Turbo camshaft duration. Much more duration on the exhaust better?

[it's just a six]

Hey guys.

I am just curious as to what benefit you can get by adding more duration on the exhaust side as compared to running both the same duration on the intake & exhaust.

Having more exhaust duration, this will make the turbo spool up faster?

The camshaft I currently have has 240 degrees duration @ .050 intake & exhaust w/a lobe center of 116.

This one guy I am talking w/his specs are:
in 240deg @.050
ex 270deg@.050

valve lift i .640"
e 650"
lobe sep 112


I thought that is a big split & I was thinking that his camshaft would not work that good. His engine is only a 3.0 liter.

Thanks

 

[Nick Micale]

Sorry, you question cannot be answered as very LITTLE information is posted.

There are many factors that is needed for proper cam selection. Your entire build list and use of the car are all data points that must be considered.

A stock cam can easily run into the 10's, and even "exotic" cams are not needed into the 9's.

An easy way to select a cam is to find an owner with the same or similar build, and has the same performance as your expectations.

Every person that buys a cam, or has an engine built, will tell you "his cam is the best"! :biggrin:
[And so will some vendors?]

 

[87GN_70GS]

Typically, most turbo applications (across the sport, not just buick-specific) have the same duration pattern for int/exh and quite a few are even reverse pattern, with the intake getting more duration.

 

[it's just a six]

Thanks for that.

I am just asking in general, say you have a semi stock engine:wink: & you run a camshaft w/say 210 degrees duration on the intake & 220 - 230 degrees on the exhaust, will this type of cam help to spool up a turbo faster than if the duration were both the same?

Would this type of more duration on the exhaust camshaft make less peak power?

This is what I am thinking a cam with this type of slip would make a turbo spool up a bit quicker, but would ultimately not make as much high RPM power.

Maybe I am thinking incorrectly?

Thanks again.

 

[bison]

One thing I know is you better rethink that cam choice.

 

[it's just a six]

The cam I have is .600" lift 240 duration int. & ex. @ .050 on a 116 lobe center solid roller.

 

[LETHALV6]

I am assuming your friend is running a Supra ? There has been more than a few tests done on this reverse staggered setup and none made any more HP than a standard straight up 272 or 284 cam set (depending on the turbo setup) but these two motors couldnt be any more different in what they will accept cam wise.
I have been trying for weeks to find the cam card for the setup in my Buick, its an old style Crane Cam and has a fair amount of duration on the exhaust and a wide lobe seperation and even with a fairly tight 3500 stall converter the turbo spools like crazy.

 

[it's just a six]

His engine is a Australian 202ci holden inline 6 , 2 valves per cyl. 3.3 liter, I thought it was a 3.0:redface:

 

[bison]

The cam I have is .600" lift 240 duration int. & ex. @ .050 on a 116 lobe center solid roller.

That would be a typical production style head low lift cam for a Buick. Not many would want 240@.050 with only .600 lift. If that cam was ground with 116 ls it wouldn't complement too many applications either

 

[it's just a six]

That would be a typical production style head low lift cam for a Buick. Not many would want 240@.050 with only .600 lift. If that cam was ground with 116 ls it wouldn't complement too many applications either

My cyl head flows 320 cfm @ .600" lift. Would my cam work OK?

 

[bison]

You would want to run a lot more than .600 lift if you wanted to take advantage of that flow. The valve spends very little time at peak lift. You need a lot of rpm to take advantage of that flow potential. Looks like you have a lot if room for more cam if your heads are what you posted.

 

[it's just a six]

The cam I have I sorta got stuck w/those specs ordering it new & Isky did not have any specs I really liked & they would not sell me just a blank core, I will most likely have it reground w/less duration, it is for a street driven car.
Max RPM for engine is about 7500 RPM.

 

[bison]

The cam I have I sorta got stuck w/those specs ordering it new & Isky did not have any specs I really liked & they would not sell me just a blank core, I will most likely have it reground w/less duration, it is for a street driven car.
Max RPM for engine is about 7500 RPM.

If it's a 3 liter it will take more than 7500 to take advantage of those heads. It would depend on how light you can get the valvetrain and what spring you can get on there. If you have reasonable springs you can still cruise it but if you're looking to take advantage of those heads you will need sone really good valvetrain components.

 

[it's just a six]

Sorry for any confusion, the 240 is the cam I have & my engine is 254 CI.

If it's a 3 liter it will take more than 7500 to take advantage of those heads. It would depend on how light you can get the valvetrain and what spring you can get on there. If you have reasonable springs you can still cruise it but if you're looking to take advantage of those heads you will need sone really good valvetrain components.