No vacuum advance on new engine?

[jjzepplin]

I always go a different route. I custom curve each distributor to the vehicle. Once done correctly it will be "tuned" to the specific vehicles weight and transmission as well as tire size and the fuel you will be running in said vehicle. Never fails. But witha new engine under warranty I would do exactly as they say should it fail you want the warranty.

[Fitz]

Originally Posted by geezer#99

Fitz! Fitz! Fitz!!
Guilty of only one thing.
With some people you need to be very specific what you write.
I failed on that!
He didn't get a dizzy, but you did.
You get a roller cam in that little motor?

Roller cam & roller rockers.

[1972BlueC20]

So if I go with the 290 hp crate, do you think I'll be happy with it? Its just a daily driver, but I like to romp on it from time to time. I got a rebuilt th350 with mild shift kit and 4.11 gears.

What are the downsides of being "slightly" over cammed?

[Fitz]

Originally Posted by 1972BlueC20

So if I go with the 290 hp crate, do you think I'll be happy with it? Its just a daily driver, but I like to romp on it from time to time. I got a rebuilt th350 with mild shift kit and 4.11 gears.

What are the downsides of being "slightly" over cammed?

"slightly overcammed"? I really don't know what that means, but, duration overlap and lift determine how much of a charge you can get into and out of the cylinders. So, for a suck, squeeze, bang, blow (4 cycle) engine the cam increases the suck and the blow. A bit more of both means more response to the throttle and a slight drop in mileage. Since this truck is a daily driver, go for it. Mileage will drop from somewhere near 14 mpg to 12 or so but that's a pretty small penalty.

[1972BlueC20]

Well I don't know what that means either, a few others stated the 290hp engine has a cam that's a little much for the engine. Whatever that means. I know nothing about cams. I just want a good engine with plenty of power. I can buy pretty much any engine below $3k so I just want to make sure I make the right decision.

[turp mcspray]

The cam was designed for much more compression. Like 10.0. So installing it in an 8.0 motor is far from ideal, and thus the statement of being overcammed. It will work, but will never see its full potential. I would also run as much initial as it will take, and shoot for the 36-38 degree total range.
Most GM crate engines are all built on the conservative side, small cams and low compression, along with low timing figures for many miles of trouble free service. All of which comes
at the cost of power.

[tdangle]

Bringing this post back from the dead. I just installed a GM crate engine SP350/357 and don't think its right on a street driven engine for no vac advance. Its just a L31 with a little more cam, what have you all found about timing and vac advance on these vortec roller cam block motors?

[Mike C]

Vacuum advance has been utilized in two different manners over the years. On early cars, it adds timing at part throttle operation (cruising) to improve fuel economy. It was used to add total timing during the emissions strangled years of the HEI.

I would set my distributor up with the vac advance. You still want to limit total timing with most of these small cam crate motors to 36 degrees or so, but add in vac advance through a MANIFOLD source to improve economy and steady state operation.

At WOT with the manifold vac source you aren't adding any advance anyhow since vacuum is near zero with the pedal to the metal.

It becomes a concern when the end user does not understand how or why vac advance is used and is incapable of adjusting it properly. Crane cams offers a limiter for the vac advance so you can tune it for how much it adds on top of the initial and mechanical advances. Shoot for around 48-50 degrees of total advance at light, steady state throttle.

[garyd1961]

My MSD distributor doesn't have vacuum advance. It does have bushings that limit mechanical advance. What I did was to put a bushing to limit my mechanical advance to 16 or 18 degrees (don't remember exactly) then I could up my initial timing. I also installed lighter springs so my total timing comes in pretty quick.
Believe it or not I did all this by trial and error with no timing light. It runs great but I do intend to buy a timing light just to check and maybe do a little fine tuning.