Sarum

The reason for my thread title is that 2 members from my car club down here in NZ have told me that when they have run open headers (via electric cutouts} they have both experienced a LOSS of power.One engine is a Clevodor 302 "Boss spec" ('52 Ford F2) and the other is a 351 Ford ('69 Mustang) but I don't think it's because they are Fords!
In the case of the F2 pickup this has been backed up by a slower ¼ mile time but I do believe the guys anyway because each has spent approx.$1000 on the exhaust mods and have no reason to make up the losses.There also may be a case for a drivers belief that a car has more power purely because there is a lot more noise when cutouts are used
We came to the conclusion that the power losses most likely be caused by a reduction in backpressure which in turn reduces the exhaust scavenging effect.

I would like no hear from CO clan members with their experiences and opinions in regard to performance when using exhaust system cutouts.

MDchanic

Yes, if the engine is not built to take advantage of the flow offered by exhaust cutouts (which means radical cam, high-revving), the cutout could make it lose power, depending on exactly where it's located.

The exhaust system essentially consists of a column of moving gasses, which have mass, and therefore inertia, so once the column starts moving it tends to keep moving.

This movement provides a sort of scavenger effect, helping to pull gasses out of the cylinders, in the same way that the inertia of the gasses in the intake runners create a sort of a ram effect on the other side.

This effect is frequency-dependent, so will be most effective at certain RPMs, which is why newer cars come with variable length intake runners, which switch off as RPMs change.

There is a chance that if you ran parallel straight pipes, of the correct diameter, after the cutouts, you would gain, rather than lose power, but I am not an authority on this.

It has nothing to do with "back pressure." Pressure at the outlet doesn't help anything.

- Eric

coppercutlass

You want to make power get an x pipe. The X pipe further scavanges exhaust. Im a believer in X pipe. Alot of people on here dont like because they claim they sound too "ricey" but i did some playing around with exhaust . When my car was 14 SEC. range in the 1/4 mile here is how it would do. With cutouts ( caps non electric ) i ran 14.00. Through the mufflers it would run 14.2 . This was a very mild engine 9 to 1 compression towing cam Think almost stock engine wise. In a quest to get my car in the 13's i decided to add an x pipe. Once i added the x pipe i ran a best of 13.86 through the mufflers. On the street the cutouts will make it seem like there is a loss of power and its probably because you are giving up a little low end tq. I have driven on the street with open headers and yeah it feels like there is a loss in low end tq.

Sarum

So it looks like putting in an xpipe rather than cutouts is the best way to go unless you have an engine that is at the more highly modified, cammy rpm screamer end of the scale.Would you care to suggest a HP increase range I might expect on my '65 Cutlass 330 (ex factory 315hp) with warm cam,Summit 600cfm 4 barrel vac. sec carb and a Edelbrock Rerformer RPM manifold.I won't hold you to it so please have a shot :-).
I read a thread recently that talked about xpipe versus H pipe and it seemed to me at the time that the consensus was that an H setup was better.I wonder why?
BTW what does "sound too ricey" mean, something to do with what you guys call "import cars" I suspect? What changes to exhaust sound does an xpipe generally make?
Thanks for your feedback it's much appreciated especially as an xpipe (or H pipe) has been on my to do list for a while.

coppercutlass

From my understanding H pipe balance exhaust pulses . An x pipe actually pulls out exhaust due to the cross pulses. Even high hp race cars use an x pipe . I have seen plenty of 9 sec. Cars with x pipes. You make power with an x pipe if your exhaust flows weak. The headers already scavange exhaust in the collector but the x pipe pulls it out further improving the scavenging effect. At some point they do stop working but I think that's once you get into much higher hp levels.

Sarum

Eric,thanks for the explanation of how the exhaust flow effects both sides of the engine.I will pass this on to my clubmates with the possibility that if they were to install dump tubes from the cutouts to say the rocker panel just in front of the rear fender well they may well get a benefit from the installed cutouts.

Alex72cutty

Hmm.. Good info.. So you had X pipe and cutouts?

MDchanic

They MAY, but there are a lot of engine design variables in play, and even if I knew them all, I'm not the guy who'd be able to tell you for sure.

- Eric

coppercutlass

I ran cut outs when i had straight pipes with mufflers . I took the cut offs off and the straight pipes off installed an x pipe the same mufflers and turn downs at the axle. i have never ran tail pipes . On a diffrent engine with the same exhaust running an open x pipe it was worth a tenth in the 1/4 mile. I set up my x pipe so i can just unbolt the mufflers at the track .

z11375ss

Why does the X-pipe give the car a Euro sound? I had an 03 Cobra that I modified with an X-pipe. It sounded like Euro trash. I pulled that pipe off that day. But with the new exhausts it took me all of 15 minutes on and off.

coppercutlass

15 minutes damn! I takes me that long to put the muffler on a off lol. The x pipe no doubt changed the sound but it sounds great imo . Newer cars do sound "euro" but I don't hear it with my olds . I guess I will have to do a video sometime of it driving .

rickracer

I'm new here guys but I had a 66 Fairlane 2dr hdtp with a 289. I ran headers with an H pipe and cutout and then the rest went all the way out the back. I didn't care if the cutouts slowed my performance or not....I loved to open those cutouts wide open going down the highway. Music to our ears...

coppercutlass

To be honest open headers are annoying. I like a loud car but it has to sound good too. Unless its an all out race car then open headers don't usually sound good. I love the x pipe and they have a pretty gnarly sound . i have never had tail pipes so im assuming most guys who did not like them had tail pipes but even on my friends el camino with a healthy 355 chevy it sounded awesome with an x pipe with the pipes all the way to the back.

seansolds

I've got the 560 lift 302 bracket cam with ported factory heads, yeah with the silly high rise (I said it), I lose my power curve until about 37,3800 rpm open header. With My total exhaust bolted on it equals from the collector back about 51 to 52 inches total tuned. That's extension + straight thru muffler + short tail pipe. 17+17+17 each side give or take an inch. Pulls like a couple hundred Clydesdales from 2500 to 6000 really gets weird about 4500 on! Thinking of changing the rear gears to 4:30 ratio, chain the motor down then see what happens with some slicks and a new clutch..she been babied to long!

Octania

I was thinking about using an O-pipe for more power... the vortex circulation effect triples the exhaust scavenging.

http://kalecoauto.com/index.php?main...products_id=41

seansolds

That's pretty interesting, like to feel that power! Or hear what it sounds like. I'll have to check on YouTube.

MDchanic

I see that it improves kuneutson valve float. That's half the battle right there!

- Eric

oldcutlass

And won't damage your engine, only 17 in stock...

Octania

Should be extrememly quiet, even with no mufflers. I guess you could put mufflers before the o-pipe.

:-)

wr1970

This thread has some twist and turns. I have has race dumps on my car three bolts wide open. I have a full exhaust 3 inch that dumps just in front of rear axle. Uncapped My street/race car is faster uncapped. Not a full tenth about half. I know this i did back to back testing at race track same day with in minutes. Now a flapper cut out isn't much different than race dumps. I hope this helps. Oh as for leaks with race dumps i call BS no leaks just use good gaskets. I just updated my headers to ARH with race dumps and new engine 468 ci this car runs on pump gas looking for mid 11 seconds. The car was a 12.50 461 on pump gas before.

cutlassefi

The low end torque increase on this would most likely be because you've effectively lengthened the exhaust system.

X pipes have a tendency to "Howl" a bit more than H pipes, but I like them, have one on my car.
The difference in an H vs X pipe, as conveyed by a tech at Hedman, who makes both, is;
"An H pipe will typically add hp/torque below what is the normal peak rpm. An X pipe will normally increase above normal peak hp/tq. However the H pipe will typically lose more on the upper end than the X pipe will on the lower end".

Your combination will also have a bearing on the effectiveness of an H or X pipe.

Hope this helps.