Cam Question

[SCOOBY DOO]

At what ET/MPH does cam selection become critical?

 

[20psiofevil]

I kind of understand your ? but not certain. To me cam selection is very important piece of the puzzle and if you're like me I like to spend money once. Yes my engine is a ford v6 but very similar in displacement as the 109 and since everything from the hg down is basically an air pump the top end is where power is made.

I may be speaking out of my ass here but why does most people with a turbo buick run such small camshafts? Say if someone put a 218/218 cam in a stock head engine, bigger ar housing, and spin the motor to 6200rpm. Would the stock cylinder heads not support the flow in higher rpm? Wouldn't the engine make more power on lower boost?

I have heard this before from a guy who went big on his cam and made over 800rwhp on 25psi on a ford 4.2l v6 with older style heads that do not flow as well as the new split port style, "if the heads don't flow good hold the valves open longer" or something like that. lol And that thinking outside the box worked.

 

[Sydwyndr]

Cam selection has alot to do with how many RPMs your going to turn the engine and its main use.... is it a street car?? Race car??

 

[SS/GN]

If you keep RPM s low and power down low you usually have less parts breakage. More RPM = more maintenance

 

[bison]

The cam lobes and timing becomes critical when you want to squeeze out as much as possible out of the least. It doesn't means chit if you're going to "line up the dots". I can look at a bunch of lobes and tell which ones will make more power potentially with other supporting parts and which ones will be turds though neither is guaranteed to make more power or guaranteed to hurt power.

 

[bison]

If you keep RPM s low and power down low you usually have less parts breakage. More RPM = more maintenance

Not really

 

[bison]

"if the heads don't flow good hold the valves open longer" or something like that. lol And that thinking outside the box worked.

If the person making that statement didn't mention the exhaust pressure or valve open close events he is speaking out his ass for sure. Great flowing heads or garbage flowing heads won't matter if the ex pressure is high. Running more overlap at that point will hurt you and the engine will have increased pumping losses. So closing the valves earlier and reducing overlap will actually increase power.

 

[Nick Micale]

...........I may be speaking out of my ass here but why does most people with a turbo buick run such small camshafts? Say if someone put a 218/218 cam in a stock head engine, bigger ar housing, and spin the motor to 6200rpm. Would the stock cylinder heads not support the flow in higher rpm? Wouldn't the engine make more power on lower boost?......................

Unlike most Ford's and other non-boosted engines, an aggressive cam grind is not a "magic stick" for more HP in a stock or slightly modified Buick V-6?

This has been shown many time with a stock, un-opened engine which develops over 500 HP with basic bolt-on's.

Like Bison stated, unless you are building a competition or class engine for max HP with specific rules a cam with extreme duration is usually not needed especially is street applications.

When you have experience with a few hundred different turbo Buick engines and cams, your input would be different, as that is where Bison and I have been to obtain our information.

Everyone has opinions which is fine, but that is no substitute for actual experience and data.

 

[20psiofevil]

If the person making that statement didn't mention the exhaust pressure or valve open close events he is speaking out his ass for sure. Great flowing heads or garbage flowing heads won't matter if the ex pressure is high. Running more overlap at that point will hurt you and the engine will have increased pumping losses. So closing the valves earlier and reducing overlap will actually increase power.

It was something said in passing not in technical format. I do know the duration @ 500 was in the 240's, solid cam, bullseye racecover turbo with huge ar. Bp was very minimal is my guess. I was just basically wondering why there aren't many 109s trying to make power with rpm or create conversation on this topic.

 

[bison]

It was something said in passing not in technical format. I do know the duration @ 500 was in the 240's, solid cam, bullseye racecover turbo with huge ar. Bp was very minimal is my guess. I was just basically wondering why there aren't many 109s trying to make power with rpm or create conversation on this topic.

There are a few. Most are running the small 3 bolt ex housing which limits turbine selection and limits the useful rpm potential because the backpressure is too high. The few that fly on the 3 bolts have figured out how to keep backpressure in check. It's as big of a part of the equation as the boost. Going with more turbine and compressor will open the potential up a lot if backpressure can be kept under 1.5:1. The compressor cover becomes a problem in some applications also and can increase backpressure itself.