Home-Made Cutouts

[C9]

Here's a pair of cutouts a little different from the usual two and three bolts you see on some cars.


Five bolts to follow a theme I use on both roadsters.


I'm fortunate to own a dividing head so that makes life easy.
Even so, there are ways to lay out bolt circles and patterns without a dividing head or rotary table and obtain a fair degree of accuracy.


Cutting out the 1/4" cold rolled flange, cap and gasket is easy on the lathe.
Make the steel flange first.


As noted, this design or a slightly different one can be done sans lathe and like always a little more work is involved.


Aside from the savings in work time, with the dividing head and lathe all parts are interchangeable.
If you're laying out everything by hand etc., drill one flange and use it for a master to make the other components.
It will probably come out accurate enough to swap parts from side to side if you're careful.
Transfer punches and transfer screws work well here.



The cutout on it's 2 ½" piece of exhaust tubing.




A view from the side.



The flange will be TIG'd on the inside.
If you're careful you can keep the bead small and not much filing will be required to end up with a flat plate.


Tack in three places and do short runs so you don't tweak the flange out of shape.
A little care here will pay off in way less work when you're ready to assemble with gasket etc.



Here's a view of the individual component pieces.
The cap is 1/4" 6061 T6 aluminum and the gasket is .025 - 24 gage I believe - soft aluminum sheet.




The sheet aluminum for the gasket can be purchased at Ace or True Value.
It seems to be pretty soft and should work well as an exhaust gasket.


Exhaust heat shouldn't hurt the cap.
We used to run 3/8" thick commercially made - with fins - cutout caps back in the day and I never heard of one getting burned through nor compromised by the heat.
These were fairly short tubed cutouts as well.


Pure aluminum melts at 1100* F if I remember right and alloys take it even higher.


The cap and gasket are easily made using the steel flange as a jig.
The flange gets pattern drilled with a #7 drill for the 1/4-20 stainless allen screws.
The aluminum in roughed out shape is clamped to the steel flange and the aluminum through drilled with the #7 drill.
Tap the steel flange 1/4-20.
Drill the aluminum cap to 1/4".
This makes the clamp setup for the next hole to be drilled and tapped.


Repeat until all ten holes are drilled in the cap and tapped in the flange.
Add bolts as you go.

My machinist pal recommends very highly to use a 2-flute US made tap on smaller sizes.
There's a lot of stress on the usual hardware store 4-flute taps.
Not to mention the best tap I could find locally was a Chinese made 4-flute and Tin coated.
The Tin is a metal lubricant and you still need tapping fluid, even so, it was a nail-biter getting all ten holes tapped without breaking a tap.
I like to use a new tap on important jobs.
Seems like the smaller sizes go dull in no time.


Bolt flange and cap together and trim the aluminum cap to round and to size in the lathe.
A disc sander should work well in lieu of a lathe.


No names, but one of our carries sheet metal, but is a different type business shop quoted me $1450. for a 1' x 2' piece of thin perforated sheet metal.
I balked a little bit, she re-calculated and came up with $74.
We talked a little bit and she stood her ground.
I dunno if she can add or not, but she sure as hell couldn't use a calculator.


I gave up and went to the steel supply outfit down the street and bought a whole sheet of the stuff for $26.
Expensive for what little I needed, but it'll get used when I make a screen door for the shop.


The gasket - shown at an angle to show how thin it is - is shown in this pic.
I would have used thicker, but this is about as thick as you can buy sheet aluminum locally unless you go to a sheet metal shop.



Note also, the cap holes are countersunk with a regular drill (3/8") so the standard head allen bolts can sink in a bit - about 1/16".
This does two things.
Appearance imo is a little better.
And you won't end up with aluminum mushroomed out after several install and remove cycles.


The gasket is easy to make.
Use the flange as a template, transfer punch hole locations and drill to size.
Leave it a bit large so you can clamp it without damaging the area where it has to seal.


Clamp the whole magilla together and trim the gasket to round and to size.
In fact this is a good time to cut perhaps .005 off all three pieces so that everything is the exact same size


Now that they're done, not sure if I'm going to use them or not.


Thinking was that they would be convenient to use at the street drags next weekend.
Already tech'd and numbered as you can see.



The problem I ran into at last November's Airport drags was that I couldn't pull the collector bolts and swing the exhaust to the side due to lack of room and ground clearance if I hung them low due to the H-pipe.
So I pulled the whole exhaust system off the car.
Easy to do, the removal of 10 bolts does it.


I have to pull the whole exhaust system whether I install the cutouts or not.
Thinking I'll probably cut the H-pipe in the middle and install a couple of three bolt flanges.
The exhaust pipes would swing to the side and get re-bolted ok if done one at a time.


If you do a cutout, no matter what flange you use, be sure and cut the cutouts exhaust tubing on the curve so you get a streamlined transition as well as better performance.
Plugging the cutout into the exhaust tube at a 90 degree angle doesn't help all that much.


The roadster gets trailered to the races - 4 miles away.
Not to inclined to drive an open-headered car across town and if it breaks we're set to take it home the easy way.
Not to mention with the Soccer Mom van seat - looks like a short couch - in the trailer and a potty room for the girls we got er made.


Anyway, fun project.

[teal32]

Great article. Great details for a novice like me.  After reading it several times, I feal like I can go ahead and start. I'm saving this for a winter project, though. I forwarded it to several friends, too. THANKS!!!

[Beck]

I've been cruzing with a buddy occasionally that is using the electic cutouts. He has the slide valve ones on a 32 roadster and the butterfly type on a 63. We had the 63 at the drag strip Fri. We drove the car there. As we pulled into the pit area he reached down and flipped the switch. The butterflys opened and the volume went UP. He ran a couple of 11.5x runs and we called it a night. As he drives out of the pits he flips the switch and the volume goes DOWN. The butterfly type do leak just a little. The slide valve ones are more expensive but don't leak. The only thing we did to the car while at the track was let some air out of the rear tires. There is a gas station directly across the exit road at the track so we pulled in there while leaving and put the air back in. Racin' don't get any easier than that. Back to the cutouts, I like 'em!