[motorheadmike]

I see the header question is one well addressed, thx. I am experiencing an issue with the transmission. When coming to a rolling stop the trans does not shift into low. In order for that to happen I have to come to a complete stop. Any advise on how to circumvent this?

Install a manual transmission.

 

[motorheadmike]

Where did you get that image? By the way, that primary looks cracked and it also looks like the weld has been repaired before.

https://www.hellcat.org/threads/lets-talk-about-longtube-headers.35473/page-6#post-710593

 

[70challenger70]

Absolutely

 

[70challenger70]

Absolutely

 

[Himmelkat]

I think the long tubes are worth it. My car lost almost 2lbs of boost from better efficiency which really helps with the race tune and pulley on E85. I will never run use catless mids again just from the stupid pulse popping sound as it passes the through the tubing.

I sought out a post like this for a reason.

If a car is losing boost with freer-flowing headers, it may be the case that the valve timing itself is partially to blame, for not being optimized for cylinder fill with a less-restrictive exhaust system.

The stock headers are coupled with the stock valve timing.

If, for example, the exhaust ports vented to a perfect vacuum, you would not need as much exhaust timing, because you would be discarding fresh air, possibly with some gasoline, out the exhaust port during overlap.

The closer your exhaust port approaches a perfect vacuum, the less exhaust valve timing you need, especially during the critical overlap period.

Ironically, adding a turbocharger ALSO lessens the need for exhaust valve timing, because there is so much backpressure that having the exhaust valves open a good, long time will get you far more reversion than with a system vented to atmosphere without a turbocharger intervening.

The most timing, intake and exhaust, will be for n/a engines.

I would think that cam specs for very high-flow exhaust systems, most specifically, large-tube headers, should have less duration than cams for exhaust systems with somewhat shorter and more restrictive headers.

In FACT, since the blower acts as somewhat of a one-way valve, I think it would pay off to experiment with truly oversized (to the common mindset) headers, to take advantage of that, so that the initial exhaust rush would have a nice, big, low-restriction chamber by which to exit. Now, obviously, at lower RPM, where these engines need literally NO HELP WHATSOEVER, PERIOD, FULL STOP, you may lose some power due to somewhat reduced scavenging by the exiting exhaust gas "accordian" not stretching as far as it does with smaller-tube headers, but, hey, why not have dual-chamber exhaust primaries? It works well on intakes, such as the original Corvette ZR-1. It would not be rocket science to set it up. a butterfly positioned so it shuts off the secondary exhaust primaries could open to reduce resistance at higher RPM and tune the "accordian efffect" such that it would be optimized at its target RPM.

There is only so much magic that can happen with the same pipe serving all RPM.

 

[That1guywithahellcat]

Not sure yet. Leaning towards ARH, but haven't done much research on them for this car yet. I've had header(s) and turbo manifolds custom made by specialists on previous cars before, but that would be way too expensive on this.



Says it all. If HP is all you're after, probably not worth it. But there's guys out there dropping 10 grand for 10HP or 0.01 ET.

Did you go with ARH?

 

[16GoManGoHC]

I added 1 7/8 shorty headers and demon cam clone to my build all else the same gained nothing, 930 wheel before the build 930 wheel after the build. Only thing I gained was hotter under hood temps, I’d go back to stock if it was easy to do.

 

[Himmelkat]

headers are more efficient than the factory exhaust and they see 1 to 1.5 lbs less boost. So you wont again any power unless you up your boost by changing a pulley.

What is fascinating about this here, to me, is that the Hellcat cam is even MORE exhaust-duration-centric than a naturally-aspirated engine such as the one by Hemiride.

If you are keeping the car for life, might as well get headers and a tune. They will save you money from that point forward in normal-state driving, because with more consistency from cylinder to cylinder, the "bad cylinder drags it all down" syndrome of having less-than-consistent cylinder-to-cylinder behavior will be reduced, and efficiency and power will go up, without doing anything else, but it takes diligence tuning it.

Further, it opens up the way for even more power , complementing a cam and pulley, which would even MORE exacerbate any inconsistencies from cylinder to cylinder.

But, the stock engine does not need headers anywhere NEAR as badly as the original muscle cars did compared to their clunky cast iron manifolds, some of which would gain 50hp or more just by bolting on headers.

 

[Himmelkat]

I added 1 7/8 shorty headers and demon cam clone to my build all else the same gained nothing, 930 wheel before the build 930 wheel after the build. Only thing I gained was hotter under hood temps, I’d go back to stock if it was easy to do.
View attachment 584287 View attachment 584288

Why would you replace stock shorty header with more shorty headers?

 

[Blkout]

I added 1 7/8 shorty headers and demon cam clone to my build all else the same gained nothing, 930 wheel before the build 930 wheel after the build. Only thing I gained was hotter under hood temps, I’d go back to stock if it was easy to do.
View attachment 584287 View attachment 584288

I could understand the 1 7/8" shorty headers possibly not gaining much, its pretty much standard on the GM LT4 platform to install 2" full length headers and pick up about 25-30whp, but I'm more surprised you didn't gain anything from the cam. Does the cam shift the powerband upwards and were you able to tune the TCM to take advantage of it?

 

[16GoManGoHC]

Why would you replace stock shorty header with more shorty headers?

Because of bigger pipe diameter over stock header pipe diameter

 

[16GoManGoHC]

I could understand the 1 7/8" shorty headers possibly not gaining much, its pretty much standard on the GM LT4 platform to install 2" full length headers and pick up about 25-30whp, but I'm more surprised you didn't gain anything from the cam. Does the cam shift the powerband upwards and were you able to tune the TCM to take advantage of it?

I tried cam settings all over the place, what produced best cylinder filling was stock demon/RE cam settings. Cam lift is basically the same as Hellcat cam, durations a bit longer, I should have went with the .618 lift custom grind comp cam I had in hand at the time.

 

[Himmelkat]

Why not go with 1" Pro Stock lift?

 

[Himmelkat]

Because of bigger pipe diameter over stock header pipe diameter

Wait, the stockers aren't even 1 7/8"?
I am so disappoint.

 

[Himmelkat]

Why not go with 1" Pro Stock lift?

As an added note of interest: the slower you turn your engine, the more valve lift you can safely use. Imagine the low stresses of a 4000 RPM engine. You could do 1.2" valve lift. Wouldn't that be a wonder to behold?

BTW, the stress/forces vary as the SQUARE of the engine speed. You would need really tall springs and valve stems, but, hey, if you could do 1.2" of valve lift, what kind of craziness could you accomplish with the power output?

You could snap the valves open and shut relatively rapidly (compared to the stock lift/degree ramps) and still be below the stock stress levels.

As an example, a cam turns at 1/2 engine speed, and the valve goes up 0.618 inches. Since the duration is about 270 degrees, that means that in rpm/2/60 is the rps or 28.33 rps

since the valve event is only 3/4 of a rotation, and going up is only half of that it is 0.0132 seconds to go 0.618 inches.

This is 18g of acceleration.

Now the same engine, at 4000 rpm with a valve going twice as high off of the valve seat yields 12.65g, far less acceleration for double the valve lift and at only 4000 RPM.
1.236" of valve lift. At only 4000 RPM.
That sounds like an engine begging for a long, long stroke to me. Some are doing 440 cubic inches with these things. If we ONLY changed the stroke, that would add some leverage to the crank, and I could see torque jumping up by a similar ratio.

There are more ways than one to skin this 'cat, but most people just use drool and more boost, but at the same RPM this would have at LEAST 440/376X as much torque as the stocker, just due to the longer crank throw, and then more due to larger displacement.

I would like to see someone (as in, me) make a HellCaterpillar out of this thing and bore and stroke it, with a deck plate, and just drop the revs to HALF of stock, and see what I could do with it. Paint the engine yellow and disguise it as a Caterpillar diesel, for the shock value.

The torque would still be below the 1050 ft-lb mark, I would think. I think we could keep the stock driveline maybe with some braces and such.

I just wonder what an engine could do with absolutely massive valve events allowed by lower RPM. Those cylinders would be full as a holiday celebrator at thanksgiving.

Of course, one would have to design the lift, etc, to have the power curve, etc. all-in at 4000 RPM, as far as timing goes, but with that truly massive valve lift, one could be fairly conservative with the duration and still enjoy deep breathing.

You'd want to tune your A8 to lock up at very low RPM, also, and get a tighter-than-a-seal's-nose torque converter.

 

[munk]

I have stainless works 1 7/8 headers on my car. I do not have before and after numbers. However, I did the install myself, it was a pain mostly due to the passenger side OEM header for one bolt. Just take the motor mount loose, pull the starter, get the old ones off ( takes the longest just due to that heat sheild they have welded on makes getting at the bolt head a pain.

The car sounded way better.
Underhood temps did go up and that was with a ceramic coating.
Power numbers, I wish I could say like other users on here have that it will increase the power. Hard to say though as other mods had been put on and the tune. Never did a back to back of long tubes vs short tube on stock motor.
You will have issues with the rear o2 sensors. While I have high flow cats which introduce a problem in and of themselves, the timing that the pcm measures between the wideband and the rear sensors did show up from time to time.
The rears will also through heat codes as they will not get hot enough in the granted amount of time. In short, if the rear sensors are turned on, it will throw errors. YOu can clear them but it will probably never clear the emmissions check in the pcm by the time you try and have a smog check.

I live in a area that does not require mart / smog testing, so the rears are turned off.

The headers though I think are a good supporting mod. In my case the motor is being upgraded, so they make sense. However, I think I would have got the 2" not the 1 7/8 if I had been smart about it. I was not though.

Dont buy used headers. I did off of here. Showed up with cracked primary to flange welds that caused me to pull them off and tig the flange again. Just buy new2 if you choose to go that route. Buying used you might end up needing to have a pin hole welded up or a crack. Its a pain to pull them back off. It easier to take off the long tubes due to space to get at the bolts, still a pain though.

The heat they put off will be real though. Been trying to figure out how to deal with that as wrap I am told will cause the stainless to get brittle over time and the mild steel ones to rust sooner.

YMMV