Equal Length Manfiolds-Interesting primary size comparisons

Was doing some digging as many have been discussing different breathing mods over in the 3.8vs fabspeed intake thread. Started looking back at the exhaust side of things, there�s some size differences to consider with the name brand offerings. Some findings- there are a handful of the name brand aftermarket options for our equal length manifolds offering a 42mm primary size option. After further digging, and I�ve found there are other name brands pushing the 45mm primary size (FVD, Cargraphic,) We also have the X51 manifolds that bring a 48mm primary to the table. As it�s been discussed many times, bigger isn�t always better on our stock displacement motors/and even some larger engines- because efficiency has to be key and everything has to work in tandem from intake to heads/cam set up, to the exhaust side of things. Maybe some of our exhaust suppliers and engine builders on the form can weigh in here to. On our stock displacement 3.4, 3.6 M96 variants, what do you feel the more efficient manifold setup up would be? (42mm vs 45mm) The stock manifolds themselves I believe also are 42mm. We must take into consideration the longer equal length primary setup too. This can move the power band around a bit and offer very modest gains in some applications with the many options we have. At what point would the 42mm or 45mm benefit or hurt the car more? Does running a stock sized X pipe 54mm or larger 63mm work better in conjunction with one size or the other? I ask this related to a car with basic breathing mods, plenum/TB, 200/100 cell or catless setup. Personally on a stock displacement 3.4 or 3.6 engine non X51 car, I�d have a lot of trouble seeing the benefit of a 48mm x51 header making a whole lot of sense (with bolt on breathing mods only) On a built, higher displacement (say 3.8-4.0l) this may be where X51 manifolds really shine/with Shrick cams and head work. Id really like to hear some of our suppliers and their personal unbiased opinions of primary sizing/manifold layout design and X pipe size selection- how do they come to their conclusion and what real world testing can they share, that leads them to push one size over another? Have they experimented with both and saw gains or losses? (I�d imagine they have some data) I�ve attached an older article from Hoffman, as we all know-does amazing things with our heads. Looking at the M96 (3.4) exhaust port side of things- it appears to have a 32.5mm outlet size for reference. Cannot recall nor do I have the specs in front of me of the 3.6�s heads. Maybe someone can confirm if they are the same sizes or slightly altered due to variocam + Not sure how one determines the most efficient manifold primary tubing size related to the exhaust port size. Probably a question for the engineers in Stuttgart. Hoffman Link https://newsite.hamheads.com/porsche...age-m96m979a1/

I don�t know whatever makes sense, I can honestly tell the soul headers on my 3.4 make a good difference, I wish I could have dyno before and after. Anyway the car has a bunch of other stuff on it that is non stock.

My 3.4 heads are currently at Len's shop for performance mods . We decided on bigger valves and some port work . He stated the flow increase over stock will be 14% which is a huge gain . Per Jake's recommendation I am sticking with stock headers but on the intake side an IPD plenum and GT3 throttle body being installed . Behind the stock headers will be an FVD catless X pipe feeding stock mufflers . I am going to do a DIY version of the Fister or Gundo mod but that is more for sound quality vs performance . I hope to have my 3.4 to 3.8 conversion running by June/July timeframe .

Interesting on Jake's recommendation with stock headers. I remember in a thread when he discussed that he had tested many after market headers and was unable to find one that worked with his engine rebuild. Looks like it's a balancing act of different components, machining and specs depending on whether you increase the bore size or keep the bores as is and enhance around it with cams and bolt on parts.

Quotes source post: 17998611

Sometimes the manufacturer does actually know what they are doing. Over 20 years ago we had a similar thread on VW Vortex about how to maximize the output of your 12 valve VR6. We had over 400 pages of info. What was determined is that the sum total of all bolt on stuff could add to about 8HP. Every header tested was worse than stock, except for one that was equal to stock. Every intake was worse than stock. Cams could push the powerband around but not increase it to any meaningful amount. The expensive Schrick VGI's could slightly bump torque above 4000 RPM. The final consensus was that nothing was worth doing unless for the visual appeal. The only way to get additional power of any reasonable amount was forced induction. That didn't stop me from buying an expensive Schrick VGI because they do look really cool.

Quotes source post: 17998630

They do look really cool! Prf, let me throw a scenario out to you and others that may know the answer. Let's assume you take an M96 engine and do what everyone does, replace the exhaust with a better flowing set of headers, cats and mufflers; add in the IPD/TB; and add software that ties these components together. We know that we will get some improvement in HP or TQ. Not trying to argue how much. Instead, is their any incremental improvement at all if you have the heads done with the above set-up, or does the real improvement come from having the heads done in combination with boring out the cylinders?

Quotes source post: 17998630

we had eip remove the ramp in the throttle. The intake was gasket matched, so where the trottle body, chip and exhaust, 8 mm plug cables, neuspeed short shift kit, intake cone filter with fabricated aluminum down by the bumper, none of the other stuff work. All mods were actually dyno verified, Hennessy, we sent back one chip and one exhaust. At Houston raceway park with 104 octane race fuel 50 percent, spare tire removed, in 1996 car ran 13.81 at 101 mph in the quarter. My buddies with schrick cams could do no better than 14s. Only corrados that got me had super chargers or turbos, off course nitrous cars got me. I never told no one about our handy work with the dremmel tool and how we where checking every upgrade on the dyno. My SS mandrel bent exhaust was free because we were the testing guine pig.

Quotes source post: 17998510

my 3.4 is a cable throttle car. Anyway if you are doing the len big valves your total bill should be at round $4k. Regarding the headers a bunch of different shops have different opinions, they said the 997 headers flow better. Some like B&B, some like soul and or fabspeed, cargraphic, fvd, etc. I can�t use the gt3 throttle but my throttle was enlarged already. At one point you get to maximum power restricted by airflow, fuel flow. I heard from a California race shop that they prefer to do 3.4 to 3.6 to have thicker walls and enhance engine durability (instead of the 3.8 conversion), I can see where that would make sense. Also there is the heat factor. Same race shop said with 3.6 you just use low temp thermostat and you don�t need center radiator. I just had that and a new water pump installed and it makes a noticeable difference where the needle is at. The stock mufflers weight a ton, so does stock cat pipes. Even changing the headers you save over 2 lbs. Also from a tuner who I may finish with, their stock cable throttle tune, increases hp and torque better than their tune on the egas 3.4.

^^^ Yes my 99 is a C4 so it has egas . In regards to wall thickness or reliability of the 3.8 conversion FSI has done LOTS of them and I have never heard of a failure so not worried . This is going to be a street hot rod not a track rat . I agree stock mufflers are heavy but for now that's what I will use . I can always add lighter mufflers in the future . There are many ways to attack performance and reliability mods/upgrades . I am in no way saying the route I am taking is the best or only way to get there . But I am basically using the same path/method that worked great on my Boxster S . She performs great and reliable as a stove . Just like my Boxster S which has three radiators I will add a center radiator to my C4 . I live in Georgia in the mountains and it gets hot and humid here . I push my Boxster very hard in the mountains and never have any temp issues . It's a proven solution . I apologize for the long reply and don't mean to side track the original post . Enjoy the weekend guys .

Quotes source post: 17999159

I�ll send you a pm.

Excellent dialogue here with everything. Also appreciate some of the updates and gains that can be made with Hoffman�s work to date. It definitely seems the consensus many have is to take advantage of the head work when moving to larger displacement. I absolutely would agree and I�d go a similar route. Furthermore, focusing on our breathing side of things- the IPD plenum, TB and head work look to compliment one another with a displacement increase. I noticed another poster was asking is there any benefit with the head work upgrades on our stock displacement cars? I�d love to hear if anyone has reached Len Hoffman, and discussed this in more detail. I�d imagine something like his Stage 1 may be the only thing recommended, as working to get the balanced system fine tuned to the stock parameters is the sweet spot for the M96? Per his older article, he does outline how efficient the M96 and M97 heads can be, out of the box on our stock displacement cars

Quotes source post: 18000667

yes stock engine you pay for performance porting that�s what he said there�s a 3 percent air flow improvement in the flow bench, your headwork will be like $2k. If you are going larger displacement then the custom larger valves are the way to go. Once you get there the headwork is like $4k. At that time you should be thinking about different cams. Some race shops in Cali do 5 angle valve jobs on stock heads and they claim about 4 percent better air flow, that�s pretty believable, Hoffman is conservative on his numbers.

In the early 90s, headwork was reasonably cheap in Mexico, about $10-$15 completed in 10 minutes or less like a quick oil change. I can give a rat *** about this political correct world we now live on. Loved the oil industry days of past whatever would go and it was accepted and approved as long as you got the deal done. I wrote the red traveling guide but that�s on my head would implicate way too many people. Let your imagination live. You can�t take money or material possessions with you but life�s experiences those go with you.

Quotes source post: 18000860

3/98- really appreciate the insight and confirmation from Hoffman on stock vs increased displacement builds, and the head options. Great to know, regardless of which route someone would take� if you got the heads off and are simply freshening them up, or going to a larger displacement build, Hoffman seems to have the right recipe to compliment the build.