performance mod for 16 valve 928?

[jim ross]

Since performance chips don't exist for older 928s-- is it possible to manually rewrite the program for the earlier brains???? also , can performance fuel pressure regulators really make a difference?

[Rixter]

there are other ways to achieve more hp..
headers, no cats, rmb... euro heads and cams can run you some $$$ but the bang is awesome

[jim ross]

Ive already installed msds headers,y pipe no cat and borla kit. and k&n filter. I like the sound of euro cams!, are they compatable with americam engines????

[Danglerb]

The US motor has a lot of intake restrictions, smaller valves, smaller ports in the heads, smaller runners in the intake, and a MUCH smaller throttle with a tiny opening to the air flow meter. Exhaust isn't good at any stage either, but sounds to me like you have that covered.

I don't know if the US short block is different from the Euro, but the Euro motor is higher compression and not non interference. I do think the heads and cams will fit, just no idea on the results. What most do is build a hybrid with Euro top end and 85/86 US short block, or just build a complete Euro motor.

L Jetronic is much simpler than the LH, no chips to change that I know of, and no knock detection. I am looking very seriously to upgrading to a newer or better control system, either MegaSquirt or maybe a Euro LH system that would work with the sharktuner. Both options I guess would be easier than trying to reprogram the L from scratch.

Then you can always add boost, or just swap in a different motor, S4, or whatever your wallet permits.

[rhjames]

Jim---

all heads are interchangeable with blocks, so to speak.

Just because they will "fit", doesn't meant you should or will.......

"If" you have Ljet injection (electronic injectors), you can use the Euro intakes/throttle body from the mid '80s (84/85/86) 310 hp engine. The heads, cams, intake, throttle body are direct replacement for the US pieces. Gregg Esmell has the complete set up (in pieces) on eBay right now. Don't know what he'll want for the intake system (bids start at 6 bills and didn't include the maf sensor), but he's offered me the cams and heads for about 1500. I would buy the heads and cams, but I'm sourcing them from 2 other guys....


hope this helps----


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[Danglerb]

Originally posted by jim ross
Since performance chips don't exist for older 928s-- is it possible to manually rewrite the program for the earlier brains???? also , can performance fuel pressure regulators really make a difference?

I haven't seen anything about anyone modifying the L brain, the earliest seems to be the 85 LH either US or more recently the Euro. Its just easier to start with a better brain, LH or megasquirt, reprogramming isn't trivial.

Fuel pressure regulators really can make a difference, mess with them and the car can run like crap.

I'm no expert and this could be all wrong, but the impression I get is that a skilled person can mess with the distributor in the old fashioned way to play with timing and advance and get very good results, but it won't be as adaptive as the later electronic systems and may need adjusting more frequently.

The weak link isn't fuel, its getting more air through the motor. Improve the air flow and the existing fuel system is good to about 350 hp. Above that a rising rate fuel pressure regulator can be used as a bandaid .

[jim ross]

Thanks for the tips!! I think the logical next step would be to get my hands on some euro intake pieces.Is it possible to jump the wiring of the airflowmeter and remove it..and create a larger intake area??

[Danglerb]

Herr Kuhn used a box from SplitSecond to put a larger higher flowing MAF on his L jet turbo 928, but its not real cheap. The L jet won't run without something telling it the air flow in a way it expects.

Jim, whats your goal and your budget, might as well lay it all out for the best advice.

[jim ross]

My goal is to achieve best performance.. with bolt on external modifications.on the cheap...like used euro parts or modified stock parts. To get my us car as close to euro performance as possible.

[Danglerb]

Cheap used Euro parts, Let me know when you find some.

Cams and heads each go for about $800 or more a pair, $500 or more for an intake and throttle, maybe double that or more with the fuel injection parts and LH brains. Most heads will also need new valve guides and other machine work.

928ram has a post here in the classified section for a complete early Euro motor, last I checked he wanted about $1800.

Everybody with a early car seems to be looking for Euro and more HP parts, so deals can be hard to come buy and not last very long. Some stuff advertised as Euro aren't, or aren't complete with US cams and or heads instead of the original Euro parts.

****** Something to consider. Boost.

Here is a recipe for power on the cheap. Find a good low mileage US 4.7L motor. Pull the heads and have some big intake valves put in as well as a bit of porting. Buy a Euro S pair of cams. Chop off the top of the US intake tubes, port them, and build a plenum box using them on the bottom and bolting up to a Kenne Bell type blower on top. Get some wide tires.

[rhjames]

Jim---

now that Danglerb has said his piece again, opinions that he has, and seeing as how you guys didn't read my above post, here's the deal:

as I said in my previous post, Gregg Esmel has the stuff you're looking for.

heads (fresh with new valves guides---otherwise stock) and cams/towers $1500

intake (plenum and tubes for L-jet) and throttle body starting bid at $600

he also has a MAF sensor, warm up regulator, and probably injectors if you asked.


ram928 (another Jim) has the Euro stuff, but not the intake tubes----you need these to get the big bang. finding just the L-jet intake tubes will be near impossible, as no one in their right mind would sell just the tubes. you'll have to find a complete intake. besides, all of his stuff may be in my garage next month, if we can come to terms.....


If you want Gregg's number, PM me and I'll put you onto him.

Considering how limited the supply of this Euro stuff is, this may be the only way you can get the job done.


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[rhjames]

And no Danglerb, you don't just throw in a big set of valves.......

Call Phil Wyatt and tell him about that----he'll laugh at you all the way to the bank.

On second thought, just install his 4 mm stem, titanium valves and his custom fab'd buckets, then add a Devek R1 cam grind to the mix and you get buckets of added HP.

Better bring half the bank's holdings too, if you go that route.


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[rhjames]

seriously Jim,

without going into the shortblock, your selection of avenues is limited.

your's is already at 220 or so, so to get just the 300 number, you must use the entire Euro list of pieces, regardless of cis (Euro 300hp) or L-jet (Euro 310 hp). This will cost you the numbers I've quoted in my above post (about $2200-$2500 if my memory serves me correctly), plus TB and H2o kit ($600), and your labor, and any other misc stuff that needs to be handled in the swap.....

Here's the rub.....

you can buy one of Carl Fausset's supercharger kits for about $6000 (or less--I'll have to recheck), and it's a bolt on deal.

Everything is included in his "complete" kits (he has incomplete kits as well) to get you into the near-double the HP with bolt on parts.

Think about it before you start pulling heads and pulling this......half the money will only get you 50-70 hp, and you have to pull the motor apart. Twice the money will get you "nearly" twice the hp, and you don't have to pull the heads, change out the TB and H2o pump, and it idles like a stock engine until you gas on it......

The labor cost/time for either way you go is nearly the same, probably less by just adding the supercharger.

unless your engine is in need of head gaskets and lower end work, your really dollars per hp ahead if you just go the supercharger route......

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[Herr-Kuhn]

Jim...I have a set of fully ported 84 US heads I'd be willing to sell.

[Scott M.]

If you're on a budget, get a set of 78-79 cams. Much more aggressive than the 80-84 cams. You already have the headers/exhaust so an adjustable FPR will help if properly dialed in w/ a wide band sensor.
If you surf the other Porsche forums, do a search for AFM-944. A FR Wilk had a nice website detailing the inner workings of a DME (somewhat similar in function to the barn-door AFM of our L-jet cars).
I may add that in order to get 300 hp from a euro set up one needs EVERYTHING from the donor car... fuel lines (which have a larger internal diameter), pistons (which have a higher C/R), etc. Just the intake and cams are not enough.
With used parts and some ingenuity you can build an SC system for around $2k.

[jim ross]

WOW im learning something here....well i believe the stock '84 arrived with 242 hp (even more torque) with all the emmisions bs..all that is gone.even the belt driven fan.. freeflow exhaust and k-n filter with small airbox mods.. im guessing hp is around 260 + so im just looking for around 50 hp.No supercharging or nitros or turbo...Plus i dont think its a good idea to put too much stress on my 100000 +mile engine and tranny (auto). So will a huge air intake increase(euro intakes and throttle) give me 20 hp? it sounds like a good step. thanks JIM

[sonett3]

100,000 miles it is just getting broken in

[Danglerb]

100k engine and tranny should be fine. You aren't even remotely close to the power limits of the auto trans.

84 US is 234 hp at the flywheel, 84 Euro with a LH and Maf is 310 , but thats no cats. Headers and high flow exhaust add around 20 hp, K&N subtract from wallet, but don't add HP. Pulling the airpump might be good for 5 hp. Mark Kibort posted a run down of what changes were made in each stage of mods up a Euro hybrid.

Until you improve the flow through the heads, (valve size, port size, and cam) I'm not sure what improving the intake will do. Throttle and air flow meter are pretty small though.

[jim ross]

Is it possible to modify a -85 mass air sensor to run with -84 intake??In place of the stock mass air flow meter...(to eliminate restrictive size).Ive already found an 85 airbox bottom used.

[Danglerb]

Originally posted by jim ross
Is it possible to modify a -85 mass air sensor to run with -84 intake??In place of the stock mass air flow meter...(to eliminate restrictive size).Ive already found an 85 airbox bottom used.

The old barn door system in the pre 85 models has a vane the air moves, like a barn door, attached to a potentiometer and it sends a raw voltage from that and a temperature probe to the L brain. A MAF is a hot wire system with a bunch of electronics needed to control it.

Told ya about this in my earlier post, you need a MAF translator box like the SplitSecond PSC1-009 Herr Kuhn is using, and even better you don't need an $800 Porsche MAF you can use a freaking huge $150 GM MAF if you want.

http://www.splitsec.com/

http://www.splitsec.com/spike/Porsche-928-Turbocharged/spikePorsche928turbo.htm

If you want a place to start, look at the throttle body, the US is a tiny thing, but plan on needing to change the whole air path for real gains.