a management story on a opel gt cih engine (manta)

[graham bahr]

a while ago i rebuilt an engine from a 1.9cih engined opel gt, these cars origonaly ran a twin choke solex carb, but this one had already been converted to run Bosch L jet from a really early manta, an A series one i think, anyway early enough the car still ran points.

As engine rebuilds do, it got carried away, 2.0, then 2.2, finally it ended up 2435cc, i ported a 2.2 carlton head and it was fitted with big valves, and a solid lifter 244 cam. the 2.2 head gave a problem with the inlet manifold as the origonal one wont fit and the 2.2 one is crap, far too small ports and throttle body for any power, so armed with some down loaded pics off the web, i sawed up a 3 litre straight 6 monza manifold, and with a bit of tig welding later we had a nice manifold with a big throttle to fit this 4 pot.

idealy the car should of gone on throttle bodies or sidedrafts, but that means hacking the inner wings about on a rare and and imacculate road car, so that wasnt an option.

i then had major grief trying to make it work on the std management, 500cc bigger engine, hot cam, big throttle 244 cam, the airflow meter could be heard banging open and closed as you cranked the engine over, it was also so lean it barely would run, or on big injectors just poured unburnt fuel out the exhaust, and as for ignition timing, you had a choice of an engine which would start but pink its socks of at the merest whiff of throttle, one that would just about start but wouldnt pull the skin off a rice pudding or one that wouldnt start at all!

after taking the dizzy to bits numerous times, bending the spring pegs, and welding up the advance stops i got the timing sorted,

on the fueling front, after trying 3 different sets of injectors, 3 pressure regulators all squeezed in a vice by different amounts to raise the fuel pressure, a serious amount of tinkering with the springs in the airflow meter, it worked well enough to drive to Le Mans and back only 2 days after it was finished.

but to be honest even with the adjustments (bodges) to the management its still pretty crap, starting can be a bit hit or miss and it rarely idles, its like a clapped out pair of webers on a wonky linkage it needs constant tinkering to keep it in tune for more than 5 min.

the car simply had to go on an aftermarket management system to make it user friendly again, its going on an emerald, simply as because they are freely availiable at sensable cost anyone can have the mapping software and finally i'm well familar with it having run one for many years myself.

[graham bahr]

we needed a crank trigger or similar to run the emerald ecu, simplest from a engineering point of view is to rob the front cover and trigger wheel off a 2.4 vauxhall frontera,

but that would involve removing, a complete bastard of a job and a part strip of the engine, so that was out the question,

and there was no easy way to retro fit a crank trigger, so it was decided to trigger it off the dizzy, by chucking away the points welding up the advance mechanism and fitting a lumenition eye and trigger, you dont need the module just the eye and trigger, had the dizzy been a newer electronic one that would of also been ok with the advance locked up.

on a high reving engine a crank trigger is a better way to go as it gives the ecu many more reference points, but its just fine on a sensable reving road car.

[graham bahr]

most early OE managments dont use a throttle pot, it looks like one but is merely a couple of micro switches which tell the OE ecu, idle or full throttle and nothing inbetween, no good for proper management,

proper throttle pots are much smaller, often leaving no way to attach them, the easest sollution is to butcher the origonal throttle switch, cut the switch bit off and your find you have a nice metal strip with holes in the right place to attach to the throttle body and somewhere you can also drill a couple of new holes to attach your new smallet throttle pot.

on this engine it turned out spindle on the throttle body turned the wrong way for the new throttle pot, but as the D shaped hole in the pot went all the way through and out the other side i merely flipped it and the bracket over and found a couple of spacers and longer screws to attach the whole lot with, i didnt have to have the bracket on the outside but doing it that way ment the bracket still centralised the pot.

[graham bahr]

next came the loom, normally i get a part loom from emerald trim the wires to length and just put the injector plugs etc on.

this time i did it the harder way, cut ECU plug off the OE loom and put the emerald ecu plug on it instead, which is easier said that done, especially as i didnt have a wiring diagram for the loom.

job done, ignition on and a nice red led on the ecu, cranking the engine over it went green, showing it was reading the crank trigger and it ran, just,

after playing a bit with the mapping it idled well enough to lock the inition timing at 20 degrees BTCC and zero the dizzy on a timing light, and a bucket load of tinkering with the fueling settings in the map it ran a bit better, but i wont even attempt to do a full mapping job, i'll leave that the dave walker,

what is clear already though is the 6 cylinder throttle body is a bit on the big side, there is a definate point at still a fairly small throttle position when the fueling requirements massively change, so later on a trottle redesign migh have to take place to make it more progressive, watch this space

[GT2200]

Graham, I see the airflow meter has gone too, I suppose it's only fair if I post up a pic of the car with the engine pre-works.

And of course it then wouldn't be fair if I didn't post a picture of the car too.

Obviously most grateful for the work you've done on the GT so far.

I might add that Grahams commitment to sorting the car for the Le Mans trip back in 2005 was truely amazing, the number of late nights he put in were the only reason I managed to get there.....that said stripping and reprofiling the dizzy at midnight is not recommended for most sane people!!!!

Since 2005 the GT has probably only done about 20miles due the driveablity issues and so I knew that Emerald etc was the only way to go.

In addition to the Emerald the car is now also breathing on a new exhaust, this only took 8months to get from Germany...another reason she has been off the road for so long.

Obviously I'm now like a kid waiting for Xmas as the car is booked in for it's ECU mapping in a couple of weeks and I'll then be looking forward to getting her out on the road for the summer season.

Anyway Graham, many thanks again and please post up some more as time progresses...any pics of the exhaust?

[GT2200]

What is clear already though is the 6 cylinder throttle body is a bit on the big side, there is a definate point at still a fairly small throttle position when the fueling requirements massively change, so later on a trottle redesign migh have to take place to make it more progressive, watch this space

What you tell me Graham......more tinkering. I look forward to hearing how you're going to achieve a progressive throttle.....how about modifying a 24v Dual Ram intake:lol:

Thinking about it, is the progressive throttle what was fitted to the original 1.9 inlet plenum?

[graham bahr]

no the origonal 1.9 wasnt progressive, but then it didnt need to be it wasnt very big.

the problem only arises with very big throttles, when for a small amount of movement you get a very large increase in airflow, and thus drivability suffers and its harder to map, although to a certain extent you can compensate by moving the load sites around a bit. the way round it is for the throttle to initally open slowly in responce to the pedal movement but speed up the further you push the loud pedal, it can be done on clever linkage, car manufactures often do it using a small primary and bigger secondary throttle rather than one big one.

on the otherhand i might just leave it alone, afterall it was drivable enough on wonky management that you it drove to Le Mans and back :D :D

[bortaf]

Sweet looking car :thumb:

[Dave]

Clever stuff Graham. :clap:
I think :confused:

[lowscorts]

no the origonal 1.9 wasnt progressive, but then it didnt need to be it wasnt very big.

the problem only arises with very big throttles, when for a small amount of movement you get a very large increase in airflow, and thus drivability suffers and its harder to map, although to a certain extent you can compensate by moving the load sites around a bit. the way round it is for the throttle to initally open slowly in responce to the pedal movement but speed up the further you push the loud pedal, it can be done on clever linkage, car manufactures often do it using a small primary and bigger secondary throttle rather than one big one.

on the otherhand i might just leave it alone, afterall it was drivable enough on wonky management that you it drove to Le Mans and back :D :D

Or you could try a Suzuki (Gsxr)secondary butterfly motor setup to open/close triggered by the ecu at set rpm's (if the ecu has outputs for it?)

[graham bahr]

the car has now been on the rollers and mapped, its a road car so it doesnt make silly power figures but what it does have is a huge spread of torque and is very very drivable, it drives 500% better than before it went on the emerald ecu, its revs better freer, idles and is generally very flexable and nice to use.

it makes a healthy 183bhp and 177lbft

the only downside is that although it does idle and starts ok, it does have a somewhat lumpy 1200 rpm tickover, which is nothing to do with the mixture or timing, just that the combination of the 244 cam and a plenum intake dont go together very well, it could be cured by putting a milder cam in, but then the engine wouldnt rev not that its revvy now peaking at 5,800rpm, or by putting it on throttle bodies, for now at least i think the owner will be happy with it as it is.

[GT2200]

:woohoo: Graham......I'm only just a little bit excited

Insurance is all sorted, Graham has arranged a MOT and if all's well HUMBUG is coming home on Firday.

I may have to trailer her back, but the wife has just suggested that I enjoy the drive home.