1.6 intakes, 1.5 exhaust. Any merit?

[cuzncletus]

I'm just getting started on building the last flathead in my garage. It will be a .125 over 239 8ba at 258 c.i., L100 cam, dual intake, aluminum heads; in other words a pretty standard street flathead. Machining hasn't started yet except for having the crank turned/balancing.

My thoughts were using 1.6 intakes, 1.5 on the exhaust for valves. My reasoning is that it would give a little extra margin of metal between the exhaust seat and the bore where flatheads normally crack. I'm not sure the performance difference would be much but I'm also not sure how much insurance I'm buying myself. Either size valve and machining is the same cost. Comments from experienced builders, please?

[Bored&Stroked]

I can't see where it would make any difference at all. You'll have the same size hardened seat on both valves - just running a different size valve on one versus the other. It is not the hardened seats that crack anyway - it in the underlying cast iron block material that is around them. Going to the larger valve sizes won't make any difference either - given that you're running stock ports and nothing has really been done to increase the flow of the associated ports and bowl areas.

I'd run whatever you have available - using the highest quality valves in the process. Also, making sure that your particular machine shop really knows these engines, knows how to do a correct valve job and uses/has the correct valve equipment - THAT is the most important factor in the results you'll achieve.

Good luck!
B&S

[cuzncletus]

I forgot to post that I've gasket matched the intakes and done some minor clean up port work on both in and out sides. This has been minor, mostly cleaning up slag and opening up the exhausts to ease some of the hardest angles in the outboard ports. For machine work I'm using Dennis Hawkins in Pigeon Forge, Tenn. He is well versed in these engines, having them frequently in his shop. If I know him, he'll look at what I've messed up and won't be able to keep himself from going in with a stone to clean up my mistakes.

[JSeery]

On a mild engine such as you are building the 1.6 valves are of no value as far as flow goes.

[GOSFAST]

Originally Posted by cuzncletus

I'm just getting started on building the last flathead in my garage. It will be a .125 over 239 8ba at 258 c.i., L100 cam, dual intake, aluminum heads; in other words a pretty standard street flathead. Machining hasn't started yet except for having the crank turned/balancing.

My thoughts were using 1.6 intakes, 1.5 on the exhaust for valves. My reasoning is that it would give a little extra margin of metal between the exhaust seat and the bore where flatheads normally crack. I'm not sure the performance difference would be much but I'm also not sure how much insurance I'm buying myself. Either size valve and machining is the same cost. Comments from experienced builders, please?

Hi Pat, save your money and stay with the "standard" FH valve sizes. You'll gain nothing in the larger picture, been there and done it!

Use the "standard" lengths also, you'll avoid running into installed spring heights and pressure issues.

You'll probably wind up somewhere around 125/130 HP with a bit less Torque than a stroker would yield. With the same bore and a 4.250" arm we generally see 150/160 HP and 250/260 Torque on the dyno!

Thanks, Gary in N.Y.

P.S. I would strongly recommend the bronze-lined guides however, these eliminate any valve "hanging" issues during longer storage periods! We use and sell hundreds during any given year along with the stainless valves in a package.

[Ol' Ron]

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At one time I thought porting and increasing the valve size would improve the performance of a street engine, and most of the engines I built had these modifications. I then built an engine over the phone for Richard in Fla. Because he had never done anything like this, I told him to use 1.5 Cheavy valves in both intake and exhaust. These valves are longer and with the small base circle cam, keeps the lifters quite. A few years after the build i went to Fla nd drove the 53 HT, and was very impressed with the performance, he also got over 20 MPG. I do believe that for all out, high RPM engines this would be beneficial. We've been told for the past 70 years that this is necessary, but nobody has ever proved it.

[drolston]

Check what Flathead Jack has to say in his catalog regarding Power-Flow valves. 1.5 diameter, but the stem and underside of valve are shaved down to open the air passage. Not cheap at $16 per, but the theory is good. I also went with the cut down valve guides, again to clear the air passage. Engine runs great, but without before and after dyno test, it is impossible to quantify the performance benefit.

[GOSFAST]

Originally Posted by drolston

Check what Flathead Jack has to say in his catalog regarding Power-Flow valves. 1.5 diameter, but the stem and underside of valve are shaved down to open the air passage. Not cheap at $16 per, but the theory is good. I also went with the cut down valve guides, again to clear the air passage. Engine runs great, but without before and after dyno test, it is impossible to quantify the performance benefit.

Our 8.00 Stainless valves get the job done, same results.

These results are from our dyno testing, not "theory"!

Thanks, Gary in N.Y.

P.S. Am currently involved in a number of "mismatched" parts supplied by my customer for his own build, these were recommended and supplied by a major player in the Flathead parts business. I have a valve AND spring combo here that will be way above 100# seat pressures if we were to try to use them?? They also recommended some "aluminum" valve spring retainers, Crane stopped mfg these things some 40+ years ago??

[tubman]

I think we all know "Flathead Jack" will "Not be Oversold".