Fuel Problem on Mazda

[Vandas]

I have a problem guys. We are a team that runs a Mazda RX7 Series 2 in the Victorian State Series for Improved Production Cars. Now the problem is with the fuel tank and lines. We have a tank which was specifically built for the car, with a drop tank that had to be shortened as it is so close to the ground we feared it hitting. anyway, the surge tank holds 1.5litres the actual tank itself holds around 50 litres. and there is another tank which holds around 1.5litres of fuel, however we are having a major problem with our economy and the system itself. Where it is like the fuel is drawing in air as it reaches the engine. But not when we fill it to the top with fuel. When the tank gets just below half way that is when it starts to do it. This is a major problem as we want to keep dropping our times (seeing as we are a front runner) yet we have to qualify with a full tank of fuel so as to keep the thing running smoothly. We haven't been running with a self ventilating cap bt we are now. the top of the tank has a gap where when filled too full it leaks (which we are fixing now that there are no race meeting left for the year) what the hell is going on with it. We have checked the pumps and filters and cleaned them all out, changed them over etc. We have played with the electrics the computer and everything. Yet we are all still stumped. I think it is drawing air from somewhere else in the system. Yet why wouldn't it leak out of that spot.

Has anyone heard of, or had this same problem ever. It really has us stumped.

[yelwoci]

Vandas,
Just to clarify things, is you series 2 like mine: like the 1st RX7 but with soft bumpers and still on 13" wheels, or did you mean the 944 look-a-like?

I race mine in UK in Grp-1 spec with a 250hp 12A motor. I have an 80L tank in it to support 1 hour 70m races. It does about 5mpg, sometimes 7mpg!

Air in the fuel is usually caused by a couple of things:

1. Lack of baffles so the fuel foams as its thrown around. What with the leaks and all, I'm sorry mate (to give an Aussie feel <g>), but its sounds as if you should dump it.
Solution 1a. Get a decent tank made
Solution 1b. Go to a rally shop and get some yellow fuel safety foam blocks that you can cut up and stuff into the tank. Use fuel filters either side of pump as the stuff decays over time.

2. Air getting into lines.
Seal tank and apply 50pis or more to fuel hose at engine end. Listen for leaks....or exploding lines....ok maybe 20psi will do. Vacuum might also work if you have access to it.
Might be good time to aeroquip whole line. Use 10mm i.dia pipework

3.Fuel pickup or feed to collector tank in wrong place.
Rebuild tank!

Regards

IanC

[Vandas]

yelwoci, Yes ours is a Series 2 but we run a 13B Bridgeport which puts out over 300hp. Our tank was built professionally and specifically for our car. I am tending to think it is a problem with the drop tank or the lines. See we had to shorten the drop tank to allow for the car to go as low to the ground as possible. Anyway I will try applying pressure to the lines to see if I can come up with anything.

Also we are having a nother problem with the mazda. Do you have any trouble with the rear end. We are having a terrible time at the moment trying to locate what the problem is as to why the back of the car lets go at the peak of a long fast sweeper. We had troubles at our last round at Phillip Island (we have had a few dramas there with this). At first we thought it might be the race diff locking up the inner wheel, but we realised it is only on sweepers and not on the tight slow corners. We have a feeling it has something to do with the rear shockers and springs. We run very soft springs, and it looks like we may have to go even softer and allow for more axle droop hopefully that may fix it. Let me know what your big dramas have been.

thanks.

[THR]

u mean the car is oversteering when its highly loaded in fast corners?

when u have max roll, max accelation.

could be that the car is on the bump stops when it goes over a bump not letting the bump being taken up properly

suppose the only thing u could do is increase the damping. and springs.
is the suspension tight? no play?

[Vandas]

THR, what is happening is when the car is really flying around a sweeper, it gets to the pinnacle of the corner (not the apex) where the car is at maximum roll, and accelleration (yes as you said). The back just let's go, it is like snap oversteer. the weird thing is at other tracks like Winton and Calder we have understeer to snap oversteer (when the car isn't set up right, the only time we have any trouble with the rear end letting go is at Phillip island. At turn 12 (one of the fastest corners in Australia, and also at 9 coming over the top of Lukey Heights. Both are very fast sweepers which get really tight at the end. At first we thought it was the driver lifting off and therefore weight transfer spinning the car, but after lengthy talks with the driver we have found that not to be the case. It has happened at Phillip Island 4 or 5 times resulting in the loss of 8 new tyres and a big crash which meant new panels, and the front end of the car being straightened.

It is a really mysterious problem. We are putting in two cameras so that we can monitor track position of the driver and foot work that way we can overlay the two images on the screen and then watch exactly what his feet are doing at what point on the track. This problem is costing ours time in qualifying and also money on tyres and panels hehehe sO we are going to give the driver a clip over the ear if it is him lifting off.

[enzo]

Seen a problem quite like this many times in amateur cars of various sorts where they are still running soft springs and attempting to control the car with stiff shocks. The problem always occures in long, high load sweepers.

What happens is that too much bump damping, reletive to rebound, is dialed in in an attempt to keep car movements down. During the course of the long sweeper, the back end is being pumped up to the point where the rear is so high that it dominates the roll couple balance equation - all your available traction is being used to control roll, and there is nothing left for accelleration.

DON'T back off on the spring rates! All that will accomplish is even more body movement, which you will then attempt to control with even more damping, and the car will end up losing grip and responsiveness. If anything, increase spring rates at both ends of the car, and get someone who really knows what they are doing revalve the shocks to work with the higher spring rates.

Good luck !

[yelwoci]

Vandas
The 1st generation (Series I,II,III) RX7's have horrendous rear suspension geometry.

The top links are less than half the length of the lower links and mounted on the outer ends of the axle, rather than around the diff housing as per Toyota Corolla GT (Sprinter)

I run mine with the std Watts Linkage, which is asymetric with the pivot point on the axle tube beside the diff casing! It may work but it looks wrong!
Many replace it, if the rules allow with a traditional panhard rod.

After about 3 degrees of roll the rear geometry binds and the car skips over the bumps. Also the roll geometry (top links) causes the axle to yaw
With 210bhp @wheels I can prevoke this in almost any corner.
So with your 260+ @wheels it will be even more fun.
Also should you back off the axle 'de-yaws' and you spin off again!!

In the US SCCA it appears that cars with standard suspension run 220/160lb springs F/R, whereas I run 300/225
to try and control the tail. (I run on pseudo road tyres Dunlop D84J 185x60x13)
I also took off the rear rollbar, with a RB 1 1/8 on front.

Mine is very very good through long fast corners but you must be very smooth and progressive.

Regards

IanC

[BMWRacerITS]

Originally posted by yelwoci
In the US SCCA it appears that cars with standard suspension run 220/160lb springs F/R, whereas I run 300/225
to try and control the tail.

Dang, the spring rates on my street car are higher than that.

I race against RX-7's in SCCA (they are my chief rival) and I have to run 1000-1300lbs springs in order to compete. I like a stiff car though. I had no idea that the RX-7 guys were running such low spring rates.

Oh well...down with the RX-7's!!

[DAVID PATERSON]

Hey guys, just wondering if a swirl pot would provide a solution to Vandas' fuel problem?

[yelwoci]

Vandas,

As enzo points out damping is really important.
Mine are custom made by LEDA here in UK. There a bit heavy with steel bodies (the co. focuses on rallycars) but they are matched to my spring rates. Only one way 20 point adjustment but they work, and I probably don't have the skill and testing time to mess with bouce/rebound damping ratios.
Full soft and the cars a pig, 7-11 is good, 12-15 is a bit too fidgety.

Regards

IanC

[yelwoci]

BMWRacerITS

The RX7 is only about 1000kg/2200lb with 55:45 F:R
So 300lb Front springs carry a static load of 600lbs each and the 225 rears carry 490lbs.

These loads are about right for a car standing on road tyres (radials) and 60 profile at that.

There are two schools of thought:
1. Run as soft as possible to maintain traction by keeping the wheels in contact with the track. This approach needs good alround damping, a good chassis and a stiff front rollbar. Bad rear geometry complicates this.

2. Run hard, to keep the car as flat as possible. The car handles consistantly, but the overall traction levels may be lower, it just feels quicker.

Enzo might be interested to know, or have a good laugh:
I run my RX7 'medium-soft' and may go softer yet.
At the (macpherson strut) front at normal static loads the track control arms are level.
At the rear the body is much lower than most RX7s run and the forward links are level or lower than the axle mounts.
The roll centre/line is very close to level.
I've also recalculated the asymmetric Watts Linkage lengths and adjusted the standard lengths.

The car runs very flat and very kind to its tyres, both front and rear. The tyres probably need to work harder. This season I will be trying to raise the front roll-centre fractionally to increase the roll, or I'll reduce the roll/stabiliser bar lever ratio.

Regards
IanC

[Vandas]

Thanks for all your suggestions guys. I just got back from Phillip Island where I had my first ever Super Sprint in the race car. I have had to listen and give advice on matters without having a feel of the track so therefore not a good enough understanding. Okay to whoever it was that suggested the swirl pot, we have one but we are going to redesign it over the summer with a baffle type system above and below the point where the fuel enters. We are also getting a new fuel tank made up which has a V shaped bottom and proper baffle plates in it to reduce the effect of the fuel shifting away from the pick up in tight corners.

Now about the springs we run at about the same rate as the American cars. We are running 200 lb springs in the rear at the moment. and I found out the problem. the problem corner we had was 9 at Phillip Island which is a long flowing sweeper which tightens up on ou as you go over the crest of a hill. It makes for a very fast very thrilling ride. Now as you know the RX7 is very light in the rear and what I think has happened is the driver has gone in too hot and dabbed the brakes making a light rear end even lighter therefore spinning off into a wall. I found that the harder I booted it up the hill the more weight was transfered to the rear as common physics would tell you and therefore I had a better ride over the hill and down into 10. This is the problem when you don't run a data acqusition system and have to rely on drivers memory and honesty. hehehe. Anyway for my first drive out in the car at that track. I consistently dropped my times by 2 or 3 seconds in every session and eventually cruised into 6th without pushing it too hard. I got beaten by a couple of Sports Sedans who were seriously quick, and a guy that shouldn't have even been running in my class. Also the regular driver (well regular for the last couple of years) pipped me but he came in sweating having worked his arse off. Best part was the team got him up on the roof to watch my lines through certain corners. hehehehe.

Anyway thanks again for your suggestions I offered all of them to the rest of the team and a lot of what you said we have taken into consideration, and even they had been thinking about before I told them. but it is good to know that there are others out there going through, or who have been through what we are.

Let me know how you are all going with your cars this next season.

Oh yeah by the way I just picked myself up an extremely straight roadworthy RX7 for $2000 Australian and I have the stuff to make it even schmicker so all up it is going to cost me not much and I can seel it for **** loads. hehehe Good to be in the right place at the right time.

Camma

[yelwoci]

Vandas,
If I wanted to buy a clean and competitive race RX7:
Pre-83
12A Bridge
road suspension
glass
standard bodywork
free brakes

Any idea how much?
And where do I look or who do I talk to?

Likewise does anyone down-under race Pre-90 Cosmos?
Worst case the '85 Cosmo HB 929.

Unfortunately the latest Cosmo was made post 1Jan90

Regards

IanC

[Vandas]

IanC,

Well it all depends how you wanna go about it. I just bought myself a Series 2 Road car with 12A and everything standard. Small amount of rust (cost me less than $200 to get cut out), ****ty tyres which I replaced and the straightest rails you have ever seen. for $2000. Now those sorts of deals come along very rarely. but they are comign along more and more frequently as the arse has dropped out of the Mazda Market in fact all used cars are worth not much anymore. I am currently looking to go into business with my engine builder. we are going to be a Mazda Wrecker, Repairs and Race Cars Company. We mainly want to work with RX7s as they are a popular car in racing and on the roads. But we may stray every now and then.

Anyway if you wanted to go and buy an already built car with cage and spares and everything already decked out. For a top line car with plenty of extras you would be looking at around $17 000. Now that is for a front runner. you can pick up cars for around $5000 if you are in the right place at the right time. But they will need heaps of work, and maybe not even worth it.

As for Cosmo's I haven't seen any raced in Victoria but there could be some around. We use a Cosmo Imports Radiator in the race car, that's about all I have seen of one.

anyway either post more messages if you want more info or email me at illusionshaker@hotmail.com

Thanks

Camma