Log manifolds

« **on:** March 19, 2017, 08:33:05 PM »

I have log manifolds with the 2 7/8 hose fittings. I've heard of people machining the flange off so it will accept a 3 1/2 inch hose. Has anyone on here done this? If so, does it make that much of a difference or is it not worth the price of machining and new exhaust tips??

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« **Reply #1 on:** March 19, 2017, 08:48:13 PM »

Makes them louder. I would think the power output would be immeasurable.

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« **Reply #2 on:** March 19, 2017, 08:50:27 PM »

« **Reply #3 on:** March 19, 2017, 09:22:15 PM »

Quote from: Six-Oh-Nine on March 19, 2017, 08:50:27 PM

Typically, you can cut the step off. Yes, it does help. I've even machined off and welded 4" tube, then opened them up on the insides... on for the larger hose and tips on a old school blown deal where we HAD to keep the logs... nothing like headers, but really did wake it up quite a bit.

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Thanks Bostick. I think I'll give it a go.

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« **Reply #4 on:** March 19, 2017, 09:46:00 PM »

Quote from: Six-Oh-Nine on March 19, 2017, 08:50:27 PM

Typically, you can cut the step off. Yes, it does help. I've even machined off and welded 4" tube, then opened them up on the insides... on for the larger hose and tips on a old school blown deal where we HAD to keep the logs... nothing like headers, but really did wake it up quite a bit.

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With all do respect, this doesn't sound like a blown deal. I've done a couple, and honestly, short of being louder, we saw zero RPM increase.

One was a pretty nice 468 Chevy and the other was a built 455 Old's. The tach didn't see any change. But honestly never checked it with a GPS. They weren't available yet.

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« **Reply #5 on:** March 19, 2017, 10:12:17 PM »

« **Reply #6 on:** March 19, 2017, 10:30:04 PM »

Quote from: Six-Oh-Nine on March 19, 2017, 10:12:17 PM

Somehow I knew I would get the gtjets contradicting response.

😂

Never said it was a blown deal he was working on... just an extreme example of a log application where the difference was very much unquestionably noticable both rpm and gps.

Obviously results will vary based on application and level of how built the engine is... one size does not fit all... but I cannot recall one instance where, though sometimes slight, it did not help... but then again, I'm not working on too many bone stock 280hp 455 olds these days.

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I'm not contradicting.

You mentioned a blown application which has a completely different exhaust flow and requirement. I get that.

At the same time, going through the expense and trouble to increase the exhaust by 5/8" does not seem to be worth it and I've tried it with no measurable gains.

I would rather see you remove the exhaust hose and go rigid pipe from the log outlet to the tip with small chunks of hose connecting them, you can then reduce the amount of water going through them, which would be similar to lager diameter outlets. Cheaper and easier. Not to mention, reversible.

And the Old's in the discussion was over 450 horse. So there's that.

No disrespect intended, just trying to keep expectations in check. I don't see the 2% gain worth the effort.

GT

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« **Reply #7 on:** March 20, 2017, 06:53:15 AM »

I would think that removing the step would allow the exhaust pulse to stay constant all the way out and help with pulling in more fuel?

« **Reply #8 on:** March 20, 2017, 07:53:50 AM »

It's not blown. Just a built 460. I know the logs limit how big you can go with your cam due their lack of scavenging abilities and what not. I was hoping that opening the logs up would be beneficial with my limited options.
Thanks for the reply's.

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« **Reply #9 on:** March 20, 2017, 11:56:48 AM »

Quote from: tunnels on March 20, 2017, 06:53:15 AM

I would think that removing the step would allow the exhaust pulse to stay constant all the way out and help with pulling in more fuel?

Just thinking about this from a physics standpoint, the pulses would remain the same whether the outlet was large or small, I would think the step could actually enhance the scavenging effect by allowing two different pulse intensities. Unless force inducted, which makes the exhaust pulses linear and mono directional.

Hard to say for sure, but would love to see the hard numbers on it.

What we used to see with just hose connecting the tips to the risers is the hose would throb, basically deadening the signal and we always believed this killed flow (read; reduced scavenging).

I did a tournament boat a while back and pulled the 2' chunks of wire reinforced hose off and used copper pipe to the mufflers from the elbows and the owner said it picked up almost 100 rpm, this is a extreme example, but it proved the theory that something was being taken away.

A large volume of cooling water in the exhaust would amplify this effect.

Something we did on the Jet Skis years ago was to install a pressure relief on the cooling to the wet exhaust and cut the water in half. The difference was immediately noticed, but also noticed the sound increase.

Water doesn't compress, so it's taking up space within the pipe, less water, more exhaust flow. The pulse signal can really help or hurt depending on what the application is. I used to build "H" pipes for wet exhaust for this exact purpose, the biggest differences were noted on the most stock applications. Never got a chance to wrap my head around why.

GT

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« **Reply #10 on:** March 20, 2017, 09:13:52 PM »

Have done this several times... You can even ad a bit of 3.5 on the shoulder to make it 4 if your tips are 4. Make sure you double clamp at least the log side... I double clamped both ends just cause.

« **Reply #11 on:** March 20, 2017, 10:51:03 PM »

Gt you mentioned a pulse in the exhaust semi ridgid wire hose. I see most boat have the soft walled hose. Is there any advantage to using semi ridgid exaust hose with the wire. Or is this just splitting hairs. Nice polish on those logs."your mom

« **Reply #12 on:** March 20, 2017, 11:40:28 PM »

Quote from: seapat on March 20, 2017, 10:51:03 PM

Gt you mentioned a pulse in the exhaust semi ridgid wire hose. I see most boat have the soft walled hose. Is there any advantage to using semi ridgid exaust hose with the wire. Or is this just splitting hairs. Nice polish on those logs."your mom

Double wall, wire reinforced hose is the bare minimum. Red or blue stripe, prefer red stripe for oil resistance.

Think of it like this, the scavenging of the ports at the head depends on the bubble of hot exhaust gases traveling toward the outlet, that creates a "negative" on the other ports until the next exhaust valve opens, then that bubble (or pulse) creates the next negative as it travels out to meet the world.

If the hose throbbed during every pulse, it will absorb the negative and get the signal essential for scavenging off sequence. I have seen it violent enough to blow the hose clean off the riser.

Notice Your Mom mentioned double clamping? This is not only because of the limited clamping area, the pulses get gnarly enough too blow the hose off.

I always use weatherstrip adhesive on large hoses.

Anyway, Rigid pipe not only lacks the flexibility of the hose, it also lacks the ridges and corrugated texture in some hose.

The more rigid and equal length you can get the ports (or pipes) the more effective the scavenging can be.

Getting that extra 5/8" to me is less important than cooling water control and proper materials. The riser itself is the restriction truth be told.

JMO

GT

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« **Reply #13 on:** March 21, 2017, 07:41:41 AM »

Quote from: Your Mom on March 20, 2017, 09:13:52 PM

Have done this several times... You can even ad a bit of 3.5 on the shoulder to make it 4 if your tips are 4. Make sure you double clamp at least the log side... I double clamped both ends just cause.

Man those things are shiny. I tried to polish mine but they still look dull.

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« **Reply #14 on:** March 21, 2017, 09:43:56 AM »

Quote from: Your Mom on March 20, 2017, 09:13:52 PM

Have done this several times... You can even ad a bit of 3.5 on the shoulder to make it 4 if your tips are 4. Make sure you double clamp at least the log side... I double clamped both ends just cause.

If you don't mind me asking, where did you pick those up from. I'm having trouble finding the long bolt style logs. Mine are pretty beat up and was looking for replacements.

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« **Reply #15 on:** March 21, 2017, 03:13:10 PM »

I buy em when I find em up for sale... sometimes I polish em an resell. I have 1 backup set left but not sure I'll part with em as of now. Once your done with the polish use flour powder or corn starch on em with a micro fiber...

« **Reply #16 on:** March 21, 2017, 03:25:56 PM »

Quote from: Your Mom on March 21, 2017, 03:13:10 PM

I buy em when I find em up for sale... sometimes I polish em an resell. I have 1 backup set left but not sure I'll part with em as of now. Once your done with the polish use flour powder or corn starch on em with a micro fiber...

Got it. Those look like the Harman logs and I'm pretty sure nobody makes them anymore.
Thanks for the info.

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« **Reply #17 on:** March 21, 2017, 10:32:33 PM »

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« **Reply #18 on:** March 21, 2017, 10:45:05 PM »

No, not what I said, but since you're in a pissing match mood, what I said was the gains versus the amount of work aren't showing value and a better approach would be reducing the amount of water within the exhaust and installing pipe, not larger, expensive, hose.

I have never one time seen sizable gains by simply installing larger hose.

That's what I said.

By the time you buy tips, cut the hull, new hose and clamps and modify the risers, you have spent potentially over $500 with nothing to show for it, my way costs very little and the gains are the same, not to mention totally reversible.

That's all I meant. And virtually exactly what I said.

The large gains I've personally seen were on jet skis and they are two strokes. Different animal all together.

Why you all up in my shit?

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« **Reply #19 on:** March 21, 2017, 11:45:50 PM »

Disregard anything I have said... not going to argue anymore... gt as ALWAYS, right about everything.

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« **Reply #20 on:** March 22, 2017, 12:08:04 AM »

Quote from: Six-Oh-Nine on March 21, 2017, 11:45:50 PM

Disregard anything I have said... not going to argue anymore... gt as ALWAYS, right about everything.

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Show me where I'm wrong.

I'm thick skinned dude. I never contradicted you nor said you or any one else was wrong. I simply shared what I've experienced, so did you. Your example was a blown deal, mine was not.
Said it before, I would love to see some hard numbers on it.

I simply don't see the increasing of a hose and outlets worth the efforts.

That's all I said. If I'm wrong, so be it, but you haven't shown me I'm wrong.

I'll take some pictures of the pages of the notebook. I'll get it tomorrow.

This like a riser versus OT pipes on logs comparison. The differences are not all that incredible. Not sure why the butt hurt, but whatever.

I'm out.

GT

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« **Reply #21 on:** March 22, 2017, 06:49:12 AM »

💁🏼

BECKY WITH THE GOOD HAIR!

« **Reply #22 on:** March 22, 2017, 06:48:05 PM »

LOL geeze GT and SIX....We all appreciate all of the knowledge you guys have...It's up to whoever is asking for it to take the advice or not...its all good advice...Thank you BOTH for all the help you give us 😁

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