I am building a super light Hill Climb Evo VIII.
the progress on the body shell preparation is going on perfectly.

the turbo charger inlet should restrected to 38 mm according to hill climb regulations.

my engine setup is 2.3 strocker (8.8:1 compression ratio), 272in/272ex HKS cams, Megan Exhaust Mainfold, FP Green Turbo charger, full HKS TBE, Custom Tune the original ECU.

without the restrictor the engine produced 365 WHP running 26-28 PSI on VP C16 race fuel. (DD Dyno)

with the restrictor (38 mm) fitted to the turbo and running the same fuel C16, and after tuning for 1 hour on the dyno, the max WHP was 290. (mainly because the car is not able to boost more than 21 PSi and tappering to 16 PSI)

Now, i am looking to share experince with any one who has rally experince or has a secret formula for how to build engines for restrictors and be able to make good power.

also i need to know who is the best engine builders with experince in rally cars fitted with restrictors so i can discuss my new engine build.

some of the tips i was toldso far:

- build a high compression engine. (10:1 or 10.5:1)
- use Anti-Lag system, Motec or Autronic.
- Alcohol or methanol as a fuel.

looking for some help

 

to make power with a restrictor you need to know what flow rate the restrictor chokes at. there are equations online that you just plug the radius or diameter in and it will tell you. from there, you need to pick the turbo based off where the motor will choke. with the 2.3L it will choke at lower RPMs then with a 2L obviously. but keep in mind if you run a ton of boost, your going to have a higher mass flow rate, so both the boost pressure and engine RPM will be needed to estimate the flow rates you'll see. so generally you'll want to go with a smaller quick spool turbo plan your effincy range to be prirmarily located below the restrictor choke point. also, the cam choice should be critical, as you want your maximum VE to be in the lower RPM range where you aren't effected by a pressure drop across the restrictor.

one thing to note, when you begin to get close to choking the restrictor (i.e. max mass flow rate), the pressure drops behind the restrictor. this is also right in front of the turbo. thus even if the boost pressure you are running doesn't change, the pressure ratio still goes up (see a compressor map to see how that effects your compression efficiency).

overall, to avoid any downsides of the restrictor, youre going to build the motor to make tons of torque and not worry about the top end HP as everything gets inefficient up top. you want to run very high boost at lower RPM. as broad a torque curve as possible. cams geared for low end torque, water/meth/high octane gas to run higher boost, higher compression whatever you can do to make more torque. WRC cars only make 300-340hp, but they make boatloads of torque, and they use really tight gearing to keep the turbo spooled, yet not choke the restrictor by revving it out to far.

 

thanks for your reply and all the info.

now lets translate the above into, engine setupcorrect me if i am wrong)

- 2.3L is better than 2L because it produce more touque at lower RPM. Bigger stroker like 2.4 or higher is even better.

- the TME turbo may be better than the FP Green? spool earlier and produce torque at lower RPM.

- Higher Compression 10:1 is better than 8.8:1. what is the max Compression can i run maybe using custom pistons?

- Race Fuel is better because it will produce more torque. will alcohol (as a fuel)produce more torque?

- stock profiled cams is better than higher profiles, or higher profile with cam gears set toward low end torque are better?

- super close ratio gear box will keep the turbo spooling better. already got a custom rally cross dog box.

i apriciate if we start to list specific part / modifications list to help in the restrictor case.

i will list some modifications and what

 

install a tach so you have some idea where you are on your compressor map, or at least you will know if you are at the point where trying to turn it up any higher is a bad idea.

 

^that can be achieved very easily with a pressure differential setup as well. install one probe just in front of the compressor, downstream of the throat of the restrictor, and the second just outside the compressor. if the pressure ratio starts increasing rapidly you know you are choking. if you have a datalogger, you can record the Pr as well as engine speed, air temps and or mass air flow and get a good idea of VE of the motor, and the mass air flow of the turbo. it will be very apparent when you choke... set your rev limiter below the choke point and use shift lifts to let you know when your getting there.

 

FYI, knowing where your restrictor chokes will decide everything for you, so do that first

 

If you plan on building a stroker motor or a motor that operates at a low rev range, which is a good idea... be sure to match your gearing in the gearbox and final drives. you will be left with a very low top speed if you don't plan accordingly.

You might also consider an ECU that's on par with the rest of your build.

PM me if you need a suggestion. I know someone that might be able to work remotely with you on tuning if you need help.

 

the trick seems to be getting as much airflow as you can, as early as you can.

 

Everyone has already posted great suggestons on how to proceed with your buildup. I'm just curious if you could fill us in on the dyno comparison. All you've qouted is max HP...what were the results on the rest of the dyno comparison?

Thanks,

Dave
p.s. hilllcimbing in Colorado, there are no restrictors.

 

You're going to be limited to roughly 35.5-36 lbs/min of airflow by the 38mm restrictor. WRC rally cars run roughly the same restrictor size limiting them to roughly 300hp. They make like 450 lb-ft of torque though!

So the key is a turbo that tops out around 36lbs/min and spools as quickly as possible to maximize your torque/hp everywhere below where your engine will choke. I'm going to guess that you'll choke somewhere between 4000-5000rpm depending on how you size the turbo.

 

the wrc restrictor is about 25% smaller based off throat cross sectional area then what you get to run.


to increase power with a restrictor, remember dense air will have a higher mass flow rate through a restrictor then warm/hot air.

make sure the air going into the restrictor is as cold as possible.