Finally broke 400 rwhp, DynoJet myth, muffler comparison
05-29-2006, 02:18 PM
#1
Drifting
Thread Starter
Finally broke 400 rwhp, DynoJet myth, muffler comparison
For those of you who are not getting tired of all these posts I make about my DynoJet runs, I have some more news.
My latest numbers recorded on Saturday were 401.84 rwhp and 424.28 rwtq, SAE corrected. Not too shabby when you consider that the motor consists of a ZZ383 short block and cam, Dart Iron Eagle heads, Edelbrock Performer RPM intake, 9.5:1 compression, Demon carb, and cast iron exhaust manifolds running through a 2-1/2" exhaust system with a Dr.Gas 'X' pipe.
The other interesting point is that my first set of runs back in January produced 344 rwhp and 386 rwtq, SAE corrected. Doing the math, this means I have picked up appx. 57 rwhp and 38 rwtq.
My latest increases were due to the switch from the 750 Speed Demon to the 825 Mighty Demon. I started with the 750 producing 391.33 rwhp and 413.07 rwtq and, after switching to the 825 Mighty Demon, ended up with 401.84 rwhp and 424.28 rwtq. This represents a gain of 10.51 rwhp and 11.21 rwtq. It took me 13 runs to get the carb/timing dialed in but the results speak for themselves.
Now for the "DynoJet myth" portion of the title. I have heard for years that going to a lower rear gear (higher numerical) will hurt your rear wheel horsepower. I have heard people spout numbers from 10 to 25 rwhp. This really didn't make sense to me but I was never in a position to do any actual testing. I had made some runs with my 327 in 3rd gear as opposed to 4th gear and the horsepower actually increased. On my '67 coupe with the 632, I changed tires from 25.7" to 28" and there was no change in rwhp or rwtq. Since these were not technically the same as changing rear gears, I couldn't really prove anything.
Well that changed on Saturday. I made a few runs with the 3.36:1 gears that were in the car and then switched over to a 3.70:1 rear gear. It took me about 4 hours to complete the swap and then it was time to make a few more runs. I was not surprised to see that both the rwhp and the rwtq were virtually identical. That's right - no significant changes. The rwhp was 391.33 with the 3.70 and 391.40 with the 3.36. (This testing was done with the 750 Speed Demon.) I suspect that the people that have done gear changes and claimed a decrease in rwhp, have not done them on the same day with the same conditions. Also, who knows what else they have done to their car between rear gear changes.
Finally, I mentioned in my last thread that I would be performing a muffler test. Well, things didn't exactly go as I planned. The reason for the muffler test was not to try to pick up any horsepower, rather it was to try to get rid of an extremely annoying resonance that occurred between 1600 rpm and 1900 rpm in any gear. Actually, calling the noise "extremely annoying" is an understatement. The sound was so bad that it was actually embarrassing to drive the car.
I currently run the DynoMax Ultra Flow oval mufflers which are a straight through design. I "modified" the rear of my exhaust system to allow me to somewhat easily swap mufflers for this test.
I thought a reverse flow muffler might actually kill the objectional noise so I got in two sets of DynoMax Super Turbo mufflers in the 4.25" x 9.75" case. One was 2-1/2" and the other was 3". I got in a set of DynoMax Super Turbo mufflers in the 5.5" x 11" case. I got in a set of Hooker Aero Chamber 2-1/2" mufflers. Oh, and I got in a set of DynoMax 2-1/2" race bullets. I had a set of Power Effects capsules that I thought I would give a try and I also had a set of SpinTech mufflers.
I started out with the Power Effects capsules. These are mufflers that I had previously run on my 1990 Callaway Twin Turbo Aerobody. It's a real neat concept that incorporates an adjustable butterfly valve that lets you manually increase or decrease the "straight through" flow. With the car stationary, it sounded like the resonance was gone when I revved the motor. Based on that, I made a run with the valve closed and a few with the valve open. The rwhp and rwtq numbers with the valve open were the same as the runs I had previously made with the DynoMax Ultra Flo's. With the valve closed, it lost appx. 20 hp. Unfortunately, the noise was still there under any kind of acceleration. So off these came.
When I took a look at the 4.25" x 9.75" case Super Turbo mufflers, I got sick. The inlet and outlet tubes that are on either end of the mufflers extend appx. 4" inward. On the 2-1/2" muffler, the ID of the tube that extends inward starts at appx. 2.4" and by the end of the tube it has necked down to 2.0". On the 3" muffler, the ID of the tube that extends inward starts at appx. 2.6" and by the end of the tube it has necked down to 2.1". This is pathetic. I didn't even attempt to run these, I just packed them back up. The 5.5" x 11" case Super Turbo had a much better inlet tube design and didn't neck down anywhere near as bad as the other two. I hooked it up to the exhaust but unfortunately the ugly noise was still there. The real unfortunate part about this mufflers is that it is physically too large to fit the car if you want to keep the spare tire carrier. There was no use in making any dyno runs since I wouldn't be able to run it.
Next up was the Hooker Aero Chamber mufflers. The design was interesting and appeared to have a good flow system. I put them on the car and was shocked by how loud they were. These were way too loud for me so there was no use in making any dyno runs. Oh, and to add insult to injury, the resonance was still there.
By now I surmised that there wasn't anything a muffler would be able to do to get rid of the ugly noise. The reason I brought in the 2-1/2" Race Bullets was as a resonator. I placed one of these Race Bullet resonators directly in front of the Ultra Flo and, to my surprise, the resonance was gone! I then made a few runs with the Race Bullets in front of the Ultra Flo's and then with just the Ultra Flo's and there was no power difference. And the best part was the ugly resonance was completely gone. The next step was to put these Bullets right between the frame crossmember and the rear camber rods which means directly behind the 'X' pipe. When I finished that I made another few runs and sure enough, the power was still the same. Alot of work but the results were well worth it.
Steve
My latest numbers recorded on Saturday were 401.84 rwhp and 424.28 rwtq, SAE corrected. Not too shabby when you consider that the motor consists of a ZZ383 short block and cam, Dart Iron Eagle heads, Edelbrock Performer RPM intake, 9.5:1 compression, Demon carb, and cast iron exhaust manifolds running through a 2-1/2" exhaust system with a Dr.Gas 'X' pipe.
The other interesting point is that my first set of runs back in January produced 344 rwhp and 386 rwtq, SAE corrected. Doing the math, this means I have picked up appx. 57 rwhp and 38 rwtq.
My latest increases were due to the switch from the 750 Speed Demon to the 825 Mighty Demon. I started with the 750 producing 391.33 rwhp and 413.07 rwtq and, after switching to the 825 Mighty Demon, ended up with 401.84 rwhp and 424.28 rwtq. This represents a gain of 10.51 rwhp and 11.21 rwtq. It took me 13 runs to get the carb/timing dialed in but the results speak for themselves.
Now for the "DynoJet myth" portion of the title. I have heard for years that going to a lower rear gear (higher numerical) will hurt your rear wheel horsepower. I have heard people spout numbers from 10 to 25 rwhp. This really didn't make sense to me but I was never in a position to do any actual testing. I had made some runs with my 327 in 3rd gear as opposed to 4th gear and the horsepower actually increased. On my '67 coupe with the 632, I changed tires from 25.7" to 28" and there was no change in rwhp or rwtq. Since these were not technically the same as changing rear gears, I couldn't really prove anything.
Well that changed on Saturday. I made a few runs with the 3.36:1 gears that were in the car and then switched over to a 3.70:1 rear gear. It took me about 4 hours to complete the swap and then it was time to make a few more runs. I was not surprised to see that both the rwhp and the rwtq were virtually identical. That's right - no significant changes. The rwhp was 391.33 with the 3.70 and 391.40 with the 3.36. (This testing was done with the 750 Speed Demon.) I suspect that the people that have done gear changes and claimed a decrease in rwhp, have not done them on the same day with the same conditions. Also, who knows what else they have done to their car between rear gear changes.
Finally, I mentioned in my last thread that I would be performing a muffler test. Well, things didn't exactly go as I planned. The reason for the muffler test was not to try to pick up any horsepower, rather it was to try to get rid of an extremely annoying resonance that occurred between 1600 rpm and 1900 rpm in any gear. Actually, calling the noise "extremely annoying" is an understatement. The sound was so bad that it was actually embarrassing to drive the car.
I currently run the DynoMax Ultra Flow oval mufflers which are a straight through design. I "modified" the rear of my exhaust system to allow me to somewhat easily swap mufflers for this test.
I thought a reverse flow muffler might actually kill the objectional noise so I got in two sets of DynoMax Super Turbo mufflers in the 4.25" x 9.75" case. One was 2-1/2" and the other was 3". I got in a set of DynoMax Super Turbo mufflers in the 5.5" x 11" case. I got in a set of Hooker Aero Chamber 2-1/2" mufflers. Oh, and I got in a set of DynoMax 2-1/2" race bullets. I had a set of Power Effects capsules that I thought I would give a try and I also had a set of SpinTech mufflers.
I started out with the Power Effects capsules. These are mufflers that I had previously run on my 1990 Callaway Twin Turbo Aerobody. It's a real neat concept that incorporates an adjustable butterfly valve that lets you manually increase or decrease the "straight through" flow. With the car stationary, it sounded like the resonance was gone when I revved the motor. Based on that, I made a run with the valve closed and a few with the valve open. The rwhp and rwtq numbers with the valve open were the same as the runs I had previously made with the DynoMax Ultra Flo's. With the valve closed, it lost appx. 20 hp. Unfortunately, the noise was still there under any kind of acceleration. So off these came.
When I took a look at the 4.25" x 9.75" case Super Turbo mufflers, I got sick. The inlet and outlet tubes that are on either end of the mufflers extend appx. 4" inward. On the 2-1/2" muffler, the ID of the tube that extends inward starts at appx. 2.4" and by the end of the tube it has necked down to 2.0". On the 3" muffler, the ID of the tube that extends inward starts at appx. 2.6" and by the end of the tube it has necked down to 2.1". This is pathetic. I didn't even attempt to run these, I just packed them back up. The 5.5" x 11" case Super Turbo had a much better inlet tube design and didn't neck down anywhere near as bad as the other two. I hooked it up to the exhaust but unfortunately the ugly noise was still there. The real unfortunate part about this mufflers is that it is physically too large to fit the car if you want to keep the spare tire carrier. There was no use in making any dyno runs since I wouldn't be able to run it.
Next up was the Hooker Aero Chamber mufflers. The design was interesting and appeared to have a good flow system. I put them on the car and was shocked by how loud they were. These were way too loud for me so there was no use in making any dyno runs. Oh, and to add insult to injury, the resonance was still there.
By now I surmised that there wasn't anything a muffler would be able to do to get rid of the ugly noise. The reason I brought in the 2-1/2" Race Bullets was as a resonator. I placed one of these Race Bullet resonators directly in front of the Ultra Flo and, to my surprise, the resonance was gone! I then made a few runs with the Race Bullets in front of the Ultra Flo's and then with just the Ultra Flo's and there was no power difference. And the best part was the ugly resonance was completely gone. The next step was to put these Bullets right between the frame crossmember and the rear camber rods which means directly behind the 'X' pipe. When I finished that I made another few runs and sure enough, the power was still the same. Alot of work but the results were well worth it.
Steve
05-29-2006, 03:16 PM
#4
Wow! That was an informative read. Thanks
Did the HP increase or decrease when you did your run in 3rd gear?
This has been done by manufacturers for many years (on newer cars), I guess that’s where you got the idea. I wouldn’t have thought that there would be no power loss! I personally like the resonance, at lest the one I had in my 84 TA with dynomax and no cats ~3000rpm.
Did the HP increase or decrease when you did your run in 3rd gear?
Originally Posted by 632C2
I placed one of these Race Bullet resonators directly in front of the Ultra Flo and, to my surprise, the resonance was gone! I then made a few runs with the Race Bullets in front of the Ultra Flo's and then with just the Ultra Flo's and there was no power difference. And the best part was the ugly resonance was completely gone. The next step was to put these Bullets right between the frame crossmember and the rear camber rods which means directly behind the 'X' pipe. When I finished that I made another few runs and sure enough, the power was still the same. Alot of work but the results were well worth it.
05-29-2006, 03:24 PM
#5
Burning Brakes
Great stuff!
Wow, I wish I lived near you just to be your wrench hand! Ok, so I have a few questions. Are heads seriously ported? What cam are you running? And HOW did you get that power through exhaust manifolds? Are they ported or what? And if so who did the work?
Oh, and to me its obvious that a gear change will NOT reduce/add to RWHP.
carbster
Oh, and to me its obvious that a gear change will NOT reduce/add to RWHP.
carbster
05-29-2006, 03:33 PM
#6
Drifting
Thread Starter
gator79: You don't know the half of it!
redc3: Best numbers were 11 degrees initial, 39 degrees total, 10 degrees of vacuum advance.
75 Stingray!: The horsepower increased on my stock 327 in 3rd gear as compared to 4th gear. I can tell you emphatically that you wouldn't have liked the resonance that I had. From what you are stating, the resonance in your TA would be the kind I would like as well.
carbster09: Sometimes I wish that there was someone to help me as well. I do everything on my own. The heads are not ported but I did do an intake port match and cleanup. The cam is the ZZ383. I did port the exhaust manifolds. Thanks!
Steve
redc3: Best numbers were 11 degrees initial, 39 degrees total, 10 degrees of vacuum advance.
75 Stingray!: The horsepower increased on my stock 327 in 3rd gear as compared to 4th gear. I can tell you emphatically that you wouldn't have liked the resonance that I had. From what you are stating, the resonance in your TA would be the kind I would like as well.
carbster09: Sometimes I wish that there was someone to help me as well. I do everything on my own. The heads are not ported but I did do an intake port match and cleanup. The cam is the ZZ383. I did port the exhaust manifolds. Thanks!
Steve
05-29-2006, 03:46 PM
#7
Can you give me some numbers on your cam (lift, duration) and I have been ready to change carbs from the speed demon I'm currently running to a mighty demon, seems for more flow helped your numbers....
05-29-2006, 03:59 PM
#8
Safety Car
Great info !!.......I also wondered about a gear change effecting rwhp and tq numbers and got the same results as you (no change) but wondered how it is so......."you're putting MORE torque to the rear wheels" I argued to the dyno operator.........."BUT, that's only because the RPMs have increased", he answered, "check back at the lower RPMs and see that the numbers have not changed".
....I had to agree.
.....again, great combo.
....I had to agree.
.....again, great combo.
05-29-2006, 05:20 PM
#10
Le Mans Master
On my 99 TA, I dynoed 399 rwhp and 374tq, that was with 3.42s and old BFG 275/40 comp TAs. A few months later I changed to 4.10s, had 315.35 Nitto DRs and it dynoed 381rwhp and 368q. The AFR was still at the same 12.8-1 at WOT. They told me it was due to the lower gearing but I think it was more to do with a softer sidewall tire and a tad wider(more reciprocating mass) but I did lose hp. Ironically I ran 1-2mph slower with the 4.10s and DRs backing up the loss of HP.. SUX.
You have a killer setup on your vette. 400rwhp. What all have you done to go from 344hp to 400hp? I know the carb change but was it mainly timing and jetting changes etc? ignition curves? You are getting a lot of power out of a relatively small cam and manifolds. Your motor is making 460-475hp at the crank! VERY NICE...
You have a killer setup on your vette. 400rwhp. What all have you done to go from 344hp to 400hp? I know the carb change but was it mainly timing and jetting changes etc? ignition curves? You are getting a lot of power out of a relatively small cam and manifolds. Your motor is making 460-475hp at the crank! VERY NICE...
05-29-2006, 06:46 PM
#11
Drifting
Thread Starter
73jst4fun: The numbers on the cam are as follows: 112 LSA, 222*/230* @ .050, .509"/.528" lift. These numbers are with a 1.5 rocker arm and I am running a 1.8 rocker.
C3 Stroker: Thanks! Adding just a little more info to the database.
Gordonm: The jetting I ended up with is 76/93. Incidently, those are the exact same size of jets used on my 750 Speed Demon.
ajrothm: Interesting info on the gear change. You may be on to something with the softer sidewall and wider tire. Also, the air conditions could have changed enough during those few months to add to the difference. Thanks for the comments. There are a few threads I created in the past that outline in detail what I have done to the motor/car. If there are any questions about something I have left out please ask me.
Steve
C3 Stroker: Thanks! Adding just a little more info to the database.
Gordonm: The jetting I ended up with is 76/93. Incidently, those are the exact same size of jets used on my 750 Speed Demon.
ajrothm: Interesting info on the gear change. You may be on to something with the softer sidewall and wider tire. Also, the air conditions could have changed enough during those few months to add to the difference. Thanks for the comments. There are a few threads I created in the past that outline in detail what I have done to the motor/car. If there are any questions about something I have left out please ask me.
Steve
05-29-2006, 07:08 PM
#14
Drifting
Thread Starter
Originally Posted by Gordonm
That is a big one on the secondary side. I have to hook up my wide band sensor now! Thanks for the info. 
Originally Posted by CGGorman
Thanks for the time you took to let us know your results.
Invaluable!
Invaluable!
Have I told you guys that I love doing this stuff?
It really is my pleasure.Steve
05-29-2006, 07:09 PM
#15
Racer
I find this all to be very facinating however the one point that is the most interesting is that you run this whole set up through a set of factory exhaust manifold. Correct me if I am wrong but all the advice I have read on basic performance upgrading is to replace your rams horns and exhaust. The engine must breathe to perform and that cannot be accomplished with the factory style exhaust set up.A person must have headers, true duals and low resistance mufflers. I seems that you disproved that thinking.
05-29-2006, 07:35 PM
#16
Burning Brakes
Steve, thanks for posting this. Your posts are always full of quantifiable information that is backed by hard earned testing. Congratulations first on eliminating your resonance as I know this was the reason for your testing. Secondly, congratulations on exceeding 400 RWHP w/ your combination – that is VERY impressive. And with factory exhaust manifolds in a very stock configuration. Nice!
And thanks for sharing your data on the (non) effects of gearing on RWHP. Nothing like back to back ‘A’ to ‘B’ testing to dispel conventional wisdom.
Take care,
Mark
And thanks for sharing your data on the (non) effects of gearing on RWHP. Nothing like back to back ‘A’ to ‘B’ testing to dispel conventional wisdom.
Take care,
Mark
05-29-2006, 08:08 PM
#17
Drifting
"For those of you who are not getting tired of all these posts"
I never get tired of posts like this. Its as good as reading a car mag.
Thanks!
When are you buying headers?
And: congratulations!
I never get tired of posts like this. Its as good as reading a car mag.
Thanks!
When are you buying headers?
And: congratulations!
Last edited by jpatrick636; 05-29-2006 at 08:21 PM.
05-29-2006, 09:22 PM
#20
Race Director
Those are great numbers 
I wish you could have made a run with those bigger Super Thrubos, that's what I have on mine, I was tipped off about the smaller ones with the smaller pipes inside, what a joke
Have a couple of questions if you don't mind
Are the heads ported ? Platinum version ?
What cam are you running ?
and are there any disadvantages to your knowledge of making a duno pull in third gear as opposed to forth ( 1:1 ) ?
I wish you could have made a run with those bigger Super Thrubos, that's what I have on mine, I was tipped off about the smaller ones with the smaller pipes inside, what a joke
Have a couple of questions if you don't mind
Are the heads ported ? Platinum version ?
What cam are you running ?
and are there any disadvantages to your knowledge of making a duno pull in third gear as opposed to forth ( 1:1 ) ?