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Forced induction

 
Old 02-17-2019, 10:20 AM
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Justin Tyme
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Default Forced induction

Chaps,

Can anyone just answer this for me ?

Why are all the supercharge/turbo kits all pretty well made only for 32v engines ?

I don't understand.

I get the whole mechanical vs electronic fuel injection thing, but some of the 16v 4.7 engines came with EFI and electronic injectors.

Is it a manifold thing ?

I know there's one supercharger kit floating around for the mechanical bosch systems, but I understand they're really not the best as the K-jet isn't well suited to that application.

So, what gives ?

What's needed for a decent SC/Turbo setup for a 16v EFI engine. (assume aftermarket EFI).

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Old 02-17-2019, 02:18 PM
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A knock sensor and knock control comes to mind.
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Old 02-17-2019, 02:21 PM
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The short answer to your question is: cost.
The cost to supercharge an 16V car is about the same as a 32V car. That may seem obvious but the power differences are huge. The Murf928 setup made a repeatable 500rwhp while most 16V setups struggled to reach 300-350rwhp. The general consensus was, start with a 32V car so you get more power for your overall investment. Why spend that kind of money only to have a little more power than a stock 32V car?

Here's my 81, which was an early prototype for the Murf928 system, my car was built alongside Tim Murphy's personal car.

The L-Jet system doesn't allow an "easy" way to tune the computer like the 32V cars.
Therefor, to keep costs down and to simplify the setup we used a Vortech Fuel Management Unit (FMU) which increases fuel pressure under boost (blue thing in upper right corner). This is an incredibly crude way to do things, but it works. The early 32V cars also used this method, but once the Sharktuner was available, we ditched the FMU for custom tuned chips supplied with every kit. Something that isn't possible with the L-Jet or CIS cars.

If you go with an aftermarket ECU, then it's just a matter of finding a competent tuner to build you a tune. In my opinion, the best way to tackle this is find the tuner and use whatever system they support. A competent tuner installing their own system is the best way to go. But again, this adds significant cost (especially with the tuning) most don't feel is worth the expense when the power output will still be quite lower compared to a 32V car.

There are "piggyback" systems that go between the injectors and computer, I've never played with those, I've never been a fan of such devices even though others have had good success with them.

After several years with the FMU on my car, I swapped out the computers / harness for the LH / EZF from an 85 EuroS which can be shark-tuned. This could be seen as a more cost effective way to go with a tunable ECU compared to a complete aftermarket setup. Hindsight I think I would have been better off going with something like AEM Infinity.

Tim Murphy never pursued offering a kit for the 16V cars due to an agreement with another vendor who supplied those, Tim focused on the 32V cars. That vendor broke their end of the deal so when I recently talked to Tim Murphy about getting the Murf928 kit back on the market, we agreed the 16V kits will now be looked into using my 1980 as the test car since my 81 is too far removed from stock for that purpose.
Mechanically they share most of the components.

The intercooler in this photo is an early prototype I'm no longer using (actually have two of them). My car now uses the same intercooler made locally by Twin Turbo Todd for the 85/86 cars, which can be seen in this thread:
https://rennlist.com/forums/928-foru...s-new-car.html
It's a bit embarrassing I cannot find any photos of my car with that intercooler. My 81 is currently in several pieces. I learned the hard way don't start a major car project around the same time you buy a fixer-upper house......

Now if we are talking about the 84/85 EuroS with LH / EZF, those can be Sharktuned. If you have an 84 you will need to find an 85 brain, they are not the same and the earlier unit cannot be tuned.

Locally there is an 84 EuroS race with a Murf928 system installed. It's a one off system the owner put together incorporating a large air to air intercooler.

Anyway, hope this answers your questions.






Here's my 81 on the dyno:

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Old 02-17-2019, 08:14 PM
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Justin Tyme
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Thank you. That's very informative.

The problem I have is that I have two 16v cars. I don't have a 32v car and they're hard to come by in OZ, plus I don't really feel like chasing one.

So, maybe an LS/LT swap is the go then ?

There are myriads of aftermarket EFI's around. I'd be tempted to just use a spitfire or megasquirt or something.

Thousands and thousands of these units are in use all over the world in all sorts of v8's. The knowledge bank is huge.

I wouldn't bother trying to retrofit some later model Porsche ecu/wiring.
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Old 02-17-2019, 09:11 PM
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Originally Posted by Justin Tyme View Post
The problem I have is that I have two 16v cars. I don't have a 32v car and they're hard to come by in OZ, plus I don't really feel like chasing one.
I never liked the mentality of "just buy a 32V", I enjoyed the project and my car made over 375rwhp with the L-Jet setup. With a 200lb or so lighter car than a typical 32V, it sure wasn't a slouch.

It's easy to get caught up with big numbers, when just trying to modernize an old 928, 350-375rwhp isn't outdated. Here's a 2011 Corvette, around the same weight as my 81 putting down 383rwhp:
https://www.corvetteforum.com/forums...ne-dyno-s.html

Originally Posted by Justin Tyme View Post
So, maybe an LS/LT swap is the go then ?
The big question, one I ask myself before starting any such project is: How much power do you want to make?

Originally Posted by Justin Tyme View Post
There are myriads of aftermarket EFI's around. I'd be tempted to just use a spitfire or megasquirt or something.
Thousands and thousands of these units are in use all over the world in all sorts of v8's. The knowledge bank is huge.
Yup, a lot has changed in a very short amount of time. There are a lot of ECU's to choose from these days and you don't really need a fancy one for a boosted 928. We don't have variable intakes, variable cam timing etc...

Colin aka Lizard has worked a lot with VEMS and Megasquirt on 928's. I'll be going with Infinity due to a very knowledgeable local talent pool.

Originally Posted by Justin Tyme View Post
I wouldn't bother trying to retrofit some later model Porsche ecu/wiring.
It was a fun experiment. A lot of what I did with my 81 was just to see what would happen and to see if we could get it to work. It's fun to see how far you can push stock components. It sometimes feels like "cheating" to toss out everything and buy new stuff, at some point you start to ask yourself "Then why not just buy a newer car?" I ponder stuff like that all the time.

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Old 02-17-2019, 09:36 PM
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I'm after nice streetable power that will get the old girl moving, and more power lower in the rev range.

It won't be a drag car.

350-400 RWHP would be fine.

I have the early model 5 speed man trans and a 4 speed auto. Not sure which one to go for just yet.

I'm not going top be thrashing the thing, no tracking, no drifting..lol.... just want something where you can put the foot down and get nicely kicked back in the seat.
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Old 02-17-2019, 09:42 PM
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Is your car an 84/85 EuroS with the twin distributor?

Yes, my 81 is a lot of fun. I cannot wait to get it back together and finally tune it with the new ECU.
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Old 02-17-2019, 10:00 PM
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Yep. One is....the other is a euro spec 1982 928S with mechanical injection.

The EuroS twin dizzy motor needs a rebuild though...and as it's the one with the EFI I thought I might go for that one, but in the 1982 body.

Long story but I have the 1982S car with a 3 speed auto...that isn't running but is all complete....and the later model car with the EFI engine that snapped the camshaft wheel off one of the cams a while ago, with a 3 speed auto in it....and a complete 1982 manual 4.7 litre Euro spec driveline (motor-TT-5 speed transaxle) laying out (condition unknown right now), plus another 4 speed auto transaxle and TT spare too.

So out of all that I want to build up the 1982 928S (as I like its looks better) with a supercharged engine and either the 4 speed auto or the 5 speed manual.

Then get rid of all the excess stuff I have.
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Old 02-17-2019, 10:19 PM
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Sounds like a solid plan.

The Supercharged EuroS race car owned by a local friend an 928 Guru put down somewhere in the ballpark of 385rwhp. That's with the stock cams and 10.4:1 compression ration. It's an all out race car and Jean-Louis is a very good driver.
He bought a pulley / bracket for the Murf928 system and made the rest himself.

Keep me posted on your progress.

As I mentioned before the intercooler Twin Turbo Todd designed for the 85/86 cars is a work of art and fits nicely on the 84/85 EuroS intake system. You can see the intercooler here:
https://rennlist.com/forums/928-foru...s-new-car.html

I have designed an even bigger version since the 16V intake offers a bit more room to work with. We just haven't pulled the trigger to weld it up yet
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Old 02-17-2019, 10:33 PM
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Twin turbo on the 4.7 EFI engine ?

That sounds interesting....

We need to talk further.
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Old 02-17-2019, 10:46 PM
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Sorry for the confusion, the twin turbo part is a nickname for the person who built this car:

https://rennlist.com/forums/928-foru...deo-added.html

He's a welder / fabricator by trade and is very much the reason why the Murf928 kit was so successful. It was based on a bracket / tensioner design he came up with almost 30 years ago for a motorcycle (not kidding).

That car is a 100% one off, nothing is "bolt on" although the base 5 liter is mostly a stock engine (different rods / pistons & valve springs)
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Old 02-18-2019, 10:10 AM
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The Powerdyne setup I have on my '79 K-Jet mechanical fuel injected 928 is superb. I've been driving it around with the supercharger removed for a few weeks and it's not the same car - it's nice, and I've enjoyed feeling what an original 928 drove like, but definitely miss the 130 HP increase I was getting with my forced induction setup. My kit is a Stage 2 with heat exchanger from 928 Motorsports. I've been driving it without it because I sent the supercharger head itself back to them for an upgrade to find a little more boost - lighter, billet machined impeller with different vane design, upgraded bearing, stronger internal belt, and vented the case. Here it is reinstalled, but I'm waiting for some different upper radiator hoses that arrive this week.



Airbox work and powdercoating I did custom and are not part of the 928MS kit.

The car makes 350 HP & 350 TQ at the motor (about 292 HP at the wheels) and that was prior to these supercharger upgrades, so figuring a bit higher now - maybe knocking on the door of 400 HP. Tracking AFR values, it's always between 11.5 and 13.5 and under full throttle closer to the 11.5 - 12 value, so definitely on the richer (safer) side. The K-Jet system, when in good operating condition and setup properly, works just fine for supercharging, as it adjusts the fueling to correlate to the air it's metering. I will be closely watching the AFR values when I do the first couple drives with the upgrades, as I want to make sure the fueling will still match up to the increased air, and not lean out under high RPM, high boost situations.

Both the car and the supercharger have been perfectly reliable since I built it 4 years ago. If you want a HP & TQ monster, then starting with the 32V motor is surely the way to go, but when I saw this convertible, I bought it for the body style and then wanted to make it perform a bit better than stock, which is why I spent the money to upgrade a 16v motor and the rest of the car - 6-speed transmission, GTS brakes, Konis with sport springs, etc.

It's a lot of fun to drive and has the right balance of comfort, power, and cool-ness.
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Old 02-18-2019, 10:47 AM
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but I understand they're really not the best as the K-jet isn't well suited to that application.
That isn't true. We have many supercharger kits on K-Jet cars and they are just fine. Many years and many miles on them. The key is a complete understanding of the K-Jet air metering system, and the right engineering to size a supercharger kit to what the K-Jet can fuel - which is what we have done. The K-Jet and early L-Jet cars have excellent camshafts for supercharging, and low compression too - also a + compared to the 32v cars.

I have dyno charts that show the K-Jet fueling the system just fine. And because the 16v distributer can be adjusted, dialing the ignition advance back a bit is a simple thing.

The Stage 1 kit start at just $4895.00 complete.
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Old 02-18-2019, 11:41 AM
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There are three reasons why the early K-Jet and L-Jet cars lend themselves particularly well to supercharging
  • They have low compression ratios, either 8.5:1 or 9:1
  • They have mild camshaft grinds with little valve overlap
  • Adjusting the ignition timing is very simple.
On the other hand, the early K-Jet and L-Jets do not have a great deal of adjustment range for tuning. As a result of this, instead of putting in all the boost we could and then wondering how we were going to fuel it; we opted to make a Stage 1 kit that puts in no more boost than the stock K-Jet or L-Jet can fuel. This makes for a simple and successful install for our customers with great engine safety.

Typical output for these kits is 300 to 320 BHP, where stock they were from 219 to 229 HP.

Please let me know if you have any questions.
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Last edited by Carl Fausett; 02-18-2019 at 04:36 PM.
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Old 02-18-2019, 12:02 PM
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BAck when I was looking to do the same thing I wanted the MURPH supercharger set up based on all the talk back in 04,05 06 about the system, I was naive, I tried to contact murph and was told to be patient he is a very busy man, etc.....
little did I know the threads were actually subtle advertisements that were at the time hard to tease out from the prose, I eventually went with 928 motorsports and had nothing but great service with awesome products !!!
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