cam specs
Thread Starter
Member
Joined: May 2005
Posts: 114
Likes: 0
From: Ooltewah, TN
Car: 87 camaro, 98 Z-28
cam specs
What do ya'll think?
XR270HR roller cam
218/224 duration
494/502 lift @ 110
That should sound pretty good and give me some good mid to upper RPM power.
XR270HR roller cam
218/224 duration
494/502 lift @ 110
That should sound pretty good and give me some good mid to upper RPM power.
Supreme Member
Joined: Jul 1999
Posts: 18,457
Likes: 16
From: Loveland, OH, US
Car: 4
Engine: 6
Transmission: 5
For what?
That's about the MAXIMUM POSSIBLE CAM for a stock L98, where it won't go slower than stock. TPI doesn't take kindly to being over-cammed. It uses acoustic tuning (the "T" in TPI), such that the pressure wave (sound wave) created by the intake valve closing event of one cyl in the firing order, reinforces the cyl fill of the next cyl in the firing order. The length of the runners was chosen carefully to produce a peak in this effect, at about 3600 RPM. The downside is, at any RPM above about 1.5 times the peak reinforcement, the pressure wave INTERFERES DESTRUCTIVELY (tends to cancel out) with the next cyl's fill; meaning, the designers gave up ANY POSSIBILITY of power above 4500 RPM, in exchange for the "boost" at 3600 RPM. As Steve McQueen said, "It seemed like a good idea at the time". Anything you do with TPI, you need to understand that compromise, and how to either alter it or work within it. If you want higher RPM power, you do things like siamese the runners, shorten the runners, etc., which REDUCE that 3600 RPM peak, and also reduce the higher RPM penalty; if you want to run the stock stuff, you need to pick parts that work WITH the design, i.e. run a cam that puts the peak of its torque band near 3600 RPM
It's too much for a 305 TPI. The one right below it is about as far as you'd want to go.
It's not really enough cam for a carbed 350, unless you're running a computer-controlled Q-Jet and passing CA emissions. Which I don't think is an issue in E TN.
Be certain that you use the recommeded valve springs!!! No excuses, no substitutes, no "I'll get around to it". Stock ones will not work, certainly not for more than a couple of hours of operation; and may cause instant parts failure the first time you crank it up. They will also void the warranty on the cam.
That's about the MAXIMUM POSSIBLE CAM for a stock L98, where it won't go slower than stock. TPI doesn't take kindly to being over-cammed. It uses acoustic tuning (the "T" in TPI), such that the pressure wave (sound wave) created by the intake valve closing event of one cyl in the firing order, reinforces the cyl fill of the next cyl in the firing order. The length of the runners was chosen carefully to produce a peak in this effect, at about 3600 RPM. The downside is, at any RPM above about 1.5 times the peak reinforcement, the pressure wave INTERFERES DESTRUCTIVELY (tends to cancel out) with the next cyl's fill; meaning, the designers gave up ANY POSSIBILITY of power above 4500 RPM, in exchange for the "boost" at 3600 RPM. As Steve McQueen said, "It seemed like a good idea at the time". Anything you do with TPI, you need to understand that compromise, and how to either alter it or work within it. If you want higher RPM power, you do things like siamese the runners, shorten the runners, etc., which REDUCE that 3600 RPM peak, and also reduce the higher RPM penalty; if you want to run the stock stuff, you need to pick parts that work WITH the design, i.e. run a cam that puts the peak of its torque band near 3600 RPM
It's too much for a 305 TPI. The one right below it is about as far as you'd want to go.
It's not really enough cam for a carbed 350, unless you're running a computer-controlled Q-Jet and passing CA emissions. Which I don't think is an issue in E TN.
Be certain that you use the recommeded valve springs!!! No excuses, no substitutes, no "I'll get around to it". Stock ones will not work, certainly not for more than a couple of hours of operation; and may cause instant parts failure the first time you crank it up. They will also void the warranty on the cam.
Thread Starter
Member
Joined: May 2005
Posts: 114
Likes: 0
From: Ooltewah, TN
Car: 87 camaro, 98 Z-28
I'm running a the original 1987 305 roller motor with a Edelbrock 4bll, long tube headers, y-pipe, Dynatech 3" powercat and 3" american thunder cat-back exhaust, it has an edelbrock performer intake, mallory HEI billet distributor, taylor wires, etc... I'm using the recommended valve springs and retainers from comp cams on this set-up, also the heads will be shaved, ported and polished, all new bearings and seals, roller timing set, etc..
the tranny is a T-56 6-speed and gears are 3.73's through a posi
That cam should pull good on a non-computer controlled roller motor should'nt it? I removed the factory quad and all the wiring to run the old style set-up
the tranny is a T-56 6-speed and gears are 3.73's through a posi
That cam should pull good on a non-computer controlled roller motor should'nt it? I removed the factory quad and all the wiring to run the old style set-up
Thread
Thread Starter
Forum
Replies
Last Post
