heads with 42x37.5 valves

[Project_X]

Does anyone see a problem with running heads with these valves running them on like a combo of 74x85.5 or a 69x87?I can get the heads in standard bore, and also port and polishing is and option.Plus there in my price range if there ok to use?
If not, what kind of issues would I have?Its a daily driver, but I dont mind if its a high reving motor.

[Donny B.]

Not much room for that valve size with that small bore.  Why not 94s where you will have plenty of room for the valves and can unshroud them so they flow well.

[Project_X]

I dont understand how theres not much room, when 87's are smaller than 94's.

[Ohio Tom (DdK)]

Those "large" valves in a "small" bore will be badly "shrouded" by the cylinder walls. Basically, the valves are very close cyl walls and actually impede "tulip" flow around the valve.

Personally, if you really want to stay with small bore (small displacement), then those valve sizes are way to large, even for a race motor.

I have a 78 X 90.5 drag motor. It pulls past 8,200rpm. It only has 40 x 35.5 valve heads (with some serious port/chamber work).

The point is this: You can get alot more flow thru smaller valves than you may think. Spend your money on portwork and you'll be better off.

Just my opinion.

[Project_X]

ok gotcha, but why do they make the heads with that size valves for the 85.5 bore then if it is not good for them?Can the large valves be used on the larger stroked 85.5 bore motors?
Like say 76x85.5, 78x85.5 an so on?

[stealth67vw]

Your still gonna have the cylinder wall crowding the valves.

[Project_X]

ok lol i was just curious is all. By the way I was looking at the Mofoco 050 heads as a possibility. But I guess a set of there 043's with dual rev springs and a P&P will do.
On another note, can someone tell me what the point is in welding your heads?

[Bruce]

.... but why do they make the heads with that size valves for the 85.5 bore then if it is not good for them?

Because people buy them.

[stealth67vw]

.... but why do they make the heads with that size valves for the 85.5 bore then if it is not good for them?

Because people buy them.

People buy them and then bore them for 90.5/92 or 94s.

[Tobi/DFL]

ok gotcha, but why do they make the heads with that size valves for the 85.5 bore then if it is not good for them?Can the large valves be used on the larger stroked 85.5 bore motors?
Like say 76x85.5, 78x85.5 an so on?

...why do they sell chromed engine tins?

[javabug]

.... but why do they make the heads with that size valves for the 85.5 bore then if it is not good for them?

Because people buy them.

Lots of money to be made from the "Bigger is Better" crowd.

[Project_X]

.... but why do they make the heads with that size valves for the 85.5 bore then if it is not good for them?

Because people buy them.

Lots of money to be made from the "Bigger is Better" crowd.

i guess im a part of that crowd lol