Exhaust Manifold Info

[kc92awd]

I'm looking for information on exhaust manifolds. I'm not worried about appearance. From a performance perspective, what are the advantages and disadvantages of each available type (spool, top end, etc...)?

Mainly, what are the perfomance differences between a stainless tubular manifold and a ported, cast manifold like the evo III?

 

[silverbulletAWD]

A few things to think about.

Cast-
A decent cast manifold should never crack on you. So if you want a manifold for a daily driver that gets alot of miles then you should probably stick w/ cast. But then again if you’re putting lots of miles on and daily driving your race car you’re probably not very serious about racing IMHO.

A cast manifold will retain heat well and will typically place the turbo as close to the exh. ports as possible. Both of these, by theory are the best ways to make power w/ a turbo. By this I mean focusing as much heat as possible on the turbine wheel to make boost.

Tubular-
If you use a tubular manifold that is shipped of the shelf and has been designed to place the turbo in the factory location, it is safe to say that this manifold WILL crack at some point on some day. The only difference in time is in the quality of the manifold. Almost every single tubular exh. manifold I have seen lately is either not quite or not even close to being equal length. This, again IMHO, completely negates the purpose of having a tubular manifold so one might as well stick w/ a cast model. Obviously, the more the unequal the more worthless.

ELEM's-
The whole point of an equal length manifold is to time the individual pulses to converge in the collector in a rhythmic manner. This, in fewer words than more "can" give you two very worth while attributes to your systems performance. First, each pulse will be evenly spaced and instead of varying pressures throughout the cycle each will be able to be focused on spooling the turbo. This should in turn spool the turbo slightly quicker than an unequal length manifold. Second, If the runners are "tuned" to the proper length to match the application a scavenging effect could actually take place which will in turn help the exh. pulse evacuate the cylinder more effieciently and "could" even help reduce the reversion that will always take place in a turbo system. I'm sure someone will argue that last point though.

My reasoning for not wasting time with unequal length tubular manifolds is that by not using equal length runners (standard is w/ in 1/4") you won't really be getting the benefits you could from a proper setup. All you will be getting is an unnecessary loss of heat incurred from traveling a farther distance. Of course I do believe that by getting closer to equal length than stock should still help spool a slight bit. There will come a point were one difference outweighs the other. So by all means do as you please, it's been made apparent to me that by the volume of these things being sold every one does.

Andy

 

[kc92awd]

I think a lot of people are getting them because they look good under the hood. So you don't think there would be any real performance gain by going with the "off the shelf tubulars" over a ported EVO III manifold?

 

[silverbulletAWD]

I'm spending a lot of time this winter researching exh. mani.'s mainly because toward the middle of this winter I will be building a new manifold for my race car. This will end up being something similar to the crazy manifolds you may have seen on some of the pro FWD cars lately. But my point is that after all of this research I still always take time to inspect others work. So far it all sucks for the most part. The problem is trying to put the turbo in the factory location. We'll save that for another day though.

I think you could gain some performance if you went w/ the right manifold. Like I said though, the more uneven the runners the less it will help. I really haven't seen any conclusive dyno #'s either. Or more importantly the hard evidence, same day track #'s. You could blow $500-600 on a blingy manifold and let your subconscious convince you it was worth it. Or take that money and put it somewhere gains are undisputed. I don't know where you're at w/ your car but think about this, I've personally watched a 1g go 9.8x on a ported 2g exh. mani. I know that doesn't mean since he can anyone else can but what it does mean is that if he can do that w/o a tubular manifold then apparently the cast manifold isn't all to much of a bottleneck. So basically, if you want to look cool and can deal with potential cracks from time to time, get a tubular manifold. If you want reliability with a fully functional design, get a cast manifold. Shoot, if you want to hide the casting w/ some shine just PM me.

Andy