What kind of cam do you want to run with a turbo motor?
More intake duration?
More exhaust duration?
Wide Lobe seperation angle?
Phillip

 

yes
no
yes
??

minimal overlap like a blower cam (I believe) and some people put more duration on the intake side. Harlan has with both his cams (228/224 and whatever solid cam he has).

 

Why would you run more duration on the intake? Doesn't the turbo cram the air in....I would think you need help gettin the air out....

 

You can't really just spec it like a blower (supercharger cam) - sure, you have positive manifold pressure in both, but with the blower you have a very small amount of backpressure - with the turbo you can have 20+psi of backpressure fairly easily. This makes a huge amount of difference in what happens in the overlap region, as well as what the exhaust flow does.

You really need to know, or at least be able to estimate what your backpressure to boost ratio is going to be if you are going to make any intellegent choice in cam selection. You can at least estimate this from your engine/exhaust/turbo setup - but without that there isn't alot you can tell.

 

This is what cammotion recommended for me.

dur. int226/exh218
lift. int574/exh564
lsa. 116
ICL. 113
They said to keep the exhaust duration short to keep the exhaust gas velocity up.

 

Thats an interesting point of view. My thoughs were to increase exhaust duration since your getting almost double the air into the motor and you have nothing helping get it out. Most turbo cars have alot of backpressure so IMO you would need more exhaust duration. I am probably wrong on this one but dont most of the turbo imports use longer duration on the exhaust side....
Phillip

 

I had Seth from Combonation Motorsport pick a cam out for me and my single t-76 setup
He came up with a 232-230 596 591 113lsa and +2 ground in advance
He asked me about all my specs from head flow to valves compression
He has a custom Cam sizing programme and came up with that cam profile
I'm running a 370 iron block with forged internals stage 2 abosolute speed 6.0l heads

 

That's interesting. I spec'd that identical cam, and had Cam Motion grind it for me about a month ago.

I've had 3 cams in my turbo car now.

214/222 114 lsa

The above listed 226/218 cam

And currently I'm using a 224/224 113LSA 111ICL on comp XE lobes.

 

I am running the Comp Xer 224/224 114lsa 110ICL w/.581 lift. I have been contemplating changing the cam..to something like a 227/224....why did you go with a 224/224??? It seems everytime I mention that I have a 224/224 cam in my car people want to say that is not a Turbo cam...yet I made killer power.

 

In my case, I was trying to shift my powerband up. I was only able to do that by increasing the overlap. It came at the cost of slightly more lag.


The current trend is to run a reverse split and alot of negative overlap. If you look at the valve events of the 226/218 cam, you will see that the exhaust valve is closed very early. I think this can help turbo response by keeping EGT's higher, but it will also have more high rpm pumping losses.

 

FWIW, my cam from cammotion is as follows.
238 @ .050 intake
232 @ .050 exhaust
.639 valve lift intake w/1.7 rockers
.627 valve lift exhaust w/1.7 rockers
115 LSA
.010 hot lash intake and exhaust
ground to make power from 3300-6800 RPM's.

 

How did you like that cam? Did it make good power with your setup?

 

I liked it. It made 740rwhp @21psi. That's the setup I had when it ran 10.9 @138.5, 1.9 60ft, 3,720lbs.

I have since changed to the 224/224 cam, and installed a sheetmetal intake at the same time, so no direct cam comparison. It made 760rwhp @19psi, and I've since built a new exhaust system so it will be on the dyno again soon.

 

I've been told by many to use a reverse split pattern cam with a turbo setup. This is what Comp Cams suggested for a turbo 6.0.

224/222 568/566 114

 

Rule of thumb, 5 to 10 degrees less exhaust than intake, and a 114+ LSA. There's more, but I'd get killed if I talked...

 

Rule of thumb- There is no rule of thumb

A camshaft is only valve events. Once the valve events are chosen, you will have your duration/icl/lsa. Should not be the other way around.

 

Very true, poor choice of words on my part...

Way too many variables, Head flow, int/ex ratios, boost, ECT...

That's the nice thing about turbos; you can make very nice power with a stock cam. But when you're looking for the last little bit...

 

I think that it's more important to look at the power goals, turbo size, and engine combo and then let that dictate the cam.

I think you could generalize and say that too much overlap could be inefficient and blow too much boost out the exhaust. You could also say that some overlap might be useful for scavenging the cylinders. I think you could also say that bigger cams make more power. I don't think that anyone would argue that a cam with 230 duration will potentially make a lot more power than a 218 duration cam as long as you don't have excessive overlap?

 

what do you guys think of lift?
like i have a .561 lift, what would happen if i raised it to .590 or something
would i have more power through the RPM range?

 

Lift should be dictated by how your heads work.

I went 230/236//115/+2 and it's around 600 lift since my heads are still doing almost 300 around then.