Yeah, Redrose, LSA and ICL are different things. I get that (and understand what they are). You didn't make ANY point or respond meaningfully. You might as well said "blah, blah, blah....". Are you deflecting?

 

AH, YES! There-in lies the problem.

You can't compare two camshaftS that have different Lobe Separation Angles and then conclude that one is "retarded" as compared to the other. You can't, that is, if you're looking for accurate results.

Each cam must be installed, degreed-in and the degree-in specs that result then compared to IT'S cam card specs, not to the specs of some other cam. To do otherwise is like comparing apples to oranges; two different animals.

Jake

 

I agree. Maybe some people are comparing modern FI cams to older carb cams? Or maybe they're just looking at the ICL?

Consider this...If you rotate the L98 cam and put the ICL on 106ATDC, you'll also rotate the exhaust opening the same amount. So the ECL would move from 118 to 128BTDC. If (as an example), you're comparing some older 108LSA cam (installed at 106ICL/110ECL) to conclude the L98 cam also needs to be set at 106ICL (for best performance), notice your exhaust valve will be opening 18-degrees sooner. That's alot. And, that's a lot of compression bleeding out the exhaust pipes at the end of the power stroke!

GM engineers aren't stupid and they aren't just looking at emissions. When you're building a longtube runner setup (that's primarily based on it's ability to catch reversion waves in the mid-rpm band), opening the intake valve at 116-degrees isn't such a bad idea. Why? It's going to create more reversion which is air pushing back into the intake. Who says that won't create a bigger mid-range TPI bubble? The wider LSA is commonly thought to help give a broad powerband. But, the relatively early exhaust opening (associately with a wider LSA) is also to balancing compression with the need to evacuate exhaust.

While a 106ICL might be a great idea on a short-runner carb setup, don't be so eager to conclude the same is true for a TPI! More importantly, don't conclude it's cam is retarded! It's just designed for different parameters.

Edit: I should have said "setting the intake valve to a 116-degree ICL isn't such a bad idea" in my statement above. Obviously, that's not when the valve actually opens.

 

I have been following this thread, so now i am really confused? Is there a benefit in advancing the factory cam or will it hurt bottom end or is it even worth doing?

I am looking for bottom end gains......

 

It could be, too, that he's confusing valve timing with ignition timing. I know that GM, for whatever reason, altered the ignition timing on earlier engines. Why GM did that is unimportant for the pupose of this discussion though.

In true Learned Professional circles, like scientists, physicists, medical practitioners, etc., this is referred to as "Peer Review". Whenever a new "theory" or differing results, etc., are submitted, the author's peers "check it out".

The author's presentation isn't accepted at face value, it has to be "reviewed" to find if it's valid and correct as presented. Also, the peers aren't reluctant to voice their disagreement when the new presentation doesn't pass muster.

So, one of my New Year's resolutions is that whenever I come across a questionable post, in a polite way, I'm going to ask "Cite your source and evidence".

Now we're going to get down to the 'nitty-gritty' and details. I can't wait; this is gonna be FUN!

Jake

 

I'm not going to say it won't make a difference, but 88-89 years would be the ones I'd choose this option only as a last resort. As mentioned above, the LSA is so wide, I'd be concerned any gain by closing the intake valve earlier would be offset with the exhaust valve opening earlier (and bleeding off compression). Other L98 years have a bit more room to "play with" -- so they'd probably respond better.

I'd be more inclinded to bump distributor timing 4 degrees (or 6) and run best premium gas in your neighborhood.

Of course, this assumes everything else is in "perfect tune" -- including the timing set. If it's not particularly new, people who rotate timing teeth -- while switch to a new set (during the process) -- are more likely to get a bump because their new chain IMO. That's because a newer chain puts valve events back where they belong.

Another option (for a little bump) is to install 1.6 rockers -- especially on the intake side or... install a new cam. LOL

 

Ok I know this is a little old but it caught my eye doing a search. I have a short block out of an '88 that I was going to freshen up and drop in my '90. Lets say due to class rules I have to use a stock cam. Which one do I use, the '88 or the '90? Why? Is the ICL on the '90 cam the same just different LSA and duration?

If I were to advance or retard the timing (+/- 4 degrees using the different keyways on the crank gear) which cam would respond better to what change (advance or retard)? Just thinking out loud, Greggpenn said he would use the '88-'89 cam as a last resort. Would advancing my '90 cam +4 on the 114 LSA be more effective and hurt the exhaust less?

 

Here are the cams specs you're choosing between...

90 cam: 202'/207' Lift (w/1.5) .413"/.428" LobSep 114.5'
88 cam: 207'/213' Lift (w/1.5) .415"/.430" LobSep 117'


The cams are the same lift but the older cam has more duration on both sides. In theory, the older cam will produce a bit more power up top,,,probably 5-6HP with a smooter, straighter power curve. If you were running it for 1/4 mile times, the older cam MIGHT trap a hair faster -- if you can shift it higher.

However, the 90 cam probably has more low-mid torque because of the lower LSA and less time with the valve open. As such, I think the 90 cam advanced 2 or 4-degrees would probably feel and run faster (at the lower rpms you see) on the street -- esp with a stock intake.

It's splitting hairs though. FWIW, I think either cam would respond better to 1.6 rockers (than advancement) -- if allowed by your rules.

(BTW, as far as comparing stock times for 88 vs 90 cars, the 90 is faster but I'm thinking that had more to do with a compression bump IIRC. Obviously 88 is MAF and 90 is SD,,,which also muddies the water.)

 

Wow, you guys know alot about cams.

The experts in this thread, how many cams have you installed?

 

Wow! What a question.

Got me to thinking though, and in trying to remember all the pure race engines and the street/strip versions, no way can I recall all of them.
Now, we're talking over 40 years and, on average, 6 race teams that I did engines for back in the late 80s/early 90s, then my personal engines, family members engines . . . . . I even use to get cams for Xmas and Birthday presents.

GEEZZZ! Just thinking about all that work makes me tired, LOL

If I had to guess, I'd say somewhere around 100, but as I said that's just a guess.

Why'd you ask that, anyway?

Jake

 

Curious if anyone has experimented with the stock LT4 cam (not the HOT cam) on this type of setup (L-98 w/LT-1 intake).

 

I cant install rockers. Sounds like I will stick with a the '90 cam as I am using a ported plenum, SLP runners and TPiS base, I could use the torque more. Thanks for the input.