Why does my power seem to lop off?
10-10-2011, 02:34 PM
#1
Why does my power seem to lop off? I've been fairly happy with my recent build, but I've been haunted by a little voice in my head saying it should be making more power. Here's my dyno thread that has a lot of info on my setup. My car is a '98 Camaro.
https://ls1tech.com/forums/dynamomet...in-cutout.html
here's a quick list of the mods:
Freshly built LQ4 (50 miles when dyno'ed)
stock internals
ARP rod bolts
799 heads shaved .030
PAC 1518 springs
236/242 XER cam .601/.610 114+4
LS7 lifters
LS6 intake
SLP lid
stock TB
stage 2 T-56
LS7 clutch
PST 3.5" aluminum DS
MWC fab'ed 9", 4.11 gears
And here's the dyno graph
Now here's a thread of a setup that was just posted in the dyno section that is very similar to mine. Basically the only difference is that they are using an MS4 cam and unmilled 799 heads.
https://ls1tech.com/forums/dynamomet...o-results.html
Now I'm not comparing the numbers between the two, as that is futile. My main concern is the curve of the power, and how mine seems to lop off, especially the tq. It was my understanding that the drop off of tq after peak tq is a main factor tied to heads and flow, but I might be wrong. But, we are using the same heads and his graph seems to carry the power better than mine. We have similar cams that should be carrying power to the relatively same rpm, and both of us have LS6 intakes.
Now my graph isn't showing any obvious signs of things like valve float, but that doesn't mean it's there. I didn't measure installed height on the springs, nor did I shim them any amount. I suspect that this might be a problem.
Basically I wanted to get some other sets of eyes on this and see what you guys think.
Car feels great and doesn't seem to break up at all in the upper rpms. I've run a best time of 11.8@117mph with a 1.69 60' in 1300 DA. Car weighes about 3700lbs now with me in it with the iron block (3630 before iron block).
https://ls1tech.com/forums/dynamomet...in-cutout.html
here's a quick list of the mods:
Freshly built LQ4 (50 miles when dyno'ed)
stock internals
ARP rod bolts
799 heads shaved .030
PAC 1518 springs
236/242 XER cam .601/.610 114+4
LS7 lifters
LS6 intake
SLP lid
stock TB
stage 2 T-56
LS7 clutch
PST 3.5" aluminum DS
MWC fab'ed 9", 4.11 gears
And here's the dyno graph
Now here's a thread of a setup that was just posted in the dyno section that is very similar to mine. Basically the only difference is that they are using an MS4 cam and unmilled 799 heads.
https://ls1tech.com/forums/dynamomet...o-results.html
Now I'm not comparing the numbers between the two, as that is futile. My main concern is the curve of the power, and how mine seems to lop off, especially the tq. It was my understanding that the drop off of tq after peak tq is a main factor tied to heads and flow, but I might be wrong. But, we are using the same heads and his graph seems to carry the power better than mine. We have similar cams that should be carrying power to the relatively same rpm, and both of us have LS6 intakes.
Now my graph isn't showing any obvious signs of things like valve float, but that doesn't mean it's there. I didn't measure installed height on the springs, nor did I shim them any amount. I suspect that this might be a problem.
Basically I wanted to get some other sets of eyes on this and see what you guys think.
Car feels great and doesn't seem to break up at all in the upper rpms. I've run a best time of 11.8@117mph with a 1.69 60' in 1300 DA. Car weighes about 3700lbs now with me in it with the iron block (3630 before iron block).
Last edited by black00ssFL; 10-11-2011 at 07:32 AM.
10-11-2011, 05:52 AM
#3
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The curves look totally normal to me...carries power pretty well to 7k. The numbers are just lower than expected. Maybe you'll see some more ponies once the motor is more broken in? Port the TB? Pulley? Exhaust setup?
10-11-2011, 07:31 AM
#4
Stock TB is ported, although that really doesn't add any hp. and the exhaust is 1 7/8ths Kooks longtubes with a 3"-4" y and 4" cutout, here's a pic
Another thing too. Last track event I went to much clutch (LS7) wasn't liking 6000RPM dumps and the new power it's making. After the first run the smell of burnt clutch was prominent and wouldn't go away, even after about an hour and a half cool down. Now I'm not sure exactly how clutches "go out" but I always thought it was something that was obvious like rpms climbing faster than usual, etc. Could it be the clutch starting to slip too?
10-11-2011, 08:35 AM
#5
Nothing seems too far out of line to me. Maybe you were just overestimating based on it being a 6.0?
I almost bought a lq4 but the numbers are unimpressive to me. They seem to come in around the same hp as a similar ls1, just a little more torque and more dead weight on the nose of the car.
Unless I was planning boost in the immediate future or got one for basically free, I don't have much interest in them. The loss of compression would be somewhat disappointing to me.
I almost bought a lq4 but the numbers are unimpressive to me. They seem to come in around the same hp as a similar ls1, just a little more torque and more dead weight on the nose of the car.
Unless I was planning boost in the immediate future or got one for basically free, I don't have much interest in them. The loss of compression would be somewhat disappointing to me.
10-11-2011, 10:34 AM
#7
The ? I have, relates to the loss of 30RWHP when the dump is closed. That sounds to me as A LOT.
Was the engine tuned w/ the dump open or closed? If closed, and you dyno'd open, there's a significant leaning of the AFR...What was the AFR during the pulls???
Looking at the pulls... the tq and hp don't come close to matching at 5252...Am I missing something??
Was the engine tuned w/ the dump open or closed? If closed, and you dyno'd open, there's a significant leaning of the AFR...What was the AFR during the pulls???
Looking at the pulls... the tq and hp don't come close to matching at 5252...Am I missing something??
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10-11-2011, 10:45 AM
#8
The ? I have, relates to the loss of 30RWHP when the dump is closed. That sounds to me as A LOT.
Was the engine tuned w/ the dump open or closed? If closed, and you dyno'd open, there's a significant leaning of the AFR...What was the AFR during the pulls???
Looking at the pulls... the tq and hp don't come close to matching at 5252...Am I missing something??
Was the engine tuned w/ the dump open or closed? If closed, and you dyno'd open, there's a significant leaning of the AFR...What was the AFR during the pulls???
Looking at the pulls... the tq and hp don't come close to matching at 5252...Am I missing something??
I'm still using a stock catback after the cutout (I don't like headaches while driving), so that's why there's such a power loss. The graph shows the very first pull with cutout closed and the last/best pull with cutout open. Best cutout closed run was 374hp. AFR was the same, wideband was put in the extra bung on the kooks headers. AFR was 12.6-8, tried 12.9 and only gained 2hp.
10-11-2011, 06:12 PM
#9
i would be looking at the difference of lsa. a cam with a narrow(er) lsa is going to carry power after peak better than a wide(er) lsa cam.
for example: look at some of the trex dynos. it peaks at 6300 and floats to 7k and above.
something else to consider, i specd a 236/242 xfi lobe 109+0 lsa cam for a friend to use with a vic jr 370 build. it peaked at roughly 5800 and basically flatlined to 7300, where his limiter is. i think he has a head flow issue, but the point is...the 109+0 lsa is most responsible for carrying the peak power. i'm sure the vic jr helps, but the low peak number to start with tips me off that it's not moving as much air as it is capable of.
for example: look at some of the trex dynos. it peaks at 6300 and floats to 7k and above.
something else to consider, i specd a 236/242 xfi lobe 109+0 lsa cam for a friend to use with a vic jr 370 build. it peaked at roughly 5800 and basically flatlined to 7300, where his limiter is. i think he has a head flow issue, but the point is...the 109+0 lsa is most responsible for carrying the peak power. i'm sure the vic jr helps, but the low peak number to start with tips me off that it's not moving as much air as it is capable of.
10-11-2011, 07:50 PM
#10
I did think about retarding the cam, but didn't think it would make that much of a difference and hurt low end too much. I did install a cloyes adjustable cam gear set when I built the engine since I found it locally for a good deal. You think it would be worthwhile to retard the cam 2 degrees?
10-12-2011, 07:47 PM
#11
your ls6 intake is more or less forcing a 62-6300 rpm peak, as it will do to most any cam over 230*. it makes 380whp+ from 5500 to 7k, that is reasonable. you have a broad tq curve as it is. all you can do is slightly skew it by retarding/advancing the cam.
10-12-2011, 08:18 PM
#13
I guess I'm too worried about it. I'll just leave it be for now while I finish out school and enjoy it as it is. I literally have less money into this engine than a set of high end heads, so I can't complain too much.
