[Vckline313]

I have a pontiac 400 that I currently have 5c heads on, that doesn't perform as well as I'd like. It has an edelbrock intake smi built carb, Dougs headers and msd hei ignition. Car doesn't have the down low torque like it should. Also has a cam idk which due to me buying the car and motor as it is. It runs good, just doesn't perform well.

What would the better option economically be to take a set of 6x-4 heads I have and take them to a machine shop and have them worked (ported polished, valve job....) or wait till company's stock back up on aluminum heads.

Car also has a 2800 Hughes converter and 3.73 gears

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[lust4speed]

Originally Posted by Vckline313

... Car doesn't have the down low torque like it should...Car also has a 2800 Hughes converter and 3.73 gears...

I usually think of "down low torque" as being in the 2,000-,3000 RPM range and this usually favors small carburetor and small stock runners which the conservative iron heads should be great at. Your converter and rear gear should be great and I'd think the only problem you should be having off the line is tire smoke with street tires. Can you give additional information on what the engine is doing and at what RPM.

My only guess with the limited info is that your compression ratio is so low that you just are not producing power at any RPM range.

[Vckline313]

It just seems like a turd off the line. Like you said no spinning or smoke lol. Car also has a 4 link setup, Dbl adjustable coil overs, and subframe connectors. It Flys on the freeway if I let it (but I like to keep the rpms low so I don't get into it much past 70mph) the bark is much worse than the bite in this car

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[NeighborsComplaint]

5C, 4X, 6X are all about the same unless you have the large chamber heads making compression under 9:1. More likely than not your timing curve is too slow and not bringing in enough mechanical advance. You should be running 10-12 degrees initial and around 28-30 degrees all in by 3,000 RPM.

[74Grandville]

What version of 5c? 4 or 8? I would also degree the cam if it was me. Timing tape on balancer and a dial indicator on the pushrod. What psi is your cranking compression?


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[Vckline313]

Originally Posted by NeighborsComplaint

5C, 4X, 6X are all about the same unless you have the large chamber heads making compression under 9:1. More likely than not your timing curve is too slow and not bringing in enough mechanical advance. You should be running 10-12 degrees initial and around 28-30 degrees all in by 3,000 RPM.

Last I checked trying to check the timing by myself, I was 12 initial and 34 all in at 3k

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[Vckline313]

Originally Posted by 74Grandville

What version of 5c? 4 or 8? I would also degree the cam if it was me. Timing tape on balancer and a dial indicator on the pushrod. What psi is your cranking compression?


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No clue on any of the questions but I can find which version of the 5c I have.

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[67Fbird]

what rpm are you at 70 mph? how much cam do you THINK it has?...,mild, lumpy or Big bad thumper?
All the power in the world strapped by 2.73 gears and NO converter is going to be a turd. A 400 can be a beast down in 2200 area but.... 8:1 compression and a RAIV cam with no gears.....aint going to do it as those items are exactly WRONG for each other.

Is it a converted points dizzy? or points?

[Vckline313]

Originally Posted by 67Fbird

what rpm are you at 70 mph? how much cam do you THINK it has?...,mild, lumpy or Big bad thumper?
All the power in the world strapped by 2.73 gears and NO converter is going to be a turd. A 400 can be a beast down in 2200 area but.... 8:1 compression and a RAIV cam with no gears.....aint going to do it as those items are exactly WRONG for each other.

Is it a converted points dizzy? or points?

Cam is pretty lumpy
Car has 3.73 gears and a 2800 stall and msd hei ignition as stated before

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[steve25]

First off, the bigger intake and exh port overall volume and minimum port area that is contained in any aftermarket Aluminum head will do nothing for increased off idle torque, so drop that possibility / notion fast!

Stock intake ports as in your 5C heads are 154CCs in volume, the smallest port volume you will find in any aftermarket Head is 182 CCs, or some 18% larger then what you have now.
Installing such a aftermarket head would reduce the low speed torque you have now unless you used a aftermarket head that picked you up a full point or more of compression from where you are now.

Especially considering the faster heat rejection of a Aluminum head over a iron head!

Is your air filter really as dirty as it looks in that photo, or is it a natural Brown color?

Give your motor a check up.
What cranking compression does the motor show?

If you do not know you should find this out.

Have you checked how good or bad the timing Chain is?

Is the carb working right at least at idle, if with the motor fully warmed up and the choke fully open and locked by the lock out lever, if you then turn the idle mixture screws in and out do they effect the idle?

[Vckline313]

Originally Posted by steve25

Is your air filter really as dirty as it looks in that photo, or is it a natural Brown color?
What cranking compression does the motor show?

If you do not know you should find out.

Have you checked how good or bad the timing Chain is?

Is the carb working right at least at idle, if with the motor fully warmed up and the choke fully open and locked by the lock out lever, if you then turn the idle mixture screws in and out do they effect the idle?

New filter since pic, no idea on cranking pressure, carb seems to work fine and idles well. Changing a/f screws does change things

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[PunchT37]

You can prolly tune some more power into that engine.

But, the original question, on a 400, the 6x 4’s are not going to make enough compression to run the larger cams. Money for porting, valves, guides, etc is going to be the same as new heads. Wait for some 72cc aluminum heads.

[Vckline313]

Originally Posted by PunchT37

You can prolly tune some more power into that engine.

But, the original question, on a 400, the 6x 4’s are not going to make enough compression to run the larger cams. Money for porting, valves, guides, etc is going to be the same as new heads. Wait for some 72cc aluminum heads.

OK I wasn't familiar with machine shop prices. So when looking for aluminum heads go for 72cc and not 87?
I hate having a pretty turd lol

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[steve25]

Yes, if your short block is staying stock as I assume it is now then wait for the 72 cc heads.

Also if your Cam is stock then during the head swap would be the time to change to one with no more then 221 @ .050” duration and with at least .470” lift.
Plan on rejetting the Carb with these two changes.

Also you did not mention ( and this is a big one) in your first post if your MSD HEI has vacuum advance.
If it does not, or if you do not have it hooked up to provide at least 8 to 12 degrees of additional timing off idle then that will be a big lost source of part throttle power below 3000 rpm!

What rear gears does the car have might I ask?

[Jay S]

For the way the car is set up with the 4 link out back, if you want to come off the line a lot harder it appears like you could use a lot more converter. Likely would not even need a change on the engine. The Hughes are usually pretty loose for the stall speed compared to other higher end converters. I know this wasn’t the question that was asked but you could move up to a 4000+ stall from PTC, Dynamic, UCC, or TSP and gain a ton of drivability and power off the line over the 2800 Hughes. Add the 72 cc E heads on to that and it would be really quick.

One of my cars I drive has a 4200 9.5” Dynamic 4200 stall with 4.10s and 295/65R15 M/T drag radials. Not geared a lot different than a 3.73 with a shorter tire. Driving it around you can’t tell it has a converter in it other than stock, but when you go full throttle the tach rockets to 4200 rpm and it gets up and goes.

Sounds like you might not know enough about the engine to do a proper converter set up, the more details the closer they can come to a home run setting it up. But they can likely get it a lot closer than what you have. I have a number of cars with high stalls, I have never regretted spend the $$ for quality converters. To me Hughes are a budget converter, they are ok, but leave a lot to be desired, especially on the bigger stalls.

[PunchT37]

Originally Posted by Vckline313

OK I wasn't familiar with machine shop prices. So when looking for aluminum heads go for 72cc and not 87?
I hate having a pretty turd lol

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If you leave it a 400, then use 72cc. Common 4.25 stroker, then 87cc. Although I use 72cc with a 20cc dish on a 463.

[78w72]

3.73 gears, 2800 stall....

just a suggestion but 6x-4 heads can be milled to get to 9-9.5 compression pretty easily. that would help with a bigger cam & since you dont know for sure what cam is in there, maybe consider doing a cam swap & having the heads milled & gasket matched or even mildly ported. that would be a lot cheaper than going to aluminum heads which would require a new cam anyways if you cant confirm what you have now.

& as mentioned the 5C heads are almost identical to the 6x, one test showed they flowed a tad more... confirm what version they are by looking under the boss on the side of the heads, might need to use a mirror to see it.

http://www.wallaceracing.com/head1.htm

if everything else is healthy on the engine & compression test is good, sure would be a lot cheaper to get the 5C or 6X up to around 9.5:1, could even consider a HR cam & still be less $ than alum heads.

car looks nice by the way, not my choice of wheels/tires though, & with that thin of sidewall it would ride much better on 15 or 17" with more sidewall.

[steve25]

Speaking of tires, how tall are those?
They could be taking your 3.73 rear gears down to below 3.55?

[mchell]

….putting aluminum heads on a poorly tuned engine is not going to solve your problem. Sounds like you’ve got some cumulative smaller issues that are killing the Performance. I’ve had low compression big cam combo’s that have run very very well..

Your problem is you have no idea what your working with. Unfortunately, trial and error will be necessary to sort it out, UNLESS you go hog wild and build your own combo. No guarantees there either.

Internet troubleshooters can only provide opinion. Without actually driving your car it’s impossible to guess what your issues may or may not be.

Seek out some friends or clubs near you that can actually put their eyes and ears on your car… might help

Good luck !

[67Fbird]

Just a recap of the basics here:
3.73 gears, 2800 stall good working/running 400 cid with no bottom end torque!
Too much cam, not enough compression or BOTH.

You don't need to replace half the engine to make it work but you MUST find out exactly what you actually have in order to proceed with a plan.