at WOT where it matters there is very little if any difference in performance.....There are 2 4age powered starlets that race here one with efi the other with 50mm webers, and they are any differences between the two if anything the starlet with the carbs are quicker...

by the way....Injection is actually older than Carbs.

With a big cam & quad TBs the vacuum signal is unstable as, causing the ECU to fuel all over the place - most Quad setups work on TPS mapping which is, as stated above, not that crash hot in certian circumstances

I'm interested in why you cant use MAP sensor to work out the air pressure on a competition engine.

I'm not disagreeing the fact I would just like to understand why.

BTW I'm learning a fair bit from this topic.

Oh and the main reason I'm going EFI is because I picked up the TB's cheap and am goign to use megasquirt... hopefully learning more about EFI and how it works.

hmmm, 20L is 12 laps of Manfield for me....

Having been in both camps, I can say that carbs are great, like anything, it's what you're comfortable and familiar with. It took me a whole season to learn enough about EFI to make it as good as the carbs were.
There is no difference in absolute power between a well sorted carbie setup, and throttle bodies.

Now, on any decent competition engine you arent going to be able to use a vacuum signal to tell your ECU what's going on, so you have to do it with throttle position. This means that carbs actually have an advantage, in that they're self tuning, eg, if there's less atmospheric pressure around, the carb just naturally see's less vacuum across the venturi, therefore less fuel goes in.
The throttle position sensor knows nothing of this!

I did get major gains in driveability going from 50pph's to throttle bodies. It is a bit of a nutcase engine though... I also got good gains in horsepower by playing with the spark curve, which wasnt possible with a dizzy, however this isn't a carburetor limitation..!

you normally fatten up the mixtures to about 12.5:1 at WOT

Quote:
I got 260km out of a tank (I think they're about 35l) in last year's QLD Challenge road rally including a number of special stages. But at sprint meetings last year where we were dual entering the car we went through more than 20L per day for under 50km of full noise running

hmm, maybe that was 20L for the weekend...

Yep I think you guys are right, both rallycar and myself have had bad runs with webers, which probably give us a really bad outlook... whenever someone says weber to me, I just think $$$$.

And just as a side note, I thaught u wanted to get your car running as lean as possible without detonation.... If this is the case why should webers use more fuel?

I tend to notice if your higher in the rev range, including track work you almost get better economy than city driving.

Quote:


I couldn't agree more.
I could have chimed in with a blurb about how my s/c worked out cheaper than sidies. (I have done in the past) But I scored a pair of 40mms with an oval port manifold, jetted for a cammy a14 for $300.
AND, like Morgan said, To pay someone to build my set up would cost the bloody earth.
Certanly for compettion where you want to stay in a certain class, the carbs would win $$ for $$$

Carbs like Webers and Dellortos are best suited to performance engines/cars. Yes they can be thirsty, you have four accelerator pumps instead of one, and most people going to the expense of modifying their engine including sidedraft carbs is probably tuning for power, not economy, so will be running richer than the average road car. A competition car running EFI would also run rich and use more fuel than a road car, wouldn't? And if people go to the expense of modifying for performance, they have to be prepared to use more fuel.
No, carbs can't compensate for engine temp, but they are usually tuned at operating temperature, and then used at operating temperature, ok, carbs may give a slight disadvantage if you're the type who likes to thrash your car from cold.
Carbs DO know more than just WOT, that's why they have an idle circuit, progression drillings, accelerator pumps, etc etc. I'm not saying they match EFI in every area but they have done a good job for a long time, and still do a good job, a look under the bonnets of cars at a race meet will tell that they are still doing the business.
If carbs have an advantage over EFI, I would say that it IS in COSTS. Most of the costs rallycar talks about apply to TB EFI too, such as manifolds, linkages, trumpets, filters, tuning labour, etc. Plus the added cost of the ECU which generally start round the NZ$1000 mark, and the TBs which are at least $500 ea. Yes new carbs are expensive, but secondhand ones are much cheaper and still quite available. There are bugger all secondhand TBs kicking around yet.
I would love to have TBs and EFI on my coupe, but I can't afford it, so I run 45mm DHLA Dellortos. The engine has a big cam and is entirely driveable from 2000 up to at least 7500rpm.
Yes a home made EFI single throttle setup will be a lot cheaper, and with turbos has good potential, but for motorsport especially, a turbo is not reeally a viable option as it puts you up into a higher class against really high HP cars. And an OEM single throttle NA setup will not realise the same power that a good set of carbs will.
Rallycar, you say L18 and others have had good luck, but how much would it cost someone to achieve a setup like yours if they had to pay a mechanic to do it all? I like what you've done and it's a credit to you for your skills in thinking outside the square, and being able to build it and get it to run well, but your setup would be harder to realise for the average guy than just getting a good set of sidedrafts.
It soundslike you had a bad run with your Webers. Its a shame because they are very good carbs.
ps good on you for starting such a provoking thread! makes people get off their arse and contribute a bit more!

I use different 'airs' at Morgan Park out at Warwick which is around 5-600m above sea level. Takes about 5 minutes to change all four. Its so easy in fact that on the QLD Challenge road rally last year, I changed them just before checking into control for the stage at Toowoomba (which I won outright up against lots of EFI turbo cars including highly worked WRXs), and then changed them back again before the next stage at Gatton.

Just a quick question a bit off topic...

I've seen a few weber dyno sheets which dont look very smoth at all, every 2000 or so rpm it seems like the fuel is not mixed properly causing peaks and troughs. Is this a charactoistic of webers (not sure as I've never had a dyno sheet of my own).

A few more things:

* webers dont take into account intake temp or engine temp both of which effect fuel mixture.
* Different jets would be needed in differant altitudes if you wanna get it right

PS its almost worth me driving to perth if you can get weber bits that cheap!!