Problem with performance after cam.

Guantero · June 27, 2012

Ok, just did a tr220/112 in my 2004 silverado. My supporting mods are springs, push rods, headers, cai, circle d 3000 converter, transgo shift kit, flowmaster exhaust, and blackbear tune. The run quality of the truck seams good but felt a little light on the power. I went to a local guy to have it dyno tuned and sure enough I was right. He modified the tune a little for air fuel but my best run was 226hp and 255tq. After 4800rmp, power drops off. Timing was set to 27 degrees. He kept bumping up the timing just to see what would happen. Around 34 degrees, it started to knock with 87 octane. He said that the engine has great air flow but just does not make the power. The number on similar setups I have seen are about 100 higher! The only thing we can come up with is that I might be off a tooth on the cam or I got a bad grind. Any input would be great before I have to tear this thing apart again to figure it out.

Thanks

Scott

vettelovralexand · June 28, 2012

Dynos can all tell a different story(peak number wise), but I do agree that you should not be having the power drop off anywhere near that low of a speed with that large of a cam. You sure you aren't getting any valve float?

Guantero · June 29, 2012

Don't think so, I am using comp 918 Valve springs. I know that cam is no where near pushing them to the limit. I think I will just pop the timing cover tonight and take a good look and check the rockers and re-torque.

Thanks

Scott

Prokopchuk_9 · June 29, 2012

I would go thru valve train, check compression of the engine as well. Maybe a leakdown test...

Guantero · July 1, 2012

Ok, took everything apart again and looks like everything is installed correctly. After talking to people from thunder racing, comp, and a local engine shop, looks like it might be a problem with the cam. I will send it back this week to get it checked out. Anyone ever hear of getting a cam that was ground wrong?

Guantero · July 24, 2012

Just heard back from thunder racing and they sent the cam back to comp to be checked out. They say it is ok and is on its way back to me. I am running out of ideas. The only other thing I can think of that would affect the timing would be a loose timing chain. Chain and gears look good but there is a little slack on the back end of the chain. After 100k, how much play should be in the chain and could that be my problem? The only other thing on the motor I changed is plugs. I got ac delco iridium gapped at .040. Any other help or advice would be greatly appreciated.

Thanks

Scott

Carder09 · July 24, 2012

Wow, when I installed a cai and got a BB tune, I had 93 octane tune for both performance and normal driving but I was seeing the same numbers you were when not in performance mode! performance mode is my tow/haul button now. When I engaged the t/h, I was at 250rwhp and almost 300rwt, so something is definitely going wrong somewhere.

GMstrong · July 24, 2012

is this "local guy" that tuned this truck respected and known or what.

Guantero · July 24, 2012

Yup, he tunes ford an gm motors of every type from stock to forced induction. I don't doubt his ability to do a good tune. Like I said, I used him after I already had a blackbear tune so he didn't have much work to do. I did talk today to a guy a a local corvette shop since the motors are similar. He said that even though comp checked the cam, the lobes may be right but not in the right alignment with the dowel pin and holes on the end. Does anyone know how I can check this after it comes back?

Doug_Scott · July 25, 2012

Do a search on degreeing in a cam. You will need to get a degree wheel, most any speed shop will have one. If I read you right though, you did not change timing chain and gears with the cam swap? Not usually a good idea. If it were me, grab a timing chain set (chain and gears, been out of this side of it for long time, get full double roller chain and matching gears. You may also want to look at a gear set that has the extra cam timing holes in it. Easier to advance or retard cam timing. Use degree wheel set up to do this as well.

You may also want to start using high octane fuel. That much mods to engine should like higher octane fuel.

GMstrong · July 25, 2012

i agree on doing the timing chain and gears when installing a new cam,i would actually make sure the valves where adjusted right when i first read this the first that came to mind was what vette said valve float.start a thread on performance trucks dot net

Doug_Scott · July 26, 2012

i agree on doing the timing chain and gears when installing a new cam,i would actually make sure the valves where adjusted right when i first read this the first that came to mind was what vette said valve float.start a thread on performance trucks dot net

Valve adjustment would have to be pretty bad to effect performance like this. There would be other obvious signs, noise or inability to idle, backfiring/popping back. Running valves too tight have the effect of advanced cam timing. Too loose, retarded cam timing plus noise. Plus you would need to be outside the operating range of the lifter as well.