When you CC heads, how much variation did you find??

92rrrandall · Post by **92rrrandall** » Mon Mar 22, 2010 6:57 pm

Just wondering how much variation you find when CCing the 4.0/4.6 type heads??

The 4.0 has swept volume 444cc per cylinder. With 9.35 C/R, there would be 47.5cc of volume above the piston at TDC.

Just wondering how much variation you found in the 28cc combustion chambers.

Randall

sidecar · Post by **sidecar** » Mon Mar 22, 2010 7:38 pm

92rrrandall wrote:Just wondering how much variation you find when CCing the 4.0/4.6 type heads??

The 4.0 has swept volume 444cc per cylinder. With 9.35 C/R, there would be 47.5cc of volume above the piston at TDC.

Just wondering how much variation you found in the 28cc combustion chambers.

Randall

When I buretted my 36cc heads the biggest chamber was 30.5 cc and the smallest was 29.4cc (That was after a head skim). The 28cc heads are only 36cc heads with a factory skim anyway! My heads have been worked on by V8 Developments, I don't know if they equalized the chambers.

My heads were then skimmed again in order to remove another 4cc out of each chamber.

My piston dish volume plus the "down the bore at TDC" volume was around 32cc per cylinder. The head gaskets were 6cc

All of that lot sits on top of a 4.6 block. (568cc per cylinder)

I worked out that most of my cylinders are running at around 10:1 or just under.

Muscle-Manta and I buretted his heads recently, hopefully he will post up some info when he see's this thread. (His are also V8 Dev heads).

Hope that helps!

Pete

kiwicar · Post by **kiwicar** » Mon Mar 22, 2010 7:48 pm

Hi
I make 47.5 cc chamber on a 444cc swept volume equal to 10.34:1, (444+47.5)/ 47.5= 10.34.
As for variation, you should aim for all the same, ie none

+- .25cc is probably a usable range on a lightly tuned engine, but if you are using 10.34:1 target that gives you a range of 10.4 to 10.3 :1 which is really on the wide side if the engine is being tuned for maximum output (which if you are running 10.35:1 would be the type of engine you are building).
Part of the reason for being weary of this much variation is the reason it comes about. The reason being the variation in how far the valves are set back into the seats, resulting in the valves in the bigger volume chambers being further into the seats, this leads to more shrouding of the valve and less mixture getting into the cylinder when the valve is open lowering the effective CR further. You want all the cylinders to be as identicle as possable so you don't have to set it up the most demanding CR/VE combination and have the rest along for the ride.
Best regards
Mike

CastleMGBV8 · Post by **CastleMGBV8** » Mon Mar 22, 2010 9:40 pm

Randal,

Swept Vol of a 4.0 is 493cc. so you need to recalculate.

The critical numbers are piston bowl HC = 13.23cc comp gasket 8cc chamber supposed to be 28cc. deck height approx 5cc. These engines are not precision built and the tolerances can vary by quite a few thou and cc's

Interestingly those figures don't calculate to a CR of 9.35, nearer 10/1 so possibly the piston bowl volume figure may be incorrect.

Kevin.

92rrrandall · Post by **92rrrandall** » Mon Mar 22, 2010 10:48 pm

Thanks for your responses.

By knowing what the volume is above TDC, and also the variation in stock combustion chambers, you could decide if it is worth it to CC your heads. I just quickly divided 8 into 3552 to get 444cc. Then divided that by 9.35CR to get 47.5cc

The main thing that I am after is trying to determine if it is worth it to buy a burrette and go to the trouble of CCing.

The engine is in a mildly tuned TR8.

sidecar · Post by **sidecar** » Tue Mar 23, 2010 6:08 am

92rrrandall wrote:Thanks for your responses.

The main thing that I am after is trying to determine if it is worth it to buy a burrette and go to the trouble of CCing.

If you are going to raise the CR then I'd buy one, its cheaper than a set of pistons!

Also you would know for sure what the CR is. You might be surprised anyway as you can not trust Rovers figures!

DEVONMAN · Post by **DEVONMAN** » Tue Mar 23, 2010 10:15 am

92rrrandall wrote:Thanks for your responses.

By knowing what the volume is above TDC, and also the variation in stock combustion chambers, you could decide if it is worth it to CC your heads. I just quickly divided 8 into 3552 to get 444cc. Then divided that by 9.35CR to get 47.5cc

The main thing that I am after is trying to determine if it is worth it to buy a burrette and go to the trouble of CCing.

The engine is in a mildly tuned TR8.

Don't you mean 3952 divided by 8

kiwicar · Post by **kiwicar** » Tue Mar 23, 2010 10:40 am

Just to repeat Myself, Cr = (swept volume of cylinder + chamber volume)/ chamber volume, not, swept volume/ chamber volume. Likewise re-arranging the formula to calculate chamber volume from CR and swept volume gives then

Chamber volume = swept volume /(CR -1)

No matter how you measure it if you use the wrong formula you will have problems.
Best regards
Mike

SuperV8 · Post by **SuperV8** » Tue Mar 23, 2010 12:51 pm

I used a syringe from a pet shop, and an old number plate with the backing peeled off.

When i'm home i'll post up my results & variation.

I just did it to check the compression ratio wasn't too high after having top hat liners/ deck skim and head skim.

Easy enough to do. I'd recommend it if your engine is anything but standard just so you know what your playing with.

Tom.

92rrrandall · Post by **92rrrandall** » Tue Mar 23, 2010 2:47 pm

Yes, meant to type 3952cc. If ever I do calculate the actual CR, then will be sure to use the correct equation.

A baby formula bottle is accurate to about 5cc. Have used that to CC intake runners. But would use a proper burrette if going for zero variation in CR.

Based on your replys...will assume that exact volume varies by ~1%.

Randall

The V8 Owners Forum -

When you CC heads, how much variation did you find??

When you CC heads, how much variation did you find??

Re: When you CC heads, how much variation did you find??