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 Post subject: Re: So this turned up today
PostPosted: Fri Nov 03, 2017 11:24 pm 
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Joined: Tue Dec 29, 2009 11:16 am
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Location: Stoke On Trent
Model: Supercharged 924
Just caught up with this!

I had the same thoughts. In summary;

- 61bhp loss / correction factor seems a bit high.
- 209bhp @ 1bar is decent, but not amazing for a newly built engine with FMIC and EFI.
- 150whp is a bit lower than I'd expect given the above.
- all this dyno stuff is just black magic and very very variable!!

In long form!

At the dyno I used up north my car made 225bhp corrected flywheel @ 0.95 bar boost. After talking with the dyno operator / tuner I discovered he didn't use a calculation based on drag to calculate the BHP. He just uses a standard 20% loss for all RWD cars - the reason is to give a consistent factor so he can see what difference a tuning change has made without a variable in correction factor from one run to the next, or over the course of the day, skewing the results of his tune.

The most reliable is wheel hp, but even that is subject to tyre friction, the way the car is strapped down etc etc.
As a comparator, my wheel hp of about 180bhp equated to the 225bhp I quote for my car. A bigger correction factor would potentially increase that max BHP figure.

Ultimately though, it's all riddled with fudging the numbers!!

I'll be honest though - I love your car John, it's one of my favourite 3 in the club, but I'm surprised it didn't make more power and think there should be much more to be had out of it. I can't remember what Steve made at the wheels, but I would have thought at 1 bar you should be marking more like the 180bhp.

If everything is ok with the engine (sort the oil leak etc) I would be booking it in with Emerald to have another look at the tune and ensure it's optimised. It may have been a 'safe' tune with relatively retarded ignition and there is a significant improvement to be had. Obviously having it tuned on 99 Tesco fuel is a winner if you can run it on that all the time (I think I had mine tuned on 97 or something so I could put 99 in and have an added level of safety.)

Most important though is how it feels! The rest is just willy waving rights for down the pub!

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924T engine with Eaton M90 Supercharger (DB7), 565cc injectors, coil pack ignition, Adaptronic ECU, Custom Air/water charge cooler, Wideband O2 + 4x EGT. 4pot Brembos, Spax adjustable dampers. 951 G'box with LSD & cooler, 944T style bumper. HID Lo-Pro headlights. 968 mirrors, handles + spoiler. Zender rear valance. Custom side skirts, Forged 17" wheels (8J front, 9J rear). Custom hubs (5x114.3 PCD), Twin circuit coolant re-route (2 pumps, 2 'stats, 2 radiators), 6 gauge centre console.


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 Post subject: Re: So this turned up today
PostPosted: Sat Nov 04, 2017 12:03 am 
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Model: TheOnly Way Is Turbo
If it’s running the S1 K26 2470 6.10 turbo, then this may be its ultimate restriction. That compressor wheel may not be able to cope with 1.0bar or more boost. It’s also noted to be of poor match to a tuned 924 turbo. I haven’t reread Jays thread to recall what turbo he ran or what the tune was used at Emerald.

On the dyno sheet posted above my car ran 173bhp at the wheels at 1.0bar, corrected to 225bhp at the engine. On two previous dyno sessions my car ran 256bhp with limited roller drag and I felt was too optimistic, and then 206bhp on another session which lowballed everything that was tested on that day. The car also felt lethargic on the drive to and from that session. Both were not with the mittelmotor dizzy and other elements I’ve added to the car since. I’ve also changed the timing and boost since the last dyno day in 2016 so really do need to run it on rollers again. A different day, dyno and operator will see differing results. Lies, damn lies and statistics. Butt dyno often wins over what the printout says. But it is nice to know your numbers even if there may be 5-10% of tolerance/fluctuation depending on prevailing factors

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1981 924 Carrera GT/S rep race car - Speed Yellow Too much to do, to little time and money!
1979 924 Turbo Series 1 - Alpine White & Guards Red 10yrs owned and counting
2021 Skoda Superb Sportline Plus iV Estate Hybrid awaiting delivery...
2017 VW Passat Variant GTE Advance soon to be retired....
2015 Nissan Leaf Tekna Continues to 'build trees'


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 Post subject: Re: So this turned up today
PostPosted: Sat Nov 04, 2017 11:39 pm 
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Location: emsworth hampshire
Model: 924 gt 924 n/a
Its a'll a black art this dyno thing
I could put it on a different dyno tomrow and get 230bhp I reckon
The rear brakes bind so that won't help, fuel that's not high octane would make a difference and the throttle body and inlet manifold would play a part In it to I think.
I have a s2 throttle body and inlet manifold to go on instead of the s1 manifold and ford Granada throttle body and some other little mods on the induction that should help And maybe rethink the turbo and pistons when I build a new engine. but at 210bhp all be a little less than expected it's quick, enough for the roads I have around here and feels much quicker than my old s1 s2 hybrid so I'm very happy with that Jay built an amazing car and I'm pleased to own it :smile:
But all points are noted and ticking over for more improvements In the future :whistle:
On the plus side the oil leak was a loose bolt on the turbo oil feed and now all fixed so that's a bonus

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 Post subject: Re: So this turned up today
PostPosted: Sun Nov 05, 2017 10:02 am 
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Agreed mate!

The variabliity between dynos is fairly large I think. 10% easy and that's 20bhp so your 230hp guess isn't unreasonable or unrealistic. It's all nonsense really - but I'm a big a slave to the numbers as the next guy!

Glad the oil was an easy fix.

Enjoy the improved performance and only once the novelty starts to wear off should you think about messing with it!! Enjoy whilst you can!! :beer:

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924T engine with Eaton M90 Supercharger (DB7), 565cc injectors, coil pack ignition, Adaptronic ECU, Custom Air/water charge cooler, Wideband O2 + 4x EGT. 4pot Brembos, Spax adjustable dampers. 951 G'box with LSD & cooler, 944T style bumper. HID Lo-Pro headlights. 968 mirrors, handles + spoiler. Zender rear valance. Custom side skirts, Forged 17" wheels (8J front, 9J rear). Custom hubs (5x114.3 PCD), Twin circuit coolant re-route (2 pumps, 2 'stats, 2 radiators), 6 gauge centre console.


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 Post subject: Re: So this turned up today
PostPosted: Sun Nov 05, 2017 3:39 pm 
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looks like a little torque monster to me.
Dont care about the decent power...over 300Nm of torque from as low as 3000RPM flat to 4500 and tailing off just a bit to redline makes for a very very good driving experience and thats all that matters.
Maybe the top end power tailing off is due to mixture not being optimal at high rpm?


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 Post subject: Re: So this turned up today
PostPosted: Sun Nov 05, 2017 4:11 pm 
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morghen wrote:
Maybe the top end power tailing off is due to mixture not being optimal at high rpm?


Good point on the torque. Top end could be also compressor and/or cam timing related. Mine also drops off at the top end as I have the cam advanced to for low end spooling and torque.

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Steve - Joined: Sat Jan 30, 2010 10:13 pm......think I have lost far too much time in this forum.........
1981 924 Carrera GT/S rep race car - Speed Yellow Too much to do, to little time and money!
1979 924 Turbo Series 1 - Alpine White & Guards Red 10yrs owned and counting
2021 Skoda Superb Sportline Plus iV Estate Hybrid awaiting delivery...
2017 VW Passat Variant GTE Advance soon to be retired....
2015 Nissan Leaf Tekna Continues to 'build trees'


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 Post subject: Re: So this turned up today
PostPosted: Sun Nov 05, 2017 7:38 pm 
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morghen wrote:
looks like a little torque monster to me.
Dont care about the decent power...over 300Nm of torque from as low as 3000RPM flat to 4500 and tailing off just a bit to redline makes for a very very good driving experience and thats all that matters.


Totally agree; an interesting result. The torque figures are a better result than headline high rpm power.

It begs the question, which turbo is fitted? Couldn't find the info in the original thread. The engine was definitely S1 as it had the S1 pistons but no mention about turbo spec other than it had improved 360 thrust fitted for higher boost use.

The torque is 225lb/ft versus 207lb/ft for a stock Carrera GT and it's making it a good 500rpm earlier. I bet the butt dyno result is favourable :cool:

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 Post subject: Re: So this turned up today
PostPosted: Sun Nov 05, 2017 8:50 pm 
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I had a look at the turbo today there's no plate on it or any numbers I can see is there any visual signs to find out what it is without removing it

The man running the dyno said it's got a bit of poke and would buy the car from me and offered good money too but that's not going happening :whistle:

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 Post subject: Re: So this turned up today
PostPosted: Mon Nov 06, 2017 9:54 am 
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have a look on the turbo housing..there should be some numbers embossed that should identify if its an S1 compressor or not.
Would also be interesting when we could learn what the hot side is as well.

Its a nice car, don't make the same mistake the previous owner did (to sell it) :)


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 Post subject: Re: So this turned up today
PostPosted: Sat Nov 11, 2017 5:29 pm 
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Location: emsworth hampshire
Model: 924 gt 924 n/a
jay has kindly sent me all the pics he took when building the car the first pic shows numbers on the cold side of 4720
Attachment:
924 turbocharger 001.JPG
924 turbocharger 001.JPG [ 3.44 MiB | Viewed 3891 times ]

i cant make out the numbers on the hot side
Attachment:
924 turbocharger 003.JPG
924 turbocharger 003.JPG [ 3.38 MiB | Viewed 3891 times ]

Attachment:
924 turbocharger 005.JPG
924 turbocharger 005.JPG [ 3.26 MiB | Viewed 3889 times ]

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