Originally Posted by Bardman

Without CATs you can trigger CELs as well as have problems with Smog testing and Sound testing (depending on where you live).

I think the thing to pay attention to though, is how a particular set of headers can influence the power/torque delivery of your car. Most of the manufacturers are only talking about peak gains. +X hp, +Y lb/ft. They are not (currently) providing any dyno charts for their headers. But a dyno chart can tell you more about what the overall change will feel like, and in some cases this may not be what you want.

Take this dyno chart from Fabspeed sports headers as an example (not picking on fabspeed, but they are the only manufacturer providing dyno charts for their headers for which I applaud them):



You can see that these headers add peak 10 hp and only a couple of lb/foot of torque. But where it gets interesting is that at 3600 rpm you get about +40 lb/foot of torque. That's a 17% boost in that low/mid range.

Great, but. Move along to 4000 rpm and the torque has dropped below stock. So its reduced the magnitude of the torque dip and pushed it higher up the rev range. This may be a compromise you are willing to make - overall the area under the curve is larger. But if you spend all your time higher up the rev range then this may not be desirable.

As another example, look what happens at about 4800 rpms. Almost 20 lb/ft higher than stock, but watch it dip to around the same level as stock. Stock pretty much flattens out but doesn't really dip. So with the headers you will feel like you are "coming off the boil" a little at that point before going back up again. Overall the torque numbers are higher in this range, but you may not want that drop off feeling which you wouldn't get with the stock manifolds.

Given this car is all about feel, I think its important to understand how a certain set of headers can influence the feel - and that is more important than any peak gains. My 2 cents.

For the record, my car is for the street, so I'm pretty excited about reducing that torque dip at 3600rpms, I just want to see what the other header solutions dyno charts look like as well.

Originally Posted by BGB Motorsports

Great question...yes I have and I had planned this as a Plan C but it required drilling and adding an O2 bung to your stock PSE system. I actually ordered a pair and had them ready if the fix didn't work. I've used these things before. i think they last about 15 track days before you nuke them but they're cheap to replace. I found out about them because one Sunday i came up with what i thought was a brilliant idea to make a pseudo cat, but alas, someone had already come up with it.

Originally Posted by jmartpr

If you go back to the post with the header pictures you can relate some of the above figures to the header design. The shorter primary tubes before they merge into a single one on the Fabspeed will result in the above scenario while if you have a longer path like the one on the Cargraphics it will spread the gains over a wider rpms range an hold it better.....this is for Sport headers as Race headers all have the longer path before the collector. IMHO The CGs have better flow characteristics (physical from a picture analysis) than all the other sport headers.

Originally Posted by BGB Motorsports

Ladies and Gents,

I got as much as we could from Cargraphic in Germany. We need 10 parties and we have about 13 so therefore we can offer 10% off the "Race" Manifolds without cats and 15% off the "Sport" Manifolds WITH cats and an additional 50% off shipping in the lower 48. That puts you well below the price of other competing brands of race manifolds with a nice discount on the sport manifolds. Interested parties should call the shop and ask for Miguel so that we can take billing and credit card information because i would like to turn around and pay Cargraphic immediately so we can get parts in the queue and ready for shipment. The offer will run through Memorial Day 2016. If during the summer more GT4 owners want to participate then we will consider running the offer again.

Thanks for the positive support on this forum. We are lucky to have such faithful followers.

Originally Posted by Ferrarisimo

I opted into the group buy as well. The headers will get here before my car.

Originally Posted by jmartpr

If you go back to the post with the header pictures you can relate some of the above figures to the header design. The shorter primary tubes before they merge into a single one on the Fabspeed will result in the above scenario while if you have a longer path like the one on the Cargraphics it will spread the gains over a wider rpms range an hold it better.....this is for Sport headers as Race headers all have the longer path before the collector. IMHO The CGs have better flow characteristics (physical from a picture analysis) than all the other sport headers.

Originally Posted by krell

I too purchased parts for the car before it arrived. It's a disease that has no cure.

Originally Posted by CAlexio

Did I miss where CG has a picture of their torque /hp gains vs stock, or is this just theory?

Originally Posted by ShakeNBake

All I can say is that is f'in complicated to tune headers....to take advantage of inertial and wave scavaging. Diameter, length, collector design, steps - all play a role. BMW is a master (when they are not using FI or worrying about US emissions). I used to think I could look at a header design and judge how good it is, but so much more CAN go into the design that I just look at dyno plots now. You can screw up any design if you just focus on one design parameter - like length. it's probably more important to know WHO designed them since it still seems like a dark art.

Article talks about F1, Nascar, MotoGP designs. Cool stuff - but now probably not so important with FI.
http://www.epi-eng.com/piston_engine...technology.htm

Originally Posted by CAlexio

thank you.. which is what I've been saying.. this whole "long tube headers" thing may all be accurate, but I wish there was info and a full dyno graph vs stock to show these vs shorter configurations etc. Seems like bandwagons form on this forum and everyone just jumps on without checkout out the data first.

Originally Posted by CAlexio

thank you.. which is what I've been saying.. this whole "long tube headers" thing may all be accurate, but I wish there was info and a full dyno graph vs stock to show these vs shorter configurations etc. Seems like bandwagons form on this forum and everyone just jumps on without checkout out the data first.

Originally Posted by jmartpr

One thing is if you are playing with 1" increments before collector and things like that used for tuning the powerband and another is looking at the whole picture of the design of the header. So far GMG, CG and FVD (M&M) have similar designs placing the collector right at the entry of the cats. The Fabspeed is the only one deviating from this design, which IMO will have it Pros and Cons. Also to consider...why all race headers merge at the very end?


I do agree that a dyno chart would be a 1,000-times better but we don't have those so we have to guesstimate on what's available until someone can provide solid dyno data.

Originally Posted by CAlexio

thank you.. which is what I've been saying.. this whole "long tube headers" thing may all be accurate, but I wish there was info and a full dyno graph vs stock to show these vs shorter configurations etc. Seems like bandwagons form on this forum and everyone just jumps on without checkout out the data first.