ZD75blue

Hey guys...

I'm looking at the differences in the comp cams extreme energy lineup... And thought about something... The stock converter engaugement RPM, this could play quite a big roll in my selection! The choices currently for me are the 256/268, the 262/270, and the 268/280.
* 256/268 is 1000 - 5200 RPMs
*262/270 is 1300 - 5600
*268/280 is 1600 - 5800

All the major magazines use the 268 and achieve wild horsepower numbers... but what RPM does the cam need to start for me to get decent milage on the highway? Or not try to die when leaving a stop sign!

The way the car was originally options was:
Coupe
L48/auto
A/c
Powersteering
Power brakes

And, I really dont want to have to swap in a new converter when the motor goes back in... if it doesnt work like I want it to!

Part 2.

Does anyone know where I can find a bunch of automotive calculators? I remember there being one out on the web... smokedtires.com or something similar, but I cannot find it to save my life! :smash:

ZD75blue

TTT :cheers:

Perfomer

It depends on the use of the car, part time or daily driver. I have a 270 in my 350 in a 49 P/U with a 2200rpm stall and it gets about 15mpg it has a nice lope and idles at 800rpm . If you use a 280 you will have higher stall and gas mileage will go down but it sure has a nice rumble at idle. I would use a after market stall with any cam larger than stock. Any cam much larger than 270 will have a effect on your power brakes .

Metal Wulf

:lurk:

i'm trying to decide between the xe262 or xe268

1979toy

Always listen closely to the camshaft manufacturers recommendations on what torque converter stall range to use. They are the people that know what RPM range the cam needs. When you call it would help if you had your vehicle weight, gearing and intended uses.

Metal Wulf - I have the Comp XE262 and a stock converter with 3:55 rear gears. The engine seems like it would work much better with a bit higher stall converter, but overall I'm happy with the stock converter as I spend a lot of time cruising below 2000 RPM.

Ganey

Yes, converter plays a role as does rear gears, etc.

For a stock L-48 auto./converter/gears (about 3.08) w/o rebuild, you would probably be happiest w/ XE256. For best gas mileage 260H or XE256 about ideal. This gives more low rpm HP/TQ to get you off the line & only about 20 less hp at high rpm than HE268H. If you went to HE268H or more w/o rebuild, you can expect it to take off about 3000.

LiveandLetDrive

I've got a HE268H (with matchings springs and ProMag lifters), Performer intake and 2" duals are my only other modifications to the driveline. It seems to really take off at about 3500, maybe a little less. I'm very happy with it, I don't think my gas mileage has changed significantly from before the swap, it might even be a little better.

What would be an ideal stall value for me? I know the basics of how they work, but don't have a clue how to choose one. 3.08 gears, daily driver but my ideal of "streetable" is a little more flexible than most.

-Chris

ZD75blue

Thanks guys...

I am thinking that the 268xe is to much for the current buildup.

Going with:

flat top pistons
Vortec Iron heads
Headers/side pipe combo
Dual plane intake to match cam...

Block has been machined 30 over, so dealing with a 355.

By the calculations at smokemup.com depending on the head gasket, and piston type... i'm looking at 9.5-10.5:1 comp... plenty but low enough that I might be able to squeeze by on pump gas (cough... 87... cough)

Anyone know the stock converter's rpm of engagement?

Thanks for the help and ideas guys! :cheers:

Jvette73

With a stock convertor, definatly not the XE268. Comp Cams say its ok to use this cam with a stock convertor but they under estimate the negitive effects on bottom end in my opinion. I had the 268 and downsized to the 262. The car runs smoother and got better ET with the smaller cam. I have 2200rpm stall. With a stock convertor and gears I would recomend the 256 with 1.6 rocker ratio. This way you can boost the lift with the rocker ratio to get more tq, and not suffer the ill effects of higher duration in conjunction with stock stall speed.

ZD75blue

Thanks Jvette...

I'm betting the gasmilage increased on the highway also! :reddevil

Ganey

Depends on you. Many like 2200-2500 for street. When 2 nos. are given for same converter, go by the lower no., the higher no. is for more C.I.

There are tradeoffs i.e., since you mentioned gas mileage w/ a higher stall or looser converter, then less gas mileage & more off the line takeoff.

Do you power brake? You might want to rebuild engine before converter.

For a drag race setup, one would run a higher stall speed like 3000 in your setup.