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Lotus Elise K24 turbo build

2507 Views 80 Replies 11 Participants Last post by  Zhonda, 
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I thought I would create a thread to take advantage of the collective experience on K20a.org. I have a similar build thread on LotusTalk.

My build will utilize a JDM K24a RBB-3, an EFR 7163 turbo, RBC intake manifold, Skunk2 70mm TB, and custom exhaust manifold. Intake cooling will be air to water. The Haltech 1500 Elite will be used for engine management as well as controlling electric pumps for the engine and charge A/W cooler. The plan is for a flex fuel set-up with ID 1300xds injectors and all the appropriate sensors and safety controls including individual EGTs. I could go into a lot more detail if anyone is interested but you get the gist.

My goals are a street/track car with great drivability. We are keeping the K24 stock other than upgraded oil pump (at least for now ;)) so boost will be limited in the low RPMs to avoid bending rods and such. The Haltech 1500 has multiple boost control strategies and the EFR comes equipped with an integrated boost control solenoid, wastegate and recirculation. We should have a lot of options. It is also a pretty compact set-up which makes things a lot easier for an Elise build.The HP will be whatever can be achieved with comfortable margin of safety given a K24 with stock internals. My builder has extensive experience tuning K-series so no issue there. My plan is to leave it to him but I must say I am more than a bit excited after seeing the results of other K24 builds with low boost and stock internals.

My Elise's had a REV400 SC 2ZZ and we will be carrying over the Toyota e153 tranny. It might seem an odd decision but it turns out there are e153 to K series conversion kits readily available for MR2 swaps. My e153 has a close ratio KAZ gear set with a LSD and 3.9 FD. It is pretty much new with beefy axles so why the heck not. I haven't really come across any Lotus K series turbo e153 builds so maybe it's something unique.
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LotusElise
Eyelise said:
I thought I would create a thread to take advantage of the collective experience on K20a.org. I have a similar build thread on LotusTalk.
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I really appreciate this! I am excited to read more about it.

Eyelise said:
My build will utilize a JDM K24a RBB-3, an EFR 7163 turbo, RBC intake manifold, Skunk2 70mm TB, and custom exhaust manifold. Intake cooling will be air to water. The Haltech 1500 Elite will be used for engine management as well as controlling electric pumps for the engine and charge A/W cooler. The plan is for a flex fuel set-up with ID 1300xds injectors and all the appropriate sensors and safety controls including individual EGTs. I could go into a lot more detail if anyone is interested but you get the gist.
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I like the Haltech Elite stuff, especially with the new NSP SW of the Nexus ECU, which is now available for the Elite series too. With that it get a very comfortable tuning process. That push the Elite hardware further, from a tuner perspective.

For your built the EFR 7163 is a bit too big, the compressor map working point is not well placed at rated speed of e.g. 7800 rpm. There, the 400 hp at flywheel would be available at around 9 psi, that is already at the choke line and the efficiency falls down hard.

The ID injectors are something I do a big way around,
  • spray pattern (5° shower type) is the worst ever, every carburetor has a better mixing capacity of fuel with air then this senseless style
  • quality of the injectors is below the BOSCH basis
  • the only advantage would be the matching, but they don't deliver a document proving this
Eyelise said:
My Elise's had a REV400 SC 2ZZ and we will be carrying over the Toyota e153 tranny.
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How did you like this Toyota 2ZZ engine on boost? I really like the Yamaha head cast, but the valvetrain is a mess for racing, quite wearing on high speed cam. The Alu-liner MMC coating is nicly on friction and cheap on the OE side, but on boost and racing application use they wear down quite fast...compared to the K-series, they are princesses, even if the head casting is awesome.
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LotusElise, Thanks for your insights. The 7163 was chosen, in part, to allow for engine modifications in the future. There is a good chance I will be building the engine and increasing the boost in the future. I have played around with MatchBot but I don't have enough knowledge to make it useful. I know from testimony it is a very quick spooling turbo that has had favorable results in k20 builds. Here is the compressor map. It would be helpful to know what parameters you used to size the turbo for my build and how it relates to the map.

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LotusElise
I made a quick calculation of the working point at 7800 rpm (pressure ratio and air flow demand). The 400 hp point is around a pi of 1.6 and 38 lb/min. The compressor sees Mach 1 there at the throat, that is not gonna happen, pressure control is unstable, fuel demand is unstable, everything is not stable. If you aim for less at the same pressure that would make it or increase the pressure ratio, the so called Greek letter pi = p_out / p_in. But be aware of, if you increase pi the engine working point drifts right and up to, it is an question of gradient it take. E.g. if the intake till head intake valve flow is more restrictive then I assume in my calculation then the operation point will be at a higher pi and same flow demand. But we talk about 0.1 points in pi at max, not more. At 1.7 it would be more stable, but still very inefficient.

The MatchBot is a very easy to handle tool, but it is also a very simple power calculation tool, which need some base experience on the engine. It sees your engine working point at an lower air demand and higher pi, but still outside the 0.6 choke matching efficiency. Didn't you say your tuner has much experience on that?
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Lotus
I think you‘ll need more like a pressure ratio of 2.2 to see 400HP.
1.6 would correspond more to like 300HP and some 30 lb/min airflow.
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Lotus said:
I think you‘ll need more like a pressure ratio of 2.2 to see 400HP.
1.6 would correspond more to like 300HP and some 30 lb/min airflow.
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I agree 1.6 looks a bit low. I would be surprised if my build will make 400HP on 8 or 9psi at the turbo outlet. LotusElise is correct when I run the calc. using MatchBot with low boost the turbo tends to choke but only at high engine RPMs. The convention is usually 40lbs/min=400HP which on the compressor map can be delivered by the turbo at numerous pressure ratios. Too far to the right though and the turbo chokes, not good. The 65% efficiency island on the choke side is at 1.7. That corresponds to 10psi at the turbo. I would bet we will be running higher pi than that at 7800. It might actually take a pi of 2.0 to make 400HP. If so the efficiency of the turbo shoots up. I am just not sure how well you can predict.

It comes down to what MAP will be required to achieve your goals and what pressure ratio at the turbo outlet corresponds to that MAP across the range of RPM of your engine. That has all to do with the engine, build, and I suppose application. This is what MatchBot attempts to calculate. Parameters like displacement, volumetric efficiency, boost drop, intercooler efficiency, turbo efficiency, fuel type and many more are used. The list is exhausting. That is what LotusElise was making a quick calculation for. The empiric method often works best. I may just put a speed sensor on the turbo to see where it sorts out.
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LotusElise
Lotus said:
I think you‘ll need more like a pressure ratio of 2.2 to see 400HP.
1.6 would correspond more to like 300HP and some 30 lb/min airflow.
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We have enough dyno examples here, proving the K-series efficiency, I've used for the calculation, is not out of range.
Sure, the engine efficiency of the K24 is a bit lower, but 400 hp (around 340 whp, see post #2) are achievable with 9 psi of boost at 7800 rpm on a 87x99 engine.
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LotusElise said:
We have enough dyno examples here, proving the K-series efficiency, I've used for the calculation, is not out of range.
Sure, the engine efficiency of the K24 is a bit lower, but 400 hp (around 340 whp, see post #2) are achievable with 9 psi of boost at 7800 rpm on a 87x99 engine.
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I'm sure you know as much as anybody that not all psi is created the same, boost can vary dramatically for the same BHP depending on turbo selection, EMAP, IATs etc etc.
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LotusElise said:
We have enough dyno examples here, proving the K-series efficiency, I've used for the calculation, is not out of range.
Sure, the engine efficiency of the K24 is a bit lower, but 400 hp (around 340 whp, see post #2) are achievable with 9 psi of boost at 7800 rpm on a 87x99 engine.
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This is great empiric info. thank you. As you said these numbers are from K20 builds and the heads do flow significantly better than the RBB see below. How much additional boost the K24 will require is TBD. Fortunately the casting in the RBB leaves a good deal of room for porting :). I assume these are manifold boost numbers as read on a gauge. In your experience how closely does the boost at the turbo outlet match the boost in the manifold? I know it depends on the build ie piping, intercooler, etc. but what do you find? Is that something noone really measures? Given all the factors above I am going to take a wild stab and estimate my "OEM low boost" build to require 1.8 pi ie 64% efficiency and result in 425 flwhp. How's that?

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Kowalski999
@Eyelise Regarding head flow @LotusElise has tested multiple heads on his flow bench and I would go with his results.
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As for turbocharger options, Richard has some good data so there can be something useful info for you there.
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mrluke said:
I'm sure you know as much as anybody that not all psi is created the same, boost can vary dramatically for the same BHP depending on turbo selection, EMAP, IATs etc etc.
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Very true but LotusElise is correct. My initial build the turbo will be operating in an inefficient range. Once we have the build sorted (acceptable IAT management, solid maps etc) then the idea might be to swap piston and rods (correct ring gapping) and maybe do valve springs/seats/retainers possibly cams. Just light mods to sure things up LOL. Then of course the boost could be turned up a "bit".
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LotusElise
Eyelise said:
How much additional boost the K24 will require is TBD.
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One would have to experiment with the RBB head on the K20 block size as the friction power demand of those engines is different to be exact. But way less then 1 psi below 7000 rpm (quadratic character of pressure drop with flow flux).

Eyelise said:
I assume these are manifold boost numbers as read on a gauge
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Yeap.

Eyelise said:
In your experience how closely does the boost at the turbo outlet match the boost in the manifold? I know it depends on the build ie piping, intercooler, etc. but what do you find?
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Depends on many things, on a 1200 hp 2-Liter engine it can be e.g. over 1 bar due to density change and velocity. On a low boost it can be some 100 mbar. Depends on surface and gradient of temperature drop over the intercooler. Measuring the boost is always coming with a failure due to dynamic pressure. Pressure drop can only be validated on total pressure = static pressure + dynamic pressure. Only the first get's measured with an simple pressure sensor. Measuring the total pressure means one would measure the dynamic pressure too or rebuild it to static pressure, then both are equal, static and total pressure.

Eyelise said:
Given all the factors above I am going to take a wild stab and estimate my "OEM low boost" build to require 1.8 pi ie 64% efficiency and result in 425 flwhp. How's that?
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I would be interested what your tuners experience is on that.
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As for turbocharger options, Richard has some good data so there can be something useful info for you there.
[/QUOTE]

Thanks for the link I took a look and will check out some of the other content. That is quite a bench engine: race header, ultra race cams, race manifold and set-up: E85 great A/W cooler low ambient temps. So hard to extrapolate but I understand his intent mainly comparing responsiveness. He tested much bigger turbos than mine (7582 7875), even tested some pretty cheap stuff. Never once considered a compressor map LOL. Everything made crazy numbers and it doesn't take as much boost as you would think. Although my turbo is on the larger size it was designed to spool up quickly with the Gamma-Ti turbine. I don't believe I will be suffering for power in the lower RPMs. In fact the plan is to limit boost/torque by RPM and gear.
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Lotus
a k24 offer plenty of torque in a Elise of boost. It will be nice even off boost or on very little.
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Lotus said:
a k24 offer plenty of torque in a Elise of boost. It will be nice even off boost or on very little.
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Agree, I think I will be maxing out that internal wastegate quite a bit.
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Lotus
do you know this chaps insane K24 Turbo Exige build?

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If EMAP is a concern, there's always the option of the EFR 7064. It's basically the 7163 but in the B2 frame (Which is almost identical in outer dimensions to the B1 frames). It also has a more favorable mid range efficiency island. I know a few people who have the 7163 and really enjoy the spool up. One on a 20psi SR20 and another on a stroker 944 making big numbers with a nice torque curve.
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Newt Gomez said:
If EMAP is a concern, there's always the option of the EFR 7064. It's basically the 7163 but in the B2 frame (Which is almost identical in outer dimensions to the B1 frames). It also has a more favorable mid range efficiency island. I know a few people who have the 7163 and really enjoy the spool up. One on a 20psi SR20 and another on a stroker 944 making big numbers with a nice torque curve.
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I gravitated to the 7163 for the spool up. I also have testimonials that is essentially "instant on". I guess we will have to see if the EMAP is an issue.
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Here is how complex sizing a turbo can be.
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Stefanzoh
LotusElise said:
For your built the EFR 7163 is a bit too big, the compressor map working point is not well placed at rated speed of e.g. 7800 rpm. There, the 400 hp at flywheel would be available at around 9 psi, that is already at the choke line and the efficiency falls down hard.
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Hey guys, I'm trying to learn a bit more about turbos and I'm having a bit of trouble understanding.
Why is this turbo too big, especially if OP says he plans to up the boost in the future and you mentioned the turbo will choke up top. Did you mean the turbo is too small?
By looking at EMAP, you can tell if the turbo exhaust turbine/housing is too small causing an increase in exhaust pressure right?
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