I am trying to decide on one of two exhaust systems for my 13B standard bridgeport.

1.Either a dual 2" header that collects into a 3" before the rear axle

2.or a dual 2" header that collects to 3" at the back of the header

What would collecting the pipes sooner do to my power or power range compared to collecting later? Is one better for horsepower and one for torque?

Thanks

 

I think collecting near the header gives you more low and mid-range power band and the longer primaries, before the collector, give it up high. There is not much of a difference, according to how to modify your RX7 book, I have It also says to use a megaphone to exit, if your not running mufflers.

 

Thanks, I just found out that I may have some blow by issues with my new motor. I think this explains why my HP numbers are low, and peaking at an rpm to low for a bridgeport.

I will go back to exhaust tuning after I get a few things worked out.

 

There are multiple tuned lengths of headers. Two of which racing beat publish for the car. They supply a short length and a long length. In practise those two lengths are probably very similar. The long length probably having the widest band which it highlights, which would be why more race cars use that length.

If you want to move the rpm band which is highlighted higher or lower, you would increase or decrease the tuned length slightly. I am of the opinion that making the headers longer than either of the RB tuned lengths will highlight lower rpm more, and making them shorter will highlight higher rpm. This is based on the assumption that the exhaust waves will travel faster at higher rpm, which I feel is a pretty sound assumption to make.

 

Also, smaller diameter pipes should have the effect of making the pipes appear long, and larger pipes should have the effect of making the pipes appear shorter.

 

Here is the published data...

 

a long primary setup will have better scavenging effects for a bridgeport.

 

It would be almost impossible to run a megaphone exhaust if you run the long system. Almost 10 feet of primaries followed by a muffler and megaphone.

Why does the long primary have a better scavenging affect. I was considering running this equal length and varying diameter header from rotary shack.

Not sure what to do after this header though. Either run 3" mandrel to a muffler, or megaphone/expansion chamber exhaust. It seems difficult to know which parts will work the best together without spending a lot of time on and off the dyno.

 

 

Now available at the shack, the MAX POWER header! This new product has been in testing for some time to insure maximum power/torque output with longevity in mind as well. This finished product ending up being made from 16 guage 304 stainless to minimise cracking. The primarys are 1-7/8" to a 2" merge collector to a 2-1/2" to a 3" collector, while the exit size is 3". They are available with or without the crossover tube, as well as 12A or 13B. Also, an o2 bung or EGT bungs can be added for optimum tuning. These headers are guaranteed to make more power than any other production run header sold!!! These headers are built to win races and break records!!

 

http://px6.streetfire.net/0001/24/58/1604285_600.jpg

I'm still still trying to find 230 whp on an SAE corrected Dyno Jet. My slicks eat up a lot of HP, but I've been told that HP is realistic, even with a standard bridge port. I've seen up to 217WHP on a dyno jet with my current exhaust setup.

 

Actually, I need more like 240whp on the dyno jet to maximize the power/wt ratio allowed for my race class. I have a close ratio 5 speed with 4.875 final drive, so I'm not concerned with having a peaky engine power band.

 

That's a nice looking header, What are you using for a fuel system ? carb or FI ? If you think about it Mazda's all out rear engine race cars have a short exhaust systems. RB road race header, it says to count that as 27 inches of the total 120-125 for weber long system or 113-118 for a Holley. If you look in the Racing Beat Tech Manual, " There's virtually no power difference between the long and short systems. The short system is simply well suited to certain applications, such as rear engined cars " Did they set a price for that new header ? The HKS that they offer is $1200, ouch !

 

There is some pretty bad info in this thread as well as a lot of "but's" and "what if's". Needless to say I've seen nothing but generalizations and one just plain false statement so far. The short answer is that either a short or a long primary can be made to work. However just having a long or short system is not enough. You need to be within a certain range in both areas and this range is different among various porting styles. The more aggressive your porting, the shorter the pipes need to be on either system in relation to a less aggressive style of port. What this means is that even a header that is "guaranteed to make more power than any other production run header sold" is still only working within a certain range and only maximized to one type of porting. Namely the one it was developed on. It will not always be the best for any situation. There is no setup that is always the best.

From personal experience I have found that long systems produce more average power than shorter with more low end power. Shorter systems definitely do not produce more low end power and I've compared them on multiple engines and porting configurations. Then you get to the true duals which fall flat on their face with anything more aggressive than a good streetport. Saying that though it doesn't mean that a long system is always better. It isn't ALWAYS. Nothing is always better.

The reality in this is that you are probably going to have to do some experimentation. You may try a short system and hate it but find that changing it's length a little bit also completely changed the powerband. The same hold true for long systems. Design a system that is modular and adjustable so you can play around. It's as easy as a couple of well placed flanges and pipes.

I know you are wanting a straight answer as to what you should do but unfortunately there is not a single person here who can answer that with anything other than a best guess. Play around a bit. You'll figure it out. That's where the fun is!

 

As far as off the shelf headers go, that is one of the best one's I have seen. It is critical to have equal length primaries and you notice on this header how long the primaries go straight from the block before they turn- this makes a big difference.

 

I'm running MOTEC FI with a stock 3rd gen manifold. I plan on changing the intake manifold soon.