craigmakes321

Looking into 4 into one headers, wanted to hear of any experience/recommendations from fellow s2 owners.

Thanks

Tiger03447

The Tri-Y type header is great for torque especially at lower RPM's. The 4 into one is a higher flow type header and is built primarily for high RPM usage. All of this is determined by pipe diameter and length to get the wave pulses correct. If this is going to be a daily driver or a street machine, you might want to consider getting the stock headers ceramic coated internally to improve the flow. If it's a race car, then go with the 4 into 1.

V2Rocket

the Stahl header available from Racers Edge is supposed to be the best S2 header.

KEVIN ANDERSON

What model do you plan on putting 4 into 1 headers on? I have a 1991 944S2 Coupe and have been doing a lot of research on them. I also took information from my Porsche Technical Specifications book to plug into a formula that gives you the most efficient inside diameter of the header runners. The problem with the stock 944, 944 Turbo and 944S2 Tri Y headers is that they do not use a proper Y shape. On all models they use a long single pipe from cylinder 1 and the pipe from cylinder 4 attaches at almost a 90 degree angle to the single pipe, so it basically directs the hot gasses into an abrupt intersection while cylinder 1 is flowing smoothly. It does form a Y shape but, it really should use a separate Y shaped pipe that connects the runners to the collector. Same thing with cylinders 2 and 3. If you look at the Speed Force headers they are a true Tri-Y. Also, aftermarket Tri-Y headers use 1.75 inch ID for NA and turbo engines. The NA headers have too large a pipe diameter and you lose torque at the bottom end. With the formula I used, the ID for 944S2 headers is 1.62 inches. Now I doubt anybody makes a pipe in that size so you must round it to the nearest larger pipe size. The 4 into 1 headers didn't say what their runner diameter was. I would like to find a set of used 4 into 1 headers even for an 8 valve and weld on the S2 flanges. Personally I like proper Tri-Y headers. With NA cars you can't just slap on the biggest headers possible and expect gains. They have to be tuned more than turbo cars to get proper scavenging affect, for the headers to pull the exhaust gases along with the opening and timing of the exhaust valves. So there is some info for you. I even wondered about the diameters of the runners and X-Over pipe on the 951. If 1.75 ID headers are used on a stock set up and you modify the car with a huge turbo, MAF, larger injectors, it seems reasonable to think that the headers and X-Over pipe should have a larger diameter because you are sometimes forcing 50-75% or higher amounts of hot gasses through the exhaust designed for a 217 HP engine. I think this would lead to much higher back pressure and heat. Or with the stock setup, some people would complain about turbo lag. Wouldn't a smaller ID of the pipes increase the velocity of the gasses and make the turbo spin faster sooner? Just some things to think about. The 968 Turbo RS used the 3 liter block but used the 951 intercooler, charge pipes, AFM, airbox, headers, X-Over pipe, down pipe, intake manifold, throttle body, 8 valve head and even the cycling valve. That car was kept at 350 HP, because any higher they kept melting head gaskets, which leads me to believe there was enormous back pressure and heat probably backing up back into the head through the exhaust valves. So at 350 HP the 951 exhaust setup was too small of ID for the headers, downpipe and X-Overpipe . Also the intercooler and charge pipes were too small for the 968 Turbo RS. Nowadays, getting 350 HP from a 951 is pretty easy, but guys still use the stock exhaust except from the turbo back,( where a 2.75-3.00 inch down pipe and wide open 3 inch or larger exhaust system). which is able to flow a lot more and reduce back pressure allowing for 350 HP without melting head gaskets. Again, just some things to think about. It would take a ton of money through trial and error to find the most efficient sized headers and X-Over pipe for modified 951s. I thought about 1 7/8 ID runners on the headers for a highly modified 951 along with say 1/4 inch larger ID X-Over pipe. It may or may not cause slight turbo lag, but wide open it would flow more gasses freely with less back pressure than the stock parts and I think it would allow a 2.5 liter turbo engine to increase the safe amount of power. You would have a multiplying effect. You have a much larger turbo turbine getting more freely flowing hot expanding gasses that in turn makes the compressor spin faster which sucks in higher amounts of air into the intake system which flows faster and cooler into the combustion chamber, which then leaves the exhaust valves repeating the cycle. You would have a more powerful engine but using less boost. The intake manifold, intercooler, charge pipes, throttle body would all have to be enlarged as well. Sucking in 50 to 75% or more air through the stock intake system would limit the volume or mass of the incoming air which would cause the engine to be less efficient and less powerful than if you used something like the Speed Force intake manifold, larger intercooler, wider charge pipes and slightly larger throttle body ID. Those are just my thoughts and please respond in any way you want. Thanks, Kevin

KEVIN ANDERSON

Sorry, I saw at the end that you are using them on a 944S2

V2Rocket

Kevin,
1.75" OD pipes 16-ga are right about 1.62" ID, which is ~0.05" or so bigger than the stock 8-valve NA/951 exhaust port (40mm/1.57"), not ideal but not a huge deal.

Gas velocity isn't really what makes a turbo spin, it is HEAT energy believe it or not.

I think the NA headers are the right size (they match the port) but the rest of the system might be a hair too big, but not a big deal there either.

The Stahl header with a 2.25 or maybe a 2.5" full exhaust on an S2 with hotter cams would make a nice powerband. Tip I got from a 968-racer ex-Ford engineer was to abruptly step up the exhaust size from ~2.5 to 3.0" about 30" from the collector on these headers; it adds an extra layer of exhaust pulse tuning at the expense of all-out flow and found an extra 8hp on a turnt-up 968 racer.

951and944S

So many variables go into a properly tuned exhaust, if the engine was all around stock, I'd go with the RS Barn or R/E header.
IIRC, MM had a hand in designing one or both of those.

When you start changing compression, cams, ports, valve sizes, a header has to be specific to your modifications to get the most gains.

Personally, I prefer the 4/2/1.

Look at the budgets of NASCAR, they could do anything economically in exhaust development, they run tri-y.

Those that say only a 4/1 for max hp at higher rpms have never seen a 14,500 rpm Japanese, 160bhp @ 1 liter NA engine.

I have a couple of exhaust modelling softwares (4T and PipeMax) if anybody is interested in supplying all the inputs.

Then we can check the stock exhaust vs the optimum primary sizes, lengths, etc.

T

KEVIN ANDERSON

Hey Spencer, Thank you for the good info. I honestly don't know what the ID is for the stock 944S2 headers. I have an extra set of 951 headers and measured the ID of the runners where they are welded to the flange. Tomorrow I will go outside and measure the OD of the 944S2 headers. Thanks man, Kevin

wildcat077

As per Karl Poeltl , he also suggested to me to go from 2.5 to 3 inch after the collector and his muffler of choice was a Hooker Aerochamber with 3 inch center inlet and outlet.
Anyhow , that was before i went with a Stahl header and straight unmuffled exaust on the race car ...

KEVIN ANDERSON

Just to get a wider range of information I go to American hot rod website like Enginebuilder's Magazine.com and a couple other sites where the guys are making incredible amounts of power out of Chevy small block V-8s. Guys that are getting over 600 HP out of 350 ci Chevy engines that are NA. I watch a lot of Summit Racing videos on Youtube and they used different sized 4 into 1 headers, shortie headers, stock headers and coated and non thermal coated headers on an engine that is bolted to a Dyno so they can see the differences in gains and losses pretty fast. With the 4 into 1 headers the best gains were runners a little wider than stock and with a high quality collector that increases in size very quickly. The thermal coated headers didn't make a huge difference on power for one dyno. pull, but the temperature of the headers was 600 degrees cooler using a laser thermostat gun. So having coated headers with a true thermal barrier, not just regular paint or powder coat would definitely give you more power while driving because the amount of heat in the engine bay would be lower, heatsoak from the headers into the head would be almost non existent and these benefits would be even more pronounced on a turbocharged engine. Ceracote makes piston top / combustion chamber thermal barrier that you can buy and if you have an air compressor and powder coat kit, you can do it at home and they don't have to be baked. A lot of the headers in the photo gallery were sprayed on the inside with the piston coating and regular thermal barrier powder coat on the outside so most of the heat is kept in the exhaust pipes and combustion chambers in the heads. It can handle 2000 degrees F, so you could probably coat the combustion chamber, intake and exhaust ports and of course the piston tops on an NA head and use it on a turbo engine. They also sell an ultra slick high temperature coating for piston skirts, camshafts, crankshafts and any place else were you want to reduce friction. It is slicker than Teflon but is 4 times tougher and can also be applied at home with no oven. I read a study that Swaintech did using 2 Dodge Neons with one engine left totally stock and the other coated with thermal barrier and lower friction coating. They beat the hell out of the cars for about 50,000 or more and when they tore the engines down, the Swaintech engine looked like it didn't have any miles on it, it also increased the amount of power the engine made. The non coated engine looked like it was destroyed, extensive wear on internal parts and less power. So to go along with gains with the exhaust, coating certain parts is also a great benefit. When I rebuild my 951 engine I am definitely coating the headers, X-Over pipe, down pipe, turbo and first couple feet of the exhaust system after the down pipe along with the pistons, crankshaft, rod bearings, camshaft, intake and exhaust ports, combustion chamber and valve faces and the intake manifold. I'll probably take the headers and intake manifold off of my S2 and coat them. I have a powder coat gun kit from Eastwood.com. Ceracote sells a mil. gauge so you know how thick the coating is. They recommend .0005 inch thickness with the ultra slick coating and .001 to .002 inch for the thermal barrier. I've read that 60% or more of all of the friction in the engine is from the piston rings sliding up and down. That's probably if the engine has steel or iron cylinder liners. Alusil or Nikasil would have far less friction. That's why you can find 944s with 200,000 miles and more and the compression is still perfect and the bores still look new. If I sleeved my block I would still get the bores coated with Nikasil, for the reduced friction. Thanks guys, Kevin

KEVIN ANDERSON

That would be really cool to use your exhaust software. Since we are going for gains, we have to figure out the best stock dimensions and then for what you anticipate your engine will gain if you rebuilt it with higher compression pistons, hotter cams, larger valves and things like that. Or if the software can give dimensions that will increase power on a stock engine. I know that proper Tri-Y headers will flow much better than the stock headers. Like I said earlier, the stock headers just weld one pipe to another pipe at almost a 90 degree angle which is like running the exhaust gasses and pulses straight through the intersection and hitting the wall on the other side where that pipe's exhaust is flowing smoothly. This causes so much turbulence and messes up the flow of the entire header because Porsche did it for cylinders 1 and 4 and 2 and 3 on the separate Tri -Y headers. It's disappointing to know that Porsche did it as a cost cutting matter. Anybody that has the basic knowledge of flow dynamics can easily see how Porsche cut corners with the headers and they continue to do it to this day. You just have to look at the exhaust systems made by Fab Speed for the 996, 997, 993 Turbo and GT cars and the gains they make over the stock exhaust. You would think a $150,000 to $200,000 car wouldn't leave any gains to be had after leaving Stuttgart, but Porsche will even cut corners on those cars. That's what caused the whole IMS bearing problem on the early 986 and 996 engines, pure cost cutting.

951and944S

Definitely a fan of coatings.

Bring up the topic quite often here.

T

951and944S

Equal length will beat non-equal in every test...., that said, the factory headers on all variants has a lot to do with the 4 cylinder's firing order.

The term flow is used a lot re. exhaust but realistically, it's pulses.

Your exhaust should be your last engine configuration item because it's dependent on all the other engine parameters.

Your goal is to have the most negative (vacuum) pressure at the camshaft (valves) overlap as possible..

Steps in diameter past the collector (as mentioned above in other posts) enhance this feature.

For the record, on the current SP2 car that I built for my son, one of the fastest car/driver combos in the country in class, I use the stock 944 NA 4/2/1 header.
I have two steps, eventually to 3" with a bullet and a turndown tip that terminates 1.5 feet in front of the rear axle.

A year or so ago, at Barber Motorsports Park, having already broken the track record in the first couple of sessions, then resetting his own record again early Sunday, the weld in front of the bullet muffler broke, leaving the pipe and muffler attached by the hanger, which for all intents and purposed, a wide open exhaust at that point..

You can hear when it happens in the on board video so I had a reference to go back and check.

Son reported that the car felt faster when and after it broke but lap times show opposite...

T

craigmakes321

Wow, that is a Tsunami of information, thanks very much. I guess I should have narrowed my question to the choices of 4 to 1 out there, and any experience with those brands. I am leaning to the RS barn as they are stainless, and $500 less than other stainless I have seen.

Thanks

KEVIN ANDERSON

Yes you are correct. The pulses are traveling at the speed of sound so they get down the exhaust tubes and ricochet back faster than the exhaust gases. That's where length and diameter come in to play to properly tune the exhaust. I have seen some muffler companies advertise that their 3 inch muffler flows better than a wide open 2.5 inch exhaust pipe. I know the Rothman's Cup cars used a straight 2.5 inch open pipe from the down pipe back. I can see if your son's car lost some torque after the muffler cracked off. It could be that the length of the total exhaust affected the pulses or maybe the bit of back pressure that the muffler provided messed up the pulse timing. Tuning an exhaust to extract every bit of power is a science. Thank you, Kevin