How does lobe separation affect the FI?
03-02-2002, 09:18 PM
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Car: Bee-Bowdy
Engine: blowd tree-fity
Transmission: sebin hunnerd
Axle/Gears: fo-tins
How does lobe separation affect the FI?
I'm swapping my cam out next week. In all my readings I learned that you don't want to go below 110* lobe separation. The cam I bought is fairly small (196/206 @ .050...431/.451) and it has 109* lobe separation.
I asked once before on the TBI board and got mostly "yes". I just want to double check with you fellas to make sure before I commit to this cam.
TIA
I asked once before on the TBI board and got mostly "yes". I just want to double check with you fellas to make sure before I commit to this cam.
TIA
03-02-2002, 10:21 PM
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I think the most important thing to be carefull of is that you don't get a cam that has very little vacuum at low rpm. This will drive the ecm crazy because the map sensor will make it think that the engine is running faster than it really is, or under a load when it isn't. Or something like that.
03-04-2002, 11:40 AM
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Car: '87 Camaro IROC-Z
Engine: 385 HSR
Transmission: 700R4
Axle/Gears: 3.42 posi
It's really the overlap that's what screws up the computer. Most cam manufacturer's don't advertise overlap, but it can be calculated from the duration and lobe separation numbers (I don't remember how though). The stock 305 "peanut" cam has an LSA of 109 degrees and it idled just fine, but with duration numbers of 178/194, the overlap was quite small compared to much-bigger cams.
03-04-2002, 05:13 PM
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Thats the cam I'm running. Its the same cam as the Ram Jet EFI crate engine, but i believe the RJ has 1.6:1 Rockers. I've got it in my PU with a 165 MAF TPI setup. It idles a little rougher than stock. It's runs good since I found this site and have tweeked the PROM (Thanks Guys!). The only issue I have with it right now is it is hard to start warm after sitting 10 or more minutes
. I'm working on that issue though.
. I'm working on that issue though.
03-04-2002, 10:23 PM
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Car: Bee-Bowdy
Engine: blowd tree-fity
Transmission: sebin hunnerd
Axle/Gears: fo-tins
Cool...thanks for all the input. A little rougher idle can be good considering my ride 
I was perusing desk top dyno once more and I saw that it calculates overlap. For reference I used the LT4 cam and the PowerMax/CompuCam 2031.
The 383 truck cam has -17* of overlap, the 2031 has -15 and the LT4 has -23.5. That puts me in the middle.
I was perusing desk top dyno once more and I saw that it calculates overlap. For reference I used the LT4 cam and the PowerMax/CompuCam 2031.
The 383 truck cam has -17* of overlap, the 2031 has -15 and the LT4 has -23.5. That puts me in the middle.
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