[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.

[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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[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 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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[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.

[lust4speed]

Originally Posted by 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!...

Fully agree. Aluminum heads will reduce low RPM torque, and the more money spent on porting will make the problem worse. Hate to see people talk the OP into spending money on aluminum heads only to have less low RPM torque.

[PunchT37]

Originally Posted by lust4speed

Fully agree. Aluminum heads will reduce low RPM torque, and the more money spent on porting will make the problem worse. Hate to see people talk the OP into spending money on aluminum heads only to have less low RPM torque.

Gimme a break. How much port volume and cfm does my daily driver 5.3 have? I know it`s OBD2. But, it doesn`t have VVT.

[NeighborsComplaint]

KRE told me 12 weeks … that was 2 weeks back. No heads in stock.

[Vckline313]

Originally Posted by NeighborsComplaint

KRE told me 12 weeks … that was 2 weeks back. No heads in stock.

Are they taking pre-orders or will it be a fcfs basis when they stock

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[Dragncar]

Originally Posted by NeighborsComplaint

KRE told me 12 weeks … that was 2 weeks back. No heads in stock.

At least they are made here and you are not waiting for some container ship from CHYNA to be unloaded in Los Angeles.
Worth the wait for Made in the USA.

[78w72]

Originally Posted by lust4speed

Fully agree. Aluminum heads will reduce low RPM torque, and the more money spent on porting will make the problem worse. Hate to see people talk the OP into spending money on aluminum heads only to have less low RPM torque.

agreed. thats why i suggested milling the 5c or 6x he has now to up the comp to 9.5 with a good performance valve job & with the over $1k+ left compared to alum head price, changing the cam to match the comp, converter & gears. would be a better matched all around combo for street use.... & still have some $$ left over for other things or maybe some different wheels & tires?? no offense if he prefers them.

unless the plans are making a lot more HP that alum heads can support, the price doesnt really justify the performance gain, especially with an unknown cam, vs the cost of upgrading the 5c or 6x & picking a good HR or FT cam to match the rest of the combo.

again just a suggestion of a different way to increase power/tq based on the parts he has & spending less money than alum heads.