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Topic: Enlarging Exhaust Exit Hole (Read 644 times) previous topic - next topic

Enlarging Exhaust Exit Hole

For those of you that have moved from 4" exhaust to 5" how did you enlarge the hole in the fiberglass? I was thinking of using a rasp on a drill motor but I'm wondering if I can get it looking right. Thanks.
jor
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Re: Enlarging Exhaust Exit Hole

Reply #1 –
Quote from: jor –
For those of you that have moved from 4" exhaust to 5" how did you enlarge the hole in the fiberglass? I was thinking of using a rasp on a drill motor but I'm wondering if I can get it looking right. Thanks.
jor
Sounds good with perhaps some resin and micro-balloons to smooth the rough edges after you get it opened up. I can photo our 5" OEM opening if it will help.

Make sure to wear overalls and a mask/w/cap as this stuff really itches and not good to breath.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Enlarging Exhaust Exit Hole

Reply #2 –

Jor,

Here are a couple of photos of our OEM 5 inch exhaust and the bodywork around it. The phenolic microballoons are available online or surf shops, etc. Here is the source: Phenolic Microballoons filler for epoxy and polyester resins 1/2 gallon:...

I like to pour some of the balloons in a big dixie cup and then add a little epoxy (or poly) resin until I have a thick slurry. Once the larger opening is made, you can add the slurry keeping it in place with the use of wax paper and masking tape. Good to use fast hardener if available. You can then sand and shape it easily.

Our chrome pipe is sitting on the bottom and not in the middle of the opening.

The Fiberglas thickness is approx 5/8" at the bottom of the exhaust pipe, thinner at the top. If adding to the inside, degrease the inside surface well before glassing.

PIerce

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Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Enlarging Exhaust Exit Hole

Reply #3 –
Quote from: jor –
For those of you that have moved from 4" exhaust to 5" how did you enlarge the hole in the fiberglass?.....................
John,
I'm curious as to why various owners move from 4" to 5" exhausts with the 8.3 Cummins.
If you are doing it simply for the looks or deeper exhaust note aesthetics, then I understand. 
But, for a 4 cycle, 8.3 Cummins diesel, at low exhaust system flow rates, the turbo benefits from a small amount of back pressure.  The right amount of back pressure causes the turbo to spool up more quickly, significantly decreasing turbo-lag as well as building torque faster and more smoothly.  A 4" exhaust system does that almost perfectly.
Conversely, of course, at the high end of exhaust flow, a 5" exhaust system gives a tiny bit more HP (5 to 10 HP maximum gain at 500 HP or higher) but who has dialed their 8.3 up to 500 HP or runs their stock 8.3 at max HP (high RPM) for long periods of time?
I much preferred the low end torque enhancement, and stayed at 4".  I felt that it worked well.
Haven't studied the 2 cycles, so I don't know how they are affected.
Just curious,
Neal
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Neal (& Brenda) Pillsbury
'02 U320 SPEC, 4200, DGFE, Build #5984
'04 Gold Wing
'07 Featherlite 24'
'14 Jeep Grand Cherokee Summit
MC #14494
Exeter, NH & LaBelle FL
Quality makes the Heart Soar long after Price is Forgotten
 

Re: Enlarging Exhaust Exit Hole

Reply #4 –
Having a little back pressure allows the EGR to operate for emission reduction on a Cummins. Detroit 2 cycles come with 5 inch exhaust stock as every stroke is a power stroke and they all have four exhaust valves plus the blower to push an huge volume of air through the engine. With a six speed behind the 8.3, low end from a stop sign is not like the poor 4 speed response our Detroit has. The 6.xx first gear leaps across the intersection compared to our 4.xx first gear in our Allison. I know the resonator conversion helps
 the 8.3 Cummins and can't help but think the increase in exhaust pipe size will also help a bit.

Here is a quote from the late, great Dave M., one of the most knowledgeable forum Detroit and Cummins authorities. Larger engine but the results should be the same.

"Having worked larger engines, such as truck etc all mu working life, when I purchased my new to me 2001 Foretravel 5 years ago, it has the ISM450 engine, I replaced the Cowl muffler with a Walker Resonator, and bingo, right off, it was very clear that it was much more power, as the turbo can spin up faster with so much less back pressure etc..
You can buy the fancy and costly chromed jobers, but me I just want it to run sweet. Now I have also up graded the ISM from the 450 hp @ 1450 torque, to the newer 500 hp @ 1550 torque. yes, it jumps just dandy, as for fuel burn, I am certain it would get better fuel mileage, however it is so hard to keep my foot out of it, that the fuel mileage is the same, it just runs quicker.
Dave M"

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)