Cam Selection help...

Andy(UK) · #1 (**permalink**) 08-19-2004, 12:07 PM

Hi,

Im trying to decide between the comp cams 268H and XE268H, Im after a cam which does not idle roughly, Id like it to idle smooth but a very slight lope wont hurt I guess. Ive looked into the High energy 268H & now found the XE268H. Desktop dyno says the two are fairly identical up to 5500rpm, the 268H has started to tail off by then hitting peak at 5500 but the XE goes on to 6000 to hit peak power. I guess this would mean the XE wouldn’t run out of legs if I set my rev limit to 5500?

This is going in a ’71 Ford 302 with Edelbrock rpm kit.

Has anyone got experience of the XE268H or the 268H? The 268H has 0.456 intake & exhaust lift with 268 advertised duration and 218 at 0.050”.
The XE268H has 0.509 intake and 0.512 exhaust lift with 268 intake & 280 exhaust advertised duration & 224 intake & 230 exhaust duration at 0.050”.

As always any advice / help greatly appreciated.

Cheers

Andy

Mr.Fixit · #2 (**permalink**) 08-19-2004, 02:07 PM

Without providing details about what parts are in the engine, it would just be a guess.

doesn't Edelbrock have a suggestion to go with their "kit"
Why go with the "RPM series" parts if you aren't going to spin it past 5500?

jayem · #3 (**permalink**) 08-19-2004, 02:24 PM

I've run several cams in the 512 to 525 lift range. I think you will be happy with the XE cam. Good idle & low end torque,small lope.
Set your rev limiter at 6k, 5.5k is a little low. Just my opinion. Jay

Andy(UK) · #4 (**permalink**) 08-19-2004, 02:54 PM

Thanks for the replies.

Im not using the Edelbrock rpm cam as many over here have found the idle to rough for use on the street, queing in traffic etc. Hence I am after something that gives power but doesnt idle like a bag of spanners.

The XE268 caught my eye and I think Ill give that a go. Im using the rpm kit as it makes more power than the standard Ford heads my engine came with, the basic performer heads appeared to be little better than stock do I went for the rpm versions. I may however check out increasing the rev limit!

Cheers Guys, help really appreciated.

Andy

Mr.Fixit · #5 (**permalink**) 08-19-2004, 04:24 PM

you won't get the results you are looking for with your pick and choose method of putting a combo together.

Every part has to work well with every other part in the engine.

How high of an RPM is your shortblock good for?
Now pick heads that make their power before that redline.
Get an intake and cam that works in the range too.

right now it sounds like you have:
very low RPM shortblock
mid to upper RPM heads (which takes away from low end power)
Mid to upper RPM intake (same issue as heads)
Low RPM cam

Pick the powerband you want, then get the parts that work in that RPM range. High RPM heads don't work at low RPM. One type of head doesn't always "make more power" reguardless of the rest of the motor, it makes more power under very specific circumstances, if you aren't going to operate under those circumstances, you have the wrong heads.

Goober · #6 (**permalink**) 08-19-2004, 05:15 PM

I aggre with Mr. Fixit. Need to match up components to work together. Companies like Edelbrock don't spend $$$ testing and building for nothing. Heads, cam, intake, exhaust, carb, and everything else needs to sing on the same key. I put a Comp 305H cam in a chevy 355 once when I lived in the UK and it almost killed it. Didn't like anything below 4,000 RPM. Just an example of street use vs track use.

Just my 2 pence
Mark

Andy(UK) · #7 (**permalink**) 08-19-2004, 11:36 PM

OK, Thanks for that, maybe Ive gone about it the wrong way, first engine build and all that!

So it looks like my top end is aimed at mid to upper rpm, I can live with that, how would you suggest I alter the block and cam to match? Bearing in mind I still want a fairly smooth idle, and Im not interested in squeezing every last hp out of the motor, its gonna go fast enough as ity is!!

Cheers

Quote:

Originally posted by Mr.Fixit

you won't get the results you are looking for with your pick and choose method of putting a combo together.

Every part has to work well with every other part in the engine.

How high of an RPM is your shortblock good for?
Now pick heads that make their power before that redline.
Get an intake and cam that works in the range too.

right now it sounds like you have:
very low RPM shortblock
mid to upper RPM heads (which takes away from low end power)
Mid to upper RPM intake (same issue as heads)
Low RPM cam

Pick the powerband you want, then get the parts that work in that RPM range. High RPM heads don't work at low RPM. One type of head doesn't always "make more power" reguardless of the rest of the motor, it makes more power under very specific circumstances, if you aren't going to operate under those circumstances, you have the wrong heads.