Originally Posted by Mike
The set up tool, in simplistic terms is it as easy as this;
get the car on a fast idle by using the throttle screw, use the airflow meter to check the balance between cylinder 2 and 3, use the balance screw until these are the same, seems easy....?
T40's set up by an amateur (not doubting you ability) and no other mods probably will not be much faster. You'll certainly need a decent camshaft and some mods to make it flow better (such as an exhaust manifold and some head work) to see any decent gain 40's alone even if set up right won't give you that great an improvement of performance.
Trumpets will totally change the airflow into them and increase it by probably 5-10% as the air doesn't like the sharp edge at entry. (Although 5-10% is based on flowbenching heads with and without a shaped entry made up, might be a bit less on a carb but I'd expect similar)
It's most likely missing when you boot it due to the pump setup being for a 1.8, it's probably washing it with fuel, it's also probably then running lean as hell on the 1.3 setup.
Get it set up properly, save yourself hours of hassle and never have to think about it for the near future.
The only way (as has been mentioned before) to set up carbs properly is on either a static dyno, or a rolling road. No amount of "tweak and drive" will do. A good RR operator will do the biz.
With no trumpets, you will suffer "stand off" where the pulsations in the inlet tract cause the carb to "burp" fuel-air mix out of the carb. This can (and has) led to engine bay fires. It also reduces performance. You see it as wet fuel deposits on your bulkhead (if you're not running filters - which is a no-no), or fuel soaked filters!
There are many trumpet designs, but the best of them can't be used on a Nova because there isn't room. Ideally you want something like a 60mm rull radius ram pipe (these are the ones that have a big rounded edge, not the short sharp jobs). Dave Vizard, a god among engine tuners, published a lot of his work in this field, and he developed a number of designs that worked exceptionally well, though some of them were impractical for use on car installations, but his findings showed the benefit of rull radius pipes over conventional abrupt ending ones.
Don't forget you need filters on there too. The best solution is to build an air box, plumbed to a large flat panel filter for maximum flow of clean air without interfering with the area immediately around the inlets. This means that the best length of ram pipes is going to be about 40mm to allow for bulkhead clearance, and that will allow an airbox to be fitted. I found that pipes of less than 25mm didn't stop the stand-off sufficiently.
The 60mm figure came from Vizard's formulas which take inlet tract length, distance from throttle butterfly, cylinder capacity, stroke, revs, and some magic constants, and is taken as the idea.
The longer the pipe, the larger improvement in mid-range torque.
Moving on - balancing. If your ears work, get a length of hose. Listen to each inlet either side of the balancer. You will notice when they are in balance - they will sound the same. That's old school balancing.
I spoke to Ricky Gauld this morning who is apparently considered a bit of a god for tuning up north. He reckoned I'd get about 2 seconds difference (0-60) times going from standard carb to twin 40s tuned and running properly. I explained to him what I have done with the pierberg and that I am getting (0-60) between 1.5 and 2 seconds faster with the modifications. He said that I probably would get very little more out of the webers with the 1.4 block without a lot of head work/piston work etc.
So I'm off to remove the webers and put my pierberg back on!!!
Thanks everyone for the advice etc though
Interested to know what you did to the Pierburg to get more out of it.
changed the jets to ones from an unknown pierberg (think it was an astra?) I had lying at the back of the garage.
Made sure all the vacuums work, did my pen test to see if the second barrel opens when it should and the fuel goes through it.
Nearly blew the engine up doing this once when idling as the carb stuck with the 2nd barrel open at way out of the range for the rev counter...how a valve at least wasn't bent is a miracle.
Put a physically bigger vacuum thing on the 2nd barrel (again from the donor carb) and the vacuum thing at the back was also replaced.
Cleaned it etc,
Took the advance pipe for the distributor and put it on the 2nd barrel vacuum to give an earlier opening.
Adapted a K and N air filter to fit.
Basically now at 3500rpm with the foot flat in any gear the 2nd barrel opens, not just a bit but completely and throws fuel in the wee pipe bit above. You can tell the differenc ein every gear. 0-60 (on the speedo) moved form 10.3 as standard to 8.3-8.8 in our test runs, depending on my driving!!!!
But even with a consistentish 8.8, not too bad for a 1.4 although it was one of the slowest cars on the track but I think no-one else hafd anywhere near as small an engine.
The pierberg still is ok for normal driving but...is very thirsty when driven hard. Although any type of 2nd barrel/2nd carb would be thirsty I expect anyway.
That's what I did, not sure if it should be recommended though and not sure how long it will last.
Although i have taken the 40s off for the moment, I had to take brackets form other carbs and adapt them etc for the speedo cable during the last few days. Pic 1 shows what it was like before and pic 2 is what I have adapted it too, does this look ok? It was certainly easier to pedal and seemed more secure.
You never know, I may be putting them back on in the future......
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