Experts Input (Porsche Dry)

[LeonT]

Hey Guys; Over the last couple months i've been learning and piecing together a dry nitrous setup and while it was enlightening i have come to the conclusion that you are WAY better off buying a complete system right off the bat from one of the vendors here.It will be a lot easier,end up being better quality,save on shipping 15-20 seperate items,have warranty and of course have the tech help you might need down the road...and no,i have no affiliation with any company!Anyways,The car i'm setting up is an '88 Porsche 928S4.The car is a 5 Litre DOHC 32V EFI V8,316BHP.It uses 2 Bosch computers,an LH and an EZK.One for fuel,one for timing.It uses a MAF with the sensor wires mounted inside.At WOT the car retards timing 6 degrees(switch) and goes into rich mode.Also the aluminum intake is very well engineered,the runners AFR flow within 1 of each other.It's like they almost designed the engine for a decent dry hit of N20!My plan is to mount 2 nozzles,one smaller 90 degree shot (.038)3-4 inches from the MAF wire,shooting directly at it and the other larger hit in the airbox about 6-8 inches away from the MAF.I would like to eventually work my way up to a 150rwhp dry shot with this setup.The car dynos a wimpy 259rwhp right now n/a.I know the injectors are a weak link right now #19's @ 57 PSI. Your thoughts?

[Robert56]

I absolutely love it. i have alot of experiance with LSx and dry before and after the MAF. What we have found is it is better to take control of the MAF via the computer rather than relying on the MAF wires. Seems, due to air dynamics in the intake tract that the spray can miss the wires somewhat sometimes. So By taking command of the same parameters in the computer directly, we can have a stable a/f ratio at all times. We now have dry plate kits that mount after the MAF in the air stream. then we have a small micro computer that interfaces with the stock GM PCM.

Sounds like you have direct control abilities your self, for fueling and timing pull? Might be something to think about and consider. IMO, for at least the LSx platform, the before the MAF nozzle style dry kits are dated technology with better ways to go now. Check in the EFI section you might be able to glean some insite with my street/strip direct port dry system using the stock PCM for fueling and timing pull.

Anyway, I am very interested in what you are proposing, which ever route you take. I had pretty good success with the nozzles before the MAf dry hits, but others had varing success. Please keep us updated on your progress. If I can help anyway let me know. On my site is some dry tuning stuff that might help in some way. I don't know the Porsche computer, but still may be able to help?
Robert

[LeonT]

Thanks very much Robert.Actually most of what i've learned about dry is from reading your posts and writeups on LS1 and the corvette forums! I used to own a vette back in the eighties and have been toying with the idea of getting another one this coming year,but the wife wants a 60's Mustang for her 50th Bday,so that may have to wait...but we'll see:D My first priority now is to get new injectors,i think i'm going with High Impedance 4 Pintle Bosch 24s for now.I descreened the MAF this past summer and there were no issues.Idle AFR was 14.5,but a little Rich at WOT 10-11.5. The few N20 928 guys that are out there think wet is best,we're going to show them they are wrong!

[Robert56]

Most say they think wet is better only due to lack of knowledge concerning dry technology, plain and simple. For the guys interested in EFI tuning anyway, the dry tech will fit right in. Why not use the computer that the engineers designed for dry control, more and more people are begining to take this route.

I have set of 60lb injectors replacing my Ford SVO 42's that served me well. Hopefully your computer allows changing injectors as easily as the LSx platform. By the way, I had a '65 Mustang back in the day and wish I still had it, lol.

Keep us updated.
Robert

[Robert56]

Oh yea just a note on the MAF de-screening for those reading along. We always want to de-screen the MAF when running dry hits. Why? Well what can happen on a humid day is condensation can collect and freeze on the screen making for a wild a/f ratio.

Once de-screened we may need to re-map the MAF tables for a slight increase in intake volume. For most, and especially the latest EFI cars, this will not be needed as the small discrepancy can be dealt with via the VE tables. On the LSx platform this can work up to a 20/25% error at any one spot on the fuel table. So the computer can adjust for slightly leaner readings. The guys that have problems usually already have their tunes out of whack enough that they may be already compensating at 20/25% and once we reach that point then the next step is a code will be thrown.

One more thing to point out, the MAF screen is there to straighten up the air flow so the MAF wires get a nice even reading. However, this is only really needed on set-ups that have numerous 90 degree turns, like the truck plumbing. What GM did for cost savings was to add the screen to all the MAFs so as to have one part number, so the cars that didn't need the screen got one anyway.

One of the ways that GM upped the HP rating on the '02 thru '04 Z06, from the previous 385bhp to the new 405bhp, was by removing the MAF screen. They opened up the air box and found the MAF screen to hinder flow for best power, so they removed it. That is why you will see a separate, or different, part number for the '02/'04 Z06 MAF, and the '01 part # staying the same as other GM cars. Other than that, they are same as other GM MAFs of that era. Also, the MAF freq range was increased, IIRC, at this time over prior MAFs, partly I believe due to the better flow that increased the range (GM guys should run the Z06 MAF if ya need a replacement). Just thought I would through this info out for any nitrous geeks that might care, LOL.
Robert

[LeonT]

Great post Robert,clears up a lot of the confusion about MAF descreening.Thanks.

[tlcurt]

a little off topic, but so the z06 maf are different than a ls1 maf?

[Robert56]

a little off topic, but so the z06 maf are different than a ls1 maf?
Yes. The Z06 is 85mm, IIRC, and the LS1 is 75mm, or something close to this. The early LS1 MAFs had a freq top end of like 1100 hertz and the Z06 like 1300hertz, now those numbers are for examples only and I do not have the specific numbers off hand.

We should have also stated, MAF part numbers in groupings. We didn't mean that there were exactly one or two MAF part numbers, but more on the lines of fewer part numbers by putting screens in most all MAFs.
Robert