Eakster

So I took the LT4 to a dyno day at Creations n Chrome in Valencia yesterday. Very excited, lots of cool cars. Expected it to be a little down on power, but not this much:



Video:


Car has 110k, generally well looked after, not shy of the redline when I drive it. Plugs and leads are only a few 1000 miles old. Just gave it an oil change and new air filter. Have had slight water pump leak for some time now and it was pretty much sitting for a year until recently. I am now commuting in it it again. Had a worse leak for a few weeks from a hose connector which I finally tracked down and fixed, but this wan't near the opti.

Anyway.. this was the second run in 3rd. First run in 4th was even worse and the power was jumping all over the place. One guy said he saw a little black smoke and it was probably richening out on that run. It seems to be cutting out at two spots, at 5k and 5.7k -being starved of fuel or dropping spark or something, and then dropping off power way too early.
It did sound great though and others commented how healthy it sounded!

Any thoughts from the experts? I am thinking bad opti and/ or injector issues. I plan to replace both now. I am doing the water pump anyway.

One other thought - I saw several cars get disappointingly low numbers. One supercharged pretty new Camaro in particular was showing in the 400s when they were expecting 600s. Bad dyno? It was my first time doing this so I don't know about that kind of thing.

Cheers

cv67

depends on the dyno

Wonder if your valvesprings could be getting tired also that will kill power quick. Go back and forth about putting mine on the rollers..few places close by. hmm.


They can be humbling believe me most with a modded car think they are going to see 4-500 rwhp doesnt always work out that way lol; know lots of operators will (shh!) fluff thier numbers to increase return business.
If it helps there are dyno queens that cant get a decent track time and vice versa. Fun to get a baseline to compare repairs or mods against if anything.

Eakster

Right. I was planning to hotcam it with the original springs soon. I will have to ditch that idea These cars are getting on in years and who knows what kind of life this one's had - I am the 5th owner. It's generally in pretty good shape though.

I wish I'd stayed to see more of the other cars, but I had to get back down into LA for the Corvette show at The Petersen

Fastmax32168

300 Engine HP x .80 drivetrain loss = 240 RWHP.
Perhaps they slipped you an LT1.
Roy

88BlackZ-51

Something isnt right there....

Seen a few stock LT-4's on the rollers and they were in the 29x range.

Corvettress

I have a question unrelatd to his problem. My mechanic told me my wheels were reversed. They looked just like "Eakster's" wheel. Is his reversed? Mine is an 86, so slightly different, but the directional ribbing is close to this. Please clarify.

Blue 92

If you have stock 86 wheels and the spokes are oriented like those above then yes, they are on wrong.

Eakster

I know, I'm asking for ideas what the issue (s) might be

Corvettress

Holy cow! You mean they changed the basic rule of getting air to the brakes from 1986 to 1996? I would have bet $1000 Eaksters' were wrong - but they are ok? But mine are wrong. Well I changed them to right anyway. My mechanic is pretty good.

93Rubie

How old is that gas? I run Sunoco, car seems to like it. BP in my area sucks. Sheetz gas sucks.

Those valve springs have to be weak. That mileage combined with running it.
I just changed out my 60K LT1 springs for new LT4 springs from Summit. Just for this reason. 20 years old, 60K, I run the poop out of it. For $50 its cheap insurance.

Cutting out could be a lot of things. Check fuel pressure under load at RPM before thinking injectors. Then spark.

Kevin Woods

Yep.....worn valve may not be your only issue, but I'd bet a nickle it's your MAIN issie.

Rather than the HOT cam, give serious consideration to the CC-502 cam. Also, if it were my car (yeah.....I know it ain't....but 'IF') I'd look at the CC-918 valve springs. A bit more pricey than the LT4 springs.....but much, much better.

KW

96 lt-4

If the car drives well and pulls hard to redline I doubt springs are costing you that kind of horsepower.The dips in power could be many things,coil,opti,module,or who knows?

Could be a stingy dyno if everyone else seemed low on power.

If you know you have water dripping on the opti then start there and a water pump obviously.Although on the later optispark wasn't the vent moved to help prevent this?


You can look at a lot of things including oxygen sensors and a fuel filter but I would consider trying a different dyno and having your car tuned on it to help uncover any extra hp.Did they give your a/f ratio for the pull?

1985 Corvette

Fifth owner....one of those previous four owners money shifted and found a nice LT1 block as a replacement. At least that's my conspiracy theory anyway. Those numbers look pretty low, indeed. Would hate to see an L98 dyno.

856SPEED

Well, just looking at your dyno sheet tells me something is going on with it when you see the sudden dip in torque/power right at 5,000 RPM. There is something not quite right there that I believe may be the either the culprit or part of the issue. I am not sure what a stock LT4 should be pulling anyway, but even not knowing for sure, that power curve is telling; either there is fuel related issue, spark issue, or A/F ratio issue going on. The only way to know is to have it tuned and look at the A/F ratio which I don't see on this dyno (because they were not tuning). But before that (and it sounds like you might have done this already) is check all of the obvioius things first; fuel pressure, plugs, wires, fuel filter, etc.

STL94LT1

Looks like it might be an ignition/opti problem to me.

scottermis

Make sure your throttle is opening all the way your adjustment cable may be set too long. I bought my 94 vette as the second owner with 28k. The cable adjustment was off and the throttle only opened 2/3rds of the way the first month i had it and i knew something wasnt quite right. Adjusted the cable so the throttled opened all the way and all was good you might check that....

96GS#007

93 ragtop

If your waterpump is leaking, I would go ahead and replace the opti at that time. As others said, its likely to be causing the problem and knowing you need to replace the waterpump, well you are almost there to the opti. With 110,000 miles on it, the opti would be preventive mantaince at least.

Tom400CFI

As others said, might be a dyno issue. May very well be a problem w/your car too, but I'd confirm with a trip to the drag-track or another dyno.

My stock, 150k LT1 put down 277 to the wheels on a dynojet, so...

Check fuel pressure, and ignition. You get any tech needle wavering when your make a pull the the redline?

dizwiz24

gas station preference is going to be like underwear...everyone has a different preference.

BP is the only gas I use in mine. 510 rwhp at 5400 rpm (more if I would have stayed on it) with BP 93 on my supercharged vert.

I utilize BP because if Im in virginia (vs. ohio) I can be assured it is similar to what Im running in ohio (ethanol content, etc.). In fact, the guys at procharger told me that if they are driving a promotion car to different cities/ dynoes across the US, BP is what they also seek out.

Consistent gas is what Im after. A bad tank of gas (someone put 87 octane in the 93 octane dispenser) can ruin my stock bottom end motor thats why I run what I do.

On my daily driver toyota corolla 5spd - running the exact same highway route to work everyday, I came up with the following conclusions on local gas (back in 2008).

Winter blend vs. summer blend: summer blend is better mpg.

Sunoco/ Marathon / Shell = worse MPG

BP = best MPG

Sheetz = 2nd best MPG