PERFORMANCE CAMS FOR STOCK FI MOTORS

[So Cal Mark]

close to normal, slightly lumpy

[sptcoupe]

Mark - I have a header, 2 1/4" exhaust from header to rear resonator, no cat and a K&N on my 1981, othewrise stock FI engine. Is the stock compression enough to make the cams work? Thanks.

[So Cal Mark]

yes, that's a perfect combo for the cams.

[joshuagore]

We have any dyno numbers yet?
Do you raise the fuel pressure at all? Does anyone make a specific fpr for this car?

I have headers, 2.5in exhaust(yes I know overkill, but I wanted to build for potentially a boosted future), kn intake, and in the near future some intake work. I can bring the car more fuel through pressure, but want to make sure the injector duty cycle isn't near 90% before doing so, and make sure the car won't lean out if I run it richer?

The real question is whats the seat of the pants review on these cams? If its decent I will send some cores asap

Josh

[So Cal Mark]

what are the header specs? tube diameter and length? collector diameter?
Your stock injectors can only flow enough for about 6k rpm, so that should be a factor in your motor mods. The cams I've listed here are mid-range cams with reduced overlap, so they're matched to a stock FI systems operating range.

[joshuagore]

what are the header specs? tube diameter and length? collector diameter?
Your stock injectors can only flow enough for about 6k rpm, so that should be a factor in your motor mods. The cams I've listed here are mid-range cams with reduced overlap, so they're matched to a stock FI systems operating range.

Headers are IAP.. yes I know. Do you know if the stock injectors are low or high impedence?
Josh

[So Cal Mark]

what are IAS headers?

[pope]

I am sure he meant IAP.
Those are low-impedance injectors

[JFreeman]

Mark,

Several years back I rebuilt my original engine using high domed pistons. The FI system was left stock and needless to say I could not get the motor to run without serious pinging if it was stressed. A couple of years afterward, I did a second rebuild using a donor motor. I built this one up using the small dome pistons and installed the mild IAP cams. The engine has been sitting preserved on the engine stand for the past 3 years. I'm getting ready to pick up and start messing with the Spider once again with the first step being to swap out the engines. After reading about your reground cams here, I'm wondering if you can give some insight on using yours verses the mild IAP units. The Bosch FI system will be standard aside from a rising rate fuel regulator, but there has been some mild porting on the head. Manifolds will also be standard.

The reason I'm asking is that it would be far easier to replace the cams now verses waiting until I get the install completed.

Regards,

James

[So Cal Mark]

do you know what the specs are on the IAP cams?

[JFreeman]

These are the specs:

DOHC Performance Cam

Timing IN EX: 40-80 80-40
Lobe centers: 110° 110°
At Clearance: .016" .016"
Duration: 300°
Duration @ 0.050": 248°
Overlap: 80°
Lift: 10.35

Based on what has been written in other threads. it sounds like these might not be ideal, but I didn't know of the other performance mods would make the better suited.

[So Cal Mark]

you'll have trouble tuning the stock FI motor with those cams. Higher compression will help some, but you really need a programable FI to have the engine run well. If you use adjustable cam sprockets you can lessen the amount of overlap some, but if you're set on those cams I'd suggest only using the intake cam. A very free flowing exhaust will also help; that means a good header and exhaust with zero or very low back pressure

[JFreeman]

you'll have trouble tuning the stock FI motor with those cams. Higher compression will help some, but you really need a programable FI to have the engine run well. If you use adjustable cam sprockets you can lessen the amount of overlap some, but if you're set on those cams I'd suggest only using the intake cam. A very free flowing exhaust will also help; that means a good header and exhaust with zero or very low back pressure

I won't say that I am 'set' on using these cams. I do have the adjustable sprockets, but would prefer to use them to account/adjust for the machining of the head/block, etc. Using the intake only is an option that I had head about as well. How would a set of your cams run on the same motor? I can always sell the IAP ones - while they have been installed, they've never been run. I still have the old cams and can use them as cores if I were to buy yours.

[So Cal Mark]

my cams are milder,so you won't get the big lumpy idle, but will make peak power within the range of the stock FI. The 40-80 cams make power from about 3500-7000 rpm. Your stock FI is really only good to about 6k

[JFreeman]

Okay, that makes good sense. I remember that the Bosch L-Jet gets to the point where the injector pulses hit the ceiling around there. A rising rate regulator will help some, but even with pressure increases, there is only so much fuel you can cram through them. I'll probably be ordering set from you in the not-to-distant future.