For you 351C fans....turn up the volume!!!

[eschaider]

I didn't know you were funning me, Brent. I took it at face value and it blew me away. I know how hard I fight for low speed torque and, well, I was wowed.

I owe you one


Ed

[olddog]

Brent,

I heard it claimed that there is nothing you can do to improve the flow on the 4V Cleveland intake port, as it already flows more air than a 351 engine can suck in. You can debate that, but the point is it is already one very good head.

That said the exhaust port has undergone many modifications by racers over the years. So we know the exhaust port has room for improvement. In fact, it is the bottle neck or handy cap of the 4V Cleveland.

So let's talk cams a bit. Back in the day, I don't recall ever seeing more than a degree or two difference in intake and exhaust duration for any engine. Today it is quite common to see more duration on the exhaust. Typically 6 deg split range. I think the Clevland 4V needs very little duration on the intake compared to the exhaust side. Perhaps 220 -225 on the intake and 235-240 on the exhaust.

I know the 4 valve modular 4.6 ltr can make 400 Hp with only 228 deg durration @ 0.050 at about 7K rpm, with a relatively flat torque curve because the heads flow so good. Take that to the intake side of the 4V Cleveland which also flows well, and my theory is that everyone runs too much cam for the intake port.

So if you are playing with a dyno mule, I sure am curious what such a cam would do.

[olddog]

Let me further expand on my Huge ports require less duration theory. Out of curiosity I was looking over Diesel designs. We all talk about getting away with running more compression with long duration cams do to the dynamic compression being lower than the static compression. Well the Diesel engine cannot start if the dynamic compression is to low, as the lack of compression will not get the air hot enough to light the fuel. So Diesel engines cannot allow the intake valve to stay open much past BDC. Running turbo chargers at high pressures limits valve overlap. So today's typical Diesel has an intake duration of 175 deg @ 0.050. The aftermarket performance cams are not going over 180.

Now these are huge port low duration engines, but they are still able to rev to 4000 rpm and make good torque.

I have also noticed over the years that big block gasoline engines in dump trucks tended to go the same way. These engines run out of torque by mid rpm, but I'm not sure if it is the cam or if they are limited by the carb size. I know they purposely limit high rpm high power in favor of low rpm torque, but I also believe they want to limit power to keep the heat down. A truck could work hard long enough to melt it.

On a poor flowing head the cylinder is not full at DBC and leaving the valve open longer allows air to continue to fill the cylinder. At higher rpm this really pays off. However ports that flow well are getting the cylinder full and leaving the valve open too long is just pushing the air back out of the cylinder, as it was already full. So my theory is to leave the valve open no longer than necessary to fill the cylinder at the desired peak torque rpm. If that is around 5500 rpm, a good flowing head does not need a radical cam.

[blykins]

A 351C 4V intake port can be improved. We can pick them up 40 cfm with just some short side work and it will pick the power up on a 351.

The exhaust side stinks in comparison and work needs to be done there.

I specialize in Clevelands and have spent years trying different cams. A stock 4V head needs a cam with 8-10 degree split and a tight LSA. Too much split is a waste of overlap.

On this particular build, I had a custom cam grinder offer to grind me a camshaft for it and if it didn't make more horsepower than the cam I had chosen, I could send it back to him. I gave him every spec of the engine including flow numbers, rod lengths, you name it, INCLUDING the cam specs that I had chosen.

His cam made 587 hp. Mine made 615.

His cam had 17 degrees split between intake and exhaust. Mine has 8.

His selling point was that the exhaust side is so poor that it needs a ton of extra duration and that he was confident that his cam would make 30 hp more than mine.

[olddog]

Well it sounds like the cam grinder is thinking along the same lines as me. Obviously you proved that wrong.

However you are going for way more power in the upper rpm range, where I would not go. I know you don't like to pull bellow 3500 or so. Have you ever played with trying to get a good street engine that pulls from about 2000 and peaks around 5500? The Cleveland is said to be gutless down low. I suspect the right cam would go a long way to making up for the over-sized intake port and still pull strong to at least 6000.

[blykins]

Sure, I've built a lot of street Clevelands that peak at 5500-6000, from stock stroke to 4" stroke.

The same cam specs come into play and you use the exhaust side to help the low velocity intake side.

Pulling an engine down to 2000 on the dyno is a no-no though and doesn't really prove anything as far as engine specs go.

[Mark O'Neal]

Originally Posted by blykins

This is a stock stroke, factory headed, custom 351C engine that I dyno'd this past week. 615 hp @ 8000....



https://www.youtube.com/watch?v=lIpAUnqZmKw

That carburetor is SLEEK!...

[blykins]

Glad to see you somewhere else besides Speedtalk, Mark.......

BTW, that's one of those new fangled carbs. Don't you see the 3 venturis at the top?

[undy]

That's one of the shared venture carbs, a Holley DCOE side-drafter...

[YerDugliness]

Originally Posted by blykins

...it's easy to crank out 427-460 inch Clevors that make over 700 hp on pump gas.

Now THAT'S what I'm talking about! I have always wanted to try a 427 CID Clevor, since my body style is the 427 model.

I'm hoping to make it to a 289 body style at some point...but I'd still really like a Clevor, even if it is a small block motor.

Cheers!

Dugly