Single Inlet restrictors

[racesport]

Can someone advise where I might go to get advice of how to determine the cam and rpm range I should be looking to optimise for a road race engine? It will be twin cam 4 valve 1.8L. Looking for max performance. Inlet restrictor will be in the neighborhood of 24 to 25 mm. What help can you provide?

 

[Marquis]

I would either use a vehicle simulation package or employ the services of someone that knows how to use one.
Typically you input data such as frontal area of the vehcile, torque curve, the CD value, the wheel base, the vehcile mass, gear ratios, losses, rotational inertia of the drivelne etc etc

Then this vehicle simulation package would then be used to simulate the kind of track or road use the vehcile would be subjected to. You could then change your cam timings, lift chatacteristics and re-input the data and examine the effects.
Vehicle simulation packages are usually very accurate-as they're very simple. I've completed several models, for Porsches and BMWs and compared the performance with REAL measured vehicle cycle test data or with magazines quoted performance figures with excellent agreement.

 

[GregLocock]

Bosch lapsim is great for the circuit simulation sort of stuff and it has a free demo version that may be good enough

For the engine simulation side you might have luck with something like Performance Trends, which seems ok for cam timing but I'm not sure it can handle a restrictor.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

With Performance Trends you can set the CFM for the throttle.

If you can determine the CFM of the restrict or that should suffice.

As a rough estimate, I would get a Holley catalogue, work out the CSA at the venturi restriction for a range of sizes, then extrapolate the restrict or plate from that.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Warmington]

The mass flow through the restrictor is governed by the fact that as volume flow increases, density falls. The formulae of Q=V*A where Q is the volume flow rate and A is the area of the restrictor, and delta P = P0 * 0.5*M^2 will tell you how much actual mass airflow you should be using for calculations (M is the mach number for a given density). Of course rho = P/RT, use this to find the density at any volume flow rate.

Quick calculation shows that for the 1.8 litre engine, you will have a pressure drop of only 0.23 bar at 7000rpm. This means your air is around 3/4 as dense as it normally would be if there was no restrictor, hence you should see a reduction of 23% in peak power due to the restrictor, all things being equal.

Try to get a copy of GTPower for analysing your system.