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EXTRACT FROM JIM LANGER FROM RACING BEAT .USA

On what he thought was the most serious performance defect in the RX-8 Jim responded that he believes that it is the non-return fuel delivery system. Since the fuel pressure regulator is located with the fuel pump in the tank there is no way that a constant pressure can be maintained in the manifold to the injectors while under stong acceleration. This is due to the weight of the fuel in the long line being forced to the rear of the car during acceleration. This results in a dip in fuel pressure and pressure drop in the line due to increased flow just makes the problem worse. If a constant pressure is not maintained at the injectors the amount of fuel delivered to the engine can not be properly determined by injector timing.

When asked what performance modification delivers the most "bang for the buck" Jim replied that in his opinion it is sway bars. He said that Mazda designers don't seem to understand how important sway bars are to handling.

Surely if the amount of fuel cannot be properly timed and regulated then the rotary engine must be near impossible to tune by getting the AFR FIGURES ONLY HMMMM

CHEERS
MICHAEL

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ZOOM 2X

Was the first to post this thread in the disscusion forum under Racing beat focus group in USA

CHEERS MICHAEL

neit_jnf

As long as you have a wide band lambda sensor with logging then you should be able to relate injector timing to afr like MazdaManiac did with the Greddy E-Manage and Canzoomer did with his piggyback ecu.

About the swaybars it seems like they never drove a 3rd gen RX-7... The 8 was compromised for a wider audience.

Dez

time to go get standard issue rick shaw installation front and back.

currently the RS swaybars are now #3 on my top 15 things to be added to my version of the RX8.

--dez;

Hymee

iTrader: (1)

What was the drop in pressure do to the inertia of the fuel in the line?

I'd like some real measured facts about how much that changes things - i.e. changes in the fuel rail pressure during acelerating and braking. I guess what you loose during acelleration, you gain when breaking LOR!

IMHO - It sounds like a nice way to justify selling a hi-flow fuel pump, and all the associated plumbing to have a return line from the fuel rail back to the tank, and the additional regulator.

I'm not going to get too excited about that just yet, boys and girls.

Cheers,
Hymee.

PS - News Flash from Hymee Labs.... I have just started to design the Hymee Gymble-Mounted Injector Nozzles. Under hard acceleration, the fuel spray from the injectors was thought to be travelling towards the rear of the chamber and colliding with the trailing end plates. Thus, the atomised fuel would drop out of suspension and formed a pool of fuel on the combustion chamber wall - a mixture that is not very conducive to "a good bang". The HG-MIN design overcomes this problem by utilising a 3 axis accelerometer and a hi-performance computer control unit to vary the angle of the fuel injector spay to take into account the g-forces on the vehicle, in any direction. Thus, the inertia of the fuel dose will be corrected, and the does will flow as intended evenly across the width of the inlet tract and combustion chamber. A side benefit of the computer controller, is that it can also make adjustments for the inertia of the fuel in the delivery line by changing the regulator pressure in the tank in proportion to the X-axis acelerometer measurements.

:D :D :D

Customer Testimonials: Eager customer L&L reported he didn't have a f'ken clue what Hymee was raving on about, but he was prepare to spend the "f@ck bucks" on the modification, as he always believed it was always worthwhile to get "a good bang".

:D :D :D :D :D

emack

I appreciate your attempt at humour Hymee, but Jim Langer and Racing Beat? With all due respect, I think they may have a few more Rotary hours on the clock than you?! IMHO:D

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HYMEE

So far all MY best and cheapest mods have come from the house of hymee .

Knowing your obcessive **** character for detail and quality products if you did design the hymee gymble injector nozzles i am sure youd sell a few , not to me or paul , however maybe JIM LANGER COULD BE INTERESTED TO HEAR YOUR VIEWS .HA HA HA

Good to see that you are in good spirits and firing on all rotaries oops i nearly said cylinders .

be wise

michael

takahashi

LOL!

Hey Dez. Why #3 for sways? Oh I know I know modified the blonde sitting next to you and yourself first!! :D

Hymee

iTrader: (1)

:D

I didn't say it was BS, but I did say I would like to see some quantitative evidence.

Maybe with all of Brocky's experience, I could believe if I put a Polarizer on my RX-8 it would fix the problem :p. Polarize them Pete!

Cheers,
Hymee.

rotarenvy

well you might get the fuel to move in the pipe (you do need baffels in your fuel tank) but it is under pressure so will it reduce the pressure that much? I'm with hymee need some measurements.

where is the stock fuel pressure sensor?

maybe the problem lies when you change the injectors and need to control the pump to provide aditional pressure. might not be that easy to do.

pepe

I would have thought the obvious answer was to only drive down hills, never up them or on flat roads, then gravity would counter the inertia and the world would be a happy place again

sco

He he pepe .. it's just like having a model T Ford.. you drive up the hill backwards that way you can get the same effect up hill as you have down.

I'm fitting a custom fuel line (12v fish pond pump and irrigation line to mine tonight). Will let you know how well she performs when I take her for a run tomorrow.

timbo

This is all far too esoteric for me (and I suspect for the 99% of everyday driving we all do).

Although fuel starvation was a confirmed problem for all the 8's at Wakefield once the tank was less than 1/4 full.

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Timbo

I see the possibility of a fuel problem only if the car is driven under total race type conditions , and lets face it most of us will never even drive on this sort of situation .

IMOH

The most serious performance defect in the RX8 is the DRIVER from reading a lot of the threads i came to the conclusion that a lot of the RX8 owners simply do not know how to drive a high reving rotary engine .

I dont consider myself to be a top driver however i feel that i am at one with my RX8 .

No problems with gear changing , or knowing when to change gears and use them correctly .

cheers
michael

sinkas

hi all,

I wonder if Jim from racing beat was mis interpreted, and was really saying the fuel system was more of problem for tuning potential.

These one way fuel systems do seem to bea problem for tuners, so the expenese of changing to a circuit system comes into the preformance equation.

if your injectors are running at 95% duty cycle in your bridgeported street rx8 in 5 years time, and you boot it down the street you might lean the engine out enough to make it detonate..?


Case

mlx8

Fuel starvation in long sweepers is an issue in the cars. I'm not enough of an engineer, or mechanic to know what effect, if any the single vs. double with a return line has, but IME once the feed line emptys and fills with air, it can, at least on the track, take what feels like a significant, i.e. very long time without power for the engine to restart. Its bad enough when one has this happening at 1/4tr of a tank. It's positively annoying, not to mention hazardous when this starts occuring at the 1/2 tank level as conering speeds go up with suspension &/or tire improvements. BTDThis. IMO it needs to be fixed.

takahashi

I agree but which stock car does not do that It is a known fact (well at least I was taught) to fill up the car when it is half empty on the track and never run less than 1/4.

Well it is for all cars, not just the 8.

Fixing it is great idea, but why spending money on something else. I will rather lose 15kg on myself and get 15L of fuel in the tank :D.

rotarenvy

Taka your going to end up anorexic if you keep saving on weight by dieting :p

15kg for your fuel, 9kg since you don't have aTi exhaust etc your wasting away man!

Lock & Load

Last time i saw Taka he had plenty in reserve no need to concern himself with becoming anorexic , in fact he looked like a happy smiling buddha :D

takahashi

Haha.

I DO save up some in reserve just for special occasions. I will get those 15kg for this summer. If it is that cold this winter, we will get a stinking hot dry summer ahead.

I want to convert my one pack to a 6 pack!

labrat

Hymee,

How much of the injected fuel is in the liquid phase and how much in the vapour phase? Also, what is the droplet size distribution of that fuel remaining in the liquid phase? This would go to the heart of how much of the injected liquid fuel (and to what extent it) is subject to intertial forces (on the basis of 0.5*m*v^2). The are so many factors I can see coming in to play here. The smaller the droplet size, the more they are going to be affected by Brownian motion considerations, i.e., collisions with gas molecules inside the combustion chamber which will tend to hinder any movement toward the rear. Also, the velocity of the fuel entering the chamber will have an effect both from a vector point of view and its physical state of aggregation. There was a report in the New Scientist automotive section on experiments by scientists on single pulse injection in common rail diesel systems that have shown that under very high (supersonic) injection speeds, the very fine mist of particles entering the chamber creates a shock wave front which causes the fine particles to coalesce (thus destroying much of the work of the injection system). The result of this work has led to the use of piezo-electric valves which split the fuel charge into a number of pulses during the combustion cycle to minimize coalescence and to better utilize the fuel. I have heard that this technology is now being applied to petrol motors.

I don't know how much of this work is relevant to petrol rotary motors, but it does seem to be an enormously complex field which might not lead to a simple solution. I'll be the first to confess my total ignorance of this field, since I am only armed with dimly remembered concepts of basic physics. That said, it would seem to me one should be aiming to deliver the fuel charge in fine a state of aggregation as possible (to maximize surface area and thus improve combustion efficiency) and at the most appropriate time(s) in the combustion cycle.

Hymee

iTrader: (1)

I actually am using a very precise technique to arrive at this important variable. The fudge factor will be arrived at by taking the average age of the members of this forum who can say "carburettor" and "venturi", and multiplying by the % of forum members who have taken my new invention seriously I reckon that will be close enough to be extremely precise.

Cheers,
Hymee.

MattRX

Hi All

I am aware of how important accurate and consistent puel pressure is, but I still have trouble believing that the acceleration of the RX8 causes a noticeable drop in fuel pressure.

I would have thought the biggest problem with a non-return system would be that the fuel gets to sit aound in a hot engine bay for a long time and heats up causing a change in density which would have a leaning effect.

Matt

Gomez

It's just the opposite, in fact. The purpose of this system is to stop the return of hot fuel to the tank, which causes emission issues and increases the fuel temp. Not having a return and regulating the fuel pressure at the tank allows a "just enough" scenario which avoids having to return fuel.

aa@uow

hey Taka, mind explaining why we should fill up the car when its half empty and never run less than 1/4? u r talking on the track only or?