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Need to know what it was dynoed with from intake to exhaust and what kind of transmission/clutch/converter. If there were some mechanical issue past 5500RPM I think you'd likely have a mechanical failure(boom!) not power loss(so probably cam, etc. not geared toward high RPM). That's nice numbers for relatively low RPM. I'd put that in the Jeep any day. If that is in an RX7, hold on to your butthole when you hit the gas. Likely cam/intake swap would move the top end out a bit but you have better than 400 tq from 2500-6000. That sounds FUN.
Aside from regular maintenance, limiting RPMs is one of the easiest ways to increase the life of your engine..so don't frown on it just because it isn't peaking at 6500-7000 like some other motors.
Thanks for the replies guys. I'm not frowning upon it for having lower peaks, just concerned because I'm not sure if I've seen an LS1 engine perform like that. The last thing I want is to buy a car and having to pay for it to sit you know? Anyway, it's reassuring that you say it might not be a mechanical issue and just perhaps cams.
If anyone else wants to chime in, here are the specs:
383 Forged LS1 with less than 2000 miles
Built by USA Racing Engines in Houston
TEA 5.3 Stage 1.5 Milled to 61cc .650 Dual Springs
234/238 .650/.650 112 lobe separation
Forged JE Pistons and Rings
25% UnderDrive pulley
Forged Callies Crank
Forged Eagle rods
All ARP bolts
Morrel Lifters
New Improved Racing oil pan baffle
New Engine Accessories( starter,alternator,power steering pump by TurnOne)
Custom 3" exhaust from header to Y pipe, 3.5" back to removable cat then to Apexi N1 muffler.
All exhaust components v-banded. Test pipe can be swapped in for the cat.
FAST 102mm Flow ported intake
FAST 102mm Throttle body
FAST billet Fuel Rails
60lbs. Fuel injectors
Aeromotive A1000 Fuel Pump, Filters, and Fuel Pressure Regulator
Sumped OEM fuel tank
-8an Braided Fuel from fuel sump to FPR to Rail. -6an return line to top of the tank.
Transmission:
TR6060- From 2010 Camaro SS with 700miles
New Monster Stage 3 clutch with new gm slave and throwout bearing.
New Hinson modified 7/8" clutch Master Cylinder
Samberg 8.8 Cobra Cradle.
2004 Cobra 8.8 Diff.
New DriveShaftShop upgraded axles and Aluminum Cv drive shaft
That looks like a stout motor. Stroking a motor will bring RPM down..how much depends on the setup. Stage 1.5 heads, 383ci, fairly big cam, big intake seem a little mismatched. Perhaps the extra cubes with the smaller heads might be the reason you are seeing the low power peak tight LSA on the cam will move things down a bit too. And theoretically you would want that in a truck. I think a set of 2.5 or aftermarket heads might make the difference you are looking for. I would like to see more opinions though.
Ok thanks Mercier. I'm going to see if the current owner thinks bigger heads will show higher peaks.
The motor was built for a drag truck. I'm assuming it's set up the way it is to get a heavier vehicle off the line faster and going. I just want to make sure this RX7 is daily driveable lol.
The lower RPM power band makes it more drivable, especially in that light car. Verify the heads, their valve sizes and springs and flow numbers if you can. Valve float could be hurting top end a bit too if the valvetrain is not capable of handling the cam.
Seems normal to me for torque to peak sort of early. On many performance cars torque peaks 1000-1750 rpm before HP does. The HP ramps up right to 5500/5900 rpm depending on which set of runs you're looking at. My stock LS1 redline begins at 5500 rpm. Once the car is going 80-100 mph the HP should be the most important thing as the torque has already done the job of getting that 3500 lbs moving. Peak torque on that first dyno sheet is maintained from 4750-5500 or the entire upper end power range. What's wrong with that? The old big block muscle cars from the 1960's that had real stump pulling low end torque in 383-396-440-426-454ci variants often reached max torque at under 4,000 rpm.
The first graph was of a dyno done earlier by tuners that did not finish the job for the owner because they were too busy. The tuners then referred the owner to another local tuner (LSX Power Tuning) who did the dyno shown in the second graph using a Dynocom 6000.
Some people are saying the Dynocom 6000 is rather "generous", sometimes reading about 3-4% higher than average.
However, the owner says LSX Power Tuning then verified that everything was accurate by testing another car with known numbers on the same dyno.
The only thing he changed between the two graphs was rerouting his fuel system I believe (feed the rail first, then hit the FPR and return to the tank).
Yeah, anyway seems like four people so far don't believe there is anything wrong with the engine mechanically. Maybe just a cam and heads combo thing.
Owner also says he was informed that 383s will normally have the RPM shift point at 6000-62000 rpm and the stock rev limiter on a 98' Trans AM is 6200. He also mentions it may be because the engine may be aiming to have its peak HP/TQ to be before 6200 for the auto trans to have faster shifts. Says the tuners told him the car sounds great and pulls very strong.
I did the current tune on the car earlier this year, it was brought to me with an unfinished tune. I re-tuned it from scratch (easier to me) vs trying to work on someone else's tune. Unfortunately I just tuned the car and didnt spec out any parts or do any of the work so I have limited knowledge on the actual car build itself. When I was tuning the car it didnt act like it was hurt or show any external signs (smoking, knocking etc) of having anything wrong with it. Not all heads cam combo's are made to pull to 7k + rpm which is probably the case on this one IMO. The dropping off at the very end of the run could be exaggerated by when I was hitting stop on the run vs when I was letting off the gas also. It was definitely peaking around 5500rpm though.
Dyno's are tuning tools, some dyno's are better for tuning than others but you cant say x dyno brand reads higher than y dyno brand, its simply not that easy. On almost any dyno except dynojet the calibration can be adjusted in the computer to make the dyno read almost anything, dynojets can still be cheated but not as easy as changes a couple numbers in the dyno computer. I have taken more than one car to 2 other dyno's and all the were within 5hp. My own car made within 2 or 3hp on the dynocom as it did on another mustang dyno. The dyno definitely does not read high compared to other dyno's within a couple hundred miles that I use to use on a regular basis. There are only a couple dynocom 6000's out there that I know of but I cant say how they read. I have owned a dynojet 224x and prefer to tune on this dynocom hands down. We are pretty methodical on procedures when tuning and setting cars up on the dyno but there is always the human factor involved. Just like the very first dyno pull (not pictured) the numbers were really crazy, due to myself messing up calibrating the optical sensor. 99% of the time common sense catches those errors when the numbers dont seem right for that combo of parts.
If the dyno sheet is making you question buying the car see if someone can bring the car back by and I can re-dyno it, I highly doubt the numbers will change but the very end of the graph could look a little better just by stopping the run before I let off the gas. I dont have anything to do with the sale of the car or even know the owner but I don't want him to lose a potential sale over a dyno sheet either.
^How convenient for you to drop by lol. No re-dyno is necessary but thanks for taking the time write that out.
I'm just relaying what others are saying but I by no means am an expert on dynos or LS motors (that's why I'm here). Just doing my research and getting expert opinions.
I wanted to make sure nothing was too out of the ordinary shown on the graphs. So far, every reply has been reassuring so thank you everyone.
Dat torque curve.
Looks like a great DD engine. I would give up some horsepower to have a fat torque curve like that any day of the week. HP does drop off fairly quick but that could be any number of things.
i had a dyno that showed my power dropping off around 5k and stopping the pull at 5500 when i know the car was going wot past 6200rpm. the numbers were weird too. this was on a dyno dynamics.
08-30-2014, 01:30 AM
Anything wrong with this LS1? 
