I was not sure how the opti works in relation to the cam drive pin.

 

it's one of those things you'll wish you didn't ask...92-95 the cam pin mates with the opti center shaft...the opti cs has a 'trigger wheel' attached to it by screws...the trigger wheel has two sets (rows) of 'apertures', the inner set of aps vary in width as seen by a scanner inside the opti to tell the ecm where the crank is in 90* increments (cyl indicate), a second outer set of apps read by another scanner (the two scanners are cellmates in one sensor) to tell ecm exact crank position...96 adds another crank mounted wheel and scanner to play obdII games.

to deceive the sensor/ecm 92-95, there is an aftermarket trigger wheel that has slots for the mounting screws (MSD maybe) to allow relocation, or mod the oem wheel mounting holes...DNK what happens if you try this on a 96...reposing the wheel is obviously a pita compared to turning the dizzy on sbc1 noiseys.

 

You need, or someone needs to load all parameters and run a simulation with something like "Engine Analyzer". With enough detail, it can do a pretty good estimate of an engine's potential (and/or how changes will affect the build.)

 

In my experience, moving the cam less than 4 degrees wasn't noticable SOP. The track has too many variables for me to attribute a less than 4 degree movement to the cam movement.

However, at the track, a 4 degree movement in an 8 second 1/4 mile engine DID show up on the time slips and in driver appreciation.

Jake

 

Here is what Lloyd Elliot says

"difference would be with it on a 108 ICL, it will make another 5-6 RWTQ below 2000 RPM, about the same power from 3000-4000 RPM, about 2-3 HP less at 5000 RPM and about 5-6 HP less at 6000 RPM.

If you have to adjust the timing at all, make sure that the tuner knows what you did to do it. Anything done to change the cam timing will effect the ignition timing also. "

Lloyd Elliott
972-617-5671
Elliottsportworks.com

I tried all day long yesterday to get thru to Comp Cams Tech line but it is permanently busy. I think I will just leave it as is. I don't care about anything below 2000 and will pick up a few HP on the top end.

Eddie

 

During my search on this subject, I came across your posts on a couple of other sites about degreeing an LT1 cam and the affect on timing. Looks you got about as much info as I did. A lot of folks just simply don't understand the subject.

 

If you have a stock converter in there it would be 1500 stall. So you could definitely use that TQ. Some people want all the torque they can get down low. If it were me (I like RPM HP) I would leave it.

 

super easy!

I run a off set key on my L98 set up works like a champ. If your looking to get 2* at the cam then at the crank gear install a 4* offset key.

 

In all due respect you do not know what you are talking about here at least on this subject.. LSA is the lobe separation angle that is the angle between peak lift on the intake and exhaust lobe and can not be changed in any way on a SBC other than grinding a different cam. The Intake centerline is the relationship between tdc and peak lift on the intake lobe of the cam and can be changed with keyways bushings etc... but has no relationship with LCA... as LCA has no reference to TDC or anything else that is not ground into the cam itself..
Dave...

 

6 speed ZF6

 

Ok genius tell me what I got wrong. Your post makes no sense. Did you by chance read the whole thread? Where did I say anything about changing the LSA? I am well aware of what LSA is and what the ICL is. The discussion is about the relation between the ICL and the LSA. I am referring to the term "straight up" which usually means that a cam with an LSA of 112 would be installed with an ICL of 112. Comp calls for the cam to be installed with an ICL of 108 which would mean it is 4 degrees advanced. Mine comes out at 110 which means it is 2 degrees advanced. No one has said anything about an LCA. Tact doesn't seem to be your strength.

 

There is no relationship at all between the two.. LCA and itake centerline.. Any relationship is inferred by you... you be the expert and I will continue to set world speed records and win races..LOL...

 

Do you realize you are talking jibbeirsh? If you are going to quote me, do it accurately. Where in the cornbread hell have I ever inferred any mention of LCA ever? You invented it. This whole discussion is about the change in static ignition timing caused by changing the rotational relationship between the cam and crank on the LTX motor. I am by no means an expert on cams but I have spent a lot of time recently talking to several folks who are. I am at a loss to explain your hostility. Learn a little tact.

Eddie

 

As odd as it may sound, I think everyone was right in this thread. rklessdriver and Aardwolf were right saying exact placement of a cam is the best goal. If there's leeway to rotate the cam one way or another, a different grind might have been better.

For the ones (self included) who think a couple of degrees is no big deal, that's also right -- depending on your goals. For a street car, it's not going to make/break driveability. If (like here) there was more room for a bigger cam (or top end power), the retarding the installation might be "good" vs "bad". Power is shifted upward at the expense of some dynamic cylinder compression.

I made the statement "Anyone wonder how retarding a cam can make more power up top?" That was partly a rhetorical comment. I think redrose realized it but didn't explain the answer. My guess,,,though not for sure,,,is that timing and reversion are at play. At higher rpms (when the window for air to enter the chamber becomes shorter and shorter), an increasing opportunity/need arises where the intake of compressed reversion air becomes more efficient. So, while actual cylinder compression may be dropping, the volume of dense air within the intake tract may actually rise.

Another issue was about the relationship of LSA and ICL. Those who say there's no relationship are correct. Consider two cams; one with 116ECL and 108ICL; the other with 112ECL and 112ICL. Are these cams really different? If you install the 1st cam in the 4-degree retarded position of your timing chain, is there a difference? I say no. That means neither cam has more "advance/retard" built into it than the other. That means the user has defined the "installed" ICL based on how they hook it to the timing chain. Hence, the comment "Any inference of ICL relationship is made by you." would be correct.

If you call an installation one where 108 becomes the actual ICL, then 4 degrees of advance is built-in. But, not in the cam. It's thru it's relationship to the stroke of the motor. The cam did not change. It wasn't rebuilt. While it's common to say 4-degrees of advance are built in, I now see how that's misleading. It's not built into the cam. It's only built-in to the motor thru it's installtion/orientation.

LCA and LSA mean the same thing. The terms are interchangeable.

Tact...Hmmmm....What should I say. More is better,,,in general.

So,,,that's my ending to this story. It's an ending long overdue. Anyone feel like adding an epilog?

 

The advance is "built into" my cam due to position of the dowel and mounting holes. That establishes the relationship between crankshaft and cam and therefore the timing of a stock timing set.

When you start off by telling someone they don't know what they are talking about, it usually doesn't end well. I try never to say anything here I wouldn't say to your face. The original point of the thread was lost.

Eddie

Eddie

 

Last year I tried getting a handle on how advancing (or retarding) a LT1 cam's installed position would effect ignition timing and what I received in responses were a mixed-bag. Some said ignition timing IS effected and others said it ISN'T.

At that time, I was considering re-phasing my son's cam 2 degrees more advanced. Not being able to get a consenus, as since the contemplated move was only 2 degress, I decided just to leave his cam as is.

I do know from the few times I advances or retarded the cam on trailered race cars that there is a definite difference in the time slips and from feed-back from the car's driver.

I do know, ALSO, that each time I re-phased a cam, the ignition timing had to be adjusted also. I repeatedly asked in posts for someone who'd actually re-phased a LT1 cam and whether or not they addressed the ignition timing but no one posted they had. What I received were opinions and, basically guesses.

ALSO, from past experience, I learned that it took a minimum of a 4 degree cam movement to achieve the noticable difference.

I also posted how a high 8 second car's engine I built went flat at the first MPH light and that retarding the cam 4 degrees allowed the engine to continue to pull all the way to the finish line. Cam was a Crane Inverted Flank Roller.

I explained to another guy, running a Jesel belt drive, how to re-phase his cam at the track. He called me complaining how the car was a DOG off the line and further discussion revealed he'd forgotten to re-adjust the ignition timing.

So my conclusions are:

It takes at least a movement of 4 degrees to realize any difference AND
The ignition timing has to be re-adjusted once the cam is moved and
To date, no one who has ACTUALLY done it, has come forth with a step-by-step.

I still don't know how to deal with the LT1 ignition adjustment.

Jake

 

It is my opinion that changing the valve timing from the manufacturers numbers changes the static timing on an LTX and must be dealt with in the tune since that is the only control you have over it with an OEM Opti. You are changing the rotational relationship between the crank and cam which can't help but affect the opti. That's why I decided to leave mine alone and not go the bushing route. The affect was minimal and actually more to my liking.

Eddie

The problem you had trying to nail down an answer is the same thing that happened here. Someone latches on to one post without reading the thread and it all goes off track.

 

Jake, there is more and more of that on this forum, alot of Internet Experts. Although we don't always agree on everything, it is nice having someone like you on this forum "that has been there and done that".