I’m building a 296” flathead with Potvin super 3/8 cam. I’m thinking about using Manley Race Flo 1.6 for the intake and 1.5 for the exhaust. With the head .030 thinner that’s like getting free .030 more cam lift. The undercut stems seem like they would flow so much better. With the block fully ported, the biggest restriction on airflow are the stock valves and guides. What do you guys think?
Probably would work quite well/I have run larger and better flowing valves and every little bit of h.p. You are able to gather along the way will contribute to the overall performance/however, bear in mind that the large bore(3 3/8) and the longer stroke(4 1/8) will CONTRIBUTE heavily to how long the engine will continue to perform at peak power. The longer the stroke is a gr8 thing, but in the long run the HIGH piston speed will MAKE THE ENGINE NOT PERFORM AS STRONG IN AS LITTLE AS 10,000 miles. Many pistons only have three rings compared to pistons that have a 4th ring near the bottom. Yes, the 4th ring will contribute to the overall “drag” but the 4th ring also lessens the amount of piston ROCKING in the bore which will wear out the already large bore rather quickly if u drive lots of street miles.Bigger bore and stroke engines are gr8 fun, but their longevity is a constant battle to remain”strong”. I would rather build a 3 5/16 bore with a 4 in shaft(276) to get more wear than a large bore and a larger stroke. Flatheads Forever!!!
My builder used Manley hi-flow 1.6 in the exhaust and 1.65 titanium hi-flows in the intake. I also run the Potvin 3/8ths and have a 292 ci motor. Makes sense and why not use them to get the most flow you can.
The valves will certainly help the engine perform better as you noted by the improvement in port flow due to the undercut stem. An additional bonus is the reduction in gram weight compared to the stock valves. Less weight on the valve train will help reduce lifter and lobe wear. Plus increase top end RPM which is always a good thing . The Potvin 3/8's Super profile is a great choice as well. My experience running the 3/8 has been eye opening for sure. Ronnieroadster
I did a 110 mile round trip run this weekend. Averaged about 55 mph. Motor got approx. 11 mph with an Edelbrock Slingshot and two 97's. That Potvin is one hungry stick but I don't mind. When you smash the pedal to the floor, the motor responses immediately and the tires start to spin. Tons of fun. I didn't build it for economy. LOL!
Those valves are ok for a stock engine. They can be lightened considerably for longer life. They have 45 degree seats. That is not good for a performance flathead. 30 degree seats alone will improve flow 15% and last just as long. If you want more performance and longer valve train life, get friendly with a NASCAR or WORLD of OUTLAWS engine builder and buy some "take out" titanium valves from him. They change them out after X number of hours and they will last almost forever in a flathead. Be sure to specify ones that the head diameter will finish at 1.7". You will have to make guides for them but you should be doing that anyway. On that cam in a 296, I don't think you will be happy with it. It is not enough. Go to a 425 Potvin and use stock steel lifters. The idle on both cams is about the same, the off idle power is about the same but mid range on up is no comparison. I have run both grinds on the street and at Bonneville and had many of the engines on the dyno so have seen it first hand. I was also in the cam business for 74 years.
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