I now have my rolling frame finished with the drive train in. My question is: With stock manifolds are there any real benefits or issues putting in 2 1/2" exhaust pipes?

 

Don't know about the exhaust, but nice work on the undercarriage and engine!

 

Nice work on that W31!! When I blew my '68 442 apart for detailing back in '13 I was going to add headers & a better flowing exhaust system. My original manifolds were in such nice shape I just couldn't bring myself to toss them( plus the hassles of the tight fit with a BBO with a 4spd).I'm running an Edelbrock O4B intake so factory correct isn't a priority. I ended up going with a set of pipes from Inline tube, the fit was excellent. The front pipes are the stock 2 1/4" but they offer oversize 2 1/4" tail pipes instead of the stock 2" which I figured had to help some. I used Thrush turbo mufflers since they listed them as "the new replacements for the old Hush Thrush mufflers"like I had on my old '68. If I have any complaints it's that the new Thrush mufflers, while they sound good, they are quieter than the old Hush Thrush mufflers.

 

The fact that the manifolds create a restriction doesn't negate the benefits of the larger tubing. The exhaust system restrictions from valve to tailpipe are cumulative. If you cut off the pipes at the manifold, you'll still have less restriction (and more flow) than if you leave them on. Will it be perfect with stock manifolds? Of course not. However, the smaller pipe will still cause more restriction downstream than the larger pipe. Also keep in mind that non-mandrel bends are much more restrictive than mandrel bends.

 

2.5" is 10% bigger than 2.25", so that will let the engine breathe better.


I went from a 2.25" compression bent system to a 2.5" mandrel bent system.


The seat of the pants improvement was really noticeable.


I used W and Z manifolds and DynoMax long case (21") Super Turbo mufflers.


The exhaust sound is perfect too.

 

kinda depends on what your plans are for the car.

but HIGHLY recommend 2 1/2" mandrel bent exhaust system, with the turn downs at the rear bumper. The only issue is the driver exhaust manifold has a tiny 2" outlet. you'll need an "adapter" pipe to mate with the 2 1/2" headpipe. You can use a few inches of a 2 1/4" head pipe or a single exhaust y pipe and slip that inside the 2 1/2" head pipe on the driver side. This will lessen the change for any exhaust leaks at the head pipe to manifold connection when using 2 1/2" head pipe.

 

You might want to check your math.

The cross sectional area of a 2.25" pipe is 3.98 sq in. The cross sectional area of a 2.5" pipe is 4.91 sq in. That's almost 25% more area and thus almost 25% more flow. In fact, the difference is ever greater, as airflow is reduced by the boundary layer drag near the walls of the pipe. Since the area of the pipe wall increases with radius and the cross section of the pipe increases with radius squared, there is proportionally less boundary layer drag with the larger pipe in addition to the increased surface area. THIS is why your "butt dyno" registered the improvement.

 

Do the 2.5" exhaust and never have to upgrade it again even if you dial up the HP on the engine.

 

Great info guys!!

My 69 W-31 has the Magnaflow 2.5 inch SS system (original owner already installed it before I bought the car) I am going to go back to manifolds. Original manifolds as I want to go to PSMCDR in the future!! Keep the info coming!!

Ryan

 

Never do math with a Shrewsbury native......

 

Thank Mr. Houle, my fifth grade science and math teacher at good old Calvin Coolidge School.

He drove a Karmann Ghia, for what that's worth.

 

I changed my single stock exhaust on my 70 Cutlass convertible to a dual 2 1/4" with Dynomax super turbo mufflers. What a big difference. My other 70 Cutlass has 2 1/2" with Dynomax VT mufflers with turn downs before the rear axles.

 

Thanks for the feed back. I had ordered a 2 1/4" system from Waldrons Exhaust out of Centreville, MI; however, they do not use mandrels. Any suggestions?

 

I upgraded my original exhaust to a full 2 1/2" system w/vx series muffler VX2543 (just like flowmaster but half the cost) and used the flowmaster 2 1/2" prebent tail pipes and pypes exhaust 2 1/2" stainless trumpet tips.


muffler site
http://www.apexhaust.com/product/per...ance-mufflers/


video of my car at idle and take off


one more at idle

 

I would look up prebent mandrel bent tail pipes I got mine off of summit from flowmaster and any good modern exhaust shop can bend you the fron pipes if you have the originals they can use them as a exact guide to bend the new large pipes. My exhaust guy did it that way.

 

Thanks for the heads up on the Inline Tube systems. They look nice, and are probably what I'll go with for my survivor '72 Supreme. The OE look and sound should be just what that car needs (the 1988 single exhaust system needs to go!)
Terry

 

I went with a kit from Pypes, 2 1/2 stainless, kit fit perfectly, I highly recommend it. Here are some pics on my rolling chassis.

 

On a big block Olds pure stock car that is a very factory engine (e.g. not blueprinted), the gain from stock exhaust to 2.5" system was around a 0.2-0.3 second ET drop, can't remember MPH difference since it was a few years ago.

 

X2, I also install a Thornton's exhaust manifolds with Dynomax turbo mufflers.

 

there was/is a place in Canada, Musclecar Exhaust(?) that a friend used for his 69 H/O he was pleased with it and he is VERY picky. I tried to google, but couldn't locate it, no idea if it's still in business or not. I believe they advertised on 442.com

Torque Tech is going out of business and no longer have systems for manifold applications. in fact, they don't have much left.

ILT, I don't believe they offer full 2 1/2" mandrel bent systems.

Pypes, they do not offer turn down tail pipes, which is what a W-31 would need. I've seen a 69 F-85 (claimed to be a W-31) with the Pypes system and the straight tailpipes made it look horrible IMO. It was like an 85 Monte Carlo SS system on the car or similar.

Ram Air Restoration Ent, I did a REAL quick search on their website and couldn't determine if they offer a complete system for manifolds with turn down tail pipes for an Olds

 

I'm quite surprised nobody touched on the inlet size of the trumpet tips. I think the aftermarket tips have a small inlet and might require some tweaking.

 

My pypes 2 1/2 trumpet tips fit perfectly over the tail pipes and welded up nicely. But did the W31 have the pipes tucked under the non cut out rear bumper?

 

yes, turndowns.


I'm sure Dave knows this being a 31 owner, even though he brought up the trumpets.

years ago, I bought a Torque Tech BBO exhaust system with turndown tail pipes and the Dynomax long body mufflers for my W-31. very nice fit and I used the adapter pipe I mentioned earlier in this thread to hook up the 2 1/2" driver side headpipe to that tiny 2" outlet on the driver manifold. sadly, Torque Tech is going out of business and selling off what they have left. So I'll need to locate another source for turndown tailpipes.

 

Randy (RROLDSX) just pur a 2.5" Pypes system with trumpets on his 1969 442. I heard it and it sounds great.

Ask Randy to post some details and a pics and maybe a sound bite.