Big Valves and porting?

[Gene F]

My car has the bigger valves, and the Stipe IB-330 higher lift cam. When you stop, and turn right onto a ramp and step on it you can feel the acceleration. Especially when going up a grade.

It's a choice Chris. Have you thought about going for a spin in one of your local club chapter members cars so you can see the difference? Granted you only need, or want to feel that difference at certain times. One of the guys in our club and I went for a spin in my car. I pulled over and put him in the drivers seat. At the first light he said "man you got some really good brakes on this A". I did tell him beforehand, but he was still surprised. My point is I'm a big try it before you buy it kinda guy whenever possible.

So what do you think Chris, got a buddy in your local chapter?

[GeneBob]

Brent, I was hoping this thread would peak your interest and thank you for adding some information. I am not trying to flow an engine for Bonneville, just looking for where the typical Model A port issues are to look for some improvement. I suspect there are some places to look at in the ports that are common problem areas.



Jim, I will look in your book. I frankly forgot to look there.


Thank you both you have valuable experience.

[BRENT in 10-uh-C]

Originally Posted by GeneBob

Brent, I was hoping this thread would peak your interest and thank you for adding some information. I am not trying to flow an engine for Bonneville, just looking for where the typical Model A port issues are to look for some improvement. I suspect there are some places to look at in the ports that are common problem areas.

Thank you. Gaining efficiency is like cooking, and everyone has their own recipe. The closest engine to the Model-A that has seen extensive R&D done is the 5 horse Briggs & Stratton engine used in both drag racing and tractor pulling. You might also follow that ‘circle’ to learn some tricks.

[nkaminar]

Exhaust scavenging depends more on the exhaust system than the exhaust valve. The exhaust pulse produced when the exhaust valve opens travels down the exhaust pipe at the speed of sound and reverses when it reaches the end to become a negative pulse traveling up the exhaust pipe to help suck out exhaust. The speed of the engine and the length of the exhaust pipe have to be matched to get this advantage. A diffusing cone at the end of the exhaust pipe will extend the rpm range where scavenging has an effect. Having equal length pipes that combine will allow each cylinder to reinforce the scavenging effect. You can see this on older race cars where the exhaust pipes combine and then there is a diffusing cone.

[BRENT in 10-uh-C]

Originally Posted by nkaminar

Exhaust scavenging depends more on the exhaust system than the exhaust valve. The exhaust pulse produced when the exhaust valve opens travels down the exhaust pipe at the speed of sound and reverses when it reaches the end to become a negative pulse traveling up the exhaust pipe to help suck out exhaust. The speed of the engine and the length of the exhaust pipe have to be matched to get this advantage. A diffusing cone at the end of the exhaust pipe will extend the rpm range where scavenging has an effect. Having equal length pipes that combine will allow each cylinder to reinforce the scavenging effect. You can see this on older race cars where the exhaust pipes combine and then there is a diffusing cone.

You are correct ...if you are quoting 20+ year ago technology. That outdated technology mindset also applies to surface finish on port work. Much has changed since then.