ajrothm

Yesterday I went and picked up my 99 Trans Am(LS1 6spd) from the premier shop here in Houston (Motorsport technologies). I had them diagnosing a fuel system issue and do a full tune up. Well they had dynoed the car before I got there and only made two pulls, one on motor and one on spray. Well they did not top off my near empty bottle nor did they use the bottle heater, later testing showed my bottle PSI at 850 which is useless. Anyway their dyno is a DJ 248 and the car made 391.5 hp SAE and 533hp SAE(that sucks).

So after I left there with my $982 bill for a fuel pump, plugs and tune, I am following my buddy home and he told me an old friend of ours just opened a shop and bought a dyno, so we call him up and he says bring it over and we'll play with it. Now his dyno is the new, state of the art Superflow with eddy current brake for load control AND inertia (which is what a DJ is). So we strap the heat soaked car on the dyno after a 40 mile drive back, and make a pull. On the "STPPWR" which is the Superflow column, it made 370whp, on the "DJWHPW" column which is the "Dyno jet conversion" column, guess what? it made 391.6. Virtually the same as the DJ248 at MTI.

So we let the car cool, heat up the bottle with whatever little nitrous is left in it, couple lbs maybe, and make a pull, it made 515.9hp on the "STPPWR" column and 545.6hp in the dynojet column. That is about what the car normally does on a full bottle.

Now this is where our testing came in, I have a Borla exhaust system like the one below, it has the adjustable plates but I have an electric QTP cutout valve in mine that replaces the plates and lets me go loud to quiet at the flip of a switch.



All of our first pulls on both dynoes was with the cut out wide open letting 95% of the exhaust come out the right side. After the car cooled down from the nitrous runs, we closed the valve completely, forcing all of the exhaust through the huge 19"x4" thick muffler. It is a straight through design but its quieting abilities will make this thing as quiet as a stock oem exhaust system or almost as loud as 400hp with no muffler at all. I wanted to see how much HP gets killed when closing the valve. So we closed the valve and made a pull, the car made 371.5hp on the "STPWR" and 392.5 on the "DJPWR", not believing it, we made another pull immediately and it made 369.5 and 390hp. So the big a$$ muffler that COMPLETELY quiets this thing down to the point of a baby could sleep behind it running, had no real affect on power yet it adds tons of bottom end tq at part throttle operation. Our last test is to crack the valve open slightly, JUST to let some sound echo through the right side pipe just so the car would make SOME sound. We cracked the valve about 1/8", letting about 99% of the exhaust flow through the muffler and just a few whisps coming out the right side for the noise, let the car cool down a good 30 mins, we were rewarded with a 373.5hp "STPPWR" and 395.1 "DJPWR".

We were all amazed that the muffler could quiet down so much noise, so quietly and not kill the power, maybe actually even gain one. Ofcourse that is on this particular setup, which is basically a cam only LS1 with exhaust and a tune. We had made 8 pulls on my buddy's dyno and he only charged me $75 for 3hrs...We had a lot of fun yesterday. I will take my vette back to his dyno just for fun and knock out 150rwhp.

Sorry for the long post but I figured some of you dyno/hp guys would get a kick out of the test.

Budman68

Very interesting read. I haven't dyno'ed my LS1 with the headers, but I feel I lost some power down lowwith the 1 7/8" tubes. What have you done to the motor? Mine dynos a pretty consistant 319 rwhp on a dynojet, which is 360 to 375 hp depending on who's percentage you use.

Big2Bird

Seal up the tail pipe. Torque should go thru the roof.

zwede

I used to have a 96 Z28 w/ LT1 and a borla cat-back. I found the same thing on the dyno. No real difference in power between the quiet and loud setting on the exhaust.

big_G

Same here. On my 383, almost no difference between capped up and un-capped. Me thinks muffler restriction is over rated.

ajrothm

Yeah you would think from the amount of change in sound from open to close, there would be a BIG decrease in exhaust flow but....nothing noticeable.

We also tried to dyno it on the spray with the exhaust open and closed but ran out of juice on the closed pull so...never got any results

Something else I found after reviewing the dyno charts, with the cutout open, the engine made about 2-3hp more in the mid range from 3800-5800. Then I had a dip in power from 6000-6300 where the HP actually dropped about 5-7hp in that dip, with the cutout closed, the dip is completely gone and at one point makes 11 more hp.The peaks were about the same but on the last pull with it closed, we had a longer cool down giving it an extra 5hp at peak.


For the most part, I will drive with with the cutout cracked open about 1/8" or so, just to give it some sound but keep the throttle response and low end power up some. Then when I spray it, I will open the cutout. Its GOT to help on the spray.

Budman78-the setup is cam only. Stock 35k LS1, "Magic Stick" cam(237/242*@.050, .603/.608 lift), LS6 intake, 1 3/4" headers, 3" off road Y pipe, Borla cat back, Racetronix fuel pump, custom MTI tune.(Stock: throttle body, air pipe, MAF, pulley, thermostat)

My next mod will be ported heads, MTI gets $2700 installed/tuned for their custom ported LS6 heads that flow 310cfm at .600 lift. That would gain me between 30-40hp at the wheels but....$$$

I would rather work on building the 408" for the vette.

427Hotrod

Impressive!! Thanks for the writeup. Maybe there IS a reason Borla stuff costs so much huh?? It WORKS!!


JIM

Budman68

I've got to buy a bigger cam. I bought a Comp Cam, but it's only .575 lift with 1.85 rollers, now I'm starting to think I should go bigger.

427Hotrod

Now THAT's the way I like to hear folks talk!!

We can pick one up for you at Comp when we stop by on the way to the Cruise In.


JIM

ajrothm

Budman, to be honest with you, I would have gone with a smaller cam then what I have. Although my cam makes good peak power, its a dog down low. The dyno charts show 300lbs tq at 3100rpms but it doesn't feel or run like it. My car is really a turd below 4k. My cam is even on a 113lsa and its still a dog. I think with an auto and a big stall(4k) it would run really well but in a 3750lb car with a stick, it just doesn't run the numbers. I am running a 7.5" 10 bolt with 4:10s(tiny pinion) therefore I can't launch it over about 3500 rpms and it just doesn't pull hard down low. My 330's suck and it really kills my times.

If I could do it over again, I would go with a cam like a 228/232* @ .050 and .580 or so lift....The .600 + lift just kills valve springs... Area under the curve is where its at.

This cam I am running is what TSP(the cam builder) recommended for a cam only setup but other then the nasty sound it produces, I am not happy with it. A stock 02 ZO6 KILLS my car from a slow roll.