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Old 06-10-2020, 05:22 AM   #1
gpzTurbo
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Default Did anyone else's twin cam conversion fall on its face?

Hi
I have a 93 940T with stock turbo , stock ecu, and stock injectors.
i drank the KoolAid a few yrs ago and jumped in with both feet but without a proper plan. I bought the parts, borrowed the jig, broke out the tools, enlisted the help of a mechanic-friend, and went to town all full of piss and vinegar.
https://drive.google.com/file/d/13bO...ew?usp=sharing
I ruined the car.
It ran so well as a slightly tweaked 8v car I should've left it alone. We finished the head swap, drove it down the road, it came to full boost immediately, then fell on its face .
I asked questions at the time but no one had a solid definitive answer about where to start or what I did wrong.
With a few health issues now I am finishing all of life's unfinished projects or getting rid of them. I'm hoping there's more of a "formula" now.

I will put a small amount of effort into making the conversion work before I yank the powertrain out of the donor car I just purchased yesterday , put it all back to a happy 8v setup, and sell/scrap the rest.

Maybe you'll say helpful things (all of which may start with "you're an idiot") like :
- that setup was never supposed to go with the stock turbo dummy! you have to upgrade to a larger unit
or
- you can run that setup with the stock turbo but the original injectors are way too small dummy!
or
- that whole LH engine management will never work with what you're doing, Idiot.

An ultimately dreamy response to hear would be "that sh!t should've been fun as hell. you just overlooked something simple. go back and triple check your cam timing" (or something similar)
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Old 06-10-2020, 05:48 AM   #2
hessam69
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What actually happened?
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Old 06-10-2020, 07:00 AM   #3
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What they said /\

Does the car not run anymore, or does it just run out of juice on the top end?
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Old 06-10-2020, 07:04 AM   #4
gpzTurbo
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hi. I'm putting this car back on the road. I'm going to fix it one way or another.
and now i'm trying to remember events from a few years ago while fighting memory issues, lol

it runs out of juice before the top end
the car came to full boost (11 psi) immediately then just seemingly would not make more power, or at least not incrementally so as you'd expect. It "fell on its face" is the best way I can describe it.
the car was slower.

It made me wonder if the larger head simply flows too much for the small turbo. I'm hoping others with 16v conversion experience chime in with whether or not they had success keeping original turbo

btw I'd love to see your Grand Nat'l. I never had one but I did have a well tuned Syclone that ran 11's.
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Old 06-10-2020, 08:34 AM   #5
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What ECU are you using? What are the AFR's when it seems to stop making power? Double/triple checked cam timing (with a verified TDC, not trusting the front pulley mark)?

I'd assume you're using stock 16V car cams, which are pretty good. They're no tractor cams like the 8V T cam is.
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Old 06-10-2020, 08:52 AM   #6
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https://forums.turbobricks.com/showthread.php?t=351238
Jack had a similar issue...not sure if he ever got it sorted out.
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Old 06-10-2020, 09:04 AM   #7
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sounds like you're hitting the airflow limit if it's stock LH.
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Old 06-10-2020, 09:05 AM   #8
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if you're still running the 13c, that could do it as well, that's waaay too small for a 16v
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Old 06-10-2020, 09:46 AM   #9
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I'm in your neck of the woods and would be happy to take a peek at it if that would help.
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Old 06-10-2020, 09:47 AM   #10
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Quote:
Originally Posted by linuxman51 View Post
sounds like you're hitting the airflow limit if it's stock LH.
Depending on how abrupt the 'falls on its face' is, this could be the deal.
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Old 06-10-2020, 11:02 AM   #11
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13c + 16v = NOPE
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Old 06-10-2020, 11:07 AM   #12
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Previous thread seemed to arrive at some conclusion: http://forums.tbforums.com/showthread.php?t=319745

He turned the boost down, then it would rev to redline. Again, no clear description of how it 'falls on its face', but I'd have to guess it's pretty dramatic to have largely not driven the car for a few years.
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Old 06-10-2020, 11:11 AM   #13
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I'm gonna agree and say more turbo needed, especially with a head that actually flows.
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Old 06-10-2020, 11:12 AM   #14
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stock ecu with stock chips and original injectors. No Wideband but i remember it didn't ping.
I've since gone through a divorce, dealt with health issues, and haven't found the lostartof chips I purchased a few yrs ago .

740atl - thank you! the car sat too long now, i just finished repairing two motorcycles , finished a v8 960 wagon, then sold two other unused vehicles and am getting the L98 vette ready to sell along with the M1009 Blazer.
I'm bringing this 940 back as a keeper. I know we originally double checked cam timing, I will triple check it then PM you when appropriate as a last ditch effort to save the 16v.
Are you running a similar setup?
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Old 06-10-2020, 11:15 AM   #15
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Describe what it does better. Does the power just sort of plateau early and then trail off, or does the motor cut out?

I'd suggest a standalone ECU and a WB, you're working fairly blind with a stock ECU and an ear listening for pinging.
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Old 06-10-2020, 11:22 AM   #16
gpzTurbo
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Quote:
Originally Posted by blkaplan View Post
13c + 16v = NOPE
I hear you!
(and she says I never listen)


IF this is the case , and I do have a GT28R on the shelf, do you guys have a solid proven formula for the upgrade as far as fueling it? Will just an injector swap and fuel pressure adjustment do it or am I screwing with aftermarket management?
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Old 06-10-2020, 11:29 AM   #17
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the motor does not cut out.
it hit max boost instantly, then plateaued
I'll get a wideband on it and update.
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Old 06-10-2020, 11:29 AM   #18
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Something like Megasquirt allows you do see exactly what's going on, and change any aspect of it you need to, or want to.

Stock chips are black box, unless you buy the tools to tinker with them, and even then, they're not as easy to mess with.
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Old 06-10-2020, 12:29 PM   #19
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Quote:
Originally Posted by gpzTurbo View Post
stock ecu with stock chips and original injectors. No Wideband but i remember it didn't ping.
When you say "stock ecu", do you mean stock 8v or stock 16v ecu?
Edit: Read your old thread and you are using LH2.4 computers from a turbo 940t. The timing maps are too aggressive and they probably won't add enough fuel. I'd stop driving the car until you can get some proper chips ion it, or you get a stand alone setup.

Original injectors for what engine and ecu combination?
Edit: Looks like stock 8v turbo injectors. Yeah, you're going to need more injector than that.

Quote:
Originally Posted by gpzTurbo View Post
IF this is the case , and I do have a GT28R on the shelf, do you guys have a solid proven formula for the upgrade as far as fueling it? Will just an injector swap and fuel pressure adjustment do it or am I screwing with aftermarket management?
My guess is that GT28 turbo is going to be way too small. Is it a real Garrett or a clone?
I don't know what your CR is, what your power goals are, or what your drivability goals are. This makes it a bit difficult to suggest anything...

Edit: Looks like you keep mentioning boost pressure, but what you need to understand is that a turbo moves a mass of air at a given pressure. 10psi on an 8v with a 13c and 10psi on a 16v with a 13c are DRASTICALLY different mass air flow requirements. With a 16v, a 13c probably can't even make 7psi at redline under load. The exhaust manifold pressure would also be about 2-3X that at least. All this to say, you need at least a mid frame or large t4/t3 turbo with a 0.63 or larger exhaust AR.
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Last edited by culberro; 06-11-2020 at 11:27 AM..
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Old 06-10-2020, 12:43 PM   #20
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What sort of exhaust manifold is that 13c using on the 16V? Stock 8V manifold on an adapter or something else?

What sort of intake manifold?
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Old 06-10-2020, 02:09 PM   #21
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Yes, more details of what manifolds? But in general as you can see. A 16v turbo needs a completely different tuning for it's engine management. A plateau in power could be because lack of fuel, lack of air, or even both would be my guess with a 16v turbo at 11psi on a stock turbo, and stock tuning. You can get it going. We need more turbo redblock power in S NJ!
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Old 06-10-2020, 02:13 PM   #22
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Once you're into the 16V swap, you're sort of out of the 'cheap ways to add HP' zone.
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Old 06-10-2020, 03:01 PM   #23
gpzTurbo
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Pic of engine compartment in first post
I've been told I do not post clearly.
It has the Yoshi intake manifold with yoshi 8v exhaust manifold adapter and I think yoshi provided the 960 throttle body that's on it but I'm not sure.
It was a good running original 940 Turbo.
It still has its original 940 Turbo ECU , injectors , and turbocharger.
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Old 06-10-2020, 03:08 PM   #24
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Looks good! I sent you a pm.
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Old 06-10-2020, 03:10 PM   #25
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Assuming you're not hitting fuel cut (where the ECU goes into survival mode, assuming something broke on the wastegate and runaway boost is happening), you might just be strangling the engine with that adapter/exhaust manifold, feeding into that tiny turbo.

It would be worse if you were running short on fuel. Lean is not good when under boost. And it's not always going to result in audible pinging. Sometimes it can just melt pistons for the hell of it.

There's no real '+15 hp' in engine modifications. Everything has to support the increased amount of air moving through the motor, from the first part of the intake to the tailpipe. You're pretty much limited by the worst remaining bottleneck.

And also assuming that you can get enough fuel in to match the air, of course. Which can be limited by the fuel pump, the injectors, or the ECU itself not understanding the new hardware it's been asked to try to deal with.
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