LT1nitrouZ

So I went to get my car dynotuned today, after a few passes to get the AFR right he pulled the car farther up the RPMs and at 5270 RPMs HP was at 353, but by 5450 it was down to 282. So at first we thought the valves were floating but noone in the room could hear it, there wasnt any misfire the car just fell on its face. So the guy got to asking question and I mentioned the shitty platinum plugs that were in the car so he suggested I change them (He sent one of his guys to autozone to get me the plugs and allowed me to use his tools and leave the car strapped to his dyno while I changed them, SUPER COOL) So we ran it again with new NGK plugs and the car pulled to about 5200 levelled out at 365 HP till about 5430 and again power dropped by over 80 HP by 5630.

The car has a 396 with CNCd LT1 heads and intake, cc306 cam, Longtubes, 58mm TB. Changing the plugs netted an 80 HP gain from 5200 to 5400 so I cant help but believe that it is in the ignition system. It has a New Delphi OPTI, but has 7mm wires and doesnt have an MSD igntion box or anything of the sort. Have you guys seen this sort of problem before? I really dont think it is the optispark or I would think there would be a misfire, but I am not sure. The AFR is staying at 12.8:1 across the board even after the power starts dropping, so I am just led to believe there is a lack of power more so than a defective part.

I had it tuned at Southern Speed in tupelo, on a Mustang dyno. Not sure what other information I need to add, but just ask and I will reply.

speed_demon24

iTrader: (6)

Can you add the graph? What valve springs are you running?

LT1nitrouZ

I didnt get a copy. I really wasnt thinking much about the graph when I left. I can call them tomorrow and I am sure they can email it to me.

I have comp 918's I believe. Whatever the beehive spring comp recommends for the cc306 is what it has.

The car was dyno tuned before I bought it, and it pulled fine all the way up to 6000 RPMs. I ran it at a track though, and I knew it was running WAY too rich hence the reason I got it retuned. Beginning AFR was 11.2:1. Picked up 35 HP across the board... now if I could get the topend problem figured out I might have a fast car.

ss.slp.ls1

iTrader: (36)

Did you have your spring pockets machined down? What rocker arm ratio?

NUTS95Z

iTrader: (1)

i had this happen to me,removed the cai and left maf hooked up and gained 90 grams of air up top. i didnt fall off no more

LT1nitrouZ

I bought the car with the motor already built, and I am honestly unaware of what having the spring pockets machined means? I am running 1.6 comp cam magnum rollers.

z_speedfreak

iTrader: (3)

918's require a installed spring height of 1.8"(stock is 1.7) so machining of the seats or use of +.050 locks are required to get 1.8". let me know if you need the +.050 locks, I got some for mine but ended up just swapping my spare heads on that had already been machined so you can have em cheap if you need them. I suspect it might be something bigger than incorrect spring height tho.. wish I had some ideas... maybe check your coil?

LT1nitrouZ

Gotcha. Ill let ya know if it turns out that is the problem. As said the guy had the car tuned before I got it, but I dont think the guy that tuned it before knew alot about LT1s hence the not so great tune. However the car pulled fine all the way up the powerband, so I would think if it was incorrect spring height then that would have showed on the first dynotune. I would think as you said it might be the coil, or something that could have been working fine before, but is now not putting out the power it should be. Also as stated perhaps the airfilter got clogged or something, just looking for ideas to check to avoid just shooting in the dark. thanks man.

Z-RATED94

iTrader: (6)

Which 918s and how old are they? I myself didn't have much luck with those springs. Lasted only 1500 miles for me.

LT1nitrouZ

maybe 3000 miles. I had them on my last motor, had no problems with mine.

yonson

Here is the last pull, first one is by time, second is RPM (didn't make a full pull so that's why the graph looks like crap).

yonson

Hmmm, guess it'll only allow 1 image per post.

LT1nitrouZ

This is the captain obvious statement of the year, but dyno graph is posted. Perhaps that helps anyone?

I have an MSD 6AL on the way, MSD coil, and MSD wires and going to reset the rockers. I am crossing my fingers, unless someone has a better suggestion.

robsquikz28

iTrader: (246)

are you telling me ur graph did that.....all jacked up like that?????
if thats the case and it breaks up like that, id say optimus prime

LT1nitrouZ

Thankyou for concurring that something is not right.... Now my question is what the **** is wrong?


My car is not worthy of being called such a name.

Badazz 97 TA

iTrader: (18)

i think he meant to say opti spark

Cross

iTrader: (10)

No he said Optimus Prime because we need to jam a Matrix of Leadership into the engine that will bring it back........... lol

LT1nitrouZ

Odd thing is the first pull on the dyno looked WAY worse than that, and the car still trapped 89 MPH. I only mention MPH as it is a 6 speed with a 10 bolt and 3.42 gears and stock suspension... The E.T. was obviously gonna be bad... If I can get the thing running right it should be pretty quick. Its just how long and how much money its going to cost that worries me at the moment.