cars.  I think my original 8.2 inch rear(68 Firebird) was in fact a 2.56 open behind a standard M400 automatic and base 400 engine.  I actually picked up extra torque multiplication when I went to the 2.75 I have now.

Standard first gear ratios are 2.48 in a M400 automatic(turbo 400).  That torque converter gets the car up into an rpm area that has more torque, which makes it feel stronger, but with even a 3.08 axle, that's only 7.88 torque multiplication, and 6.34 with the 2.56.  If that doesn't seem like much, before parasitic losses, with a 428 with let's say 480 ft lbs of torque, that's 3,744 lb ft total.

In comparison, the same motor with a 3.27 low gear, 2.75 axle behind it computes to 4,315 lb ft.  That's why I have a nine inch and the Richmond, which is built to handle these levels.

With my 3.27 low gear Richmond, and as noted, the Saginaw would probably be near that, the total multiplication with 2.75 rear is 8.99 in low, over 10% greater than it was with the automatic/3.08 setup, and around 35% greater than the automatic/2.56!   Plus, an M400 has 2 gears below the final drive, the saginaw has 3, and the Richmond has 4, which generates more area "under the curve" so to speak, when rowing through the gears.  Add to these numbers the massive increase in torque going from a 350 engine to a 428(455 in my case), and the choice is very reasonable in a street car.  The car will accelerate much faster with the new setup, and if a reasonable cam is chose as suggested, it will pull from fairly low rpm's, and get reasonable gas mileage if everything is set up correctly, as cruise rpm at interstate speeds will be similar to Over-driven cars.   My 70 mph cruise rpm is 2500, which is right near the torque peak of the engine, which helps efficiency.

Somebody recommended annular venturi's for street cars.  I agree.  My Holley 4011 spreadbore, which is no longer made, has those and I think some of my economy results from their use.  They came in spreadbore and square styles, from 600 to 800 CFM. These are cheap at swapmeets, use standard Holley jets, power valves etc, are all polished aluminum, and have a top cover which allows 15 minute parking lot jet changes without draining the gas from the carb.  I've done it when travelling cross country with the Hot Rod Power Tour and was running rich at higher altitudes.  The Summit carbs and some street avengers have carried over some of these design features.  Full trick kits are still available from Holley for them, and they are great street/road carbs in my opinion.  I have a box of them, some of which I bought for 10 bucks at the swap meet.  They also made boat carbs in the same style.

One last note on gearing, is that Richmond Transmissions does not recommend any rear end ratio above 3.08 when using a 3.27 low geared 5 speed with 1:1 top gear, as low becomes of limited usefulness unless you wind it out every time, and the "too much torque" problem is multiplied.  I once had to avoid car which suddenly appeared around a blind corner at speed while I was leaving a driveway, and my only option was to floor it, try to modulate the throttle, and pray.  With full positraction leaving two streaks behind me I barely could get enough traction to stay ahead of the guy in a street situation.  I did, but just.

It's pretty simple math, and in a road car, I think the practical limit on torque multiplication in low gear pretty much tops out at 9 to 10 times.  and to use even that much from a stopped state requires good, sticky, big, tires and a fully functional limited slip or locker.  Sticks tend to "hit" the tires harder than automatics too, which changes the driving techniques needed as well.

Hang in there Terrence, and think about what you want before you spend the money.  Good luck!

"Wherever you go, there you are."..Buckaroo Banzai, 1984

terrenceo terrenceo
New User | Posts: 3 | Joined: 10/13
Posted: 10/31/13
03:50 PM

Hey guys I know my gear ratios sound crazy but I love my set up. At least with the 350. I made the decision to go to edlebrock heads to keep my compression. And my pistons. What heads would you suggest 72cc or 85cc. And same cam recommendations?  Thanks for your help guys love the car this is my 2nd and my dads 15th poncho its in our blood. But he is very old school so we are both learning the new parts and gas situation together.  

70bird 70bird
Guru | Posts: 1064 | Joined: 02/13
Posted: 10/31/13
11:22 PM

same cams i suggested.

85 cc heads if you deck the block to .005".

flat top pistons.

this gives 9.58 static compression.

if you love your gears keep em.  

Guru | Posts: 1016 | Joined: 07/11
Posted: 11/01/13
10:35 AM

a friend of mine had the 3.50 sag with 2.56 gears in his 68 bird. it ran great and got 20+ mpg with a hot 389 and tripower. he has sence upgraded to 3.73 gears in a 8.5 ten bolt and a ss700 5 speed. i think the car was faster with the sag and the 2.56 gears.

the 428 will pull the 2.56 just fine as long as you don't go to big with the cam!

sounds like a good combo 70 bird.  
76 455/4spd TRANS AM

4zpeed 4zpeed
Enthusiast | Posts: 369 | Joined: 04/13
Posted: 11/01/13
07:18 PM

I see, so you do have the 256 rear, and more than likely the 350 1st gear Sag as Row mentioned. Understandable you are happy with that combo, and with the 428 in front of it there should be no problems yanken stumps, should clean up the yard nicely. You should also be happy with 70bird's recommendation as well.

Poncho huggen gear snatchen posi piro.

gastiresoil gastiresoil
New User | Posts: 29 | Joined: 01/14
Posted: 01/16/14
09:12 PM

Just reading all the advice and it all sounds good.
My advice comes from many years experience with Pontiacs, started in 1977 on a drag strip.
I'm still running a 1969 428 in a 1978 Elcamino with a 1965 Tri-power 4WD with 33" boggers.
If your are going to run that Saggy behind that 450+ ft. lb. Pontiac get some extra drivetrain. Big displacement Pontiacs do not need a lot of gear. 3:55-3:73 will work great, just remember when the rubber grabs whatever is in between the rubber and the 428 you will need to replace. I could fill a pickup with all the stuff I broke with this unit and never hurt the motor. Let the tires slip a little. Shift it right and it will last, saw more of those in a bucket than Muncies.
So a happy balance is good. All that other advise is good.
Certain things that have always haunted Pontiacs, High RPM bad, stock rod bolts very bad, Holy carb big waste Pontiacs don't need fuel to make ponies, good heads/headwork is best, stock ones work very well. Want dependability stay close to stock, you will be happy every day you drive it.
1. Do all the good stuff to make sure your starting with a good foundation.
2. A stock ram air cam is best with anti-pump-up lifters.
3. Ram air exhaust manifolds are best, from Ram Air Restorations, their larger than headers without the heat, then match the ports.
4. Do the best balancing job that can be done, you'll get some free ponies.
5. Make sure the windage tray is put back in, about three ponies there.
6. Use a Quadrajet or a good copy, I like Tri-power best, their fun and have a full plenum that helps with low end torque, an early factory cast iron intake is as good as any 3" aluminum, so use the one that came with it.
7. Buy the best rod bolts available, the stock ones WILL stretch! Old stigma attached to Pontiacs was they loose oil pressure, this is why.
8. Larger chamber heads are best, you can only buy flat tops for this unit, if she still wants to pre-ignite get some thicker gaskets, I have 65cc heads, had to machine .o40" off and dish them about .010" each piston to run pump gas.
9. Spend the money for hardened valve Seats and S.S. exhaust valves.
10. Make sure you use the old crank gear,(save it) its an advanced gear, all the ones you buy now could be retarded, inspect the key placement with the new one if you need it, make sure it matches the old one, normally their off a 1/2 tooth but you can flop it over and grind a new chanfer to make it work.
11. Do a nice porting job on the heads and polish the exhaust ports only.
12. This thing likes lots of coolant, get a big radiator.
13. Punching that thing out .30" over works well, your going to buy pistons anyhow.
14. Most of all, keep it below 6000 rpm
15. Buy a good clutch, look for the most Ft. Lb. of torque offered, question the supplier, most don't list 428 for a reason, all will bolt up may not hold up.
16. Above all, keep it stock, spend less cash, run what ya got and you'll be happy.

I had a 69 Lemans in 1976, still got some parts, wish I had her back.
I'm stuck with a 1964 GTO convertible.

Now your 428 will make near 500 ft. pound of torque and most likely 390+ HP.
My 428 has been the most fun of any Pontiac motor ever.
My Camino weighs 5800 lb. w/3/4 ton 8 lug axles, I can lay four light black marks on concrete for about 5'. Out pulled a Power-joke Ford and stomped a 97 Trans am in 100 feet, twice.  
It has gernaded all the 1/2 ton stuff that GM has made that's why I have a full floater in it. I'm on my second TH 350 that I built, broke the housing on the first one, second transfer case, broke the chain and made 10 pounds of loose change, broke 5 drive shafts 3 yokes and the last straw was ring, pinion, carrier and housing. And I don't pound on it as much now, need to plow snow with it.
Its going in a 1968 Chevy van with a 4 speed top loader now, and of course, 4WD.

Have fun,
The GTO guy  

1 |  2 |  Next   | Last