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Discussion Starter #1 (Edited)
Hi guys,

After driving various N/A K24's for the past few years, we're stepping up to a higher competition in rallycross. This means we're developing a targeted >600hp K24 engine for our 4x4 rallycross car.

Since my experience in boosted applications is limited, I'm looking for your reviews/feedback/opinions on the proposed setup below.
Any input is greatly appreciated!

Car:
Full custom tube-frame chassis in CRX shell.
4x4 drivetrain, custom double wishbone suspension all round.
Longitudinal placed engine, sequential rallycross gearbox in centre of car (separate front/centre/rear plated diffs).

Targets:
600-650hp fly
boost treshold preferably before/around 4K
>600Nm/450lb-ft around 4.5K
approx. 550Nm/400lb-ft at 8K (8K redline)

Transient respons, minimising lag and keeping an eye on boost treshold are key. Yes, the sequential gearbox will theoretically allow the car to be between 6000-8000rpm all day, but the competitive nature of RX means the driver sometimes finds himself in the situation of accelerating from the corner at 4500rpm.

Fuel:
Dual bosch pump setup, return system
Homologated "pump" gas (RON 102, MON 90) so (r+m)/2= 96

Engine/choices:
Block/head K24A2
Cams K20A2 (or do we need aftermarket?)
Pistons: 9:1 or 10:1 CR?? 87.5mm
Rods: Manley's
Wastegate depending on turbo choice
Header built in house (twin scroll, ramhorn type)
Intercooler size TBD
Intake manifold: engine positioning means we're looking at skunk2 Ultra, since it's reversable. Will the street version be big enough for our power goals? The 90mm 3.5L race version feels like overkill to me.
Throttle body: what size do you guys recommend?

General/safety:
valvetrain supertech H-1021D (is this OK @ 30psi?)
3-stage drysump system
turbo after oiler
head studs ARP
gasket Cometic
bearings ACL
injectors ID1000 or greater if needed
downpipe+rest of system built in house (3.5-4")
clutch Tilton twin or triple plate

Control:
Motorsport ECU hooked to datalogging system
Boost control by ECU, any advice on control solenoids?
50* VTC, measured and pinned at max VTC
VTC/VTEC operational

Turbo's
Now, obviously for the million dollar question. We've played around with the EFR matchbot some but hoping for some experience from you.
Ball bearing, water cooled CHRA and TwinScroll are pretty much given.

I'm looking at:
GTX 3582R twinscroll 0.82 / 1.08
EFR 7670 twinscroll 1.05
EFR 8376 twinscroll 0.92iwg / 0.92 ewg / 1.05 ewg

I'm worried the 8376 might come on too late, can't quite decide on the differences between the 3582 and 7670. Although the EFR's feel a bit more developed with the GaTi turbines and the basic lack of TS housings from Garrett.

matchbot link: http://www.turbos.borgwarner.com/go/JJFPYZ

Again, any input is greatly appreciated.

thanks for reading!

kind regards,
Tom
 

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I have something similar... I think, 7670 is too small.

Also, it is not the turbo but lack of exhaust gas energy that will not get you 24lbs of boost at 4000RPM... in my experience.

7670 is restrictive at the top i.e. 7700+.

Anton
 

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Hi Tom, nice engine project :up:. Are you from Netherland or PA area?

600-650hp fly...>600Nm/450lb-ft around 4.5K...approx. 550Nm/400lb-ft at 8K (8K redline)
My VE calculation model gives me following: 640 [email protected] with the 87x99 engine means a compressor pressure ratio of around [email protected] % engine efficiency and see level altitude, assuming hot induction conditions.

I did prove all your suggested turbocharger, but all are too small to feed enough air mass flux. You need around 0.433 kg/[email protected] lambda and 640 flwhp at the mentioned pressure ratio. Maybe the restrictive head and intercooler helps to improve the operation point into the higher isentropic region, you would need at least 2.5 ratio to get into the 74 %-region. The response character would definitely have an advantage despite peak is risky bad placed.

Cams K20A2
If you are free too choose, a more overlapping cam with an bigger lift definitely would help to feed the Air for the VE of 2.33 you need, e.g. DC OG-series 2.2. The head will be a restriction in that business.

...Pistons: 9:1 or 10:1 CR 87.5mm
Depending on TC setup, which creates the scavenging pressure drop (+ or - and it's quantity) I would give the 9:1 CR a trial. Even if you run a 96 AKI fuel your ign. timing will far beyond MBT, the more the less scavenging efficiency. Cams, combustion chamber design, TC and head as well as header rule this. My assumption was 53 °C for MAT, so no more as 10 °C over ambient conditions!

...Will the street version be big enough for our power goals?...The 90mm 3.5L race version feels like overkill to me.
Throttle body: what size do you guys recommend?
As long as you use a stock K24A2 head, you have there the restriction. Your necessary MAP will increase near to Mach 1 conditions at valve opening and some relevant °ca beyond that. From port size all manifold would work in the boosted area, beside smaller will cost some mbar of MAP, but what you should really consider is VE balancing, because of the knock tendency of that setup. Do you a favor and build a dual type plenum.

And don't use that big TB, a no go at Rallye-driving with TC setups! NO GO! Your driver will piss in your shoes, so angry he will come back from track...you need something which is stock near to get a controllable engine setup. The TB need an influencing effect on power, but if you reach WOT at already beyond 50° of TPS...ups :D. Having a proper designed TC engine setup means you have a ton of bypass-pressure circulating just waiting for release. So do you a favor and choose a small TB, it's a rallye engine, no drag engine! This will keep your shoes dry and your driver smiling :D.

...injectors ID1000 or greater if needed
You need 1200 ccm, but this is not what you really need. A two leveled injector setup, eventually a single pre-intercooler plus single level at head is what you need to get the MAT down into the 50 °C range.

I have something similar... I think, 7670 is too small.
Anton, agreed. Good to read you here again :). Long time ago a read something from you.

Markus
 

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Discussion Starter #4
Hi guys, thanks for your posts.

I've done some more research after reading your replies, this will step by step get us in the right direction! Here's some feedback;

Regarding power goals, perhaps it's better to settle for a slightly lower goal and allow the engine to retain good driveability. However 550hp would be minimum. That should be more in de ballpark of the proposed TC's?

Also, it is not the turbo but lack of exhaust gas energy that will not get you 24lbs of boost at 4000RPM... in my experience.
Makes sense, thanks!

If you are free too choose, a more overlapping cam with an bigger lift definitely would help to feed the Air for the VE of 2.33 you need, e.g. DC OG-series 2.2.
(...)
Depending on TC setup, which creates the scavenging pressure drop (+ or - and it's quantity) I would give the 9:1 CR a trial. Even if you run a 96 AKI fuel your ign. timing will far beyond MBT, the more the less scavenging efficiency. Cams, combustion chamber design, TC and head as well as header rule this. My assumption was 53 °C for MAT, so no more as 10 °C over ambient conditions!
Ok, will try the DC2.2 and 9:1. The 9:1 will actually be ~9.2:1 with K24 head I just realized.

The head will be a restriction in that business.
(...)
As long as you use a stock K24A2 head, you have there the restriction.
What exactly would be the restriction here, are you talking about oversized valves, or porting job for more cfm, or something else?

Do you a favor and build a dual type plenum.

And don't use that big TB, a no go at Rallye-driving with TC setups! NO GO! Your driver will piss in your shoes, so angry he will come back from track...you need something which is stock near to get a controllable engine setup. The TB need an influencing effect on power, but if you reach WOT at already beyond 50° of TPS...ups . Having a proper designed TC engine setup means you have a ton of bypass-pressure circulating just waiting for release. So do you a favor and choose a small TB, it's a rallye engine, no drag engine! This will keep your shoes dry and your driver smiling.
Now after making me laugh ;), this also got me thinking as this makes a lot of sense!
When looking at TC outlet and recommended charge piping sizes, we were thinking about 2.25" hot side, 2.5" cold size charge piping. This would correspond to even something as small as a 60mm throttle body (way, way different from the 90mm I was considering ;) ).

Is that the kind of sizing you're referring to?

Af for the dual-type plenum, had not looked into that so did some googling. Do you mean something similar to the jenvey unit below? They come in 60 and 70mm inlet. Reversible as well so well suited for our application.




You need 1200 ccm, but this is not what you really need. A two leveled injector setup, eventually a single pre-intercooler plus single level at head is what you need to get the MAT down into the 50 °C range.
I'm kinda lost by what you mean here. I've seen two-levelled fuel injector setups (4+4), one near the ports and one above the stacks, and I know of some setups injecting water/meth before IC.
But what exactly do you mean here, a single extra fuel injector before IC that allows early mixing of mixture and cooling the charge air? So 1+4 injectors? Would that 5th injector be active at every rpm?

BTW, I'm from the Netherlands

thanks again to everyone!
 

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I'm using the gtx3579hta & Jenvey turbo plenum... no idea how well it works yet... still building :)

View attachment 98433
Note sure which turbo that is. Are you considering the new G25-660 which has a very high efficiency and a very high-temperature titanium aluminide turbine? It may be a bit small. The EFR 7163 is similar, but the G25 is newer. Garrett will probably introduce more and large models of the G series later this year...a major advance for them. BW may enhance the EFR to compete.

What are the fittings below at the merge collector below the turbo? Did you consider individual cylinder O2 for tuning and EGT sensor for thermal protection (traction control, anti-lag)? Are you using knock sensors? Is one of those ports for a backpressure sensor?
 

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It's from Owen developments (https://www.owendevelopments.co.uk) - actual full title is ODGT3579HTA M-Spec.

It has an Inconel turbine and billet "hta" compressor, tail v-band turbine housing.

The fittings are for the slip joint, I did consider individual cylinder O2 and EGT... but that adds a lot of cost and complexity... so I settled with a single manifold pressure and single manifold temperature sensor (both just after the collector).

The manifold is made from thin wall Inconel.
 
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