I'd like to really discuss FI cams, because I plan to order one in the next month or so...

Let's kick around three issues...

A) Should turbo cams differ from supercharger cams?

B) Reverse split versus traditional split, let's see some data or some theories...

C) LSA, let's talk about cylinder filling and top end!

 

To be 100% honest john....just call up a cam grinder who has done a lot of turbo grind and be 200% honest with what the car will see and you'll be close.

Probably not what you wanted to hear but this is something you really dont want to be messing around with just a few people's "ideas." *shrug*

If anything...i would just suggest that you have some overlap in your cam to help with bleeding off some cylinder pressure and not having to worry too much about head gaskets

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Pro Stock John:
<strong>
A) Should turbo cams differ from supercharger cams?
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong>

Definitely - a turbo is going to have significant exhaust back-pressure - which will have a huge effect on how the exhaust valve flows.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"><strong>
B) Reverse split versus traditional split, let's see some data or some theories...

C) LSA, let's talk about cylinder filling and top end! </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">With a FI setup you really don't have to worry about your intake as much - you can get away with leaving the intake valve open a little longer also if you need to.

The main concern is evacuating the exhaust charge - to do this you need a good bit of exhaust duration - the problem comes when you start getting a good bit of overlap because of longer exhaust valve openings. When the car is making boost there really isn't any purpose at all to overlap, as manifold pressure will be more effective at getting the intake charge moving than any inertial "tuning". Problem is you can't reduce the exhaust side too much (to reduce overlap) or you start having problems evacuating all the exhaust. What camshaft works well is going to depend on the exhaust port on your heads and your boost levels primarily.

Chris

 

For what i have heard, you want the exhaust durration smaller then the intake. This will cause the exhaust to have greater velocity which will spin the turbo more effectivly..
So basicly your cramming air into the chamber, then is released quickly to cause exhaust velocity.

Right now i have a 224/224-114 .56x cam, this year or next im going to be switching to a 226/220-114 cam.
I will get comparitive dynos to see if the reverse split actually does what it was suppose to do.

The main reason i went with a 114 lsa over a 116 was to rev higher. Though my experiance turbos like high rpm, plus i get a little benifit of bleeding of some pressure up top.

I think Harlan went with a 112lsa specificly to releive midrange cylinder pressure (or something like that). He went with a 228/224 .540/ 112 LSA

Matt's making 700rwhp at around 15psi i'm making around 512rwhp at 10 psi. If i added 5 psi i'd probably be around 650rwhp, lower probably because his more efficiant twin set up and his more Agressive cam (we got dynoed on the same mustang dyno). Oh yea and he gots mad tuning skillz too.

<small>[ February 07, 2003, 05:46 AM: Message edited by: smokinHawk ]</small>

 

I am taking a different angle on this. I put 12,000 miles on my car every summer, so I wasn't as interested in the 7000 rpm power. I picked up the Lingenfelter cam that they are using in their twin turbo vette. It is 207/220 .573/.580 117.5.

Their grind makes sense from a laymens standpoint. You don't need big intake duration because the intake is under pressure (you are not counting on the piston to pull vaccuum to pull air in), and the high LSA to prevent the charge from blowing through.

Hopefully it will be tuned by the end of March and I can get some good numbers on it.

-Geoff

 

I run a pretty nice sounding blower cam.
224/228 581/584 114

 

I'd call Cam Motion, they have done a ton of turbo cams. Turbo People are also good, but you don't get the specs with the cam. Some people like knowing the specs, but you can get them when degreeing it in.....found mine out that way. I had another cam from a big end company..Bennett Racing. It was along the same lines as this one. The intake opened a tad later.

The specs on both are kinda off the wall, not what I would think a turbo car would like.

 

Great comments guys.

Jimmy, why bother even typing that comment this is a discussion board DUH. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

What about supercharger LSA? Would 118 be better than 114?

I think that Harl's cam choice was more based on the fact that Dave Deel gave him a killer deal on a barely used cam. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

You can't look at LSA/Duration/ICL independently. They have to be thought out to work together.

You can't say that a 118 LSA is better than 114 LSA without knowing the duration.

What I do is -

Decide on a power goal

Decide on cubic inches and desired boost to reach desired HP.

Decide on intake/exhaust duration #'s I think I will need to reach desired HP #.

Choose LSA for minimal overlap

Choose ICL to make peak hp at desired RPM

All FI cams I would choose will be relatively short duration, so I run as much lift as possible with those lobes.

I do agree with what others have said about calling a cam company with your needs. Cam Motion has my vote.

 

I think as long as the cam valve timing has no overlap it's considered a good FI Cam. Typically a 114LSA 110ICL <220 Duration Cam. CompCam's tech said they preferred more Intake Duration for a Turbo. But look at what LPE is using.. Hard to go wrong either way. Everyone will say avoid overlap.

 

Not "everyone"

There are 2 ways of thinking about turbo cams. Let me go find the link that explains both and why

One in particular friend has a huge solid roller in his TT 427 vette and makes 1200hp on pump gas with a decent amount of overlap

here's his link:
www.montygwilliams.com

i'll be back with a few others

back...here:

http://www.thirdgen.org/techbb2/show...ighlight=turbo

<small>[ February 08, 2003, 02:57 AM: Message edited by: JimmyKash ]</small>

 

I just got home from my Dyno shop a little while ago. We were tuning a new CAS single turbo on a 90 5.0 Mustang. His cam is a 220/220/not sure lift,(498/498) 110LSA. His numbers before turbo, 274rwhp,306rwtq. At 7#'s showing on PMS, and gauge he put down 408rwhp,451rwtq. Holy ****. I can't wait to get my car. My car has a 224/224 on a 112LSA. By the way he was set up for 6#'s. Is it true you lose boost on the dyno. On the street he was seeing 10#'s. He grneaded his 3rd gear on the way home from my shop. I went for a ride after it was dialed in and nearly **** my pants. It is a 5speed with 4.10's. What a rush. Angelo

<small>[ February 08, 2003, 03:15 AM: Message edited by: A DEE O ]</small>

 

I've read some of the guys mention that you pick up boost on the street, compared to the dyno, with a SC.

To me, that makes it even harder to tune.

 

No you pick up boost on the street with a turbo if you dynotune on a dynojet. (equiv to ~2800 pounds vehicle weight)
On a Mustang (Eddy Current) dyno you can simulate REAL world load on the car and get very accurate tuning as a result.

SC are rpm dependent on boost not load dependent.
Cheers,
Chris

 

Yes, some people choose to bleed off cylinder pressure at the lower rpms like Y2KHawk and I'm sure he could comment better than I. Most people don't want any overlap for boost under 12psi. Overlap is one of the more important things to keep in mind when choosing an FI cam. If you end up with overlap do it by design rather than by mistake.

 

i dont know much about cams but i do know that both turbo cams i've had chosen for me, the fist from more performance through comp, and the second from ARE through lunati (i think)

both were heavy on the exhaust side my current one is 224 226 .510 .523 115*

this is for all around sneakyness since i bought the tubo to make the power for me instead of getting all rackety with the cam.