FlyLS6

Ok....so I get way too interested in the little stuff.

Both the attached were results on a Dynojet dyno.

The first was done late spring, the second his past weekend. Weather in both instances was low/mid 70s and pretty dry.

No changes were made to the configuration except I had a cross pipe installed right behind the transmission mount on my '73.

HP is statistically the same, as far as I'm concerned, but there was a noticeable jump in torque. One of the reasons I wanted to do this was to see if it was something I wanted to work into an exhaust pipe replacement down the road. H pipe or X, I think I'll probably work some kind of cross over in because right now I'm not seeing a downside.

1977 LS6 crate motor, 990 heads, 198 intake (no porting, etc), 770 SA, moderate Crane Cam - part number 13424, factory exhaust manifolds.

gkull

what diameter exhaust system do you have?

FlyLS6

Typical 2.5" crush bend through Delta 50 Flowmasters.

ajrothm

I would be very interested to see what your car picked up with some 2" headers, 3" mandrel bent exhaust w/ x pipe and some straight thru style mufflers (magnaflows, Pypes etc etc).. I'd be willing to bet you could hit 400rwhp after some tuning..

Thanks for posting your test results..

Dyno testing different changes is always fun..

gkull

I'm a firm believer in free flowing exhaust. I use a 3 inch system with a H pipe. It passes under my custom cross member

Silvertone

I respect your work very much, but for a moderate cam on the street I think I'll stick with the 2.5" mandrel bent setup. I've got the Pypes kit with x-pipe and I really don't believe the 3" would help the range I operate in (under 6000 rpm). All hyperbole until you put it on the dyno I guess, but there is a ton of material written about this subject.

Silvertone

Let's see if I can figure out how to post a photo.

gkull

LS-6 and big ci small blocks need help breathing

Silvertone

LS6. Oh wow, how'd I miss that little detail? Must be time to lock up and head home.

69427

You might consider the effect of an H pipe right after the collectors. Vizard frequently advocates that.

gkull

The X pipe is a nice item, but I never understood why people go to all the trouble and complexity to use the stock cross member holes. Your extremely hot pipes end up right next to the tranny.

All that work when instead of putting a little thought into modding the cross member for a pass under.

I thought of this back when I installed my first set of headers on my new 79 vette

FlyLS6

Thanks for all the comments and observations. Great resource of info here.

36 years ago (and about 18 thousand miles) when we first put the motor in, the original LS6 cam was pulled for an "equivalent" hydraulic cam was installed, along with a scatter shield, hooker headers, double pumper, etc. The motor sounded really cool at almost 7000 rpm. But being old and decrepit now (me, not necessarily the car), the motor was refreshed in 2005 with what I spec'd above.

Decided to go in a different direction, and put tried to put it together with a look that might come factory. Simply tried to optimize what I've got to work with. Do want to work on the exhaust, and goal is to get a mandrel bent system underneath, but probably stick with 2.5".

Small point....on another set of runs, one was made with the hood/airbox down, and it cost around 2hp.

cagotzmann

I guess its because we dont have any temp gauges in the tranny and dont have any before and after test to make a claim if their is any difference. With a car moving and using air as a insulator I would think the temp transfer is less than you think. Normal tranny temps are quite high anyways. I never took any temps with my IR Gun at that point, but next time I have it in hand I may have a look at what the exhaust temps are.

Thanks for showing.

jb78L-82

Probably more of an issue for automatics which run really high fluid temps normally. I never understood why folks with automatics don't run tranny coolers outside of the radiator (the cooler does all the cooling) especially today with the double stack coolers that regulate flow according to the fluid thickness (temperature) and if you run a mechanical fan, always pulling air through the cooler.

I would be very hesitant to cut the crossmember on any C3 unless I absolutely had to for a modification. The H pipe concept for a dual exhaust has been around forever-I contemplated adding an H pipe to my Nova SS back in the late 70's/80's but never pulled the trigger. The theory back then was to add the H pipe as close to the Header collector as possible for maximum benefit. I do not have an X/H pipe on my 78 but would seriously consider it if I ever decide to change the current 2.5 duals with shorty headers to FTH, different mufflers, using an X pipe like the picture above. I currently have a magna flow cat back system, High flow cat X pipe, and BBK shorty headers on my 94 Mustang GT Convertible. I did the exhaust in stages with the cat back mufflers/pipes first with the Ford tubular exhaust manifold and the Ford cat H pipe, then removed the tubular exhaust manifold for the BBK shorties later, and finally replaced the mid pipes/H with cats for a magnaflow X pipe with high flow cats. Every component change made a noticeable difference in power and sound but the last change of the Magnaflow X pipe with high flow cats made the engine scream at high RPM with a terrific sound….

diehrd

The power is made at the motor so having big tube headers is a huge benefit and from the headers back it would only make sense to have as big a pipe as can be fit. I use an X pipe and have no idea if it adds power or not bu I do know it looks cool as he!! and it never lowers power numbers

jb78L-82

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Any comment of how the X pipe changed the sound versus no X pipe?

jb78L-82

Where did you get the X pipe or was that custom made?

Danish Shark

Sounds better with the X in my opinion. Also reduces the noise level quite a bit.

gkull

It is not just bends, extra connection joints, and hot pipes next to the tranny. Yes, auto trannies even make it worse because of the big pan close to the cross member.

My pass under system makes it very easy to pull the tranny or take off the headers.

gkull

It is very simple as to why the H and X pipe change the sound. true duals have sound frequency of two 4 cylinder motors. so you have a lower Hz rumble sound.

When you combine the duals you end up with double the Hz and the motor sounds smoother and less radical. No more deep rumble