AU N EGL

I think he has something here.

ipuig

I can't take credit for that approach, Mike Norris tuned the car.

DeltaBravo

Check out my dyno graph in this thread. It might give you some insight into air/fuel ratios. IIRC, mine was 12.5 before tune-up and 11.5 or so after tune-up at WOT.

http://forums.corvetteforum.com/c5-g...new-vette.html

Dennis

0Mike@NorrisMotorsports

Seeing as a stock M6 car will do in the 290-310 RWHP range and also be in the 315-330 RWT range, here are my thoughts.

Even if it is all stock, that cam would most likely not do much till about 3500 or so as I did something similar with a 2004 Z06.

Seeing as you are making maybe stock HP and less then stock torque, and assuming everything was mechanically good to start, I would say you either have the cam installed one tooth off or more or the lifter preload is wrong.

I have seen the cam tooth off quite a few times from self installers as well as regular shops. Can be easily missed if not double and triple checked. More so if the oil pump is still on the car when aligning the marks. Yes, I had done this about 7 years ago and why I roll the engine every time. When I owned my larger shop, I had all of my employess check each other as well as have me check to be sure.

After lining up the gears, I always roll the engine around twice and watch the marks come together. Lining things up before disassembly and then just bolting it back up with a quick look does nor guarantee proper alignment.

Hope this helps.

Mike Norris

zeevette

Mike, if the OP installed the cam one tooth off, wouldn't it run so bad, as to be very noticeable?

trk982003

Thanks for all the excellent ideas! I dont know about the a/f ratio I'll suggest that to the tuner next visit up.

I too thought about the cam timing being off, but my living is made as both a car and motorcycle mechanic. Timing 4 cam engines isn't that bad, let alone a single cam engine where the timing marks are inches away from eachother. It isnt out of the question but it also isnt likely. I did have the oil pump off so its that much more clear to me. I rotated the engine over before putting it back together. The lifter preload however has me interested. What are you saying really? These rockers arent adjustable i followed the torquing sequence in alldata. I used what pushrods TSP recommended (7.40") Could the lifters not be pumping up or whatever?

Can anyone add input on being a tooth off? Would the HP and TQ graph cross at a different point if thats the case? They cross at about 5200rpm (i'll try to post the graph). No PTV contact on a relatively high lift cam? I'd hate for that to be the case but at least i'd know. I;m not pulling that timing cover off on a hunch thats for sure. Thanks again guys i really appreciate the help here! Makes the situation feel better anyway

MDoe8

**edit** nvm

ipuig

Lifter preload should be between .060" - .100". The shop that ground my cam stated you can go as low as .040" without concern, I do not know if that is correct.
I would focus on the F/A ratio and exhaust back pressure theories for now. There is a procedure in the service manual for checking the exhaust back pressure, you shlould be able to pull it from ALLDATA. I do not know if GM varied this value when they went from the 4 cat H pipe to the 2 cat H pipe, but for the 4 cat H-pipe configuration exhaust back pressure should not exceed 2 psig at 2000 RPM as measured from the AIR check valve fitting. The service manual calls for special tool J-35314-A/BT-8515/BT-8515A, I'm guessing this is some sort of low range pressure gage with a suitable fitting that will connect to the AIR check valve assembly. You can probably come up with something that will work. Good luck.

deadcafe

I run a 233-239 .595/.604 TSP cam 112-LS, I also have ported 5.3 heads and the FAST 92 ,LS3 TB with a full exhaust, UD pulley. I laid down 435rwhp and 386rwtq on a mustang dynanometer. My tuner said that these cams are HP consous and not built for TQ....Why... Because Horse Power sells.

This cam comes on strong at 3500rpm and keeps on pulling up to 6720rpm.
If I Had to do it all again I would supercharge it. 500rwhp with the swap of a pulley.

I would say your weak point is your heads, intake and your exhaust. I would recomend finding an LS6 intake and heads... Friend got 600.00 for the heads from his 03 Z06 and I have seen LS6 intakes go for 300.00.. then port your TB. I have seen a lot of headers for sale on here lately for cheap. At that point if you are not hitting at least 390/370'ish RWHP/TQ numbers then find another dyno.

0Mike@NorrisMotorsports

With the cam one tooth off it will actually run well and feel pretty good.

I agree that it is usually tough to get it off one tooth, but rolling it around before taking it apart is not as important as rolling her around after getting the chain and gears back on and actually watching them come together as you roll them around.

Like I said, I have been building cars since about 1976 and had put one back a tooth off about 7 years ago or so. That is why I roll it after and then do it 2 or 3 times to verify. Pain in the *** to a point, but easier then pulling it apart again.

On the preload, I usually have between 3/4-1 1/21 turns on the rocker arm bolt from the point of zero lash till it bottoms out on the rocker pad and begins to torque down. Too little preload should not be the issue, but too much can cause a valve to hang open slightly. Usually also feels to run rough also.

Hopefully the preload and other checks prove productive.

Mike Norris

trk982003

I didtn think you could adjust lifter preload on gen3 engines. In the old sbc the rocker nut was self locking, these are small bolts that all data gives a torque value for.
I have been thinking that with such long exhaust duration that any backpressure at all may seriously affect the ability to remove exhaust gasses? If there's back pressure the cylinders goin to stay full of inert exhaust? possibly? Higher combustion chamber temps = leaner/less timing right? We have a backpressure guage that screws into the 02 sensor bung.

I'm fairly sure my engine in its otherwise stock form is capable of higher than stock numbers, i understand its not near its potential with my equiptment but it should be better than stock regardless.

Dudeiwin86

13.6 a/f is "conservative" for a street car?

wow...

i think its pretty obvious why you cant get any more timing in the engine.

and considering the RPM band for that cam, and the complete lack of mods to support that RPM band (stock intake/headers/cats/exhaust)...

the results look like about what i would suspect. the engine cant breath where it wants to.

0Mike@NorrisMotorsports

Correct, there is no rocker adjuster nut as with most other engines. You adjust preload with different length pushrods. As the lift goes up, the base circle gets smaller which changes preload. 85-90% of the time, 7.400" pushrods (closest to stock) will work fine. The more lift, the better chance of needing longer pushrods. Milled heads and low lift cams may need shorter pushrods.

With that said, it is always best to check preload and not assume it is correct.

BTW, 13.6-1 AF is way lean in my book and as mentioned, a good reason there is KR.

Again, hope this info helps.

Mike Norris

trk982003

The pushrods are what TSP suggested I use, if others with the same set up use this set up and same engine and pushrods why am i having problems? I understand that my stock components are flowing at their maxes, but even still it should produce stockish hp right? At least thats my understang/assumption. I know the power is produced higher up but theres 100 hp at 2500 rpm. That graph may be invaluable to you guys i'll get that uploaded somehow asap. Thanks for stayin with me guys. You guys dont think 13.6 is conservative? I'll have to suggest we fatten it up next visit. Whats there to lose?

trk982003

Could the cam be a bum grind? starting to think outside the box can ya tell? The car seems to have more power at half throttle than at WOT.

deadcafe

Do a 1st thru 4th mild run and Video tape it. Post here

trk982003

What are you lookin for with that? You mean goin down the road or on the dyno? Maybe i can answer any questions for you

Chrisbequick

The tuner probably didn't have the motor at full throttle at that RPM. The dyno pull typically doesn't start until about 1000 RPM past that.