hacker-pschorr

oops
Yea, I found that out with the bolt holes to - I took off the heat shields.

I've been meaning to update an old exhaust thread with the spacer I had made - keep forgetting to take a picture of it on the car.

I guess everyone calls them "bolt on" since they are compared to headers.

Keep in mind what Porken found out about L-Jet. The Temp II sensor directly controls the pulse width. Add some resistance - you run richer. I added 1,200 ohms to mine one day just for kicks - under boost I was puffing black smoke out the back like a train.

mark kibort

uhhh, guys, did you forget me?

ive already posted years ago about the voltage going up to 8volts with full voltage, not just sitting with the engine off, and moving the flap around.
the full travel flap voltage is different sitting in your driveway vs on the road. 7 to 8 volts if i remember correctly at max deflection, max air flow metering.

also, i tapped into the Ljet and found that i was still NOT pegged with my 293rwhp!!!!!!!!! around 7.8 volts with less rwhp, it was less voltage. And, i did kick up the fuel regs as well to get the Air fuel ratio to 12.6 from start to finish on a dyno run.
The only draw back of the AFM is that it is a restrictor, under 5 square inches vs the 85 , euro and S4's near 7 to 8 square inches. however, the differnce of a 5 liter Ljet vs a CIS vs an aftermarket injection system is only about 10 to 15hp max.

my Ljet went from 177rwhp to 293rwhp with the only change in the system being that of a RRFR!

MK

MK

Jack Riffle

Mark, that's very interesting reading. How much fuel pressure are you running on that L-Jet car? And how much H.P. do you think the L-Jet system is capable of supplying fuel for? What are the limits? Now maybe my head is still a little fuzzy from too much DiSarrona last night, but are you saying you gained 116H.P from only a RRFR? If that's true, it would kinda bum me out to have spent so much time and money installing euro heads and cams and headers to gain only 72 H.P when I could have installed the RRFR in far less time for far less money and gotten far better results. I think Eric gained about that same amount when he supercharged his car.

John V

Mark,

If I recall correctly, you did a lot more than than just add an RRFR to get that power... didn't you go to the full Euro intake, heads, cam, TB and increase displacement?? Also, I agree with you that you can't get to max AFM voltage while driving... that's not the question. The question is, does the AFM voltage stop climbing proportionatly to air demand at around 3-4000 RPM? My understanding is that it does. You get farily proportional voltage to RPM correlation from idle to 3000 RPM, but after that, voltage stays essentially the same while RPM continues to climb. The part thats stumping me is that the air demands from 3000-6000 RPM double, and if the AFM isn't capable of reacting to air increases beyond the 3000 RPM range, how does the L-jet know to add fuel beyond the stock engine configuration that uses RPM based fuel delivery?

Jack-

72 HP is an awsome gain on a 4.5 liter! I'm jealous! I thought about going that route as well but it seemed like an awful big invesetment of time and money and other than Mark, there wasn't much supporting that this swap made that much power... with your RWHP numbers, it would seem your into EURO S 4.7 crank HP numbers with just 4.5 liters and L-Jet... thats impressive!

Like so many others, I have higher hopes for forced induction but getting around to it has been just that, a hope. I was really excited about the rear turbo set-up but it seems theres little concrete progress on that.

Jack Riffle

John, as I said, I think the 4.5 has a lot of potential but few are willing to explore it, deeming it easier to just upgrade to a 32 valve. Cost wise, it probably is, but I like the simplicity of the L-Jet and the early body style. As I said earlier, I am trying to find a few more H.P laying around before going to forced induction. I am currently looking at timing advance as a possibility, since the vacuum advance the 4.5 uses is something of a dinosaur. Possibly I can find a way to "tweak" it. I also have a Euro S throttle body that I will be playing with soon. I am also wondering why twin turbos could not be mounted directly to the header collectors. Anybody?

John V

Well having recently spent some time in that area swapping my manifolds, Placing the turbos down that low (down near the bell housing) would place the oil drains so low that a sump would be required. I'm sure its doable, but not easily.

hacker-pschorr

Well, not that long ago the majority of the 928 community had a unanimous opinion that simply bolting on a blower would not gain very much, or if it did would grenade the motor. Now between how many vendors, there are over 50 supercharged 928’s running around with no issues.

In a different thread is an S4 that gained around 40rwhp with tuning tricks & bolt ons. Why is it then considered “impossible” to gain similar results on the 16V?

Why are the 951 guys able to crank out 500rwhp with a 4-banger (using the same head we have) but talking about a 300rwhp 928 you are called a liar (ask me how I know). People will chime in “The 16V head is not suited for boosting” or other BS ideas like “The barn door cannot be boosted” Oh yea? The 951 uses an L-Jet barn door – works fine on their cars. Yes they are limited to how much boost they can accurately pump through the door, they are also starting with half the motor & a car already boosted. This changes things a bit. They are also using the same head that is on our cars!!!!

Is 400rwhp possible on a “stock” L-Jet car with some boost? My money is on the table betting that it is. Driving my 81 around last night, kicking the *** end out at 65mph on the highway is getting close. Yea yea, cold air, cold tires. I don’t care. The blond in the Mustang gave me a thumps up.

Here is how I see it – hopefully I will not get flamed here – this is just my opinion, ok guys?

Boosting a N/A car – keeping the engine 100% stock is a compromise right off the bat & not the “proper” way to boost a car. Regardless of “how” you boost it.

You look at the big picture. Every auto manufacture makes significant upgrades to their cars when they bolt on a few turbo’s to control the heat generated. It’s a fact – turbo’s get very, very hot. Extreme heat is never a good thing on a motor.

Even Pontiac added sodium filled valves and ceramic lined exhaust ports when they added a turbo on the Solstice. What does that tell you? Not to mention, every turbo car I have ever seen roll off the assembly line has the turbo as close to the exhaust port as possible. Have you ever seen under the hood of a Ur-Audi S4?

Now you take the 928 engine – heads are stock – Porsche would have never supercharged these heads without a few of the “basic” turbo head modifications. Like reinforced exhaust valves & exhaust ports. Not to mention – they wouldn’t have even considered a turbo 5 feet away from the motor. Will this work? Sure it will. IMO it’s taking an already compromised situation & adding more band-aids on top of band-aids.

This is ultimately why we (Green Bay wrecking crew) has stuck with superchargers. In a compromised situation on a stock motor, it’s the cleanest & safest solution. Todd has discovered limitations of these motors I have never seen talked about on this or any other 928 board. Limitations that have kept him from ever playing with turbo’s on these cars. Doe she want to? Hell yes, he talks about it all the time – isn’t worth the effort is ultimately what he says & the under hood temps are a factor not worth dealing with.
This coming from a guy who is hand building a 427 cubic inch 928 motor (see my sig) so if anyone has the ability to “do it right” something tells me he’s the guy.

/flame suit on – my intentions are not to start yet another boosted flame war. There are very few people spending considerable time & money trying to make some seriously go fast 16V’s. So until any turbo vendors has a tested & proven turbo setup for the 16V’s on the market – everything about a turbo 16V is 100% speculation & bench racing.

I’m off to eat some turkey in my boosted 16V – 50 degrees in Wisconsin – God bless global warming!!!

John V

Hacker,

I'm certainly no expert and am in no position to elevate one approach over another for anyone other than myself. I respect anyone or any type of mouse trap that force feeds these engines. I'm also a firm believer that 100 hp/liter is attainable with forced induction, with some impact to longevity I'm sure, but I don't consider this power level destructive to the engine if not abused. I'm not saying that I'd want to push the power that high in our stock engines, but 75 hp per liter is everyday stuff now, without forged internals or boost for that matter. IN fact, I would expect that the 4.5 liter engines would easily support that power level force fed and in some senses, are better candidates for forced induction than some of the newer 928 engines due to thier lower compression and smaller valve sizes. Thats only my opinion based on what I've read and it's only worth what you paid for it. I've been quite surprised and discouraged that quite a few efforts to up power on the 4.5 have been less than spectacular. If I ever have the time and inclination, I'd like to prove to myself that the 4.5l could cost effectively be brought up to 330-350 crank HP.

Cost effective becomes my stumbling point. I believe for everyday "Joes" that own a car thats valued at anywhere between 3-12K ('80-'84), a boosting kit that costs 4-6K, while appealing to a lot of folks, is only going to "sell" to a small subset of that market. I could be wrong but thats my opinion. I think the real appeal needs to come in at about $20 per HP. To add 110 crank HP to the 220 HP engine for around $2200, would be very appealing to me and I think doable with a rear turbo setup. Keep in mind that I'm not talking about a Kit and do beleive that figure is unreasonable for a well sorted out product. What I'm talking about is what a decent wrencher would spend on components to build around 6-8 pounds of boost into a 4.5l 928. I think the rear turbo provides the unique benefit that the forced air plenum could function as a psuedo intercooler and perhaps support 8 poundof boost if intake air temps could be controlled. The rear trubo has quite a few drawbacks too and I recognize that as well... I just think this approach is the easiest and most COST effective means to obtain this power level on the 4.5. Notice I didn't say "best" or "easy"... just the "easiest" and most "cost effective" as far as I can tell.

hacker-pschorr

Well John, I think you and I are on the same page here

I saw my first rear turbo setup about 5 years ago at SEMA. I'm sure it works, just seams overly complex to me. Doesn't matter really, 6-10psi of boost on a 16V will put the motor over 300 crank no matter what (well, assuming the air / fuel is somewhat within reason). And I'm confident these engine's can take the extra power. How many 928's are on the road stock close to or over 200,000 miles? These engines are over built and under powered.

I'm happy to see anyone taking the time & money to play with a 16V. They are the hidden gem in the 928 world. Lighter, cheaper & much easier to work on. Here's hoping I hit my 400rwhp goal
6-7psi on an S4 reaches this goal. 12psi on a US 16V should be close.

mark kibort

A few things. yes, the voltage of the AFM continued to climb from 3k all the way to redline. each mod, made the voltage go higher all the way around.

Yes, there were more mods than just the RRFRs, i ment to say that i did all these gains with only a set of RRFRs as mods to the fuel system. The mods that the Ljet system supported went in this order:
exhaust, headers, cams intake (TB, runners, plennum) at this point i was at 243rwhp. then displacement and euro head change went to 293rwhp. it all started at 177rwhp stock, and 130,000miles. ( I owned the car starting at 46,000miles)

So, the bottomline, is that the Ljet supported fuel flow from 177rwhp to 293rwhp and fuel pressure started from stock and ended up at near 53psi. stock 84 US injectors.

Mk

edit: I forgot to address the voltage going up past 4000rpm. yes, it continued to climb. I also had injector duration measurements, at near 90%. part of the beauty of the Ljet system is that part of the fuel delivery is based on RPM at WOT, and there is the fuel enrichment that goes on at 75% of full throttle to WOT. (by 15%) all you need to do, is get the two wires on the AFM, put them ot a volt meter and drive down the road WOT and watch the voltage at idle as well as WOT from the different rpms. the AFM flap is still moving and creating mroe injector duration all the way to redline.

toofast928

L-Jet can fuel 400+ HP+. Proof below. And the 4.5L stock heads flow pretty well under boost.
Here's my dyno chart , RWHP 285, 350 at the crank.
A/F diped to 10.6. 6 psi, non I/C, stock exh manifolds, X pipe, euro intake and TB.
No modifcation to the L Jet execpt for FMU. Top fuel presure reaches 85 PSI.
Winter project is installing a I/C and going to 9 PSI of boost. I'll pass 400 HP at the crank but that's the top HP without engine teardown (head port/polish, upgrade pistions, etc.

toofast928

Forgot the Dyno

toofast928

Uh

mark kibort

I wonder why you needed 85psi fuel pressure for 295rwhp. maybe thats the reason for the 10.6:1 fuel ratios. whats "FMU"?

i was at 53psi at 293rwhp with the 5 liter euro 2 valve motor and all stock Ljet stuff, with rrfr.

MK

John V

Well comtrary to what I thought, my exhaust mods did not put me into a lean condition. I just warmed her up and made several runs with my son watching air fuel ratios. I'm at 13.8:1-14.0:1 from 3000 to 6000 RPM WOT. I'm a little surprised that the L-jet appears to have adapted quite well to mods. We'll see what the dyno says tommorrow.