[Skip Fix]

Originally Posted by mchell

Don’t get too into trying to compare your numbers with “what others” are getting .....it’s a dyno.......every single one will produce a different number....best to get it to the track if you want to judge your real world power... the guess will turn into reality.....and frankly, that may be a disappointment as well....sound like a decent build, have fun with it

What he said same goes for engine dynos. My RAIV 400 with a 288/296 UD made 385 engine HP on a very conservative dyno through headers and mufflers and ran mid 12s @ 109 weighing 3900 lbs. My 455 made 400 rwhp and with some tuning at the track ran 10.90s @124 weighing 3750. Current pump gas 455 made 525 HP on a Stuska engine dyno runs the same as previous 455 and formulas show more like 550-570 hp engine HP.

[Formulajones]

Originally Posted by gtofreek

I don't understand the whole 25% loss through the driveline thing. How can they rate that in a percentage? 25% of 300 HP is 75 HP. 25% of 1000 HP is 250 HP. You mean to tell me that a certain driveline will take 175 more HP to drive simply because the engine makes more HP? It just doesn't make sense. Seems to me the driveline will rob "X" amount of HP regardless of how much power the engine makes.

I'm in agreement, and have told people in the past trying to figure out flywheel numbers on a chassis dyno from a percentage is not that accurate. I've had an engine on the dyno, and the same car on the chassis dyno later. The percentage thing doesn't quite pan out.

[Lee]

Originally Posted by gtofreek

I don't understand the whole 25% loss through the driveline thing. How can they rate that in a percentage? 25% of 300 HP is 75 HP. 25% of 1000 HP is 250 HP. You mean to tell me that a certain driveline will take 175 more HP to drive simply because the engine makes more HP? It just doesn't make sense. Seems to me the driveline will rob "X" amount of HP regardless of how much power the engine makes.

TOTALLY correct. I've had a few rants on this previously. There are few people that have done more personal testing on chassis dynos than I have. I've seen 40+ hp differences JUST from changing torque converters. I've seen 35hp swings from air filter elements/housings.

The "25%" thing is horribly inaccurate. There are just TOO many variables.

[Steve C.]

And two interesting articles related to the subject.....

Dyno Thoughts and HP Losses

http://www.sdsefi.com/techdyno.htm


Comparing Chassis and Engine Dynos – Racing Dynos

https://www.hotrod.com/articles/1106...-engine-dynos/



.

[mchell]

Originally Posted by Steve C.

And two interesting articles related to the subject.....

Dyno Thoughts and HP Losses

http://www.sdsefi.com/techdyno.htm


Comparing Chassis and Engine Dynos – Racing Dynos

https://www.hotrod.com/articles/1106...-engine-dynos/



.

Bingo.......good reading

[gtofreek]

I built a 455 with 6X heads for a friend. The heads were ported, and it had a solid roller cam. That engine ran 10.90's @ 122-123 MPH in Phoenix[73 Firebird]. He had it chassis dynoed one summer in 100+ degree heat. It has a TH400 in it also. It dynoed at 485 HP to the rear wheels. If that car had a 25% drivetrain loss, then the engine would have been making 606 to the flywheel. There is no way that engine made 600 HP. 550 flywheel HP is more like it. That's about where it dynoed on our engine dyno. That's only about a 12% drivetrain loss by my calculations. So, based off these numbers, I get more like 304 rear wheel HP from yours.

[JSPONT]

I think torque converters rob a little bit depending on what you have. A stick shift car will put a little more on the dyno, but can be slower at the track. That's why no one races dyno's. (except in the race section here! LOL)

[Lee]

^ He is not competing in any class that I know of, so no reason to NOT increase pipe size, and gain power.

[brodad]

My brother worked at an import tuning shop and they called their dyno “the heart breaker”. I saw many people show up with import and domestic engine combos expecting big numbers and get disappointed by the results. Like it was said earlier a great tuning tool.

[Formulajones]

Originally Posted by Lee

^ He is not competing in any class that I know of, so no reason to NOT increase pipe size, and gain power.

I agree, but that wasn't the point of my post. His concern, or maybe he's led to believe, his exhaust is really holding the combo back. I have a ton of experience with these transverse systems with my own personal testing and felt it needed to be pointed out that what he has, isn't that terrible and is enough to support his power level. The fact that I can install better flowing muffler setup along with an X-pipe and gain absolutely nothing shows that the Flowmaster system is capable of supporting his RWHP level, and then some, because mine was actually a bit more HP.

I'm actually in the low 300's for RWHP at this point and haven't touched the exhaust. I feel he'd be spending a large chunk of money chasing HP with an exhaust only to be disappointed. Especially considering 3" on a 1st gen isn't fun to fit either and opens other issues.
I'd be more concerned with straightening out the rich AFR he says it had first. Depending on how much fuel trimming is needed he may find 5-10 HP right there. But quite frankly, like I said earlier, I've seen other Pontiac 400 builds on the dyno that also were in the 270-280 RWHP range so I don't see any real big concern. Take it to the track. Depending on what it weighs (1st gens are relatively light) his HP level should give him some easy low 13's with decent conditions. That's doing pretty well with a mild 400 Pontiac.

[highway star]

Remove the flex fan & install a clutch or electric, less parasitic drag.

[steve25]

Improvements to go faster you ask?

Rotating mass wherever it's found on the car just eats up HP like it's going out of style, be it in the mass of the Rods, Pistons , Crank and flywheel , or the rims tires and brake drums on the car and is many times overlook looked for shinny new 320 plus cfm ported heads and big Carbs!

[1funride]

Working from memory but if I recall about an 8.3ish and 83 mph, my 60 foot times were terrible with wheel spin. Had a nitto 555 tire on there with posi, the tire just wouldnt do much. Best run was very 1st when the light changed and I wasnt ready, I just hit it and it actually did OK. I think the tires actually degraded past the 1st run, but of course since the first run seemed to grab I tried to load the converter a bit, that resulted in smoking the tires and having to pedal it. Then it became loading the converter some, take off and getting out of throttle when inevitable tire spin started, then back into it partially, then full throttle. I gave up on trying to get a clean pass as it just wouldnt hook up, and in some instances I spun through the first 2 gears and the car started going sideways. The tires generally restricted my passes to 80 ish mph and just wouldnt allow more power to be applied/

[prostreet64]

Those 1/8 mile #s could be 12.80s in the 1/4 and with decent traction who knows how well it might run. Nothing more frustrating than having the power but not being able to put it to the ground.

[1funride]

I am having a nasty resonance with the flow master transverse muffler at 40mph. I am thinking of changing it for just that reason, at times I like it, but most of the time now I either slow down or speed up to get past it. I seen several flow numbers for flowmaster vs other mufflers, and the flowmaster look to flow much less, in some instances less than 50%. Hard to believe it can be that bad. The ultra flows seem to flow exceptionally well, but I am a little concerned with true duals fitting without scrapping as my car sits lower than stock. I didn't know how the Pypes transverse muffler flowed with the race pro muffler, which seems to be closer to 2 single pipes in a single package. I like the ultra flow dual setup.

[Formulajones]

Originally Posted by 1funride

I am having a nasty resonance with the flow master transverse muffler at 40mph. I am thinking of changing it for just that reason, at times I like it, but most of the time now I either slow down or speed up to get past it. I seen several flow numbers for flowmaster vs other mufflers, and the flowmaster look to flow much less, in some instances less than 50%. Hard to believe it can be that bad. The ultra flows seem to flow exceptionally well, but I am a little concerned with true duals fitting without scrapping as my car sits lower than stock. I didn't know how the Pypes transverse muffler flowed with the race pro muffler, which seems to be closer to 2 single pipes in a single package. I like the ultra flow dual setup.

Correct. The Flowmaster claimed flow from various sources never looks good compared to other mufflers, but in this case I didn't find it to have any affect. Like I mentioned I swapped to the Pypes setup and the car gained absolutely nothing at all. The Pypes transverse system is in fact a straight through design. The pipes are separated from each other inside that transverse case and have continuous flow through each pipe. If you'll notice in the design, the driver side inlet enters and exits the top, the passenger side enters and exits the bottom, they both go straight through just like their dual Race Pro mufflers. Not like a typical transverse where the inlets enter the bottom and exit the top side, so the pipes are basically intertwined and don't flow well in that style. So technically speaking, if the Flowmasters are so terrible, I should have seen some sort of gain just from the muffler upgrade, but I didn't. This tells me that at this power level it's not making a bunch of difference.
So the Pypes transverse from my experience will typically work just as well as a dual muffler system, because that's essentially what it is, and without all the ground clearance issues.

Getting back to your drone issue, I found the same thing with that Flowmaster American Thunder transverse setup. They are exceptionally loud. Years back they also offered the same thing called a "Force II" that used a quieter muffler with more chambers. I've run both systems and the Force II was much quieter and didn't drone. That's the last system I had on the bird before I switched to Pypes. Unfortunately Flowmaster cancelled that system many years ago and now only offer the American Thunder, which technically should flow a little better than the Force II I was testing with.

[1funride]

Formulajones, yeah I think your correct. It seems logical that the Pypes (RacePro) would flow better as you have a congiguous flow rather than all the changes in direction and waves/turbulance hitting one another. There is a point where all that begins to play in and you loose power, for me I think a new exhaust is needed, I dont mind it louder on outside of car but the inside droning is terrible.

I "think" the Pypes Race Pro muffler would also flow better than the Dynomax transverse muffler, as it appears the dynomax transverse muffler is similair to an X pipe and there would be some wave fronts hitting. If someone disagress with this logic and has real world experience please let me know otherwise.


Im going to throw out a few more questions in general.

* Max HP limit of Pypes Race Pro 2.5" transverse systems before it restricts, I estimate 450 simply becuase it's a 2.5" system?

* Does anyone have real world experience/opinions with the Pypes Race Pro transverse muffler as compared to a true 2.5" dynomax ultraflo system with seperate mufflers? Just not sure if I can fit a true dual system in a lower sitting Gen 1 firebird without scrapping.

* Opinion on Tom Hands prior system which I beleive was 3" out of collectors, 3" through the X-Pipe, then reduced to 2.5" using flowmaster cone reducers, then 2.5" into and out of a Pypes transverse muffler?

[Formulajones]

There are limits but I've seen several of these Pypes Transverse systems on 10 second cars. There are quite a few of them in the FAST series as well running 10's and mid to upper 120's on F-bodies.

Yes my feeling is the Pypes race pro transverse flows better than the Dynomax. I've used the Dynomax too, but no testing with it. But I do like that muffler better for it's sound qualities.

I've also run the dual muffler system in 2 1/2" as I mentioned, it was no better than the Pypes transverse. Not at our HP level anyway. However if you go changing the pipe sizes you may find something. Only problem is though, on a 1st gen, and even a 2nd gen, the 3" stuff is a tight fit. It doesn't tuck up into the driveshaft tunnel very well, which in turn makes the mufflers hang even lower, plus the muffler cases are larger because of the larger pipe diameter, then snaking 3" pipe through the leaf springs back there becomes a challenge. They almost always create tire interference as well when it comes around the gas tank. Some aftermarket gas tanks are notched here just for this purpose.

The only kit I've used that I really liked in 3" for a 1st and 2nd gen is Torque Tech. It actually fit as well as could be expected, But they are no longer in business unfortunately.

My father runs something similar to what you describe on his GTO. He runs a 3 1/2" off the header collectors, and into a Dr. Gas "X" pipe that reduces the pipe to 3" coming out of the "X". That's the best way to reduce pipe size. Then he runs a typical 3" A-body system from there with race mufflers and tail pipes from Torque Tech. Actually a very quite system in the car, no drone.

I've done other similar things. For instance on our Z I run the Pypes transverse system but I wanted a stock appearance out the back so I substituted the tailpipes for factory 69 Z tail pipes in 2". Reduced coming out of the transverse muffler. Not only did this give me a factory appearance but it did a couple other things. It freed up a ton of room around the gas tank and leaf springs, it also allowed me to use the factory tail pipe hangers, and it also mellowed the sound of the Pypes system to a point where my wife is very happy with it. Yet it's highly doubtful the change cost any measurable HP because you're at the very end of the system where pipe size isn't critical, and it's only a short section of about 1 1/2 feet of pipe with very little bend in it.
There are tons of options depending on the sound level you want and how much work and money you can tolerate. But from my experience it's not worth spending the money if only chasing 5-10 hp. Unless you jump up in pipe size and want to deal with all those issues, then I think you'll find some gain. I have tons of sound clips with examples I've mentioned but it doesn't sound like that's what you're after.

[1funride]

Formulajones, I am absolutely interested in sound clips, if you have a means to share that isn't too much work that would be fantastic.

[Lee]

FWIW, I had full 3" dual exhaust, Dr. Gas X, large case Xlerator mufflers, and 3" tailpipes on my '67 Firebird. No rattles, no ground clearance issues, no problems at all. The guy who did the install is WAY better than the average muffler shop guy, though.