Camshaft gurus

[K5Glazier]

What is the diff. between 110* and 112* lobe separation. A performance shop is telling me that the lobe sep. is the one of the main factors in selecting a cam. I tend not to believe him b/c most cams listed in Comp Cams are 110* and he is trying to sell me one with 112*, but the one I had planned to get is 110*.
Thanks,
Joe

 

[sled_dog]

lobe seperation angle is the distant measured in degrees between the lobe centerlines on each of the cam lobes. The more lobe sepreration, the less valve overlap. Less valve overlap means a smoother idling engine, better low end power. What is the point of the motor? Rockcrawling? gonna use EFI? EFI prefers a bit more LSA.


here is something I found on a quick search, what I read quick seems like good info...

http://www.nightrider.com/biketech/camlsatable.htm

 

[K5Glazier]

Thanks for the link. The motor will be used for mild wheelin untill body damage starts to occur, but no rock crawler here. the motor is 454 TBI.
So, if I'm reading it correctly, the 112* would be considered a wide separation angle versus the 110* which would be the narrow sep. angle. Is this correct? If so, I would want the 112* for more low end torque.
It seems every parts store I've talked to all have diff. answers to the same question I asked each one.
Thanks,
Joe

 

[dyeager535]

EFI (especially the MAP you are running) is pretty picky about vacuum. You get a camshaft that is too radical, you screw up the stock calibration. Idle vacuum is where the problem is. You need a strong vacuum signal, and even then with a decent cam change, recalibration of the PROM is going to net the most gain.

I'm not that familiar with the big blocks, I know cam specs are typically far different than small block stuff, but 112* LSA is about as "low" as you commonly see recommended for SBC EFI stuff.

Some of the stock stuff I have seen is upwards of 116* LSA. I bet if you look at the "computer" ground cams, you'll see a wider LSA than the others, because the others are typically for carbed applications.

Check out Crane. When I was doing my searching, they had a MUCH better selection of cam profiles with a wide LSA.

 

[Russell]

Sounds like your performance shop knows what they are talking about!

With TBI, you want an LSA of 112, or possibly above. TBI is built for low end grunt, and needs the engine to idle smooth. Valve overlap has a very negative effect on EFI.

It essentially lets fresh air into the exhaust, which the 02 sensor picks up, and reports to the ECM as being an extremely lean mixture. The ECM then dumps more fuel in to compensate, but can never put enough fuel in to do so. This kind of extreme rich condition is really hard on an engine -- You'll get fuel vapour blowby on the rings, washed cylinder walls etc.

Also, a lumpy idle is seen as a stalling engine according to the ECM, so it'll often be running a stall saver algorithm, which is basically just increasing the rpm, then slowly lowering it again trying to reach the target idle, until it detects another "stalling" condition (loping engine) and starts the whole procedure again.

My 89 350 powered TBI truck has an older early 70s mid performance cam in it, and suffers from all the above symptoms -- So I am speaking form experience here, not just theoretics Needless to say, it'll be getting a cam with an LSA of 112 that is designed for a stock TBI 350 pretty quick here

 

[K5Glazier]

Good info here. Thanks. After more research, I'll probably go with a Comp Cam Here are the specs.
Intake lift- 0.485
Exhaust lift- 0.485
Duration at .05
intake- 210
exhaust- 220
lobe seperation- 112*
454 4bolt main, TBI, 049 heads, edelbrock intake and headers with a 3" exhaust.
Thanks for all the input.
Joe
Oh btw, does anyone know where to find stock cam specs for a '93 454?