Is 1300 rpm at 55 mph too low for a tbi 305? It is a healthy engine. The cam moves the power peak up 1500-2000 rpms and power curve is also up from stock but probably not much if any at this rpm range.

 

Your RPMs at any given speed is NOT determined by your cam. Its all determined in your gears. My car could make 100HP at 2000RPM or it could make 500HP at 2000RPM, but either way, at 2000RPM, I'll still be going 80 in 4th gear.

1300RPM sounds about right for your car at 55mph. I'm guessing its got the auto in it with 2.73 gears in the back? My car does 40MPH at 1000RPM in 4th gear, and 80MPH at 2000RPM in 4th gear.

Oh and if you need some other numbers to compare to, at 4500RPM in 3rd gear, my car does 125MPH

 

that sounds about right... but then again, the stock Tach's are pretty much... useless... you can get a vague figure from them, but most of them are pretty innacurate.. w/ my 700R4 1500rpm/55mph is just about right in overdrive...

 

That is not at all what I am asking. I know what the rpms are going to be with the changes I am making. I am wondering if the changes I could make will result in too low of rpms. Will I be short on power, vacuum, will it take excess fuel, etc.?

 

I think this is going to be determined by the sum of the changes you have made.

The bottom line is that you will need X amount of torque/hp to keep the car moving at 55mph @ 1300rpm.

As you already understand, it is possible to make changes to your engine that move your peak torque to a different spot (camshaft change). It is also possible to increase the amount of torque in the entire power band (exhaust changes)... in effect - you can move your peak, increase the area under the curve, and still maintain a certain amount of torque production at a low rpm to be compatible with the gear ratio you have.

 

Lots of third gens that run with a 2.73/2.77 rear turn around 1500 @55. I am now not expecting a drop to 1300 will make a huge difference. Pontiac in 1987 said it takes 11.9 hp to keep a TA rolling along at 50mph. In just looking around today, I see some late model vettes and f-bodies turn around 1300. I think I might go ahead and try it unless someone has some experience already in why I shouldn't.

 

What cam exactly are we talking about? Moving the power band up that much sounds like a pretty radical cam.

 

Not really that radical, power peaks are pretty low for a stock tbi. 4000 hp and 2400 tq. Its a compcam, custom, I bought off someone. I think it is 266/276. Very similar to their roller 264. So if the peaks now land at 6000 and 4500, that is around a 2000 rpm bump.

 

I've been recommended that to rev to 6k RPM without worry you should definitely upgrade the valvetrain. I'm putting an LT1 intake and cam in my 305 over the next few weeks, and was told that if I wanted to rev to 6k RPM, I should definitely look into new springs and/or a "rev kit"..

I say you get some shorter gears if you want to be faster at the track. The 2.73's won't take advantage of your powerband at the track. Something like 3.42s or 3.73s would be better for that higher powerband.

 

Not overly worried about the track, but it already has in 3.45s for that as well as "seat of the pants."

Engine not stock, all that stuff taken care of already.

 

A little hard to say just from that little data, but I'd guess peak HP would be more along the 5200-5400 RPM range.

How are you coming up with 1300 RPMs @ 55 MPH w/3.45 gears?

 

I stated 1500-2000 rpms. I'm looking at a .53 OD gear.

Out of curiousity, how do calculate 5200-5400?

 

Not a calculation so much, just based on how the cams I have in that range act. I have two engines with slightly more cam than that, they pull to 5500-5600 RPMs.

LSA also affects upper power; if it's more than 110 degrees, you probably aren't going to 6000 RPMs.

What heads are you using for this engine?

 

Ported alum. L98