Dyno pull today....

[wx briefer]

Stock LT4 except for hot cam, corsas and SLP 'claw' intake.
316 HP/ 303 torque.
Friend suggested this would be the case. He has 382 HP LT4.
He suggested long tube headers and high flow cats. (he should know).

His mods include CNC'd LT4 heads shaved .30 and open exhaust with some port matching.

Any suggestions on 'ready fit' long tubes?

 

[69MyWay]

TPIS has some nice (expensive) long tube headers that will work great.

 

[David Gordon]

I thought the LT4 would dyno higher than that. LS1 dyno around 310+ and i figured a LT4 would do close to that.

 

[Shriker]

That does actually sound a bit low ....... generally stock LT4's dyno around 290-300+ stock. Hot Cam will add ~25rwhp and Corsa's ~5-10 rwhp and intake up to 5 rwhp or so (if that). So even if the car dynoed on the low side stock , say 290 rwhp + 25 for hot cam and 5 for the catback you should still be around 320 rwhp, I guess your not that far off. May check plugs, wires, fuel filter etc. just in case. Also , the hot cam can work without tuning but really needs it to be most effective. If you have not had it dyno tuned , I am sure you would benefit ......

My car has an open lid/K&N filter, longtube headers, high flow cats, B&B catback. It dynoed at 318 rwhp and 328 rwt at MTI. I am guessing I gained ~25 rwhp from the exhaust and lid/filter.

Hope that helps......

 

[Hib Halverson]

316 from an LT4 with the Hot Cam and exhaust is low.

What kind of dyno? What was the correction applied to the data.

Also, does this engine have a reviese PCM calibration that goes with the mods?

 

[wx briefer]

Hib, I realize now where I went wrong. I never hit fuel cut off. The best run shows graph at peak at 6250 RPM. Perhaps this may explain some of the problem. Also, stock programming at this time.

 

[UB2 SLOW]

Something is really wrong. I dynoed 315 with an LT1 and a hot cam plus headers and exhuast.

 

[LT-4 CE]

I just dynoed my LT-4 with exhaust, cold air, and it made 305. Two other similarly modded LS-1 C5s made 292-305.

This was same day, same weather, same dyno (Dynojet).

 

[69MyWay]

I don't trust dynos to be true and exact. I feel they are a great tuning tool to base line, then adjust to see your power go up or down.

After running Killer on a dyno in 02 and getting some scary (LOW) results....I did as much research as I could. The more I learned, the more I learned not to trust a dyno to be the bible truth of your power curve.

There are so many factors that affect the accuracy of the dyno for true accurate numbers.

You need to get the car to the track, and make enough runs to rule out driver error. That will tell you the truth. Trap speeds don't lie, nor to ETs.

You should pump that car at or around 105 plus mph at sea level at the other end of the track.

 

[Mako]

Stock LT4 except for hot cam, corsas and SLP 'claw' intake.
316 HP/ 303 torque.

Do you have the dyno graph w/the O2 data avialable, that would be very helpful.

Also, using Datamaster or similar to log the pull and see what the timing, MAF and other data looks like would also be very valuable - did you happen to log the PCM data during the pull?

Thanks,
Mako

 

[wx briefer]

I did not log any data, however, my high flow cats are now here and just waiting on the jet coated, full length headers to arrive next week. My little engine is gonna get there, yet! I just bought a Triumph Sprint bike and now I am really spoiled! 107 RWHP and less than 500 lbs. I have to get the vette up to speed now. I have no choice.

 

[Mako]

I did not log any data, however, my high flow cats are now here and just waiting on the jet coated, full length headers to arrive next week. My little engine is gonna get there, yet! I just bought a Triumph Sprint bike and now I am really spoiled! 107 RWHP and less than 500 lbs. I have to get the vette up to speed now. I have no choice.

Well without hard data, there's not a lot I can recommend. I can speculate on some things though, mainly that the power enrichment tables in the PCM are likely wrong.

I suggest you go back on the dyno and get the O2 curves and datalog the PCM data this time. Based on that hard information, we can make realistic recommendations on what the engine wants/needs to make more power.


Who's tuning, if any, is in the PCM now? Are you experiencing cam surge or other drivability problems?

CYa!
Mako

 

[wx briefer]

Actually, Mako, the LT4 programming is pretty good as is. Of course, after the headers and hi flow cats, I will play around a little more with it. Car runs smooth as a baby's but with no codes in the last few thousand miles. It is quite a bit better than stock cam setup. OBDII system is not as easy to tune as the pre-1996 models since the only game in town is LT1/LT4 edit. I will consider that idea when I see the dyno after improvements with exhaust.

 

[Mako]

Actually, Mako, the LT4 programming is pretty good as is. Of course, after the headers and hi flow cats, I will play around a little more with it. Car runs smooth as a baby's but with no codes in the last few thousand miles. It is quite a bit better than stock cam setup. OBDII system is not as easy to tune as the pre-1996 models since the only game in town is LT1/LT4 edit. I will consider that idea when I see the dyno after improvements with exhaust.

OBD II LTx programming is now well understood in the tuner industry. I use LT1 Edit myself. I worked with Jeff Creech at his dyno shop (www.carolinaautomasters.com) over the summer and became quite familure with using a dyno properly as a tuning tool. Jeff is GM PCM wizard, so I got some very helpful exposure to LTx and LSx PCMs.

The LT4 HotCam really isn't all that "hot" cam spec wise, so the PE tables aren't that far off, but I'm confident there is room for improvement in them. I agree that it's best to make the next set of mods to the car before going through the expense of dyno testing the car again.

Just remember to fully instrument the car with wideband O2 and data logging software the next time on the rollers, the information you gather from that will be very useful to you.

CYa!
Mako

 

[wx briefer]

Mako, I don't know what you call hot, but personally, my friend is getting 382 RWHP naturally aspirated. Of course, he has a couple of other modifications including exhaust. To my way of thinking, that is pretty dang good! His pull is on the same dyno that gave me only 316 at 6250 RPM, where I let up.