Inliners International Forums General Discussion Hi Performance Lost torque by bigger pipes?

We build a new exhaust setup for the 235 (typical dual Offy/holley-weber/split exhaust/m4F/ .06 over).

The pipes are 2 1/4 inch diameter with 2 flowmasters just before the rearend.

I was kind of disapointed when I drove it the first time. It feels like it lost all of the low end torque.

Is it possible to loose so much torque just by installling bigger diameter pipes? I thought that the lower backpressure the better it is.

Thanks, Frank

my experience has been a bit more power, always heard 10%. have you checked timing.

You sure can loose torque with bigger pipes, just look at any cyl. header and the diameter of the head pipes. Stick with 2" and you would be better off. Joe

What is your primary Pipe size? are you running headers? Did you build them or Buy them? If they are headers I'm sure They are not any bigger then a 1 1/2 Maybe a 1 5/8 tops with a 2 to 2 1/4in collector. Which should have came with maybe a 2 reducer. With the bigger pipes you may have gained a little more top end But would have HURT your low end.

I have a Corvette split exhaust header on this engine. Than the two 2 1/4 pipes that go in to 2 flowmasters close to the rearend and than the same pipe diameter over the axle and to the rear bumper.

Greetings . . . Twisted is right on . . .

As I see it most hot rodders have a tendency to lean toward a 'big is better' theory on exhaust systems. This is a drag-strip mentality which is well founded at top end RPMs. But for the street you end up with way to much pipe at low RPM. This translates into lots of air mass to move - resulting in very low exhaust gas velocity - which affects throttle response.

If you're after that Ed Roth 'rat fink' look at the rear bumper you're better off with an echo-can set-up where only the lengths of pipe under the trunk are big diameter and the rest is optimized for the HP your ride is actually putting out. Check out Rap Rap's ride for an example of over the top tail pipes. Sweeeeeet!

I find this article on Exhaust Theory informative.

Considering its content I would say that any ride south of 200 hp is hard pressed to take advantage dual 2 inch pipes. I'd be leaning toward 1 7/8 especially with the cam change where there is overlap. A compromise would be 'bigger' head pipes to the muff and something less in the tail pipes (which by the way is the typical stock configuration - cause it raises exhaust gas velocity).

Years ago I had a three two seven v thingie with some significant mods in the block. For driving on the street I had it set up with stock exhaust manifolds feeding dual 2 1/4 inch head pipes into 36 baffle packs and 2 inch tail pipes. This was certianly a 'restrictive' setup for the top end - but it was very peppy around town which is where I drove that big '68 Impala most times. That engine was putting out well north of 350 hp. And with them baffle packs I could really get my foot into it and not draw much attention.

regards,
stock49

Great Article Stock49.

Thanks for the help guys, that makes perfect sense....

.... BOOOO HOOOO! All that work and money for the birds.

Well at least a chance to try my new pipe bending machine :rolleyes:

Would you say that I can keep the bigger pipes from the mufflers to the bumper or would they influence the torque too because the gasses "shrink" when they cool off?

Frank

C-Dan-DeLuxe

Unless you are into racing or building racing motors, the exhaust diameter, muffler type, header size, etc. is all superfluous to the individual taste and drive-a-bility of your own vehicle.
If you like the roar of an inline, then go with the many different types of muffler systems and keep it sounding like an Inliner motor. If you drive your vehicle everyday, keep it simple and to your tolerance of hearing. I can't tell you the countless times I've been asked, "What kind of motor & exhaust system do you have in your car?" That just gives me the opportunity to talk about my car and all of the modifications.

Personally, most of you all know that I prefer the unique sound of an inline motor. I have a free flowing streetable motor with a mild combustion chamber clean up, a 270 cam, Stovebolt's huge cast headers, 2.5" exhaust pipes, 18" chambered mufflers, and now 6" x 12" diesel truck exhaust tips. They definately give your vehicle some distinction and the "Wow" factor. Last year, I was at a car show all day and several people did the the old double take look at the exhaust tips. They got closer and really looked at the whole system then looked at me, gave me a thumbs up, and never asked what type of motor I had. I purposely kept the hood closed but they could peer through the louvers and side openings to try to get a glimpse of the powerplant. Very mysterious and a lot of fun watching their reactions!

RapRap
1940 ChoppedChevyCoupe

Before you chop the entire 21/4" system up, try installing a 24" to 36" section of 2 in pipe between the manifold(s) and the mufflers, it will act like a primary tube on a header.

Hi Frank . . .

Efi-Diy's got an I idea that's worth a try. And I don't think that I would trash the entire system at this point. Like Darin has pointed out - make sure that everything on the setup is 'sorted out' before making drastic changes - check timing, carb settings etc. The first time I built an engine with a warmer cam and higher compression I set it up lean and late. It wasn't until an old-hand taught me how to set timing with a vacuum gauge and a light that we got it right.

Also, don't forget that with the cam change you've given up some low end torque by design. With the valve events and the overlap the manifold vacuum is likely way below stock. Exhaust pipe diameter can recoup only part of this - cause like the article points out - the pipes can't make HP they can only prevent you from wasting it in moving a larger air mass.

That said, once you 'trade' low end torque and throttle response to get that larger air mass moving it will gain inertia and pay you back at higher RPMs. How's it run on the autobahn above 100 kph?

viel gruess,
Keith

100 kmh is fun but 145 kmh/94 mph (thats about the fastest I ever tried) with a 41 Chevy and diagonal plys is kind a scary. I don`do this verry offten - to say the least and having the breaks in mind.

To be honest I only did that once when an old lady in a wild 1920es sports car passed by on the Autobahn to Vienna. This vintage compressor car left me nowhere

We talked later at an Resthouse and I found out that she is an famous Millionaire from Berlin and she has 22 vintage cars and an own mechanic.

White knuckles - brown shorts... you get the picture

With a modern car 210 kmh/130 mph is not unusual over here, but most of the time the Autobahn is way to crowded anyways.

I will set timing an carbs first if that don`t help I change to 2" ore less. At least to the Flowasters.

Thank`s for all the help folks.