VVT Cam tuning question

[2000_SS]

I have a '68 C10 on my dyno with a 6.2 / TH400 in it. The engine is from an Escalade and has a Holley high rise intake, long tubes, and a TSP VVT-4 cam...and a 4k converter.

I picked up 17rwhp by zeroing out the lo/mid/high cam angle tables. I couldn't show any gains by retarding the cam anywhere. I had it set to 1* at 4200 tapering up to 6* at 6800rpm. That setting made 441rwhp. I added 2* to the tables (2* more cam retard) and dropped to 427rwhp. I then went back to the original setting and subtracted 2* and made 451rwhp. I zeroed the tables out and made 458rwhp.

Is this is typical? it doesn't jive with anything i've read really but all the threads i've found on VVT tuning is pertaining to stock stuff or stage 1 type cams. I haven't tried experimenting with low/mid range settings yet because i really don't think they'll show up because of the loose converter, just trying to get the truck dialed in before fine tuning it.

[IARLLC]

It seems that the chosen cam is big enough (for your heads/compression/exhaust/etc) that even retarding it on the top end loses power. Since 00000ing the table actually leaves you parked at 8.5 advanced I would tend to think that some retard on the top end would get you something....but clearly it will hurt your lower end numbers to retard it anywhere below 4k.

You had it at 1 tapering up to 6 then 3 tapering up to 8 (I guess). We are only hearing about peak numbers which must have been achieved above 6000 where you had about 5 retard (441HP), 7 retard (427HP), or 0 (451HP). There is a decent size gap still between 5 degrees and 0 degrees at 6000 RPM. You might try retarding 1 at 4500 or 5000 tapered up to about 3 at 6800 just to see. I would really like to know how that goes. Please update us if you try that. I have to believe that there is some benefit to adjusting that cam (compared to leaving it 8.5 ahead).

HAPPY NEW YEAR TO YOU ALL!

[2000_SS]

I actually did try retarding it in various increments and certain areas like you're suggesting and I never noticed anything but losses anywhere in the Power Band. I think part of the problem with this particular truck is the loose torque converter, but I can't see any gains anywhere from retarding the cam. With all other variables being equal or close to equal as possible, every dyno run was within 1, 2 , or 3 horsepower.

[IARLLC]

Well 458 rwhp sounds pretty good to me...just seems strange for it to make max at 8.5 advanced. Many medium-large street cams used to be (30 years ago, maybe still are) ground 4 advanced (for extra low end) but they usually showed upper end gains retarding them on top.

The one thing I can think of that might affect the results....The stock ignition timing table for VVT (VCT>VCP) has an extra 8 or so degrees of ignition timing added in by 6000 RPM if VVT is active....in order to keep the field even for comparison sake is that table 0000d out too? so that you get the same timing with and without? Maybe?

[RySmDPT14]

Well 458 rwhp sounds pretty good to me...just seems strange for it to make max at 8.5 advanced. Many medium-large street cams used to be (30 years ago, maybe still are) ground 4 advanced (for extra low end) but they usually showed upper end gains retarding them on top.

The one thing I can think of that might affect the results....The stock ignition timing table for VVT (VCT>VCP) has an extra 8 or so degrees of ignition timing added in by 6000 RPM if VVT is active....in order to keep the field even for comparison sake is that table 0000d out too? so that you get the same timing with and without? Maybe?

Same thing with my 2012, you actually notice a larger difference with a turbo or blower. With the values tsp gave me loaded in the low mid high and wot I couldn?t make over 5lbs. When I zeroed out all the tables I can make more boost.

[AJK13]

I'm no expert but i have been playing with stock VVT CAM and stock converter on my 2011 Silverado and Notice most gains at part throttle low rpms and rpms over 5200. With the combo of big of a cam, phaser limiter and a 4k stall you may have negated any benefits of the VVT and drivable issues at low rpms. Especially if the converter is loose. If I was using that big of a cam and Stall I'd probably just delete the VVT and mill the heads a tad to bump up CR.

[RySmDPT14]

I'm no expert but i have been playing with stock VVT CAM and stock converter on my 2011 Silverado and Notice most gains at part throttle low rpms and rpms over 5200. With the combo of big of a cam, phaser limiter and a 4k stall you may have negated any benefits of the VVT and drivable issues at low rpms. Especially if the converter is loose. If I was using that big of a cam and Stall I'd probably just delete the VVT and mill the heads a tad to bump up CR.

Exactly what I would have done. I did the cam first then decided on turbo set up and I don?t use the vvt at all.

[IARLLC]

I tend to agree with AJK13's thought. I get a LOT more low/mid part-throttle power with stock VVT cams. And I am sure some added compression would help optimize that cam/large head combo. The only thing with deleting the VVT is that a standard timing set would stand the cam straight up or 4 advanced if chosen that way. That cam manufacturer ground that thing for VVT knowing it would be parked 8.5 advanced.........so running it straight up with a standard gear/chain would be the same as running it with 8.5 filling all 3 VVT tables....which would kill the low end and does not appear to be helping the top end in this case. Maybe what AJK13 is pointing at is that the loose converter is negating possible low RPM VVT benefits so might as well run a non-VVT cam. Yep. I wanna believe that VVT is always gonna help but I think maybe he is right. I know that I have seen cams up to 230 something at .050" getting sizable benefit from VVT though.

I am really curious to hear back about the VVT ignition timing table (VCT/VCP). That has a very large affect (8+ degrees of ignition timing) when we start to change VVT tables. If not optimized for each test the HP numbers are going to lie about the real potential.

[AJK13]

Having a 3 speed TH400 instead of a 6 speed 6l80 probably plays into it as well.

[Philistineau]

.The stock ignition timing table for VVT (VCT>VCP) has an extra 8 or so degrees of ignition timing added in by 6000 RPM if VVT is active....in order to keep the field even for comparison sake is that table 0000d out too? so that you get the same timing with and without? Maybe?

So do you mean that there is an additional 8 degrees of retard if VVT is active from that table? So from 8.5 advanced to somewhere near 0?

[2000_SS]

I never observed the VCP spark actually doing anything. The truck appeared to only be using the high octane spark table. I don't know if it matters, but this is an E38 swapped truck with a TH400, so no manual trans + VVT segments exist and the speedo shows 158mph all the time... theres also no oil pressure sensor, so i had to disable some parameters to get the VVT to work in the first place. I don't know why VCP spark wouldn't be working then.... so zeroed out the vcp table and called it good. MBT appears to be at 24? and the spark plugs read accordingly. I'm diagnosing an O2 sensor issue with it and sending it home. I wish it had a 6lxx trans.... either way, 4.56 gears and a 4k converter make the low and mid range non existent.

[IARLLC]

So do you mean that there is an additional 8 degrees of retard if VVT is active from that table? So from 8.5 advanced to somewhere near 0?

No, it is an ignition timing table that is active when VVT is active. Since the factory uses VVT to give an EGR affect by over-retarding the cam during cruise/light throttle they also give A LOT of ignition lead during that. When people decrease the VVT retard at light throttle they get detonation because of this table. If VVT is adjusted, this table (ignition timing during VVT) needs to be adjusted too. If VVT is 0000d then maybe this table won't be operational. Not sure. 2000_SS made sure of it. That is all I was checking. I just wanted to be sure that table was not messing up the VVT dyno numbers.