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Old 06-18-2010, 04:57 AM
UngerMarkus's Avatar
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Pontiac 400 performance problems

Hi guys!

I recently installed the new 400cui Pontiac engine and the TH350 i built this winter, in my 64 Bonneville. To be honest, I was disappointed. It fires right up and it runs nicely, but it just ainīt fun. It doesnīt even really smoke the tires at a wot launch... Maybe you guyīs have a clue whatīs wrong, considering the parts I installed/efforts I made:

69' Pontiac 400 Block
69' #46 Heads (72cc) with 2.11'' intake and 1.96'' exhaust valves milled in, ported
wiseco pistons
Crank and Rods Pontiac, balanced
Edelbrock Performer intake
Edelbrock Performer carb 1406 600cfm
Howards cam 410021 dur @.050 214/224 Lift .444/.467
Rhoads variable-duration lifters
Comp Cams double roller timing set
Pontiac HEI distributor
Hooker Super Competition headers
Dual exhaust

I run the engine on 100 octane

I donīt know what gears I have, but at 60mph the engine revs a little over 2000 rpm in third with stock tires.

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Old 06-18-2010, 05:32 AM
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The 1.96" exhaust valves jumped out at me- the stock 1.77" valves are considered big enough for the 2.11" intakes for a NA engine in most every case I've seen.

The timing likely needs to be worked on. Set the initial to about 12š - 14š BTDC as a starting point. You want the total timing to be about 34š, all in by no more than 2800 RPM, this would be sooner but given the weight of the car and the high rear gears (~2.73:1, given 2000 RPM @ 60 MPH and a tire diameter of ~ 27"), this is probably a good compromise.

Use the vacuum advance (it is working, right?) hooked up to manifold vacuum.

What is the vacuum at idle?

Just as a friendly reminder, the distributor rotates CCW on a Pontiac, so to advance the timing, you turn the distributor CW- opposite of a Chevrolet. This also means the weights and cam of the mechanical advance is "upside down" as compared to a Chevy. So be sure they're right.

Last edited by cobalt327; 06-18-2010 at 05:37 AM.
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Old 06-18-2010, 08:43 AM
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Thanks for your fast reply!

Vacuum at idle (500rpm) is about 22 hg.

I just advanced the ignition but it didnīt make much difference in power, revs up better.
Seems like I need a stronger starter, the one I took from a 79' 305 Pontiac wonīt crank her any more.

What spark plug gap would you recommend?
At the moment I run Autolite 85s

Is it worth the money to upgrade the hei distributor with a pertronix/accel/what-ever kit?
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Old 06-18-2010, 08:54 AM
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Edelbrock Performer carb 1406 600cfm


Isn't the 600 cfm carburetor on the small side for a 400 engine? My 400 engine from a Grand Prix has a 800 cfm on it. You may want to consider a bigger carburetor.

BT.

Last edited by beertracker; 06-22-2010 at 06:58 PM.
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Old 06-18-2010, 09:13 AM
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When all tuning avenues have been explored, look at the camshaft.

I have the experience of Pontiac, Olds, AMC, cams that just run OK, but when changed to a properly made cam, the engine performance has a tremendous increase. I will only use Isky, or custom grind, for these engines anymore.
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Old 06-18-2010, 09:39 AM
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The torque converter is holding you back. You coulkd probably change the rear gears from (I'm guessing) 2:73's - 3:23's to 3:42's or even 4:10's.
That would help get that engine into your cams power range a lot quicker.

try changing the weights and springs in the dist. also. Poncho's like fast advance curves.

Last edited by sqzbox; 06-18-2010 at 09:42 AM. Reason: brain fart
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Old 06-18-2010, 10:24 AM
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Does anybody have a simulation software to simulate an approximate hp/tq number for this engine combination? Or could anybody estimate it?
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Old 06-18-2010, 05:50 PM
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Quote:
Originally Posted by UngerMarkus
Seems like I need a stronger starter, the one I took from a 79' 305 Pontiac wonīt crank her any more.
You prolly mean a 301 Pontiac, the 305 was a SBC and the starter noses are different (starters mount to opposite sides).

If the engine cranks hard, then gets easier if the ignition is retarded, the advanced ignition is the cause for the sluggish starter- the engine is trying to fire up while the pistons are still rising slowly by the starter- this causes the starter to labor.

Otherwise, check that the engine has the ground cable from the battery connected to it, and the engine has ground cables running to the chassis.

Quote:
What spark plug gap would you recommend?
At the moment I run Autolite 85s
0.040".

Quote:
Is it worth the money to upgrade the hei distributor with a pertronix/accel/what-ever kit?
I've used the basically stock HEI and had no problems. An MSD 6 is a good addition, it's a multiple fire set-up that helps starting/low RPM performance the most.
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Old 06-22-2010, 02:21 PM
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hi guys!

I spent some time on tuning with little results:

I re-gapped the plugs from 0.045 to 0.040. The engine seems to like this better. The ceramic insulator is chocolate brown. The ground strap has some sort of brown powder on it and changes the color slightly in the middle between tip and base ring. The base ring has a light carbon build-up all around, PLUS approximately 3/4 of the base ring are covered with the same brownish "powder".

I use 100 octane gas (100RON/88MON) plus lead substitute.

I tried every ignition advance from 8° to 14°. As well as a lot of advance-spring combinations. Little increase in performance.

Idle is great. The engine revs up incredibly, while in neutral. As soon as you tip the throttle it revs up to 3500 and drops back to idle even as fast. Except for a ticking noise it sounds really powerful! (I think itīs due to the Rhoads Lifters)


Could someone please explain me, what sqzbox wrote about the torque-converter? I use a stock unit from a 75 chevy blazer.
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Old 06-22-2010, 03:04 PM
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In my opinion, a 214/224 @.050 cam isn't big enough to need Rhoads lifters, and it made it too soft at low rpm.

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Old 06-22-2010, 06:33 PM
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also, in my experience, the huge exhaust valves stuck out to me as well. She sounds like her air/fuel combo is off. Like having too small of a cam to work well with a type of intake. That could cause the problems you are having. An easy way to fix this is to match up the cam to the intake from the same manufacturer. Such as edelbrock RPM airgap intake with an edelbrock RPM camshaft.

also, sorry to say this, but an edelbrock performer intake is pretty much the stock intake cept aluminum on a 400. that and the small 600 carb won't do diddly, especially with a calm cam.

Your cam is way too small, especially if you're running 100 octane.. might as well take advantage of it. what's your compression like? Sorry don't remember seeing it. Easy way to bump that is going with a thinner head gasket. Having even 10:1 compression, 100 octane, and a high rev cam will definitely kick you into the back of your seat. I would recommend a cam with minimum .550 lift even more would be good up to .6 and have the duration LSA tighter, around 110 minimum, 108 preferred.

For an example, Lunati has a "NOS (new old stock) Cam" of the Ram Air IV, here's her specs:
Hydraulic Flat Tappet
LSA Intake: 308
LSA Exhaust: 320
Intake duration at .5: 231
Exhaust duration at .5: 240
Intake lift w/ 1.65 rockers: .516
Exhaust lift w/ 1.65 rockers: .516
Lobe Separation Angle (LSA): 113
RPM Range - 2500-5500

it's a great cam, and has good specs. Anything bigger than that, and you'd be fine with a choppier idle. I'd keep the LSA around 110 if you have vacuum assisted brakes. Also, I'd try for a roller cam too, if you have the funds, either hydraulic, or solid preferred. Way better performance for the same numbers

with your heads, and octane, you could just switch out to a hot RAM Air IV cam. It's a hot stock setup and best thing is if somebody asks, you can reply, "nothing fancy, just a stock 400." And then run 12s with the proper hookup in the back.

my friend has a "stock" 65 Grand Prix, she's a 455 with that cam, runs 12s all day long. people swear she's running nos!

hope this helps

Last edited by NAUBandit; 06-22-2010 at 06:48 PM. Reason: found specs for Ram Air IV from Lunati
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Old 06-25-2010, 12:19 PM
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Thank you for your replys!

Iīm currently building a Q-Jet according to Cliff Ruggles book "How to rebuild and modify Rochester Q-jets". I chose the performer intake, because I bought the engine disassambled and the intake was missing. And in Jim Hands book "How to build max performance pontiac v8s" it was said to perform well...

I know, pretty much books... Unfortunately, here in Austria, I canīt go to a race-track and ask experienced people.

Do you think a 2000rpm stall converter would be a good investment? Some guy advertised a used B&M Holeshot for 150.-
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Old 06-25-2010, 12:42 PM
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Just saw the pontiac 455 buildup on horsepower tv a couple of months ago. One thing I noted was their comment that the pontiac heads were extremely poor performers and would require extensive porting to make them flow half as good as a modern set of edelbrock aluminum heads.. I know its a painful spend, but based on that information and the comments of others here I would bet the majority of the problem is the heads you're running.. if you have the budget pick up some edelbrock heads and sell your 69 heads to recoup some of the cash.. that's my .02 cents...
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Old 08-23-2010, 02:48 PM
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Quote:
Originally Posted by UngerMarkus
Hi guys!

I recently installed the new 400cui Pontiac engine and the TH350 i built this winter, in my 64 Bonneville. To be honest, I was disappointed. It fires right up and it runs nicely, but it just ainīt fun. It doesnīt even really smoke the tires at a wot launch... Maybe you guyīs have a clue whatīs wrong, considering the parts I installed/efforts I made:

69' Pontiac 400 Block
69' #46 Heads (72cc) with 2.11'' intake and 1.96'' exhaust valves milled in, ported
wiseco pistons
Crank and Rods Pontiac, balanced
Edelbrock Performer intake
Edelbrock Performer carb 1406 600cfm
Howards cam 410021 dur @.050 214/224 Lift .444/.467
Rhoads variable-duration lifters
Comp Cams double roller timing set
Pontiac HEI distributor
Hooker Super Competition headers
Dual exhaust

I run the engine on 100 octane

I donīt know what gears I have, but at 60mph the engine revs a little over 2000 rpm in third with stock tires.

old thread, but I was compelled to reply and revive it- there's a lot wrong there for a Pontiac combination:

1. With a cam that small, you don't need Rhoads lifters- take them out and put regular lifters in. That cam isn't bad but you're making it even smaller with those Rhoads.

2. HEI is a good dist. but you need to change the weights and springs to get full spark advance at high rpm- also you need to get TOTAL TIMING of around 36 degrees BTDC at the flywheel.

3. #46 heads are originally small valve, low performance heads- find a set of big valve heads with 2.11/1.77 valves or at least 2.11/1.66- the later smog heads are ok, you can mill them .065" to raise the CR and mill the intake same amount to port match

4. yes, the carb is way too small, you need at least a 750 cfm Qjet or Holley or Edelbrock carb.

5. buy a full set of 1.65 rockers to increase valve lift more

6. typical gears in a 64 Bonny were very tall, it was a luxury car- I'd wager it has 2.73 or 3.08 gears in it, don't expect it to be a tire burner unless you put in 3.55 or 3.70 gears

7. if you use the later smog heads and lower the CR you don't need 100 octane, actually the 100 octane in a low CR engine, will make it run slower- because high octane gas burns slower than low octane gas- that's how it controls ping with high octane
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Old 08-24-2010, 10:41 AM
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Yeah, I allready thought about swapping the Rhoads Lifters for a set of standard hydraulics.

I had big valves cut into my #46 heads. And since i run a MSD 6a combined with my HEI, the engine is pinging on normal gas.

I recently put on the stock Q-Jet. But it didnīt perform very well. The 650 Edelbrock Thunder AVS does better! Does a bigger carb increase high end power only, or low end grunt as well?
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