Street89vette

Set the timing marks on the timing gears a zero, dot to dot. Set timing with ecm disconnected at 8 degrees. Tuner programmed chip to a stock street setting. Not sure on timing advance. Motor seems a little sluggish up to 3k rpm. back in the day i could advance timing to 12 or 14 degrees and change that sluggish to quick throttle response.
Any suggestions or tips on this.

GREGGPENN

Your tuner probably left the spark reference angle set at 6 degrees. 6 is standard for an 89 L98. THAT'S where the timing mark should be...not at zero.

You have to disconnect the (brown?) reference wire to correctly set the timing.

If you aren't happy with the performance at 6 deg, you could try 2-deg adjustment of MECHANICAL timing by changing your timing light to 8, 10, or 12 deg. People have reporting doing that with some satisfaction.

bill mcdonald

When I built mine, super ram, 190 AFR heads, and zz9, it was a little sluggish as well. I ended up moving the timing to 10. It seemed like it wanted more but I was not feeling like going past 10.

This was going between a built engine and the TPI. The tpi is pretty snappy on the low end. The mid range to top end of the built engine more then made up for it. Trade off.

bjankuski

Have the tuner send you the timing curve and see what the timing is at WOT in the low RPM range and see if he can adjust it to take care of the sluggish response. At WOT you would like to see at least 20 degrees from idle to 2000 RPM and then a steady increase from 20 degrees to max timing at WOT by 3000 RPM (max timing will be 32 to 36 degrees depending on the engine)

GREGGPENN

I've commonly seen the hotcam listed as a bad choice for a TPI intake. Basically, when it's really starting to help engine/valve breathing, the intake doesn't give it a lot of room before "shutting it down".

Could it be the case that a straight-up hotcam installation would create less LOW-END cylinder pressure than the 207/213 stock 89 cam? (stock duration from 6yr-old memory so sorry if that's wrong.) Of course, lift is better for the hotcam to help make up for that.

Can electronic timing even "make up" for lower cylinder pressure (if present) at lower rpms? Under a TPI, I gotta think 4...or even 8 degrees mechanical (cam) advance would be a better orientation for TPI limited hotcam?

What's on top of this setup for an intake? Will it STAY that way? Is everything else stock?

bjankuski

My opinion is the hot cam is a fine choice for a TPI, because it is still a relatively small cam. While it is true that it may have slightly less cylinder pressure (Filling) when compared to a stock cam below 2500 RPM it will be a very minor difference. My gut feeling is advancing the low RPM timing will make up for the slightly reduced cylinder pressure of the cam and bring the car to life. We have no idea where the cam is installed since the timing gear was installed lined up dot to dot. typical cams have four degrees already ground into them but if it was not degreed it could be anywhere.

The only way to actually determine the lower RPM filling is to have the specs of both cams (installed CL and overall duration) so I can determine intake closing points to see which one will have higher low RPM filling. (Currently I do not have the specs of either cam memorized for closing points) so I am making a generalization.

If someone has the specs for both cams with there installed CL and overall duration and feels like posting it that would be great. I think the stock cam info will be hard to find.

The timing curve should look something like the one posted below:

aklim

Back in the day, you had mechanical advance. This day, you have electronic going off the base. Too much at any one spot and it will ping lightly enough that you wouldn't hear and the ECM will pull timing. When you can hear it, the ECM is probably past adjustment and giving up. Is this a dyno tune where they maxed out the entire curve or "guess a tune" in the mail? Any way the guy will work with datalogs to change the tune?

GREGGPENN

It looks like the LT4 hotcam is neutral or 3-deg advanced. Summit shows (112lsa with) 112ICL which means no advance is built-in. Other posts show 109ICL. As you point out, the ICL for a stock L98 cam is unavailable. After half-an-hour searching the net, it looks like no one figured it out for sure. The LSA is 117 but ICL is MIA.

If no advance is built-in to the stock cam, it's IVC event is about 3 degrees sooner than the hotcam. If there WAS any advance ground into the stock 89 cam, add that number of degrees to the IVC event.

So...we're probably talking about 3-7 degrees sooner IVC for the stock cam vs the LT4 Hotcam.


The table you posted looks closer to what I'd expect for the low-mid high-load rows of a stock bin. In your prior post, you said 20-deg @ 2k rpms. What you just posted is 25-deg. That's what I'm seeing on the two stock tables I have to look at.

Since the hotcam doesn't have any advance ground into it, I'm still inclined to suggest the OP might have been happier with it mechanically advanced 4-8 degrees....assuming it continues to sit under longtubes.

As for degreeing the cam, I used to think the ICL would be correctly "oriented" with respect to the timing mark on the cam nose. I wonder how often that's actually "off"?

When I talked to Bullet (about mine) last fall, they admitting one of the reasons for degreeing a cam is to verify correct stamping of the timing mark on the nose. They "suggested" that they are usually +/- 2 degrees from actual. So, it's POSSIBLE that UP TO 6-deg rotation might be required to orient it with 4-deg mechanical advance.

Correct me if I'm wrong.

bjankuski

My searching on the net shows a GM cam card with 109 ICL for the hot cam but it does not really matter since it can be moved around depending on how it is installed. I have also seen aftermarket timing sets that have been off by as much as 8 degrees when the dots are lined up at zero. That is why I degree all cams because you never know where you are at until this is confirmed.

When determining low speed response you need to look at intake closing numbers on the cam not .050 numbers. You cannot build any compression until the intake valve is closed. Compression at low RPM will be based on the volume of air that is still in the cylinder after the valve closes, more air means more torque potential.

As far as the timing is concerned it should be similar to what is shown, all combinations if dialed in to optimize the results will be custom built to work for the combination they have. What I have shown is a good starting point and I did not even notice that it started adding timing before 2000 RPM but that worked fine for that particular combination.

GREGGPENN

It's also true for the stock 89 combination...as the stock bins show timing being added at 1400/1600 depending on stick/auto. As I've read several times, the 89 BIN is considered "hot". It's got about 25-deg by 2k rpms.

Thanks for mentioning the timing set as a/the possible source for cam alignment issues. I hadn't considered that....though it makes perfect sense.

How many degrees "shift" does the movement of a typical link shift mechanical timing? If you can't adjust the exact relationship of the cam to the crank (less than what one link represents), then you always have to opt for "what you get". And, I would assume opting for the more advanced option (between two links) makes the most sense...since it allows for chain stretch. Unless you're building a track car...which might dictate another course of action.

Street89vette

had the lower intake manifold sent off and ported, enlarged and ported runners +10%, and plenum ported also. changed valve springs to match cam specs. bypassed TB water line, deleted heat riser tube, custom tune chip to match above. three row aluminum radiator, 160 thermo, dual fans, short block stock L98... 9.6 to 1. Street car but trying to wake up the engine without going to 383. lol

cv67

leave the cam where it is take advantage of EFI tuning
what rear gear are you using?

If tuned optimially cut your losses, build the bigger motor that extra stroke does quite a bit

GREGGPENN

I agree with Ron and Brian. Gotta find out how your tuner set the spark tables. You haven't confirmed if you disconnected reference wire when setting timing.

With all those changes, you should feel improvement...not lag. That is, unless your improvement is more noticeable ABOVE 3k rpms?

I also agree with Ron regarding the benefit of a 383. With a .550 lift 214/214 cam, AFR195 heads, headers, and mega-ported TPI, I'm pulling almost 150lbs more rear wheel torque than my stock 89.

Really, I probably average 75ft lbs more torque than a stock ZR1 below 5k rpms. (Specifically, my advantage over a stock Z is a minimum of 50rwtq from idle to 4500rpms...jumping all the way to 100rwtq in the middle...from 2.7k to 3.7k rpms). That's a lot of extra "street torque" to enjoy your Corvette....even compared to a Z!!!

Because I let my builder degree/install my cam, I'm not sure where it's oriented. I KNOW it has 4-deg advance built-in. Several months later when the builder actually bored, built, and installed the cam, I said I wanted 4-deg advance. I handed him a multi-position double-roller timing set. Since the build, I've wondered if I might actually be running as much as 8-deg mechanical (cam) advance. Bullet cams said not to worry -- even if that was the case. Obviously, the engine was checked for clearance so that wasn't an issue. Bullet also says MOST street cams come with 4-deg advance BUILT-IN. They also said 8-deg TOTAL advance won't hurt -- if clearance allows it. (He knew my application was a street car). Part of the reason for the 4-deg "normal" advance is to allow of timing chain stretch...over time.

I think 8-deg of advance would shift power downward about 400-500rpms. The intake valve closes earlier and generates more compression (as eluded to above). My PERSONAL opinion about shifting the hotcam to favor lower rpms is do to the 5k "ceiling" of a TPI. The hotcam builds power for 800rpms above that.