On the comp cams website it list the H-14 as an 87 onwards cam.

http://www.compcams.com/catalog/056_057.html


Is there a differnece between the 85 & 87 camshaft design?
Specs are only slightly dif in the valve lift.
The H-14 says best cam for 305/350 modified...the 262H would presumably be just as good for my 305 with exhaust/chip/runners etc?


Cheers Wayne
85 IROC
New Zealand
Sheep lover Oi!

 

The H14 will work better with FI or other computer-controlled setup; the regular H10 will produce more power with a non-CC carb.

As far as stock engines go, 86-back had flat tappets, 87-up are equipped with roller lifters.

 

rgr that...mine is the TPI 85 H10 still ok?

 

You'll want the XE262H-14 cam. It's ground on a 114* lobe separation angle with works better with a TPI than the otherwise-identical XE262H which is ground on a tighter 110* LSA. The 110* cam will still work, but the tight LSA typically doesn't work as well with a TPI intake

Yes, there's a difference between 87-up cams and 86-down, but it's not like what their descriptions say. These are still FLAT TAPPET cams. 87-up TPI motors with centerbolt valve cover heads and such have factory ROLLER cams in them. Obviously, roller cams are a very different beast than a flat tappet. I don't know why they describe them this way but I think it's a bit misleading.

I'm installing a XE268H-14 "87-up" cam in an old 70-s era small block this month and I expect it will be a bolt-in for the original cam. They even call for the same timing chain, lifters and pushrods as they do for the cams designed for 86-down motors. Near as I can tell (and soon to know for certain) the -14 is the eact same cam as the -10 but ground on a 114* LSA, and that's the only difference.

 

So whats the guts with the LSA? I've heard people on the board say 110' is great but gives a lumpy idle, is that true? and if so, is this the reason that the TPI engines don't like it much due to the computer not being able to keep up at idle with lumpiness?
Is it so then that the 114 will give a smooth idle??
I don't mind a mean sounding idle if the TPI ECM can handle it.



Cheers

Edit: You said above that the TPI intake doesn't like it, what do you mean?

 

Ok, after serching and reading **** loads of posts re LSA vs duration etc etc I'm starting to get a handle on this stuff, very slightly.
The stock cam for the 85/305 TPI was LSA 114.5...it idles like a purring kitten.
I want a more aggressive idle...looks like I need help with selection of a Cam.


EXPERT ADVICE NEEDED:
What do the experts say here, whats the cam for me?
I'll be doing these things at the same time as doing the cam change, so cam the car accordingly.
Its not a daily driver, but used for cruisin town & local drag strip, I want it to haul A**.

SLP runners
Port/polished head
Long tube hooker headers
AFPR
Modded chip
It has a 3.42 posi dif
700R tranny

 

Fuel Injection systems are reliant upon a strong vacuum signal in order to run properly. Thus they typically have at least a 112 LSA, and more likely a 114, so that even at low rpms the fi system can "tell" what is going on with the engine due to the strong vacuum signal.

The closer you grind the LSA, the more of an overlap you have between the intake lobe and the exhaust lobe. This allows the exhaust charge to reverse flow and enter the combustion chamber, thus contaminating the fresh fuel/air charge. For obvious reasons this is NOT desireable, and reduces the vacuum signal at idle speeds.

Believe it or not, a "lopey idle" is NOT the sign of a "hot" car. It is merely the evidence that the engine is having a difficult time trying to run at the rpms it is set at.

There are other factors involved with this subject. It requires a book to cover them adequately.

But suffice to say that the best advice for an engine intended to be driven on the street is to choose a cam that will work properly within the rpm range that it will see the majority of the time.

A "lumpy" cam, by design, sacrifices lower rpm driveability and idle quality for higher rpm power. A "smooth" cam, also by design, sacrifices high rpm power for normal rpm range power.

The sensible question is therefore, "What rpm range am I going to be driving this car within the majority of the time?"

Since it is for cruising on the street, and not drag racing at the strip, a wider LSA (and shorter duration) is the logical answer.

Now when you come across a street car with a lumpy idle you will know that it is not much fun to drive and is a dog on the street. Given two identical cars, one with a lumpy cam, and the other with a smaller grind (but smoother idle due to less lift and duration), the latter will clean the lumpy's clock on the street and probably only face a challenge at the END of the quarter mile. How many street races last a quarter mile???

I think in another thread I suggested you use the GM LT1 cam. Because you have an 85 Iroc you can't use it. It's a roller cam. So the XE 262 is pretty much the ragged edge of acceptability for what you are doing with your Iroc, due to its high lift and long duration. You might find that you are happier with a smaller grind like the XE 256 or even XE 250. They both have slightly less lift and duration but will provide better off-the-line performance and idle quality, while sacrificing very little in high rpm power--typically only around 5 hp. The stock 305 heads' valve springs will also be able to handle their slightly lower lift more effectively

But get at least a 112 LSA, and preferably a 114 LSA.

PS The Crane PowerMax 260 and 266 would also work nicely with what you are attempting to do

 

Sitting Bull : What about this Crane cam, seeing as how mine is a TPI engine. Its the Crane Powermax 2040.

210/216
270/276
.440/.454
114 LSA

I've managed to get a set of World products S/R tourqer Heads for a 305 at a good price locally here in NZ.

 

Yes, that is the old number of the Crane PowerMax 266. It will work very well.

 

Roger that..thanx mate.

 

Forgot to ask this, Will the S/R Torquer heads increase my compression ratio or will it stay the same....?? I dunno what cc teh stock heads are...

 

If they are the 305 Torquer heads the compression should stay the same.