Some people are trying to convince me to get a new cam for the turbo setup and I guess $250 isn't too much to spend. I was going to use my zz-9 cam

212/226 112LSa .526/.520

Here's my second option if I get a new one.
221/218 114lsa .514 .526

How much horsepower do you think it would gain me say at 6-8 psi starting out, then 15 tops. Or am I better off just waiting until I get a bigger turbo(60-1 currently) and figure out what to do from there. Any opions are welcome, lets talk it up.

http://www.cmotorsports.com/engine/l...ft-design.html


[Modified by mn_vette, 7:49 PM 3/9/2004]

 

Curious why you are thinking you are looking at cams with more exhaust duration than intake?
Generally that is a indication that you are expecting less exhaust pressure than intake (ie, like a blower).

For a turbo that small, you are gonna see a TON of exhaust back pressure. I would be inclined to run a very small cam to compensate.

 

Because that's the best cam I've got lying around my garage right now that doesn't have tons of valve overlap. I guess I could go back to stock and see how that works.

 

Jordan, I know that you have been doing the turbo thing for a while now and I was hoping that you could give us (me) some basics on turbo cams. I understand cam basics, but when it comes to turbo's I think I am looking at it from the wrong angle. I thought that with all the air that is going in (ie. boost) you would have to compensate for it with a large exhaust valve and/or longer duration on the exhaust side. You have told me before this isn't necessarily right. There are several guys builing turbocharged sbc's right now, so I think a little cam 101 for turbos should take place. (Please) MN- I don't want to highjack your post, but hopefully we can all learn something here.

 

Honestly, I dont think ANYBODY (including some CAM EXPERTs/manufactures) really knows. The theory is this:

A turbo opereates (if properly setup) around 1:1 exhaust to intake pressure ratio. So the cylinder (in a way) doesnt see the boost the way it woudl if it was blown. So if you have a pretty close to 1:1, you want a single(ish) pattern cam. as the exhaust pressure goes up, you will need to take away exhaust duration(fluids flow more mass per unit volume when under higher pressure). Ie, in this case he is talking about a VERY mis-matched turbo, so his exhaust back pressures will probably be insane.

I would want little duration, and probably a reverse split

 

what do you mean by "single pattern" and "reverse split"

 

A single pattern cam has the same intake and exhaust duration. A reverse split would have more intake duration than exhaust.
Now my head hurts, I have to go think about this for awhile!


[Modified by ANTI VENOM, 2:02 PM 3/10/2004]

 

I just got done running a Desktop Dyno sim of the following two cams and here's what I found.

Cam 1: 212/226 112LSA
Cam 2: 221/221 114LSA

Very similar lifter values .54's

Not much difference, Cam 1 came out slightly ahead. I ran both of these cams N/A and With boost(just picked a random turbo and went from there) There doesn't seem to be a difference either way so I guess I'm going to stick with what I've got and hope it works out with the turbo. Should be a nice idle with as small of a cam as it is. :thumbs:

 

Ok, you can do lots of stuff with the cam. The most power will be had with an intake bias cam (reverse split) with a wide LS (114+). Reason being that turbo's make back pressure. Up to 30 psi in some applications. While normally considered a bad thing, back pressure has a couple benefits:

The most wear inducing part of the 4 stroke cycle is not the power stroke, it is the top of the exhaust stroke, when the piston changes direction with nothing to push it down. Back pressure, gives the piston an incentive to change direction. Nothing like the power stroke, but it's there none the less.

Lifting the heads, and popping head gaskets can become an issue with a high HP forced induction application. By narrowing the LS (112 for example), you allow reversion to occur at the mid range RPM's. Decreasing cylinder pressure, and helping to keep the head in place. With a 112 LS, you would probably see nearly identical peak numbers, but the mid range would produce less power. In the mid range of RPM's, the peak cylinder pressure is maintained for a physically longer amount of time. I.e. the power stroke takes .05 seconds at 3,000 RPM's, where it takes .003 seconds at 7,000 RPM's. Reducing the cylinder pressure in the mid range will help keep the heads in place. Gaskets, studs and other component's are more likely to accept a big load for .003 seconds than .05. See what I mean?

By narrowing the LS even more you start to allow more reversion at higher RPM's, effectively raising the power band.

Reversion also cools the combustion event, and can help prevent detonation. Something you may want to look at if you are running the stock compression ratio.

IMO, the stock cam would be the best bet for you. yous hould be able to reach the limits of detonation, or the limits of the bottom end by simply turning up the boost. The stock cam will provide great driveability, and good power udner boost. The semi wide LS, and equal intake and exhaust bias should work well with a turbo set-up.

My .02

 

Did I forget to mention that this is a 393 ci stroker with 9.5:1 compression. I'm pretty sure the stock cam isn't going to cut it. I know that I need some negative valve overlap because I am going to be getting some of those huge back pressure numbers just from the way that the piping is set up. I'm just worried about making things safe is going to totally kill the HP factor. And acording to desktop dyno my old cam should be up for the task. If it's accurate, I'm not 100% sure on that, but going to be close enought to get me to try it.

Here's a nice thread for you guys to read: (check out the cam)
http://www.turbomustangs.com/forums/...&threadid=5226


New and improved: (changed cam)
http://www.ls1speed.com/jim.cfm




[Modified by mn_vette, 3:47 PM 3/12/2004]

 

I believe that he is selling or sold that whole turbo set up. His new system will be twins I think. Keep us updated!