E36 Racecar build - Swap to Forged LS6

[HarrisRacing]

Greetings,

I am not new to racing or new to swaps, but I am new to the BMW chassis. I picked up a 1995 BMW from a friend who was getting out of racing for a good deal. I went through the car marginally, and prepped it for a track day to get used to it, but blew a head gasket between 1-2 cylinders on the 4th session of the first track day. Car understeers too much for me out the box (previous owner had just swapped suspension to the JRZ double adjustables), but I didn't get time to sort it yet, and since the forged S52 motor was blown, I decided to just swap in an LS motor and TR6060 trans. I am using the base kit from CX Racing and will modify what I need to make it work. Currently finished building the engine and I'm currently getting the package ready to drop in. I'll detail the build as I go, but expect it to go quickly. During this downtime I also plan to install the new Willwood 4-wheel big brake upgrade that I got from UUC during their last annual sale. Plan is to use DBW GM setup to be able to tune my powerband to exactly NASA specs and run the car relatively retuned for racing/TT, but be able to uncork the throttle settings for fun runs.

Engine:
LS6 engine
Wiseco stock bore pistons
Scat rods
Melling high volume oil pump
Rollmaster dual roller chain setup
Stock 243 heads (reworked and decked .015")
PAC 1218 springs
hardened pushrods
LS2 intake
LS2 DBW TB
TSP 228/232 .600" 112LSA cam

With the headers from the CX racing kit I expect to hit 420-430 whp no problem with this setup, but it will be detuned all the way down to maybe even only 300 whp for racing (trying to stay in ST3). The previous S52 dyno'd at 294 whp so it was pretty strong for an NA inline 6.


https://www.youtube.com/watch?v=t9d2i4U9dGY

https://photos.google.com/share/AF1Q...00em41ZEhPempR

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

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https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

https://photos.google.com/u/1/share/...p2TXRDd25fU0Nn

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[Liquidity]

What do you mean “detuned to 300hp” Sure you can pull a bunch of timing but there’s a point where the engine isn’t going to want to run at all, not to mention the ridiculous fuel consumption. A tune can’t just add or subtract 120hp from a NA engine, restrictor plates are the only way to limit power on a NA engine.

[HarrisRacing]

What do you mean “detuned to 300hp” Sure you can pull a bunch of timing but there’s a point where the engine isn’t going to want to run at all, not to mention the ridiculous fuel consumption. A tune can’t just add or subtract 120hp from a NA engine, restrictor plates are the only way to limit power on a NA engine.

Drive by wire throttle body is a variable restrictor plate. I can tune the max throttle opening % table. The table available on the GM ecu I'm using has max throttle opening % vs. RPM. So I can either decide to make a 100% limited at 300 whp dyno chart where throttle is basically 100% open and starts closing at the rpm where I hit 300 whp and it closes as rpms rise from there to keep power AT 300 whp for the full powerband. Or the other method is go for a high rpm max power that is higher than the average power number but lower power is cut to make for the same NASA average dyno power number. This way on a long straight track I really could have mostly 250whp then maybe 350 whp for the last few hundred rpms. I've seen where both ways work well depending on track and transmission gearing choices.


I also will still be able to get the fuel correct after I limit the throttle table. Essentially the car should get better fuel economy with the throttle cut as I will mot be making as much power. Afterall all the cars I know of (besides deisels) get their best mpg while cruising with the throttle mostly cut.

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[RulyLSX]

Drive by wire throttle body is a variable restrictor plate. I can tune the max throttle opening % table. The table available on the GM ecu I'm using has max throttle opening % vs. RPM. So I can either decide to make a 100% limited at 300 whp dyno chart where throttle is basically 100% open and starts closing at the rpm where I hit 300 whp and it closes as rpms rise from there to keep power AT 300 whp for the full powerband. Or the other method is go for a high rpm max power that is higher than the average power number but lower power is cut to make for the same NASA average dyno power number. This way on a long straight track I really could have mostly 250whp then maybe 350 whp for the last few hundred rpms. I've seen where both ways work well depending on track and transmission gearing choices.


I also will still be able to get the fuel correct after I limit the throttle table. Essentially the car should get better fuel economy with the throttle cut as I will mot be making as much power. Afterall all the cars I know of (besides deisels) get their best mpg while cruising with the throttle mostly cut.

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I had the same question as Liquidity,thanks for response, interested to see howt he build goes and how the hp limit works

[HarrisRacing]

I had the same question as Liquidity,thanks for response, interested to see howt he build goes and how the hp limit works

This is the table from HP Tuners (attached and simple example of what I would do to keep power at ONE level). There are 2 other ways to limit as well (torque reduction) and by gear as well, but this table is global and will limit opening vs. RPM strictly to this maximum. This is made so when you drive some cars the torque application is "smoother" and gives better fuel mileage.

throttle percent.JPG

[Liquidity]

That’s the stupidest thing I’ve ever heard. And it’s still not a tune. Anyone could put a throttle stop on anything, there’s nothing special about it being DBW.

[HarrisRacing]

That’s the stupidest thing I’ve ever heard. And it’s still not a tune. Anyone could put a throttle stop on anything, there’s nothing special about it being DBW.

Oh lawd... I'll throw it on the dyno for you so you can learn something. Just for fun I'll run one DBW map as a "throttle stop" format to show you what I mean.

For your information, I've built, installed, and tuned most any aftermarket ecu available. I'm a mechanical engineer by day but helped a local shop get on their feet by showing them how to build motors and tune cars. My R32 GTR that I built, tuned, fabricated, etc 100% from the ground up myself makes 740 whp on a 62mm turbo with a measly 2.75L. Being AWD and 3,175 lbs on the scales it ain't no joke either.

To further clarify: A throttle stop will not maximize your powerband to max rules for NASA average power. It is a fixed restrictor and that restrictor doesn't magically hold one horsepower number. A variable programmed throttle body CAN do this however.

All of the top guys run tuned powerbands for the class in a similar manner (or tune with boost by rpms on turbo cars).

Did you read the part where I can make the car make 250 whp on bottom end and ramp it to 350 whp on top and still average 300? This is impossible with a throttle stop but totally possible with DBW. This way the car actually is faster as the gears progress if your ratios are running higher in the rpm range as you shift. This way on the dyno the car will make perfect average HP...but on the track you'd never actually let rpms drop into a lower number and effectively maintain a lap at a higher-than-average HP number. This way when you really need the HP (on a straight bucking the wind at high speeds) you will have max power available that will end up being more power than average.

Best of all once I get all the DBW "tunes" setup. All I have to do is flash a different one with the Ngauge or laptop at the track and head out for another session to see what actially works the best. It may be faster clipping at solid 300 whp and having a huge powerband that prevents shifting...or the other way with the peaky powerband and more shifting. Should be easy to tell once I get it dialed in. I have both T56 and TR6060 which have different ratios to test both theories...but my research shows the top guys are doing it. Also for just balls out having fun I'll just drop the map in with 100% throttle command...this is far easier than managing a restrictor plate or throttle stop.

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[Tim Mc]

Harris...pay no attention - Liquidity=nuisance.

Keep the images coming - looks like a fun build!