Hi guys, to make a long story short, I have a 3* advanced offset cam bushing installed on my cam. For some stupid reason, I though my cam was supposed to be installed advancned. I read intake centerline 106 and though it meant 6* advanced... Now I'm confused and have no idea what 106 centerline means???

Anyway, I'm thinking I should have installed it straight up. Did I hinder performance by putting the 3* advance bushing on my gear drive?

Should I compensate by retarding the timing a little?

The reason I ask is because Comp cams told me the cam should have a somewhat lopey idle in this motor, but it idles pretty smooth... I checked the numbers stamped into the cam and they matched what I ordered.

I have my ignition timing set to 8* advanced, and the motor is running pretty good. I'm running a comp cams xe268 (Cam Specs are as follows, Duration @ 0.006" 262 / 270, Duration @ 0.050" 218 / 224, Max Lift w/ 1.5RR 462 / .469, Lobe Separation 110, Intake Centerline 106) My compression ratio is 9.8:1 and I'm running a 3.23 rear end w/ a stock torque converter...

Thanks!

 

To make a short story long:

106 centerline means the intake valve reaches peak lift 106 degrees of crank rotation after top dead center.

Yes you probably hindered the engine's performance by installing the cam improperly.

No adjusting the ignition timing will not "compensate" somehow for having the valves open at the wrong time.

Best thing to do would be to get rid of the whole bushing setup; and replace it with a good quality timing set such as a Comp 3100.

The specs you posted are not the XE268. Look at the intake duration. They are the specs of the XE262. That cam will idle smooth in a 350. However, you didn't post the numbers off of whatever cam you actually have; so we have no idea what's actually in there.

 

Adjusting the ignition timing will help it spark more correctly in time with what the valves are doing but like stated above you are hindering performance either way. Your going to have to pull the thing apart and install the cam straight up.


Ive got a sloppy OEM chain and gears in the 350 thats currently in my car and i know my cam timing is off. The thing likes to run 30* locked out timing and is pretty much a sack of sh!+ anywhere under 3000RPM. But i just put up with it because i know one of these days ill have my new 350 off the stand!

 

You are correct, the cam is an XE262, I correctly typed 268, because the part number from summit was 12-238-2... Sorry.

But Comp Cams does list the 262 as having a noticible idle... What does that mean? It does not say choppy idle, but that is not what I wanted anyway...

But the biggest question I have is how much did I hurt performace by advanceing it three degrees? After working on the car pretty much non stop all winter I'm tempted to leave it for the summer and correct it over the course of next winter...

Thanks for the reply!
ck76239

 

Well we cant tell you how much hp you lost but you definately are lacking a few ponys.

Noticable idle, a very slight lope to it, not 100% smooth. choppy idle = car rocking side to side at idle

 

Offhand, I'd say about 3 degrees' worth.

No way to tell specifically, like x HP and y ft-lbs @ z RPM, it would depend on way too many other variables. Suffice to say though, it's not running like it should.

But it's not going to be a real huge dramatic thing, so it's not exactly an emergency or anything like that. It's just probably not running as good as it COULD be.

As far as "noticeable" vs "choppy" vs "smooth" or whatever, that's all pretty subjective. It's not like there's some ANSI standard somewhere for "noticeable". IMHO, that cam in a 350, gives a smooth idle; but that's just because of my particular concept of "smooth". Is it as "smooth" as a 929 or a peanut LG4 cam? probably not. On the other hand, I'm used to solids and rollers and stuff like that, so to me, about anything that will idle and stay running at less than about 700 RPM in gear, is "smooth". It's as much about what you expect, as about what you get.

 

advancing the cam 3* isn't much, but to try to directly answer your question, advancing the cam will cause your powerband to be a bit lower in RPM. you *should* have a bit more torque and less HP down low basically. Retarding the cam gives more top end.
I think i've got that right

oh, and I think that would also effectively help smooth the idle? well, barely noticeable though

 

All it will do is add a few ponies to the low end (below4000) and take away a
few up to (above4500). Comp cams extreme series cams are ground on 110LSA
and manufactured so that when you line of the timing marks on the gears the cam is actually advanced a few (4) degrees. (the intake is on 106 and the exhaust moves to 114) no further adjustment is normally nessessary.
You have moved it 3 degrees further ( assuming you did actualy advance the cam and not retard it) so your c/L's are now 103 and 117 respectivley.
Try it as is. set the ignition timing normally @32-36deg at high rpm.
If you would like a bit more top end after trying it as is, pull the timing cover and replace the advance bushing with a 0deg bushing to restore the designed cam C/L's. The effect will be modest. That cam normally does not have a "rough idle" If that is what you wanted, buy a cam with 230 deg@.050" or more. Just be aware that a big "rough idle" cam gives up low rpm power to gain top end power and rpm. needs a high stall converter, hgiher rear end gearing, and a modified ignition advance curve. ( more initial @ idle, same total timing) and has reduced intake manifold vacuum at idle.