Is it worth Biggie Sizing Valves?

CobraSix

2K+
VIP
Is it worth oversizing? I know 68clunker told me that he got a noticable increase in power from going up to 1.75" intake valves. I'm going to be going with a cam that has a lift of .444" and an offy intake...so is oversizing really worth it? It will cost me abotu $150 more to oversize the intake valves.

Thanks for the help.

SLade
 
i would say yes. the head, carb, cam and exhaust must breath the same. since the head/intake suck!, the larger valves are better - much better. the largest valves you can go is 1.88I and 1.65E per the"falcon performance handbook. if you dont have it yet get it!!
 
If you don't spend some time cleaning up the ports and bowls as best you can, probably not. If you clean up the bowls, spend some time working on the ports, and cc the chambers, then it might be wrth the effort. Keep in mind you may have to rework the chambers a bit to unshroud the valves for the max benefit.
 
I've ported the exhausts and cleaned up the bowls...I've also CC'd the chambers and plan to mill the head by .060" since it has not been milled before.

Slade
 
8) as long as you dont go too big then larger valves are worth the cost. i would use a 1.75" intake and 1.50" exhaust valve. with the restricted breathing of our little sixes anything you can do to improve things helps.
 
8)

There was a link off of Mustang and Fords website about recommendations for building a 200 I6.

In that article the guy recommended staying with the stock 1.75" intake valves but using a stainless version with back cut head. The guy said that he has installed bigger valves IIRC up to 1.84" and there was no significant difference in airfow and he lost low end torque.

On the exhaust he said go for it. He went with a 1.55" stainless with back cut head and highly recommended the exhaust port divider. A good pocket porting on intake and full port and polish on exhaust was all he recommended.
 
Howdy Slade and All:

If you're already doing a performance valve job, then by all means go with the 1.75" intakes. The three angle valve job will make the biggest difference over the factory one angle seat and valve cut. Next in value would be to smooth the transitions from milled to cast surfaces in the valve pocket. Then, a 4th back cut angle on the port side of the intake valves. And then spend some time smoothing and polishing the chamber.

For your purposes, a 1.75" intake and a 1.38" exhaust is pretty good. This exhaust is 78% of the intake size, which is pretty good. Any larger size valves in an engine with a bore this small would see marginal returns and mainly at higher rpms and at highest lifts. With the 3.68" to 3.72" bore it is very difficult to realistically (in terms of money and value in return) get bigger than 1.75" intake and 1.5" exhaust.

For street and general use, we don't back cut the exhaust and leave the margin a little wider, at .100", to help with heat transfer to the head. We've used 144 1.467" intake valves as exhaust valves with good results, so far. We have shunned 1.5" chevy valves because of the extra machining required to get them to fit, and because of the small bore and inherent shrouding. Milling will help to unshroud, by dropping the valve a little deeper into the cylinder.

Cutting the head to accomodate a 1.75" intake is not a big deal and should not cost an additional $100.

Anlushac11- I'd sure like to know a source for a 1.75" small stem Stainless Steel valve to fit our sixes? Please let me know where to find it? I had heard that Clifford was getting stainless steel intake and exhaust in 1.88" and 1.50" from SSI, but have had no luck in finding since Eric parted with Clifford. If we could source these valves direct from SSI it may be a feesible option.

Adios, David
 
8)

Well so far I am finding that the Ford 2.3L OHC valves are very similar. I am getting ready to disassemble and port my 88 turbo head and as soon as I cant rent a sawzall and cut the exhaust pipe so I can get the head off the 200 I am gonna pull a intake and exhasut valve off of it. According to my Haynes book they are within oversize rebuild of each other. If I can use the 2.3L valves in the 200 head then I can get a 1.73" intake and a 1.55" exhaust for $12 each from Racer Walsh.

Other than that someone on here ordered some Manley valves for their 200 and IIRC they paid about $17 each.
 
Just referring back to Mark's comment on valve sizing. The 1.84" intake could lose flow in some situations. Valves this large were found on the later crossflow 200s and 250s.

This topic comes back to cam selection. If you are building the engine around the cam (the hard way, IMO), sure, you'll likely have a problem at some speeds. This is like building a house on an uncleared site. It will never be a perfect fit.

IF you choose to use a larger valve set, keeping that nominal I/E ratio, simply bench the head, and go to the cam grinder with the flow specs and RPM requirements. Of course, if it's way out of line, don't expect this to make a daily driver from a race head.

Remember, you are striving for a result that is "greater than the sum of the parts". There's no black magic. Plenty of performance engine builders will have the knack of porting/sizing based on experience. If you can trust yours, then the cam profiling approach mentioned will be the icing on the cake. A "production rebuild shop with a "ream it out, sling it together" approach will never get this one.

Regards, Adam.
 
Back
Top