TheAllusionist

I am accumulating the final parts to do my build this spring when I replace the blown head gasket. I have a LR intercooler, freshly built K27-8 from Charlie at evergreen, heavily ported head being freshened up and matched to a ported intake manifold with an oversized throttle body and I have a 4" exhaust as well as a dual port wastegate. Since I am working so hard for it to breath, but I am insisting on keeping the stock airbox (it may end up being modified but to the casual observer look stock), I was wondering if I have a weak link in the intercooler hard pipes and if anyone makes performance ones for use with the stock airbox?

The reason I am keeping the stock airbox is that this is a stealth build on a low mileage car, trying to get it to breath as much as possible and keep boost reasonable for reliability. I will be boring out the stock AFM and using the housing to look stock, but will be using a MAF or MAP system, that is the last peice in the puzzle as the Vitiesse MAF I had purchased on Ebay (I know, I know) wasn't for a 951, so that part will be my last major purchase in the equation, have a 968 M030 sway bar system adn Koni Coil over front and rear to install as well and once done will take the car to Seattle to have the rear end lowered appropriately and then corner balanced and then hope to drive for years just enjoying it. I did purchase a timing belt replacement kit with tensioners etc.. so that I can do my own maintenance........

Long post, sorry, but if nobody makes them but someone made some and has them fro sale feel free to contact me. My other option is there is some guy who does custom pipe work who advertise in craigslist under Porsche that I might be able to hire, but thought I would see if they were available from some source. Or one of the knowledgeable people here telling me that the cross-section of the IC pipes breathes more than enough and that your only gain is really to reduce bends and turbulence in the pipes........ I just don't want to terribly cripple all the work I am doing if they are a big restriction, I know some will say that the airbox is already doing that, but then I have talked to people who say it breathes fine up to 400 RWHP which is above where I will be..... Or it could be I will make a custom snorkle and top section that looks basicall stock but breaths more, question is, what about the hardpipes?

Thanks for your time.

Russell

V2Rocket

thoughts...
what size is the turbo outlet?
what size are the in/outlets of the intercooler?
how big is the throttle body?

stock 951 pipes are around 2", maybe a little more, ID.

TheAllusionist

Throttle body butterfly valve plate 62.5mm (2.46 inches), not certain if the plate size equates exactly to opening size. Turbo outlet on a K27-8? Is it 2" or 2.5"? I don't know if it is all apples to apples and less restriction should equal faster spool up times, but there are things that seem to add torque vs HP, or throttle response, the Germans did things for a reason for the most part, I am just trying to learn. The intake manifold has been ported and increased to match the throttle body and it will be ported to match the head I am having built, just seems like IC pipes might be a restriction now.

I imagine the most I will see if all is done right is 340-350 RWHP (probably optimistic), could be that it isn't to a point that larger IC pipes will matter, but I don't want to leave any HP on the table if I can help it. My goal basically is to make things breath as best as possible so that I have fast spooling and throttle response for street use and have some top end (Hence the K27-8) if I can get some track time, but realistically I won't be racing this car.

V2Rocket

62mm throttle but there's an 8mm diameter shaft in the middle of it spanning the whole 62mm, that makes almost 500 sqmm of dead space.

K27-8 might have a 2 or 2.5" OD outlet, but it's the ID that matters if you're thinking about upsizing pipes.

the larger pipe that will affect spool/restriction to a real degree is the exhaust.

see my signature.

Tom M'Guinn

I made 450 horsepower and 473 ft.lbs. of torque, to the wheels, with a stock intercooler and stock intercooler pipes. That was on my 3 liter, but that still seems to confirm they flow "enough" for your 400hp goal. I also suspect that the barn door opening in the stock AFM is plenty big enough for 400hp, but the issue is the 0-5vdc signal will max out (i.e., the barn door will be fully open) somewhere south of your goal, leaving you no way to differentiate and fuel 350hp worth or air vs. 400hp worth of air, since both will just be seen as approx 5 volts on pin 7 of the DME. You could gut the AFM and hide a MAF in there (and there have been a couple great threads on that here), or gut the AFM and go to some speed-density set-up relying solely on a MAP sensor, or use some hybrid or combo of the two. I've seen products out there that simulate a MAF curve using a MAP sensor, which might be the easiest thing to do. Dave W. had one, though I can't remember the name. I've always wanted to make a box that accepts the AFM signal and a MAP signal, and rescales and relies on the AFM until it's maxed out, then adds room above that with the MAP sensor, but that's a project for another day. At any rate, I think your biggest restriction will be the snorkel and opening leading to the air filter itself. If the filter box remains in its stock location, there is very little room available to make the inlet bigger. A few have tried, but I haven't seen any that really moved the needle. Depending on how you meter the air, it might be possible to bring air in through the bottom of the AFM box (along with the stock snorkel) in a stealth way... Also, one of the corvettes had a similar issue, and people solved it by taking the top lid off the filter and zip tying the filter in place (or drilling holds in the top cover), so maybe something along those line...

TheAllusionist

Thanks for the information and input. I didn't think about the shaft down the center of the butterfly valve, I was thinking about any seat/lip for that valve, hence being a bit dense! LOL

I knew about the exhaust, that is whey I have a 4" unit but still need to buy the 3" downpipe which may not do a lot now but if I ever go with a larger turbo will come into play and I figure I may as well tranfer up to the 4" causing as little restriction as soon as possible. I just wasn't certain what things did on the intake side as I know you can tune power curve by intake runners, it seemed there may be some engineering magic on the front side.


Thanks for the real world information, not going to worry about the hardpipes it seems. That is some wicked horsepower and monsterous torque!

The snorkel was the first place I started thinking about, I was thinking about splitting two down the middle, one top and one bottom and wrapping them around a spiral ribcage (metaphor), securing them together and enlarging the penetration through the fender well to increase volume, but that seemed to have issues as well, but it kept air coming in. Currently I have thought about drilling the holes in the top of the air box and then a second top secured with standoffs to provide 1/8"-1/4" gap between the two with maybe corrugated ridge vent (for home roof vents at the peak), to allow air in but not show the holes drilled. The top lid may be just the top so it looks relatively stock, have to buy a used air box and play with it. Downside is that you are sucking warm air in from engine bay. If you look at those two options and downsides, at what point does the snorkel get big enough, as it starts to flatten out? Do you drill holes on underside starting where the cross section starts to increase to get a 'wee bit' more air? Or as suggested run another air tube up under and towards firewall and elbow it into the underside of the stock snorkle as far up as you can. I imagine smarter people than I have tried better options, but I have thought about it. I also have heard as many people say they have runt 350-400 RWHP with a stock airbox as I have heard people say it drastically limits your power, so probably look into it when I figure out what MAF/MAP system I end up using, but will make sure it is a limitation before taking on that challenge.

As for the AFM alternates, I know Vitesse used to sell stealth kits and I have seen the threads and if I go with John's system I will replicate. Raceboy also told be the basics to to it with the VEMs system which I am considering as well. Of course there is the Rogue/LR option as well, but my 1986 has 24 pin so going M-Tune requires another step. In any case even if you routed a pipe down where the AFM is and kept things stock colors, the average person wouldn't know it isn't stock, I think that will be the easier part.

Thanks guys for the input, sounds like I really don't need to worry about the hard pipes and may or may not need to worry about the air filter. Look forward to when my head and intake are done and the weather warms up so I can take on the build.