Al Amarantes

HI
I brought a 383 lt1 motor from a member here . He made 378 hp. The motor has tpis afr heads. and a zz9 cam Duration at .050 212 /226 Lobe center of 112 .with 30lb red top injectors. Now I dyno the motor 4 times it made 320-322 rwhp. A/F 12-1 The motor feels lazy when reving it and sounds like it has a monster cam in it. I did a compress check and the compression was around 230 psi.I did a leak down on it when i frist got it and it was good. I"am lost . Could i have some bad injectors or a cross injector wire. I got new plugs the opti new ebay AC delco , no skips ,no codes, Ruff Idle . I was also getting knock at idle with race gas 0-5 degrees and i had the tuned out.Auto car also .I dont know where to look. and nobody wants to work on a LT1 . PLEASE HELP Al

bjankuski

12:1 Is too fat on fuel try to tune for 12.8 to 13.0 AFR. That should add some power. Your friends car made 378 HP to the wheels or on a engine dyno? I would expect your combination to make around 330 RWHP, it does not sound that far off.

dan0617

Where is the overall timing set at when at WOT? I would think 35 or 36 degrees should be safe but I'm no expert on timing. It was obviously tuned 1/2 decent on the fuel or with all those mods you wouldn't be at 12:1 afr, which is about where you want to be. Make sure the tune is good, the more timing you can get in there without detonation the better. If you ran on a Mustang or Land and Sea DynoMITE dyno, or some other loading style dyno, then your numbers are a little low but not that far off. I'd guess you should see 350 to 360. If you were on a dynojet or other inertia type dyno then you have problems. From my extensive research it seems dynojets read 15 to 20% higher than loading type dynos. Also, auto cars dyno less than manual cars.

Al Amarantes

It was on a dynojet he ran car on a mustang Here is the dyno sheet it is a mail order tuning

dan0617

Your numbers are a little low then. You could jump to 13.0 or 13.2 on the air fuel ratio since you are not running a power adder. By looking at the chart you are in the 11's on the air fuel ratio. Definitely power to be had there. I'd bet that the sluggishness you are feeling is not enough timing, but you need to verify that before you go cranking the timing to it in the tune. Nobody will know exactly what your rwhp should be, we are just giving you rough ideas. My guess is that you should be at about 400 on a dynojet. Much of it depends on your heads and your compression ratio, as well as the tune. If the motor made 378 rwhp on a Mustang dyno then it was getting all that was there to be had. That would be in the ballpark of 430 to 450 on a dynojet. Exhaust can strangle hp but by the looks of your hp/tq curves it looks like the exhaust is adequate. Your torque curve comes on good and strong and holds nicely, so I think you have a good setup overall. Should be a nice powerful setup on the street. I think you need a good tune.

Al Amarantes

Dan i just think there is something wrong. here is the 2nd dyno sheetwith the a/f at 12/1 Timing is 42 at wot.

Al Amarantes

Here is the info on the motor
94 (4) bolt corvette block bored .040 over & clearanced for crank 9.00" deck height (10.5 to 1 compression)
Callies forged Stealth crank 3.750 (std/std mains and rods)
Callies forged I beam rods 5.850
AFR/TPIS heads 187cc with 54cc chambers 7/16" studs/guideplates 2.02/1.65 valves, 600 lift springs
(Felpro 1284 head gaskets .039")
JE/SRP forged silicon alum. custom pistons -16cc dish 3/16,1/16/1/16 Speed Pro rings
TPIS ZZ-9 billet hyd. roller camshaft 112 LSA 108 LCA 287 Adv. 212/226 at .050", .483/.520 lift w/1.5 rockers
Manley 5/16" one piece pushrods 7.250"
LT4 heavy duty timing chain with late model 95 timing chain cover
Comp cams std. Hyd. lifters
LT1 manifold machined for 58mm T.B. and gasket matched to the heads (Felpro 1284)
Rear crossover water tube assy.for cylinder heads

ScaryFast

How much did you pay for the Optispark? I've heard that there are a lot of fake Opti's sold as Delco on ebay that last long enough to get the car running then fail. If it's one of those (they're around $100) it could be the problem.

Check your spark plug routing, maybe you'll get lucky.

Otherwise, I'm with the others - sounds like it needs a tune. Who did the Mail order tune on the car now?

Al Amarantes

madz28 ion

Curveit

The "lazy revs" and rough idle... sounds like a problem with timming.

dan0617

42 degrees at WOT seems like alot. I am only getting away with about 37 before I get knock. You might be getting alot of knock retard so even tho you are set at 42 degrees the computer might be pulling alot of it out.

What are you other guys getting away with at WOT for timing? I thought 38 was about tops out of a good setup but I'm not sure.

dan0617

Keep us updated on what you find.

5abivt

First thing I would suggest is to relax and make a list of all the things to check. Getting frustrated only narrows your thought process and you can overlook the obvious. I speak from experience !

Here's what I would suggest.

1. CHeck your SPark plugs to see if any are wet. My first guess is a bad wire or connection and a plug isnt firing. CHeck the routing as well. IF there is a plug not firing for any reason This will cause the o2 to read lean not rich and dump fuel. Remember the o2 sensor is just that, it measure OXYGEN not fuel.

If your ecm is seeing a richer condition it will advance the timing. I am not familiar with the oem ecm but with a Gen 7 DFI. there is a A/F vs TIming graph. Obviously higher Air fuel ratios like more timing and lower A/F rations can only tolerate so much because of the faster burn. perhaps this is why you are seeing 42 degrees. 42 is WAY too high. It might be so far advanced that the flame is pushing down on the piston before it even reaches the top slowing acceleration significantly. My guess is the ecm is adding tons of timing because it is dumping fuel and the afr is rich.

dynojets measure acceleration which is possibly why your numbers are so low.

The more info you post the more food for thought there is

neat

Did you do anything with the cam timing? It sounds to me like the cam is retarded too far, that could be causing the lumpy idle.

Once you run the motor, or make a dyno pull, try hitting the headers with an infrared thermometer. If one of them is noticebaly cooler than the rest, that cylinder isn't firing.

The lumpy idle could also be a dead cylinder, which would explain the low power if you made no changes to the cam timing.

TenSecondZ

1) You can't compare dyno numbers because unless you are on the same dyno, or one known to mirror the originally very closely it wont be an accurate comparison.

2) 212 degrees of intake duration and 375+rwhp seems like a stretch, even with decent / good heads.

neverendingprojects

In a 383, the ZZ9 cam should definitely not sound like a monster, unless you have a huge vaccum leak.. Providing that there are no vac leaks, I agree with the other posters... It sounds like you could either have bad injectors, burnt plug wire/s or something similar.
Also, isnt 94 the first year that LT1s became Sequential, rather than batch fired? If so, you may have injector wires mixed up.....

By the way, Do those torque numbers look low to anyone else for a 383????

93 ragtop

Two other things to consider. 1. are you running long tube headers? 2. is the throttle opening 100%?

5abivt

Very good point ! DO check your throttle is opening 100%. WHen I first put on an aftermarket throttle body it took me 2 years and 6 different shops trying to diagnose the problem to figure it out. Get someone to get inside and stab the throttle and check if its opening all the way.

CorvetteZ51Racer

42 deg at WOT is WAY too high. I would say 36 max unless some serious (and professional) massaging has been done to the chambers, and then the max timing would be even less. The factory ECU detects knock, pulls a little timing out, and if it's still knocking, it goes into panic mode and pulls out a LOT trying to stop the knocking. I've seen them where they touch into knocking, and pull out to almost 22 degrees of total timing, which flattens the motor.

12:1 is too fat for WOT AFR, however, unless this kind of AFR is also being seen at part throttle settings and idle, it shouldn't cause a 50 HP drop. I've played with this on a Superflow Engine Dyno on 600 HP engines, and seen no more than about 5-10 HP from 12:1 to 13:1 AFR. It's mainly a fuel savings under race conditions thing. Get fatter than 12:! (and that chart appeared to do that) and you'll go dead quickly. If you're seeing those AFRs at low load or idle, you could be fouling plugs.

The comments about the actual delivered timing are good ones. I would mark TDC on the damper and check the actual running timing vs what the ECU thinks it's delivering. If it differs by more than a few degrees, your Opti may be damaged.

9secondflat

when i sat in the car last week and revved the car real quick, i felt a shake/vibration around 3500-3700. the engine didnt rev quick considering it is a balenced bottom end. on my car when i just touch the gas it revves instantly (i have a ls1 383 not lt1) any possible ideas with this added to the equation??