Camshaft trivia

[2seater]

First item: Checked cam timing on an original 1990 engine with 92k mles and again with new timing set installed. Cam timing was retarded 1.5 to 2 degrees with the original chain vs the new set. Essentially the stretched chain removed much of the 2.5 degree advance built into the camshaft.

Second item: Anecdotal stories have stated that the 1988 engines seem more responsive and/or powerful than '89 or '90. I have no personal comparison info. on a butt dyno. but I did compare an OEM 1988 camshaft to the '89 and '90 version by installing in my original engine on the stand in my garage. The '88 cam is larger in all respects. Plotted on a graph, the later cam lobe profiles fit almost completely inside the '88 version. 1988 cam has symetrical lobes, 192.5 degree duration @ .050", 112.5 degree lobe separation, set at 3.5 deg. advanced and .270"+ of lobe lift. 1989/1990 cam has asymetrical lobes, 187 intake and 189.5 exhaust duration @ .050", 115.5 degree lobe separation, set at 2.5 degrees advanced with about .251" intake and .255 exhaust lobe lift. At .200" lobe lift, the early cam has a 12.5 to 14.5 degree duration advantage. One last observation. The closing flank of the intake lobes of both cams are identical and overlay each other on a graph from .150" lift on down, which should make the dynamic compression of the engine very similar.

[padgett]

In other words they are all ded, just the 88 is less so than the 89-90. 91 "L" is "more". That said AFAIR the rocker ratio is 1.5 so total lift is around .380". This follows the very flat torque curve which starts early and goes to about 4400 (can wind higher, doesn't accomplish anything

[DAVES89]

2seaters comments bring up an interesting thought. Rather than install a super charger,why don't performance upgrades include an upgraded cam to go with better breathing in the exhaust?

I am curious...

[jonlabree]

That would be a great ides, IF there were aftermarket camshafts available.

[padgett]

Because at least for the "C", it is not just the cam but also the exhaut and intake. "L" can flow at least 30% more than a "C". OTOH a ded cam with little overlap is almost perfect for boost, now you just need to clean up the exhaust.

Keep in mind that I believe boost on petrol engines belongs at 20,000 feet but the C is just not a candidate for lo-buck N/A hop ups.

BTW I don't know but I've been told (HB) a Series II cam can be ground to a "C" profile but you need to turn down the journals.

[2seater]

I believe the stock rocker ratio is 1.6:1. Agree that both cams are pretty mild, but the '88 would seem less so. I have done airflow tests on an aluminum snakes style manifold and the throttle body by itself, and surprisingly, it flows the same as the vin C. It looks more efficient, but it isn't. The manifold itself flows less than the vin C at the same pressures. It would certainly tune differently with the very long runners curled around inside. The plastic version probably flows better if it has a larger throttle body. The aluminum version throttle body looks larger until you actually measure it.

I don't know if this means anything or not, but the '88 cam has "J74" cast into the barrel near the end journal and the '90 cam is J55.

[2seater]

Padgett, do you remember when I asked anyone willing to do a full throttle run to post their maximum airflow reading from the MAF? This has to be maybe ten years ago or so. If I recall correctly, you were one the kind people that responded. The reason I bring this up is your numbers were higher than expected. As a matter of fact, yours showed as much as my '90 after I had done manifold porting, cleaned up the heads, had the throttle body enlarged and a free flow cone air filter installed. I chalked this up to your living near sea level or the MAF sensors were just not accurate enough. I have several MAF sensors, and have flow tested them, so I know they have reasonable repeatabilty but now I wonder if yours was the only '88 in the few that responded??

[Guest Greg Ross]

Hal,

When I started my S/C conversion oh so many years ago I conversed back and forth with Crane Cams, Fla to do up a moderate "boost' Cam for me. I'm 3500 miles away from paper data right now but at least at that time it wasn't any great big deal.

They didn't have a casting at the time for the 3800 so I provided them with "new" stock bump stick which they built up, reground and rehardened.

Betsy Blue is in a shop here right now for clutch, pressure plate, and refacing the flywheel, with that freshened up I could do a MAF full throttle pull for you if you're interested in that comparitive number with the S/C.

Thought I was actually in serious trouble here two weeks ago when the clutch started slipping seriously. Got on the web that morning and checked the regular aftermarket sellers, talked to CenterForce and Hays and I had washed out. The Getrag Model 284 I'd elected to go with way back then was relatively rare (only offered 3 years as an option on the 3.4 OHC v6) That has since translated in to non-availability of Shifter Cables and now the clutch assembly (the Hydraulic clutch Master Cyl/ Slave must be used on other models since they still are available)

Anyway, started web searching on clutch/ pressure plate rebuilders and one link that popped up was HR Clutch in Philly. Called them for a consult and low and behold they had two complete kits sitting on the shelf including throwout bearing.

I do have inventory of trannies, one runner and one in parts minus 5th driven gear piece that failed so should just bite the bullet and buy that last kit! Since this Getrag ModelTranny was done under a license/ service contract between Getrag and GM, internal tranny parts were never available. Design is based on a German model of Tranny that Getrag produced in Europe, I made a minor effort to try to connect with folks in Europe at that time and never followed up. Managed to find a runner and that's the tranny I've been driving the past 3 years or so.

Best I had managed to come up with was a 5th Gear part from a guy on one of the GM Swap Sites and the tranny that part came out of had obviously died a very hard/ abused death, the lead gear edges on the side gear/ syncronizer were rounded right off. "Jam, Slam, thank-you Mam". I considered that very unfortunate since it's highly unusual for 5th gear to fail in a Manual Transmission, and this one being the one I had rebuilt by Getrag/ thru GM around 2003. Haven't had many manual trannys apart but this is a rather strange piece. Presume the primary 5th gear would be cast steel but, beam welded on to the side of it was this thin, sharply cut side gear-syncronizer? don't know precisely its' function but when it parted is when I lost 5th.

Adventures in Motoring!