There is most likely an inch of primary pipe in the collector. So probably not optimal buy most likely not hurting anything either.

 

Lifters.....

When I purchased my Cam Motion cam, the tech told me that the stock lifters were only good to about 6200-6300 rpm. The ones I had on backorder were supposed to be good to 6700-6800 rpm.

What happens when they are above their intended rpm range?
Do they pump up and hold the valves open, or do they collapse and not give the intended lift? (less airflow).

 

That could be a problem or the valve springs not being up to the job. I once had a situation with the Comp 918 beehive springs giving out on me. I had a dyno graph that look like yours but at a lower rpm. The motor would not make over 350rwhp and peaked at 5200rpm. Turned out to be the valve springs. Now the motor is peaking at 6400rpm.

 

When the lifters go above their intended rpm range they cannot fill with oil fast enough to pump up so you will effectively lose lift and duration. I had the comp R's in my combo with a stud girdle and AFR rev kit. However, matched valve springs, lifters and a nice stud girdle should be good to 6800.

 

OK, so here's the plan.

The only two parts that are the same from the previous LT4 hotcam conversion motor were the lifters and the heads (even though the heads were ported to stage II, they are the same heads).

So I am doing the following:

1) I borrowed a set of Comp R's that were in a race only car with about 40 passes on them.

2) I purchased an AFR hydra-rev kit and will install that as soon as I get the installation tool (tomorrow).

Hopefully I will get to the track on Friday.

If this doesn't do the trick, I have been given a set of LT4 heads with bigger valves (2.08, 1.60) that have been ported and gasket matched to the same intake gasket that my current heads are (GM #12367777).

What do you guys think about this?

 

I would not go as far as changing the heads. However, you will be able to identify if you solved the problem or not. I just have a gut feeling it is the valve springs. While you are doing that you should get a nice stud girdle for the rockers to stabilize the valvetrain a little bit better. I'll try to find a link to the ones I had.

 

I've always been a little suspect of the springs myself (blue stripe beehives) Comp 918s.

We tested two of them when I had the heads off and they met correct pressure specs. But I've always been suspect.

Any suggestions on springs? I looked at the Thunder racing web site some time ago (6 months or so) and they seem to have a couple of stiffer springs, but they're not bee hives.

 

psi springs are some of the best. I would give Advanced Inductions a call as they know their stuff about the valve springs. They will need some specifics on your cam so a cam card would be helpful as well as installed height and retainer to seal height, etc. They will get a valve spring that will match your cam perfectly. http://www.advancedinduction.com/

I contacted them a month ago about my new setup and they were very helpful.

 

Thanks for all the help. I will definitely call them.

I put the car all back together late last night. I woke up to rain. It's supposed to rain all weekend.

I'll have to wait till next week to see if the lifters worked or not.

 

Any thoughts on barometer readings?

#1 = 100.8 kPa
#2 = 99.7 kPa
#3 = 100.8 kPa

 

I don't think it's the lifters.

I installed the Comp R's and the AFR hydra-rev kit. Went to the track last night and only got one run. Problem was, I ran it with the stock ignition set-up (MSD coil and MSD Billet opti) instead of the MSD Digital 6 box with a blaster II coil and billet opti. After the first time trial I returned to the all MSD set-up.

Car ran 1.630, 4.808, 7.539 (8th), 89.64 mph, 9.843 (1000), 11.935 @ 110.84 Still about a 1/2 second off.
Had much better air. AFR was 12.7:1. Stock tach showed I shifted at 7000, but my Wideband O2 logger said I shifted at 6200 and Datamaster showed 6300. Stock tach does not do well over 6000 rpm apparently. Can't say for sure that the liters did not work but the car ran and felt the same.

After the first time trial, I kept my computer plugged in and checked my AFR and looked at Datamaster. There were several oildowns and a deer almost got clipped at the top-end. Needless to say I had it plugged in for a long time (1-1/2 hours).

In the lanes waiting for the 1st round of No-box, my car wouldn't start due to a dead battery (computer plugged in). I was pushed out of the lanes and told the starter what happened. He gave me a booster from his car and let me get back in to the lanes. Car started, I went into the lanes, and overheated due to me turning off the water pump when I was trying to start the car. Puked water everywhere and I was done for the night.

I am going back next week with same set-up to say for suew, but I think it's something else.

The AFR rev-kit adds addirional spring pressure to push the lifter down on the cam. This wpould be the same as having stronger springs, no?

So what's left? Heads not flowing what they are supposed to?

Any thoughts welcomed.

 

Hmmm... This one is tough. The ignition system probably wouldn't give you any ET. What gears are in the car? What size tires are you running? Also, did you try out any of the tunes I sent you to see if they made any difference?

Yes, the Hydra rev kit adds pressure to the lifter body and in effect does the same thing as a stronger spring without stressing the plunger. You should get a shift light to dial in your shift points to eliminate that variable.

 

There's 4.10 gears in the rearend. Tires are 28 x 11.5 x 15 ET streets (27.9" tall). I cross the line at 5900 rpm (which calculates to 119 mph if it were an M6) So there's roughly 8% slippage in the TH-350 with 8" converter) which I am told is in the ballpark.

I took your matt12.lt1 file and used the 75 MAP and up timing and fuel tables, plus the PE RPM and PE Temp tables. It ran about 11:1 AFR from 4500 rpm up. I made a couple of runs down an old country road and dialed the PE rpm table in to get it to 12.7:1 AFR. from 4500 up.

I have a sport comp tach, but its hooked up to the MSD tach signal, so when I run on the stock ignition, I need to run on the stock tach.

I screwed up by running the stock ignition first. I was trying to see if I could pinpoint something in the MSD system. I thought I could rev to 7000 on the stock ignition since that's what the tach reads, but the stock tach is way off on rpm (600-700 rpm when it blasts over 6000). I really shifted at 6200-6300 based on data loggers.


The MSD system only allows me to rev to 6500 before it breaks down. (And I mean breaks down. It gets to 6500 them breaks down and bounces all over the place - 6500, 5500, 6500,4000,6500,5000,6500,3000 back and forth with a very violent hit, not like a soft-touch rev-limiter). So that's why I screwed up and went with the stock system first.

I will go next week and see if I can do better with the MSD system shifting at 6400, I doubt it.

I need to get this figured out. Why am I only making 355 RWHP?

 

Who speced your cam? Also, do you have a set of 26" tires you can borrow to see how your car repsonds (even if they are drag radials). My car was a different car NA with a set of 26" tires vs a 28". It allowed me to be deeper in thrid gear and pull much harder in my power band.

I wouldn't worry too much on the dyno numbers as I was able to run 11.45@118mph only dynoing 351rwhp 335rwtq before I tuned in my combo. The dyno tune only netted me peak numbers above 6200 rpms but not too much on the low end.

 

Cam was spec'd by Cam Motion. Picked up 2/10ths over the prev cam.

My Ford rearend is narrowed 2" per side, so salad shooters do not fit. I would actually have to buy 26" tires and mount them to my 15 x 8 telstars (5" backspace).

I may buy 26 x 11.5 x 15 ET Streets and mount them tomorrow, so I have them before I go to the track on Friday.