Inliners International Forums General Discussion Hi Performance Exhaust dia.?

Ok, working on a 62 C10 with a 235, that will eventually see a 261. I'll be putting on dual carbs and Fentons, and if I can find one a good mild cam. I was wondering what diameter exhaust pipe you all will recommend. Would 2 1/2" be too big? I'm thinking as of now dual 2 1/4" with a crossover and good turbo-stlye mufflers. What do you all use/recommend?

Dear Joe;

Whatevr pipe fits the fenton's & forget the 'crossover' as it defeats the purpose of the headers.

If you joined our club you could get all the past/present Tech articles.

John M....

Regarding the Fenton's and Offenhaiser intake, be prepared to sped several hours fitting the intake to the headers. You'll be removing a lot of material from the intake to clear the exhaust. Would conservatively estimate I have 5 hours in that project. Good luck.

It's beginning to sound like I either need to go with a 292, or dare I say, V8. I don't think I like what I'm getting myself into...

Hey John,

I've got a question for you in regards to something you said/posted. It's something I've read on here before . . .

I have seen dyno numbers in magazine articles many times that clearly show the beneficial results of running a balance tube or the new "X" pipe style crossover. I must admit NONE of these test were on an Inliner though.

SO . . . .my questions are : . . . .

Is there something unique to the I6 that makes the use of a crossover detrimental to performance ?

I know that it kinda kills the "classic 6" exhaust note that you get with truly seperate pipes . . . . . but how (negatively)does it actually affect performance ?


Ya got me wonderin' ! ?

'Crockett

Dear Mr. Crockett;

The whole purpose of headers on the 235/261 engines is to get the exhaust out ASAP.

Aside from the 'rap' sound It's most important during high RPM conditions (5500)in the case of these small CID engines with 3 cyl. going into each pipe.

Now; The Dyno. numbers/studies you speak of probably relate to the larger V-8s with 4 Cyl. going into each pipe running well over 6,000 RPM.

If these indicate that the (X type)crossover improves performance, fine. But that's their world & not applicapble to our 235/261s.

I know it sounds confusing, but as a matter of practice "pipes" are much louder W/O the crossover which is why it was introduced for "street machines" in the early 60s.

Having the exhaust pressure 'equalized' with this (X type) may aid some V type engines under some condition, but not the old 'sixes' because it slows things down (exhaust relief) and adds extra plumbing.

John M, #3370.....

Chrysler was a big fan of crossover pipes on their large engines in the 60's and early 70's to reduce noise and also a crossover equalizes the pressure pulses which aids lower end torque somewhat. As far as inlines go none of the Big 3 ever bothered to build engines like we do with them so duals and crossovers have no history we can look back on. But across the big pond to our West, Honda used crossover pipes at one time or another on their 2, 4, and 6 cylinder motorcycle engines that are actually inlines ( not the Gold Wings).

On a full out drag engine nobody uses a crossover pipe but it may or may not have some benefit on a street driven inline depending on how the rest of the exhaust system is made up. If you just want to keep the noise down and avoid the sharp split 6 crack then larger pipes and careful choice of mufflers would be the best idea. Muffler location helps too - long tail pipes act as an echo chamber.

Mike G ( 4355 )

Hi Fred,I have experimented with cross over pipes on my old British cycles, yes they are 2 cylinder inlines so to speak,lol.
The cross over was good for bringing back mid range power that was lost to a radical cam.A slight loss at maximum RPM's,no big deal.It also makes carb tuning easier ,again,my opinion.
On the several inlines I have modified,a 261 Chevy and the recent 302 GMC,I run what some call a tri Y header(2 into 1) with a large single pipe and muffler.I'm convinced this set up adds throttle response and power at normal road speeds with no loss at higher speeds.And to me,the large single pipe gives a smooth ripping sound rather than the rough sound of duals on a 6 which sounds like a V-8 with dead cylinder to my ears.

Hi Joe . . .

I am with Tony P. on this topic. In my experience exhaust design is about compromises. The best low end performance and throttle repsonse comes from the stock exhaust manifold. Because of the close quarters it creates the most 'cross over' and suction from the other 5 cylinders (or 3 in the case of a v thingy). This is great at low RPM. At high RPM these close quarters create back pressure, causing the engine to use HP 'pumping action' to force exhaust gases out. Headers are a compromise on the other end. Long tube headers are tuned to scavenge at a specific higher RPM, but this can create hesitation in throttle response at low RPM. A cross-over pipe is another compromise. It equalizes flow in a dual exhaust system, and allows for more scavenging at low RPM by creating flow 'between' the header banks (2 halves of v8 or the split 3s in an i6). This has the effect of restoring some of the low end throttle responsiveness, and also takes some of the rap and rasp out of the exhaust note.

Tubing diameter choice is another exercise in compromises. Smaller diameter pipes create higher exhaust gas velocity, which is great for low end throttle response. But smaller diameter pipes lead to back pressure at high RPM. Bigger pipe diameters will cut back pressure at high RPM, at the expense of low end throttle response. I found this site on Exhaust Theory instructive.

regards,
stock49

O.k. . . .

First of all I want to be clear that I am NOT being argumentitve here but rather I'm still searching for an honest understanding on this issue, that being said . . . consider this:

If you divide by 6 . . .
A 261 cu.in. engine is equal to 43.5cu.in. per cylinder. Interestingly enough if you multiply 43.5 by 8 you get 348 cu.in.

So what we have found here is that on a "cylinder to cylinder" basis the "little" 261 is actually just a "350" with two less cylinders.

That is to say, the cylinders on each motor are processing roughly the same amount of air on each stroke. So this means that per "individual combustion unit" the 261 and the 350 are very nearly the same size. . . . Agreed so far ?

The cylinders all operate independently in regard to intake,combustion and exhaust and are tied together only at the crank shaft. These cylinders do not "know" what configuration they are arranged in, Inline ,V , or opposed.
The events that take place during the cycle are the same within each cylinder regadless of number or configuration.

So there-in lies my delemma . . . . . .
I agree that the whole reason for using a modified exhaust (headers) is to facilitate the rapid and smooth evacuation of gasses from the cylinder via the exhaust port and in most cases reduce the excessive back pressure caused by poorly designed exhaust manifolds.

If a V-8 engine benifits from the use of a balance tube or crossover down stream from the headers,it seems to me it does so "one cylinder at a time". So what I'm having trouble seeing is why ANY engine would not see a simillar benefit on a "cylinder by cylinder" basis.

Isn't the goal of any engine design to make each cylinder run as close to the same as each other as possible so they do not "fight" each other and inhibit performance ?

If a balence tubes goal is to help equalize back pressure to all cylinders then will that not increase each cylinders likelyhood of performing more evenly and thus driving the crank with a more simillar force ?

I understand that maybe I am oversimplifying this somewhat but I do not see any issues created by the "inline" configuration alone that would make it "immune" to benefitting from this performance enhancing modification.

I am, however, quite willing to be persuaded to believe differently based on something of a design nature. Something along the lines of port design, un-equal runnerlength or a cooling issue resulting in widely varied cylinder temperatures.

I just can't seem to dismiss it as a "Inline thing" . . . . .

Still wondering . . . . .

'Crockett

Gentlemen;

Were back to "belts or suspenders" again.

All "Hot Rod" modified engines are built for 'max' power & they all have problems at the low-end because of this.

The compromises mentioned are an attempt to have the best of "both worlds" for street use.

'Crossovers' have been a pain forever, V-8 or 6. They break/leak. You have to take down the whole exhaust system to service/work on anything as opposed to; Nothing, or just the side needed on a V-8 car/truck. Every one I've ever had, has had a problem, of some kind. Fabrication or operations wise!!

Why put on 'duals' & then connect them back together? It was a stupid, waste of time, materials and effort. I KNOW. I 'fell for' this "crossover line" when building Tow Trucks in the late 60s and was realy sorry later. All the ones W/O it worked perfectly. Almost all with it had to be re welded, redone or removed.

Looking back; What the factory had was probably better, all around.

Don't believe everything you read in magazines.

JM, #3370....

One reason V-8's need a crossover, is the fireing order. They do not fire evenly, as a six does. Draw it out and you will see the left and right banks do not alternate fireing. A crossover tube gives these uneven pulses a larger place to go, smoothing the whole thing out. A 6 into 1 header system, on a six, will develope more power but won't sound as nice (at least to my ears).
Armond

A;

Ya know, I think the P-51 Mustang has a six with an exhaust like that.

I wonder how the Viper V-10 is set up???

JM,#3370....

The P-51 had a V-12 Supercharged Allison engine it it. Just think of twin Inline 6's with a 60 degree slant.

I want one!

A nice aircraft 6 that was used in the auto world, was the Ranger 440ci inverted 6, OHC, dry sump and all kinds of cubes, too bad it couldn't rev.

Armond

The P51 models normally thought of had Rolls Royce Merlin 1650 cube V-12's.The earlier P51's had Allisons 1710 cube V-12's.By the way,V type aircraft engines are called inlines.Merlins and Allisons can turn over 4400 rpm and produce upwards of 4000 hp for short duration racing.Thats with 100 Hg of supercharger boost and 6 inch stroke.
Let's look back at fairly hi performance inline 6 cylinder engines,not the new ones with variable cam and induction systems.
What comes to mind is Jaguar,early Datsun Z cars,BMW's and the 3.0 liter 6 used in the Austin Healeys.Did these engines use crossover pipes? I'm not 100% sure,but I believe they all did,either 2 into 1 with a single exhaust or 2 pipes with a cross over.The old Jags in particular were very fast in their day,about 250 real stock HP from an ancient DOHC long stroke from 3.8-4.2 liters.The original 240Z sohc engine was good for 150 HP from 2.4 liters. The BMW's had similar HP from various engine sizes.This was back with crude combustion chamber designs and mild cams by todays hi po standards.
Do ya think these engine designer knew something?

This is what makes HOT RODDING so much fun.
Someone says it won't work, someone says it will work. There are a lot of variables involved.
I say "try it" and if you don't like it remove it. That's what makes YOU a "HotRodder".

My favorite color is red but it may not be your favorite. ??

Ed

I'm totally with John on this one. In my opinion, if you were to run dyno tests on an engine like the low revving 235 with 2” pipes, open mufflers like chambered or glass packs and no crossover, then add a crossover, the dyno “numbers” would show a very small increase.

Running a crossover is like a V running both banks into one pipe, the running that through a cat, then back to two mufflers and calling it “dual exhaust”

There maybe some benefits, but the hassle and the idea of combining your exhaust to one just sounds stupid. You could probably go to larger pipes and get the same performance boost. Just 2 cents

Luis

I can tell you from personal experience that the '68 to '72 Datsun 240Z's never had crossovers in stock form because they had a single pipe with a dual tip muffler nor did I ever encounter any in SCCA racing form. We all kind of followed what the factory teams did and that was a split manifold with straight as an arrow exhuast pipes that usually scraped the tarmac. :)They never had 150hp in stock form either,135 only. But man did they run.

I agree that it's a trial and error type of testing system. Everyone's hearing, feeling, and tastes are different as are exhaust systems. I am on my 3rd exhaust system on my Inliner. I just tried and re-tried until I got what I wanted. I did not want it to sound like everyone else so (as old blue eyes said) I did it my way. I believe that a cross over will quiet down a system no matter what size pipes you have. Any time you scavenge 2 into one, it will quiet it down. I ended up with 2.5" tubing, 18"x3" chambered mufflers(just a crimped piece of pipe ala corvette side pipe mufflers)and a 5"x12" tips.
The tips added 20% more rumble to the system!No lie! I just put new valve seals in my car last winter and it actually quieted down the system about 15%! So by tightening up the valve system, it can change the output sound of the exhaust. So basically, "tune" your system the way you want. There are so many variables it would be very difficult to give you a list and say do this and that and you'll love it. Each vehicle is different so make your system match your car.
Finally, if you are at a lost and are not sure what to do, try a system and live with it for a year. It can always be changed.

RapRap
1940 ChoppedChevyCoupe

I think some of you missed my question, I meant run the dual exhaust all the way back, but add the balance tube (crossover), to equalize the exhaust pulses, not go 2 into 1. I figured it out though, thanks.

Yes (like I said) you can on a P/U.

The pipes go (side by side) all the way past the rear axle & then turn 90 degress with small mufflers with tips that exit on the passenger side.

Patrick's has the perfect muffler (2 in 2 out)for that. But that's inline stuff.

For your 500 CID Caddy, same answer. Run the pipes the same with each turning L/R just past the rear end. Now put the smallest glasspack that will fit (clamped) there, then a short tip outside the bed. The "tip" need be only a few inches long.

If It's to noisy, switch the glasspacks for Cadillac resonaters, which is what GM/Cadillac had, minus crossover & mufflers.

JM...

Well since this 235 runs so good, I'm going to go ahead and find another rig for towing and keep this around as a toy. I think it'll be cheaper in the long run, and then I don't mess up a perfectly good pickup. I'm just going to go dual 2" on it, I doubt I'll ever do much more than cruise in town with it. Thanks for all the help!