Modifying the risers?

[Patchman]

Saw a set of risers on Ebay, that had been modified to true 3 inch exhaust. Is this a popular practice or has anyone here done it? wondering if it helps out that much? think.gif
http://cgi.ebay.com/ebaymotors/Harmon-Marine-exhaust-manifolds-w-risers-460-BBF-/110688365903?pt=Boat_Parts_Accessories_Gear&hash=item19c58a6d4f

 

[460rogers]

I have done 2 sets....most risers have a stepm that can be cut easily to open up the outlet.
I did it because i ordered the wrong exhaust tips from REX.
I ordered the 3 inch by mistake...had to get the larger hoses.
It did seem to help on a 460 with glenwood logs,but didn't notice any difference on the one with harmon logs.....just a little louder.
Just my .02

 

[Patchman]

I have done 2 sets....most risers have a stepm that can be cut easily to open up the outlet.
I did it because i ordered the wrong exhaust tips from REX.
I ordered the 3 inch by mistake...had to get the larger hoses.
It did seem to help on a 460 with glenwood logs,but didn't notice any difference on the one with harmon logs.....just a little louder.
Just my .02

Thanks, I've been told about it, but didn't know anyone who has tried it. My friend wants to do his, so I will check it out. think.gif

 

[Devilman]

What is the original size of the opening?

 

[Patchman]

It's supposed to be 2.5" but when you cut them, they are 3".

 

[Devilman]

Guess is one of those things that can't hurt, but may not necessarily be something real noticeable.

I think to get any real performance results out of that mod, you would have to also run a chrome air cleaner, probably 14" diameter...

:grin:

 

[Patchman]

A friend and I were talking about how I keep blowing out the exhaust crossover gasket on the Hawaiian. The only thing we can figure is that there is a restriction on the exhaust side. So he started looking into it and found this mod. I don't know if it will help or not. He is going to try it on his boat, but his 460 will turn up a little higher than mine. So I guess it will be a good test bed.

 

[sturat]

Kenny, I thought the 8" triangle honeycomb air filter was a better choice when this "upgrade" was done? I must have been mistaken again.

 

[Patchman]

I run the Suburban air cleaner because it is large and emissions compliant! :smile28:

 

[Devilman]

Kenny, I thought the 8" triangle honeycomb air filter was a better choice when this "upgrade" was done? I must have been mistaken again.

You are right, but I have read where a mid-grade gasoline is required to get the full effect of the triangulated air flow. Wasn't sure if Patch is wanting to commit to that level of expenditure.

 

[Devilman]

I run the Suburban air cleaner because it is large and emissions compliant! :smile28:

Depends on which way you run the lid. :smile24: :smile30: :smile17:

 

[sturat]

Kenny, I thought the 8" triangle honeycomb air filter was a better choice when this "upgrade" was done? I must have been mistaken again.

You are right, but I have read where a mid-grade gasoline is required to get the full effect of the triangulated air flow. Wasn't sure if Patch is wanting to commit to that level of expenditure.

Oh yeah I did not take the race fuel into account.

 

[sturat]

I run the Suburban air cleaner because it is large and emissions compliant! :smile28:

Depends on which way you run the lid. :smile24: :smile30: :smile17:

Are they to go on with the seal up to ensure a good tight seal with the underside of the hood?

 

[Devilman]

Are they to go on with the seal up to ensure a good tight seal with the underside of the hood?

Runnin with the seal up is actually best. But you don't get that nice "whoo-WHOOOOOO" when you mash on it like you do with the lid flipped. :grin:

Then again, running 8.5 mm spiral core sparkplug wires, preferably yellow in color, will make up for the possible horspower loss of a flipped lid. Pretty hot topic in the performance world right now.

 

[Patchman]

I have these performance mods, and I'm thinking about split fire spark plugs! Couple of jack legs  in here! crazy.gif

 

[Devilman]

Actually Steve, those mods in a stand alone configuration have been known to produce a small measure of performance. Multiple dyno pulls have shown that running them in conjunction with each other has actually proven to be negative in a performance gain application. To put it simply, they cancel each other out.

However, there are other modifications that can be done to override those particular negative effects, allowing you to at least appreciate the artistic value those pieces provide for your craft.

 

[sturat]

Are they to go on with the seal up to ensure a good tight seal with the underside of the hood?

Runnin with the seal up is actually best. But you don't get that nice "whoo-WHOOOOOO" when you mash on it like you do with the lid flipped. :grin:

Then again, running 8.5 mm spiral core sparkplug wires, preferably yellow in color, will make up for the possible horsepower loss of a flipped lid. Pretty hot topic in the performance world right now.

Mr Kenny, you miscronstrewed my previous post. the Seal up is to get the whoop WHOOOOOOMP sound in full force. As the standard issue Western Auto horse power for dummies book satates to invert the Factory OEM Surban air filter lid to the "super secret squirrel" postion. This alone is a solid 5 HP gain from the slub knocks who not know of these great secrets!! You can also get another solid 5HP if you add the chrome breather option.

And to Mr Patch as stated by Mr Kenny that is too much of a good thing.. The one and only stick on HP gain with no ill effect is the infamous Ultra Hot (in Pink of course) sticker..

 

[KONA77]

:smile16: yall letting out all of the super secret squirrel stuff  :smile25:

 

[Patchman]

Well I guess I will remove the Bad boy sticker, and replace it with Ultra Hot. Then I will incorporate some Slick 50 or maybe Zd2. I'll then retard the timing by 2.5 deg and run a hotter thermostat. I'm reducing the carb size to a 545 CFM due to volumetric efficiency. I also ran some 5/16 fuel line to increase the speed of the fuel flowing to the carb. And I'm currently working on an exhaust crossover pipe to equalize the exhaust pulses in a crossfire type setup.  think.gif All you guys need to be afraid of the crazy mad performance I'm about to unleash on the unsuspecting THB crowd. :shocked: :evil: P.s. I even started running 36 psi in my trailer tires, the speed gains have been astonishing! :smile30:

 

[Devilman]

Mr Kenny, you miscronstrewed my previous post. the Seal up is to get the whoop WHOOOOOOMP sound in full force. As the standard issue Western Auto horse power for dummies book satates to invert the Factory OEM Surban air filter lid to the "super secret squirrel" postion. This alone is a solid 5 HP gain from the slub knocks who not know of these great secrets!! You can also get another solid 5HP if you add the chrome breather option.

And to Mr Patch as stated by Mr Kenny that is too much of a good thing.. The one and only stick on HP gain with no ill effect is the infamous Ultra Hot (in Pink of course) sticker..

My apologies on my misunderstanding of the performance aspect, both positve & negative, of the log/riser combination exhaust configuration. Again I am shown my lack of knowledge on this subject as was previously shown in an exhaust flapper conversation. Exhaust flappers being a component of the aforementioned log/riser exhaust system as I'm sure you are aware.

That said, I am familiar & have myself employed the application of chrome breathers on a number of different engine combinations & have been quite pleased in the resulting positive gains across the horsepower spectrum.

I have heard of the infamous Ultra Hot decal, although its been a bit of time since I've seen it mentioned, I had thought it had fallen out of favor in the performance crowd.