Hi- I'm kind of a lurker on this forum, but I was curious as to the most horsepower being made from naturally aspirated 928's. I've seen the threads for most horsepower from supercharged and turbocharged 928's, but wonder what's possible from modifications without going to the expense of forced induction. I'll start- I have an 86.5 5 spd with a '90 S4 longblock, 86.5 intake and brains, chips and H pipe with no cats. I have dyno'd 275 rwhp and 299 rwtq. Is there any more power to be had without large $$ investment? Thanks, Dave

 

Go for an X-pipe.

 

The Highest NA HP I've seen claimed is 340 RWHP

 

my S4 with 85 cams made 335rwhp.

one thing that will work well for you, is exchanging the S4 cams for your old 85 cams! do you still have them? 1mm higher lift and its a simple mod that can be done to make those cams compatable with the S4 heads.

mk

 

I dont have the old motor, I bought the car with the S4 motor in it, although I didn't know it at the time.

 

I thought Louie was well over 400 NA RWHP, but that's a bit more than simple bolt-ons....

 

Hi Dave

Nitrous Oxide = 505 hp crank / 500 ft lbs Torque....

All for around $1000 ish.....

All the best Brett

PORSCHE 928 S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES ,RMB ,PROMAX CHIPS, KICKDOWN SWITCH, K&N, WIZARDS OF NOS - NITROUS KIT 150 HP JETTING - 505 BHP / 500 FT LBS TORQUE
PCGB UK 928 FORUM MODERATOR - Email managingdirector@pchealthcare.co.uk

 

Just to be clear, it has S4 heads not 85-86 US heads, right?

 

Don Hanson and Louie were both right around 575rwhp I believe. Those are 6.5L stroker motors though. Not much easy N/A horsepower to be had once you get the car properly tuned and dump the cats for a good X-pipe. The US 85-86 32v S motors seem to react better than the S4's to chips, but I don't know if that is a function of the stock cams or intake. If its due to the intake you may have some more horsepower available there.

 

I think he's means without spending $³.

As noted in a recent thread, bringing your engine up to factory tune, then adding mods will help greatly.

One of the first things I want to get for my new-to-me 86.5 is a rebuilt MAF, plus all the other sensors too. It'll be hard to spend money on boring stuff, but it will be worth it, down the road.

I am impatient to start playing with the valve timing, to see how the 85-86 cams respond. Advancing the cam timing will also advance the ignition timing (by changing the position of the rotors), which is the main feature of putting chips in I believe. 85-86 ignition is a bit conservative, as they don't have knock sensors.

 

Yes, everything but the intake is S4, and that reminds me, the timing belt tension warning is disconnected, is that because the 86 wiring is incompatible with the S4 sensor? I check the belt tension twice a year to be sure it's ok.

 

I think chips work better on the 85-86 because they have "less than optimal" ignition timing since there's no knock sensors. S4 heads/brains have knock sensors and therefore the base ignition map is far more aggressive.

 

I thought Gt cams were the best cams to swap into the S4. Why are the 85-86 better?

Mark, what other mods did you have done to your S4 w/85-86 cams?

 

Advancing the cams will do nothing to ignition timing. Ignition timing is related to crank position, not cam position on 84-86 LH 2.2/EZF. I don't know if that changed to hall sensors for 87+ LH 2.3.
GT cams and 85-86 US cams are very similar in profile, while the 85-86 cams are a fraction of the price and far more commonly available. It's around $400 to have 85-86 cams modified to fit S4/GT/GTS heads. The length of 1 cam and some bearing surfaces are different, IIRC.

 

Oops, , on third thought, that's right. That's probably why the rotor has such a large tip on it, so that the spark will always find the cap terminal, even if the rotor position, in relation to the crank, is changed.