sidepipes killing power
 

Hi guys, I would think I could get an informative answer here about the sidepipes on my classic roadsters austin healey sebring. I know these must have been custom built for the car since I have never seen another one with these... they are a 1 5/8" tri -y design that slip fits to a glasspacked sidepipe. The problem is the glasspack inside the sidepipes is only 1 3/4" i.d. !!
The car was originally built in 1986 and has a stock hydraulic flat tappet stock iron headed late 70's 302 in it. The only mod is a low rise edelbrock performer 289 intake and holley universal 600 vac. sec carb. It is a 4 speed car and has a 3.0 trac loc 8 inch rearend in it. Since the car is all mustang II based it is the mustang II 4 speed trans (RAD trans ?)

I would like to put a fresh motor in the car and go 331 or 347 but I am afraid I may be my wasting money with the 1 3/4" i.d. sidepipes. From googling about sidepipes I found a site that showed max h.p. for different size pipes and with dual 1 3/4" max power supported was about 210 h.p. which is probably about what my stock motor makes now. The motor runs fine, burns a nice tan color on all 8 plugs.... it is just not making much power to make the car really fun.

I have thought of several other options such as going to a t5z and 3.80 gears to make this motor feel peppier or just adding some afr 165 or tfs 170 heads to the shortblock along with linkbar lifters and a small hyd roller cam, but I have had a nice 331 in a 65 mustang and I know how much tq. that 1/4" extra stroke makes!

I love the sidepipe look and sound (makes my healey kind of like a poor man's cobra) so removing them is not an option. I would appreciate any suggestions or comments on what you might do. Thanks in advance.

Dave

The only difference between the Classic Roadsters Cobra and Sebring was the body. The chassis and suspension are the same. The front end is a Mustang II, very popular with the street rod set. But that's the only components from the MII. The rest of the suspension and chassis were sourced from various other cars.

IIRC, The CR headers were not a slip fit, so you're probably right about them being custom built.

Swapping the mufflers out for something better is pretty easy. Order a set of mufflers from Classic Chambered Exhaust and weld them in.

I would be interested in what you end up doing. I am building a Classic Roadsters Cobra right now and I am sure I will be in the same boat once I am done.

Look at what some of the other folks have done. There is a lot of power lost on restrictive sidepipes.

I wish that was the case here about only the mustang II frontend. It is not. This car was completed, registered and titled in 1986. So it was probably built between 84-86 when mustang II stuff from 74-78 was plentiful and cheap in the wrecking yards. I know for a fact that the 8 inch rearend is mustang II since it has the 6 3/4" 6 cylinder axle retainers on the 4 lug axles.... I had to pay $200 for the axles to be drilled for 5 lug wheels and have new wheel bearings installed.... I had some 5 lug axles for a 65 mustang rearend (normal small ford axle retainer plate, which would not fit the mustang II housing even though they were the same length and 28 spline). I thought it was as easy as swapping axle retainer pltes when the bearings were changed but no such luck since the shaft is slightly larger on the area where the retaining plate goes so the mustang II retainer would not fit.

Also the 4 speed trans is of Mustang II sourcing and is a weak unit that is oddball in itself just like the 8 inch rearend.

I know I could have some custom work done with Hank at Hank's hotrod shop here in Denver but I just paid to have the headers and sidepipes jet hot ceramic coated and hate to ruin the finish and have to pay to have them coated again.

This is typical for me.... another car that was running, driving and fun that I took apart for a cosmetic rebuild that is turning into a blast furnace for my wallet.... I just never know when to quit.:D

I replaced my CR mufflers with the classic chambered 2 1/2" x 30" mufflers and picked up 70 HP at the rear wheels on my 390fe motor. If you have the original CR mufflers I think it's safe to say you are loosing HP and TQ. Sounds like you have a pretty cool car. Put some pics in your gallery.

John

I was lucky enough to have gotten Don's side pipes for my CR before he
pulled the plug on the business. I just have a 400 hp W351 in mine and
the difference in power from the side pipe change was significant. They
let the poor car exhale properly! LOL

In your case upgrading the pipes will give you the biggest bang for the buck in
that area and it enables the car to breath if you start upping engine components.

Not sure 'bout killin' but defnitly burnin' !!;)

I have replaced the sidepipes on my Backdraft with Stainless Headers 3" www.stainlessheaders.com
mufflers to replace the two mufflers inside a single round core on my Backdraft.
It is like going from soda straws to a garden hose!

2 driver side axes from an 80's ford ranger will slide in to a mustang 8.8 and give you 5 luges. $35.00 at the salvige yard.

Just take the mufflers out and run them open! :)

Did I mention that I have a hearing problem?