Trio's New Bodies

[Sandy 191]

For those of you not aware of the plot up to now.... when I fitted the Accord engine into my 309, I used some Ex BTCC direct to head 50mm bodies that I'd chanced on a couple years ago. They were marvellous for top end power, as you'd expect; but the problem with such a big grunty engine in a pretty light car, is that small throttle openings give big lumps of grunt, which makes normal town driving a bit "Maureen". I'm sure you wouldn't notice in a 400+ kilo heavier car (that's roughly how much more and Accord Type R weighs). The other issue is the size of the ports. The Accord TR head has pretty large inlet ports and fuel drop out at small throttle openings is a bit of a problem, again, I don't think you'd be able to hold a steady speed in the Accord with this little load, so it wouldn't be an issue.

It's a shame when you have to give up something beautiful, but as time went on I had to admit to myself, that using the 309 as a daily driver, I needed to solve these issues for the long term. I've tried all sorts of variations on the map, improved the throttle leverage (longer pedal travel), fitted smaller injectors that could only just manage peak power; these things did improve the issues quite alot and eventually I got average economy up to 27mpg "Urban", 35mpg "Cruise" and about 30-32mpg overall. The over eager throttle response was still a problem though.

The answer had to be quite severe. I decided that downsizing the bodies was the best strategy. The 50mm DTH bodies are ideal for full throttle performance, but they are a bit too big at part load, so they had to go, great shame. Colin and I got creative by cutting off the flange from the standard ATR inlet and making a Jig to TIG weld in some fairly long 40mm bore tracts and flanges for 45mm Lotus bodies. The Lotus are tricky to space so the tracts had to flare apart slightly to get it right.

I got the new manifold back from the master welder earlier in the week and ported it ready to fit.

I've fitted the standard injectors, fuel rail and regulator from the ATR, as far as I've been able to establish, the Keihen Injectors are 345cc with the 3.7 bar regulator. I've fitted the MAP reference pipe to reduce the pressure at idle and part throttle.

I've been out a couple times and refreshed the map on the road, but it's definately changed a fair bit. Over 7000rpm it does tail off a little compared to before, and I had to reduce the advance a touch around 3-4000rpm. The fuelling at full throttle compares well for the relative injector rates, but the part throttle fuelling is reduced quite a bit, in fact holding a steady speed from about 30-60mph, the injector duration is wanting to be less than 1ms net, which is not really practical for the ECU to control, it runs ok, but a touch rich at 1ms, then if you try to dial out fuel to get a balanced mixture, it splutters as the injectors lose control. The only way to solve this currently in to run a minimum of 1ms net (net as in including dead time) and accept the slightly rich mixture, but it's a shame, because it's wasteful! The proper way to resolve this is to fit smaller injectors or drop the fuel pressure, neither of which I can do without changing parts. I'd like to point out here, that a major benefit of running staged twin injectors, is that you get great resolution at part throttle and idle, even the overrun, which makes for a much more satisfying and cleaner map! Sadly again, twin injectors weren't that practical on this set up, but I might have to bring them in!

I imagine the extra load the Accord has when it's cruising (more rolling and aero drag), means the injectors never need to go this low.

 

All interesting though. (In my world )

 

Here's the manifold:

 

With bodies/trumpets, excuse the crude trumpet bending to get the socks on until I get a backplate for the proper filter:

[deadcatdave 0]

very interesting.

 

So how does the mid range feel now ?

 

I'd expect gas speed is up dramatically in the mid range so I predict mid range torque has increased significantly..am I right ?

[Sandy 191]

Part throttle feels much cleaner and more linear, but full throttle isn't much different through the mid range TBH. Perhaps it will be once I've swung the ignition scientifically in the rollers.

[Sandy 191]

Update time....

 

Given that the Accord Type R injectors (~360-380cc) seem to not be very good at small amount of fuel for very light load, I grabbed a set of K20A2 Civic Type R ones from a friend (~310cc) (cheers Neil!), thinking I could simply swap them. I thought wrong. The Civic ones have conventional 14mm O-ring top ends, which don't fit the ATR fuel rail, they are also a different fitted length and don't fit the manifold end. Crap.

Once I'd taken everything apart and found this out, I'd discovered one of the ATR injectors had sustained a damaged air nozzle somehow (maybe during removal) and given the problems of accurate fuelling I was having with them, I didn't want to put them back in.

So Bosch or Weber Pico injectors were the alternatives, which I have a substantial stock of. I initially though the mid-sized Audi TT 317cc injectors might be ideal, but getting a seat against the Accord's rubber washer seals wasn't going to work, it had to be the 265cc 306 GTi6 injectors I'd been using before.

I drilled out the manifold side to 13mm to accept the Bosch O-rings snugly and honing the upper section of the injector pockets slightly made the injectors fit very neatly, with the Accord rubber seals as a secondary seal, which will also defeat the injector clicking noise a bit.

The fuel rail was another matter. Drilling out the ATR rail to take the Bosch 14mm O-rings was too risky, I couldn't be sure I could get all the swarf out, without pulling out the end plugs, which could be a whole can of worms! The CTR rail has the right size Injector holes, but no integral fuel pressure regulator and the mounting holes don't line up. Salvation was a GTi6 fuel rail (bit of a surprise), the hole spacing for the injectors is only very very slightly out, not enough to be an issue. One on the mounting holes lined up when over-sized and a quick bracket helped the other end fix solid. The integral modular Bosch regulator means pressure changes are quick and easy. All sounds easy enough, but the reality was almost a whole day lost to all this messing about.

I had to make a new throttle cable bracket and re- route the fuel hoses and filter too.

I mapped the fuelling again this morning, the previous fuel map wasn't much use, scaling it to the injectors never works very well in my experience and this was a classic example! It was clear to see straight away that I have alot more resolution (accuracy/adjustment) on fuelling at steady speed throttle openings. The injector opening at 60mph cruise is down to about 1.8 milliseconds now, and with a slight trailing throttle and 15.2:1 air fuel ratio, it down to about 1.2 milliseconds and just holding it.

 

Quick tutorial for those who wonder what injector opening times (milliseconds) are all about...

The theory is that fuel in the fuel rail is supplied at a steady pressure, so how long the injectors open on each engine cycle, decides how much fuel goes in. So in theory, 2ms admits half as much fuel as 4ms, not exactly true, but nearly. And at a given pressure, obviously a 200cc injector opening for 2ms will inject half as much fuel as a 400cc one opening for 2ms, again, not precisely true, but nearly.

 

So the end result is, it's cruising on noticeably less fuel, the injectors JUST cope with the top end power at full throttle (a bit iffy on duty cycle, but it spends so little time there, it's not an issue). It does make me wonder if the Accord's legendary thirst might be reduced slightly with smaller injectors and re-mapping. if anybody cares. Smoothness is much improved too, almost like a standard car now!

 

Trial fit of the CTR rail

 

Installed with the GTi6 rail

[Powers 13]

Looking good. A very informative read.

How are you finding the car now?

Do you wish you just stuck with the 50mm BTCC units?

[Sandy 191]

Very happy with it. I still need a bit more resolution for perfect mixture at idle and part throttle, but the only way I can achieve that is with staged twin injectors, which I hadn't planned for, so it would be additional fabricating. I might do it later on though.

The throttle response and low-mid rpm grunt and smoothness is much improved, if there is a penalty at high rpm, it's over 7000 rpm, but I don't get much opportunity to exploit that on the road.

Certainly for what I'm using the car for, this is a better set up. The problem with this engine is the sheer broad scale of the performance, it goes from such small effort at cruise to fairly big power. The only comparison I can make is with boosted engines, but they can use MAP fuel regulator referencing to broaden the range of the injectors.