The other day I was trying to calculate compression ratio and I called up Supertech to find out how much volume their B-series flat valves actually remove from the combustion chamber.

The guy on the phone said they remove 1.8cc total from each cylinder.

Does that seem high to anyone else??

 

I'm assuming that 1.8cc was the total reduction for 4 flat faced valves per cylinder? It does still seem slightly high. The only way to know for sure is to cc the combustion chamber. Even with flat faced valves, depending on the number of valve jobs the head had, they could still be sunk into the head to the point where the chamber would still be larger than advertised when stock.

 

Yeah I think I am just going to go ahead and cc it myself. I'll post up the results and my setup maybe it will help someone in the future. Thanks

 

No 2 chambers will measure the same from head to head with these valves ,there are so many things to take into account, seat heights, chamber volume, std is .1 to 1 cc different chamber volume on a B series Vtec head.

 

CCed the head:

Pr3 Head
.020" milled
Supertech Flat Valves

Volume = 42.0 cc


Will do a write up if anyone is interested.

 

I am interested in seeing how you CCed the head. A writeup would be awesome.

 

This is a perfect example of what most people miss. Everyone goes to the online compression calculators and says "my compression is 12.5:1 because I have a PR3 head...etc"

Then someone actually has their head cc'd and realises the combustion chamber is a lot larger than the online calculator suggests which can lower the compression ratio from where they thought it was, by quite a bit.

Online calculator says the combistion chamber size on a PR3 head is 42.7cc's. Here is a head that has flat faced valves installed AND .020" removed from the head and it's still at 42cc! I'd be willing to bet that when he started off when everything was stock, that combustion chamber would have been around 44 cc. This is why most people miscalculate thier ACTUAL compression ratios, they don't measure, they just add numbers out of the air.

 

I was just going to ask if he had CC'd the stock combustion chamber to actually see the volume differences. Those online compression calculators are an approximate guess at best. Only way to know for sure is to measure/CC your engine yourself.

 

omni was one of the few that said this from as far back as i can remember. online calculators should be used as a reference/rough estimate.

 

They're great for "estimating" and even better when you actually know the combustion chamber cc's and plug that number into the calculator. Hell I run a GSR head with .030" removed and flat faced exhaust valves (ITR intakes) and mine cc'd out to 42cc which is still larger than a so called stock combustion chamber on a GSR head. CC (Steve) did a little chamber work for me and some unshrouding which will increase CC size but if I didn't measure (like most people) I'd be running around telling people I had 12:1 compression when I actually have like 11.3:1.

 

Here is a mockup I did for the pic (note the overflow of grease into the chamber). B18C5 RM V1 CNC with Supertech flat face valves. Head was fresh from Honda before the headwork so no sunk valves from usage or previous valve jobs. I'm going to fab up a new plate that clamps to the head via bolts through the head stud holes. Takes way too long having to do it multiple times when you lose the seal.

 

Here's the write up




DIY Write Up - HOW TO CC YOUR COMBUSTION CHAMBER:

https://honda-tech.com/forums/showth...4#post43549694

 

Not worth the weight. Run the dished