N/A 4S engine with no rules, except a 25mm restrictor. 3

Not answering that, but why not have a high volume intake manifold after the restrictor to even the flow out? Ultimately you'll be limited by mach choking which is worse with the single cylinder.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

Application, please.

In every case that I know of that mandates restrictor plates, there's a rulebook that pretty much dictates the course of action.

Steady choked flow across the restrictor plate will set the max limit on the mass airflow and thus the power output. If the restrictor plate can be designed as a converging-diverging nozzle, there might be some hope of having the manifold air pressure above the choked-flow pressure ratio. It's usually going to be better to have a plenum between that and the engine to even out the fluctuations.

I have a 400cc 4 cylinder motorcycle engine with 60something horsepower and an airbox with an inlet snorkel whose minimum cross-section is somewhere in the vicinity of that size (I think it's a little bigger, but that snorkel is not intended to be a horsepower-limiter). A somewhat bigger-displacement engine tuned for mid-range torque may be able to make use of that over a wider RPM range.

Ruff numbers a 600cc 4 cylinder at 6000 rpm is pumping 30000 cm3/s and you've got about 5 cm2 so that's going to be around 60 m/s through the restriction, probably not enough to affect it much. At 12000 rpm it's going to be 120 m/s (nominally) and it's going to start noticing. A 1000cc 4 cyl the nominal flow velocity is going to be nominally 100 m/s at 6000 rpm, 200 m/s at 12000 rpm, that's going to be restrictive. You'll have to properly dig into the compressible-flow equations to get a more accurate estimation of the nozzle flow, and the cam timing of the engine is going to affect the VE. The engines that I've described are motorcycle engines that are designed to make power with revs, and the restrictor isn't going to let it rev, so it may be better off with milder cams.

Thanks for your responses, much appreciated.

Sorry, I apologise, I've been misled on the rules.

I've looked up FIA T3.1 technical specifications (which don't seem exhaustive so I'll look further) The intention is to build a lightweight 2 person 4wd buggy (almost a side by side) suitable for Australian events such as the Fink but with the ultimate potential goal of the Dakar.

It appears the engine needs to be a stock (not sure what that means yet) production engine with at least 250 units sold.

1050cc's N/A or supercharged (supercharged must have a 28mm restrictor). The wording of the rule seems ambiguous but the addition of the restrictor seems in place of the usual 1.7x factor for boosted engines.

Still an interesting decision on choice of engine. I was thinking about a de-stroked, turbo'ed, Hayabusa if allowed?

I haven't found anything on the placement of the restrictor in the intake, or the design of it yet which seems odd. It does limit the capacity of the intake to 3lt.

(I was disappointed to see they have disallowed any connections between the 4 shocks. Ever since reading about decoupled suspension I have been busting to try it.)

Kawasaki H2 bone stock but with a converging-diverging restrictor on the supercharger inlet (which is already a pretty small opening). The end!

You need to make torque.
A restrictor is effectively an RPM limiter.
Well actually RPM x displacement, since it will limit the volumetric flow.
I'll bet that in rules someplace they talk about the restrictor having a straight hole with limited edge radius and a required thickness.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

I think when F1 and Indy cars were turbocharged the "restrictor" rules quickly became irrelevant. EZ to work around.

Thanks Brian, I've had a quick look and it's pretty impressive.

I think when F1 and Indy cars were turbocharged the "restrictor" rules quickly became irrelevant. EZ to work around

Click to expand...

How so? A restrictor plate ahead of the compressor inlet will limit mass flow. How does a turbo overcome this?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

You will not improve on BrianPetersen's solution. About 200 hp over a wide range of rpm.

je suis charlie

F1 never used intake restrictors as far as I'm aware.

TMCRally said:

It appears the engine needs to be a stock (not sure what that means yet) production engine with at least 250 units sold.

Click to expand...

It means from intake flange to exhaust flange, unmodified. Your de-stroked Hayabusa engine idea is not an option.

SwinnyGG (Mechanical)8 Jan 24 16:45
F1 never used intake restrictors as far as I'm aware.

Quote (TMCRally)
It appears the engine needs to be a stock (not sure what that means yet) production engine with at least 250 units sold.

It means from intake flange to exhaust flange, unmodified. Your de-stroked Hayabusa engine idea is not an option.

Click to expand...

It depends on the rules in regards to what is allowed to comply with the capacity limit, but I agree it was a stretch. Stock can mean all sorts of things though. Usually it will include reconditioning, which is a vague term which allow all sorts of benifits. Often too there are freedoms specified in the rules that go beyond the stock engine statement which is the case here as well. At that time I didn't have the full rules.

The restrictor seems a nice, easily managed method of HP control, I haven't had much to do with them, so it's a new challenge. There are several opportunities to improve the engine performance in the rules but you will always be bound by the limit of the restrictor flow.

BrianPeterson, in his above post had me chasing C&D restrictor design, which has been fun.

The Kawasaki H2 brochure states that the supercharger is capable of delivering over 200litres of air per second. Wouldn't this be a breeze through a 27mm restrictor.

TMcRally said:

The Kawasaki H2 brochure states that the supercharger is capable of delivering over 200litres of air per second. Wouldn't this be a breeze through a 27mm restrictor.

Click to expand...

Don't know if this is meant to be sarcastic...
If serious, did you consider:[ol 1]
[li]Title of OP begins with N/A, suggesting no supercharging allowed[/li]
[li]If supercharging were allowed, obviously the restrictor would be required to be upstream of the compressor inlet[/li]
[li]the law of sonic flow through a restriction?[/li]
[/ol]


"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

Don't know if this is meant to be sarcastic...
If serious, did you consider:
Title of OP begins with N/A, suggesting no supercharging allowed
If supercharging were allowed, obviously the restrictor would be required to be upstream of the compressor inlet
the law of sonic flow through a restriction?

Click to expand...

Sorry it has been a progressive journey from when the post started. I was initially told the rules by the client, then finding various subsets of conflicting rules to now with 2024/2025/2026 actual rules from FIA, not an easy task to find all the rules and put them together.

We are now at these freedoms...
1050cc max displacement for N/A and for supercharged.
Supercharged engines must have a 27mm restrictor N/A does not need any restrictor.
Superchargers can be replaced by any commercially available part.
ECU's are free
Inlet manifold is free, the volume down stream from the supercharger is SET (not limited to) at 3lt no +/- figure given
Exhaust free

Can we have a link to Brian's 400cc 4-cylinder engine showing it? I've seen 50cc 1-cylinder engines but those have been two-strokes with simplistic airflows. (I take "cc" to mean cubic centimetres.)

It is a 1990 Yamaha FZR400. Ancient technology. Bore and stroke 56.0 x 40.5, DOHC 4-valve, one CV carburetor per cylinder (Mikuni BDS), and the carbs draw from an airbox which contains the air filter, and the aforementioned snorkel is on the inlet to that.


But, it has since become apparent that this isn't the best solution to what the original poster needs.

Remembered this while flipping through threads looking for something. Under the latest iteration of the constraints, I believe a built 1000cc Superbike engine will be a better choice than the H2 engine on account of not having to deal with the restrictor and the (ill-defined) volume downstream of supercharger, and it will be lighter. We're talking WorldSBK-spec BMW S1000RR, Yamaha R1, Kawasaki ZX10R, Ducati Panigale V4R (Not the lesser versions - only the homologation-spec R meets your displacement limit).

A MotoGP engine is probably too much to ask ...

How much power these engines make is classified information, but it's sure to be mid-200s. A well-tuned engine that size should make around 90 lb.ft of torque at its torque peak, which will be pretty high in the rev range. If it does 85 lb.ft at 15000 rpm (and the rev limits in competition use are in that range) that's 250-ish horsepower. The MotoGP engines aren't limited by having to use stock or stock-ish production-line parts, and rev higher.

I have on reasonably good authority that WorldSSP-spec 600cc engines (Yamaha R6) make around 150 horsepower. Keep in mind that these engines are not stock, they've been finessed to the extent that the rules allow by people that are in the business of doing this. A run-of-the-mill R6 makes 120-ish, and a run-of-the-mill S1000RR makes 190-ish.