Jenvey Throttle Bodies On The Mi16 - The Results

[petert 550]

Just to jump in... so if I'm running 4bar of fuel pressure the standard pump won't last/work at that? What's likely to happen then? I've still got a surge tank to fit in the fuel system and that includes fitting another fuel pump for taking the fuel from the surge tank to the fuel filter/rail... should I get on and do that then you think?

 

Yes, I'd use the std. pump as a pre-pump. Running at 4 bar will just shorten the life of the pump. Probably not much of an issue on a track car that's used ten times a year.

Edited March 9, 2006 by petert

[B1ack_Mi16 67]

Yes, I'd use the std. pump as a pre-pump. Running at 4 bar will just shorten the life of the pump. Probably not much of an issue on a track car that's used ten times a year.

 

But... I thought that on WOT with 1atm in the FPR vacum hose the system would actually give 4 bar fuel pressure, as the manifold pressure is 1 bar?

 

I'm going to set mine to 4bar constant and map it without the FPR vacumhose.

Can't be a problem can it? (Not a problem anyhow with 440cc injectors to get enough fuel @3 bar either, but I was thinking of the spray pattern, it will probably need 4 bars to be good @WOT.)

 

But if you set the base pressure to 4 bars, and still use the vacum takeoff I guess the system would work on 5bars @ WOT...

[Anthony 1,000]

But... I thought that on WOT with 1atm in the FPR vacum hose the system would actually give 4 bar fuel pressure, as the manifold pressure is 1 bar?

It's done on pressure difference compare to atmospheric, not absolute pressure. On the standard FPR, it's 3 bar fuel pressure at WOT and below 3 bar on part-throttle/idle as the manifold is then on vacuum (ie below atmospheric pressure).

[petert 550]

That's correct, 2.5 Bar (typically) at idle and 3.0 Bar at WOT.

[B1ack_Mi16 67]

Ok, that clears things up a bit, guess I should set it to 3 bar and let it sit there then.

[C_W 3 1 Cars]

It probably runs at 3BAR much before WOT though, I think anything over 1/4 throttle opening will probably be 3BAR?

[Toddman 0]

There's no point in comparing the BX that made good power on a std inlet at emerald.

 

IIRC the cams are 254deg@1mm with 11.5mm of lift (I've measured the profile) and it has Omega forged pistons. It has some headwork as well but from looking at it the only gains will be on the exhaust side.

I mentioned the BX purely because of the injectors.

The thing that interested me was that people seem to think fitting bigger injectors with just TBs will give more power.

The BX runs just over 210BHP with std injectors and 4 bar.

So in my mind either std injectors are fine when using TBs and no other major mods OR the BX will be restricted at the moment by the std injectors?

If I have missed something obvious please tell me - wouldn't be th efirst time

 

Cheers

Luke

Edited March 9, 2006 by Toddman

[PumaRacing 1]

There's no absolute measure of the power that a given sized injector can cope with because it depends on the efficiency of the engine. As an engine is tuned it tends to become more efficient and generate more power from a given amount of fuel. Standard normally aspirated road engines are generally taken to need about 0.5lbs of fuel per bhp per hour but of course some are more efficient than that and some less. 16v engines tend to be more fuel efficient than 8v ones due to better cylinder filling, more swirl and less ignition advance requirement.

 

Tuned engines using higher compression ratios and better flowing induction and exhaust systems might only require 0.45 lbs/bhp/hr or even less. Turbo engines are generally much less efficient and also use richer mixtures at WOT for cooling purposes. 0.6 lbs/hp/hr isn't unusual for them.

 

Running some quick calcs I would say it's possible for a 214cc @ 3 bar injector to just cope with 215 bhp at 4 bar if its fuel requirement is 0.45 lbs/bhp/hr. At 0.5 lbs/hp/hr that would be about 195 bhp. Those figures would be at 100% duty cycle though and not recommended for long term use.

 

Given that most rolling roads give somewhat exaggerated flywheel figures I'm not surprised that 200 bhp plus is claimed on standard injectors but then the 200 bhp plus probably doesn't quite exist.

 

However without knowing the actual fuel efficiency of an Mi16 engine this is all speculation and the only way to measure that accurately is on an engine dyno with fuel metering. It might well be that even a standard Mi16 only requires 0.45 lb/hp/hr and a tuned one closer to 0.4.

 

Assuming that the quoted flow rate for the Mi16 injector is correct and that a standard engine wouldn't go above 85% duty cycle then you can calculate back that the standard fuel efficiency is indeed about 0.45.

 

If that's correct and if efficiencies of 0.4 could be achieved from a tuned engine then the standard injectors at 4 bar could cope with 240 bhp.

[Toddman 0]

Thankyou Mr Baker

Exactly what I needed to know - very helpfull.

The car is purely for track use and should be more efficient than a std mi.

 

Cheers

Luke

[petert 550]

It probably runs at 3BAR much before WOT though, I think anything over 1/4 throttle opening will probably be 3BAR?

 

No, it's progressive, but not linear to the throttle opening. With a fresh engine you'd probably get something like 2.3 Bar at idle, 2.5 Bar at cruise and anything up to 3 Bar depending on the load. You'd rarley see 3 Bar on the road (unless at WOT). Some people map without any vacuum compensation but I can't see the point. The vacuum at idle decreases the flow enabling you to achieve reasonable injection times.

[Jonmurgie 2]

I'm not running a vacuum on the fuel pressure regulator... should I be then?

[petert 550]

I'm not running a vacuum on the fuel pressure regulator... should I be then?

 

It depends on the type of engine. A race engine has a very poor and inconsistent vacuum at idle and spends most of it's time at WOT, so it's not applicable. If you've got std. or small cams that give a decent vacuum then I would.

 

You'll need to go and map it all again though!

Edited March 9, 2006 by petert

[Jonmurgie 2]

Fine then, sounds like I don't need to bother with a vacuum

[PumaRacing 1]

Start a new thread, that sounds interesting... Does it take into account total downforce or is there a moment associated with the front and rear aero balance? I spoke to Willem Toet a couple of years ago and he told me that F1 cars do not have a linear relationship between downforce and speed, despite regs being brought in to stop wings being able to bend much, this also effects the front:rear split...

 

Anyway, that is off topic, but I think there are a few of us who would be interested in your findings if you discussed it in more detail in the 'general' section Dave!

 

Downforce, like drag, is proportional to the square of the speed. I haven't built into the program any moment for front/rear downforce because I have no data to support it but I have assumed that 2/3 of the downforce is on the driven tyres. The reason I added this facility to the program was to properly simulate the acceleration of powerful cars with downforce such as F1 cars.

 

Normal road cars accelerate fastest in first gear. As speed rises so does aerodynamic drag and each gear change reduces torque to the driving wheels. F1 cars don't work like that at all. Off the line they have an enormous surplus of power over grip so most of the power is dissipated in either wheelspin or by the traction control system. As speed rises the downforce increases grip and so more of the engine's power can be transferred to the tyres. Until drag starts to slow things down they accelerate faster the faster they go.

 

Off the line the acceleration is determined purely by mechanical grip which with state of the art racing slicks is about 1.3g. OK so F1 tyres are treaded nowadays but they are still basically very soft slicks albeit without 100% tread contact area. 1.3 g grip means 0-60 in about 2 seconds but the car is not accelerating at its fastest at these low speeds. The next 60 mph increment to 120 mph takes even less time despite massive drag losses from the front and rear wings as speed builds up.

 

Downforce increases grip until peak acceleration is reached at about 100 to 120 mph at which point the car is pulling 1.7g. To put that into perspective the 100-110 increment takes a quarter of a second. About as fast as you can press the throttle pedal. Above 120 mph drag finally starts slowing the car down. However, at 180 mph in 5th the car is still accelerating as fast as a hot hatch off the line. 180-190 only takes 0.8 seconds.

 

Running the key numbers gives these figures.

0-60 2 seconds

0-100 3.25 seconds

0-200 9 seconds

1/4 mile 8 seconds @ 194 mph

 

Unless you own a Veyron it's probably hard to get your head round just how fast and brutal one of these things is.

[charlie_sav 0]

This is a good sizing program on the web,

 

Injector Sizes web page

 

 

That do you think of Performance trends drag racing analyzer if you have ever used it dave, it also has setting for front and rear lift coefficients, I've got a 106 what would be a rough guess at it's lift coefficients ?? apart from that it seems quite accurate with what other people are getting on the 1/4 mile but tyre grip clutch control are the mainfactors that seems to make or break a run,

 

It calculates a top fuel dragster with 5000bhp, on nitro to run

 

63mph 0.5 seconds

100mph 0.9 seconds

200mph 2.3 seconds

4.73 second 1/4 @ 305.3 mph

peaks at 4.9G

 

but can not go around corners like an F1 car.

 

sorry abit off topic !!

Edited March 10, 2006 by charlie_sav

[Rippthrough 98]

Unless you own a Veyron it's probably hard to get your head round just how fast and brutal one of these things is.

 

A good way to get an idea is to look at Maclaren's press pack.

6.6 seconds from zero to 100mph

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

And back to zero again.

[Anthony 1,000]

Downforce increases grip until peak acceleration is reached at about 100 to 120 mph at which point the car is pulling 1.7g. To put that into perspective the 100-110 increment takes a quarter of a second. About as fast as you can press the throttle pedal. Above 120 mph drag finally starts slowing the car down. However, at 180 mph in 5th the car is still accelerating as fast as a hot hatch off the line. 180-190 only takes 0.8 seconds.

That's...... fast

[C_W 3 1 Cars]

A good way to get an idea is to look at Maclaren's press pack.

6.6 seconds from zero to 100mph

And back to zero again.

 

What car is that for?

[Rippthrough 98]

What car is that for?

 

The 2006 one.

[PumaRacing 1]

What do you think of Performance trends drag racing analyzer if you have ever used it dave

 

Never come across it but then my own program does everything I need so I haven't had to look at anyone else's.

[Dom9 2]

Downforce, like drag, is proportional to the square of the speed. I haven't built into the program any moment for front/rear downforce because I have no data to support it but I have assumed that 2/3 of the downforce is on the driven tyres. The reason I added this facility to the program was to properly simulate the acceleration of powerful cars with downforce such as F1 cars.

 

Ah ha... But this is my point... Downforce is NOT proportional to the square of the speed on a modern F1 car... Downforce of a fixed wing will be, but not if the aerodynamic loads on that wing are causing it to bend/move/change shape such that the wing does not stay in a fixed position as speeds rise... There are also the effects of ground effect as the car dives under braking and the front wing gets lower to the ground... It would probably make very little difference in your software, but this was one of the things I found quite interesting about the modern F1 cars aero package, the fact that the total downforce did not increase proprtionally with speed...

 

Anyway... It's off topic! Very interesting piece of software Dave...