Blade

I can't seem the be making the power I was expecting out of this engine and I think it's the cam that mismatched to my setup. Here's the specs on the cam...

Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110)

I have a basically stock TPI that I gasket matched. The heads have been ported and polished and Edelbrock headers bolted on. I think the engine makes about 275-285 horsepower right now. Reason I'm saying is, because I can barely outaccelerate a stock 95 LT1 Formula. Maybe I'll be two or three cars ahead of it by 140 mph and almost neck in neck in the quarter mile. My best G-Tech so far is a 14.4 at 102 mph which blows. I think the car can do that with the stock engine. Do you guys think I have too much cam for my engine ? I bought this cam after one of the board members suggested it would be good for my setup... Doesnt look like it though.

[This message has been edited by Blade (edited October 29, 2000).]

CamaroZ_85

im no expert on compuers but that doesnt sound like a very computer friendly cam...do you have a custom chip?? dont feel bad on my carbed 350 w/ comp xtreme 218/224 .462/.469 i ran a 15.2 my first (and only) time out...i do have trans problems (1-2 shift takes painfully long...and i think i screwed up the band) and it not totally tuned right but i was still very dissapointed as a guy i work with ran his bronco that night and got a 15.2....

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350, Comp 262, Edelbrock Performer intake 600 cfm carb and exhaust, headers

D_Amlee

I don't see a huge mismatch there. That cam is close to what I'm going to be putting in my IROC this winter. If those are Edelbrock TES headers, the tube diameter is typically 1-5/8, which may be a tad undersize for the cam, but not by much. You are correct, with that cam, good headers, and ported heads you ought to be turning much better numbers. Your stock TPI base may be holding you back some, but a good gasket match job ought to at least keep it from killing your air flow too badly. The big topic for discussion here is what is your chip doing? What is your fuel curve like? If you are running a stock chip and a stock fuel pressure regulator, then we have found your problem. With all the modifications you have done to the motor, it is inhaling a lot more air than before. The fuel pressure definitely needs to be increased in order to match the air supply. Also, with the more aggressive cam profile it is very probable that you may need to change your spark curve, which indicates either modifications to the computer chip, or increasing your base ignition timing. I would say that you need to do some testing with the car to see if it behaves better under different fuel/advance conditions. I have seen guys drop two full seconds off of their quarter mile time just by taking a motor and tuning it up well in those two areas.

Vader

Blade,

A 110° LSA is never really "friendly" to a stock PROM. It can be even worse with a speed-density system, since way too much is dependent upon manifold pressure/vacuum.

I try to suggest higher separation angle for TPI cars, which is why I like the idea of using the LT1 cams from Comp and drive the timing pin to the correct depth. Th XR-266HR-14 has lifts of .500"/.510", durations of 210°/220°, and a LSA of 114°. The XR-276HR-14 has .510"/.510", 220°/230°, and STILL has an LSA of 114° to be "friendly to the stock ECM at lower RPMs.

Don't feel bad. I'm never satisfied with a cam selection. I either feel I've way over-cammed the engine, or if everything is running right, I didn't go quite far enough with the grind. You know how we are - we always want just a little bit more...

You might want to investigate a different PROM more suited to the kind of inputs you now have.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

Pablo

iTrader: (1)

that lobe sep isnt the easiest to tune for.. an lt4 hot cam may have bee na better choice

but you can still make this one work well just might take some more chip work its probably way off right now

remember, im the guy that ran a 15.5 with a big cammed, ported headed, single planed and every other bolt on .030 over 305
but persistance pays off its running alot better now
probably the same thing with yorus

Blade

Well I have the chip burning equipment (tuner cat, lots of spare chips, burner, eraser and laptop). For starters I tried giving it about 5 more degrees advance between 90-100 KPA (full throtle) on the timing map. Didnt see any difference. Tried it giving it less fuel. It slowed down... More fuel... I didnt see a difference. I guess I'm gonna have to take Bruce Plecan's advice and tune for the the right BLMs. As it stands right now my BLMs are low which I believe indicates a lean condition. I guess the chip is the only thing holding me back right now. I don't know about 2 seconds... but 5 tenths isnt unrealistic Thanx for the comments guys.

Jim85IROC

iTrader: (2)

What do you guys think about a 112lsa on a MAF car? I'm running a 214/224 .442/.465 112lsa hydraulic cam in my 355 TPI.

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RCR

Jim,
112 should be fine. Most of GMs roller replacement cams are 112.

Bob

sparks383iroc

Blade,

What were your 60' ft times? Your car is making enough power (102mph trap speed) to run in the mid 13's. Did it hook or spin on the line?

Sparks a flyin'

IROCZZ3

Also, maybe the cam was installed a couple of degrees advanced from '0'...did you degree the cam? Just something to think about...

Retarding it a couple of degrees from '0' will shift the powerband slightly higher but you may not see much of a difference...long tube runners are sensitive to cam timing and starve upper rpm airflow anyway.

IMHO, a ZZ3/4 cam would work better in a stock TPI setup like yours...I'm running a ZZ3 cam in my car. Anyway I think that cam will work ok for you, just keep on tuning it...good luck.

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1989 IROC-Z, ZZ3 shortblock with some bolt-ons.
13.20 @ 108.69, 2.2 60'

Blade

Well the 102 mph is on the G-Tech. We all know it's always a little on the high side. Best I ran was a 14.3 at 103 on the G-Tech on the street where traction is kind of a problem compared to the track. Heheh

I dont know maybe I have high expectations, but I was hoping for at least high 13s Maybe I need to tune the chip a little more. One thing I noticed is that when I take the intake tract off and leave the TB bare (no air filter or anything) I ALWAYS gain about 1-2 tenths on the g-tech. Damn that air intake must be restrictive. I wonder what a ram-air system would do for me.

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92 Z28 L98 350
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Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

vortecfcar

I'd say its a traction problem more than anything because a trap speed of 102 can support mid 13's without a problem

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91 RS W/carbed 350, Vortec heads, performer rpm, Comp cams Xtreme energy 280 grind. BFG Drag radials. 3.42 posi,Corvette servoed 700r4, ****ty stock converter
13.24@104

Yelofvr

With a stock TPI 350 Lingenfelter recommends no bigger than a 211/219@050 and a LSA of 112. Comp cams recommends a 210/220 w/ 112 LSA. Both recommend a chip reprogram. I am sure many "big" cam advocates will take issue with me, but I think you a cammed a little big for a stock TPI setup. These comments are based on Hyd roller grinds.... I beleive you have a roller motor?

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Dave Zelinka