Hi together I`m planning a project for the comming winter season. I want to update my 1971 GS455 on the exhaust side. Right now I have what seems to be original exhaust pipes, some not too loud no-name-mufflers and cast-iron exhaust manifolds. Car is street-driven, there are virtually no tracks available around here as with some of you guys in the US, it`s got a build (and dyno-proven) 425hp and 517lbft from AM&P, 3-angle-valve-job on iron "staged 1" heads. I`m guessing I`ve not realised the full potential of the engine with the combo mentioned above. So here comes my question to you: Would you rather tend to get some shorties, or go long tube? Personally I`d might tend to the shorties if they don`t loose too much power over the long tube headers, because of clearence-issues and working on the car later on. You don`t have to decide for me, would just like to get your opinion on the subject. Have a nice weekend Jens
We recently did a dyno session on a 450hp street motor. Stock cast iron manifolds, then cast iron ported manifolds. Gained 17 hp. Then long tube headers. Gained another 19hp. So shorties are probably somewhere in between.
Long tubes will make more power and be louder. Short tubes are a nice compromise for most people on a non-race car. How much one gains over the other depends on how "choked up" an engine is with it's current exhaust....Switching to long tubes from manifolds will make a lot bigger difference on something with 800 hp vs something with 300 hp.
Hey Gary, quite a gain for ported manifolds, wow. Sean, suspension was rebuild lately, car sits so much higher now, I guess there would be no instant clearence issues.
I'm no expert but my understanding is the long tubes give you a little more hp and torque on the low and mid end. So for what you want, long tubes would be the way to go. Downside is fitting them in can be a pain. The other issue to think about is the size of the exhaust pipe after the headers. Too small is bad but you can also be too big. There is a sweet spot depending on how much HP your engine makes.
This is a picture of a Exh port in a set of heads I am working on , notice it's clean . I flow tested it stock right off a motor all carboned and rusted up as they tend to get after some 30K miles. This clean up work involved nothing more then using a 80 grit polishing roll to rid the port of the rust and carbon and to polish off a 1/16" tall ridge on the short turn from the factory cutting the valve bowl to size. The Exh flow at .500" to .550" lift went from 149 to 165, for a 9 % flow gain. Makes you wonder how much power one could pick up just from getting the inside of your Exh Manifolds completely bead blasted out and then ciramic coated on the inside, no?!
Yeah, the ported exhaust idea has been going round in my mind since Greg Gesslers F.A.S.T days...but then, in a real world, it seems those headers seem the easier approach. Still, that would be something
The Shorty Headers are a minus 10 H.P. to the long tube headers, but have less ground clearance issues, which all of the handling improvements for the A-body employ. A little more stealth for the street, if that is any consideration. Usually they are a little cheaper as well.
I imagine flat black ceramic coating on the shorties, some might even take it for the real thing .... And, keep in mind, I still have the original exhaust system. 2.5" might also show improvements, right?
you said no racing, so Long tube for the best sounding exhaust, if thats important to you. MT repops are best, but my postons were almost as good.....i wanted a stock look so had stock manifolds opened up.
Hi thanks so far for your opinions, it's quite helpful. Russ, no loud setup for me, headers would be more of a necessarity to free the horses that are held back, same goes for the exhaust system. Jens
In regards to the exhaust system itself my convertible had a fresh all iron engine with 10:1 compression and a 118 cam with the manifold dumps opened to 2.25. I gained 3 tenths and 3 mph by going from 2.25 kink bent stock replacement exhaust to a 2.5 mandrel bent system. No x-pipe nor H-pipe.
If not racing I would do shortys with 3 in flang and 3 in down pipe to 2an7/8 mandrel bent system from TA.
Wow Gary - Great test & very nice results on the ported manifolds. Shame you didn't have shorties to throw in the mix. Did you change the tuning for ea. setup? Were there exhaust pipes bolted to the manifolds? I'm hoping to someday do the same test on a 350 but w/shorties (none avail so would have to custom build) & maybe even TA vs. Hooker long tubes.
Yes,there were exhausts connected. did not change timing, 32 degrees total. Same Q jet,A/F was good through out.
I just switched from long tubes To TA shortys For street strip. I'm tired of tip toeing over speed bumps. FYI. PIPES sells very nice stainless Down pipes 2.5"
Hey Boss we talked about this once before. How ported the stock Cast Iron Manifolds? So 450HP with stock manifolds, 467HP with ported cast iron, and 486HP with long tube? Or 469HP with long tube? Sorry I'm slow
