Stavros

As title really, I used to mess with R5GTTs but its been so long I forget.

Theory and usual internet talk is that carb fed cars have far worse drivability, esp big power ones, than the same engine when fuel injected.

But how true is this when setup right? (please, i want experience, not "i heard")

My memories of the GTT was it ran mint under all conditions even tho it was running about 25psi and big fuel jets.
To be honest it was more drivable than my Cossie was on L6 (on P8 it was miles better, unsuprisingly knowing how the throttle setup works on L6).

Its lacking throttle control or low down power im concerned about, tho im not totally convinced its a big issue, especially on forced induction.

Or is my idea of it being less of a problem on forced induction engines to n/a ones wrong?

Anyone care to share their experiences?

Ta

foreigneRS

a carb can never be as good under all conditions as a proper EFI system properly mapped

most of the shit driveability associated with carbs though is mostly down to the ignition side of things. have a well setup carb with good mapped ignition (not just timing swung about with weights on a distributor) and it will be pretty good though. look at bikes, they have been using carbs (with mapped ignition) on most bikes up until the last couple of years, and have only had to change for emmissions reasons, not driveability (which many riders seem to think is better with carbs)

but don't bother reading that, as it won't be at all helpful as i have no real life EXPERIENCE of big power carb cars

Stavros

What I meant was comments that are FACT and not the usual internet bullshit heresay and quotes from books/mags/tuners with no proof.

The bikes on mapped ign is a VERY good point, nice work sir

dunketh

If you need a decent argument against EFI look at any late mini cooper.

Its all in the setup as has been said. In my experience with SU carbs you can get them pretty much spot on thanks to their design, using a metering needle that can be filed down by finite amounts to get fuelling 100% spot-on throughout the rev range.
I imagine this is not as easy with a normal carb as you only have so many fixed jets to play with.

Potentially fuel injection is better, but that depends on how mappable the system is. Standard 'factory fit' stuff is 'one size fits all' and hence a bit rubbish.
Megasquirt and similar systems can be setup in minute detail and can monitor any number of parameters.
Again from A series experience (hardly big power) the list in order of inclining preference goes: Standard EFI, Carbs, Fully mappable systems.

foreigneRS

a carb will use more fuel than EFI though, as you cannot shut off the fuel delivery completely under deceleration. and it is much more difficult to accurately meter the fuel during warm up, but that is of little concern to making good power or driveability (once warmed up).

i would guess that these days EFI is cheaper than a well set up carb though. it's far easier to change a few values in a laptop than mess about changing jets and stuff

Stavros

Regarding prices, its swings and roundabouts I reckon. EFI once all added up is generally a fair bit more to buy, and setting up, well I dunno, cost of good mapping wont be any cheaper than cost of a decent setting up of the carb(s).

Chip

iTrader: (3)

How do you want people to relay their experience, based on what it drove like, or based on what a wideband said?

Ive driven turbo carb cars that have driven perfectly fine, no problems at all that you would notice from driving, no flat spots, no loss of power etc.
However, stick a wideband up them and you see that altough "acceptable" they arent "optimal" like with a fuel injected setup.

Carbs are crude, you cannot get the same detail into the fuelling that you can with FI, but that doesnt mean they cant still "drive ok" and make massive numbers, cause they can and frequently do, both for NA and for FI

Markb_s1

what he said basically. i do have some experience with carbs runnning decent power NA engines and would say that if you bin the dizzy and get proper ignition on there then they can be very good. Throttle bodies when properly set up will give better economy and normally also slightly better low down drivability though.

Chip

iTrader: (3)

Mechanical distributors versus mappable ignition isnt too dissimilar an argument IMHO, its perfectly possible to get reasonable results on a mechanical distributor if you know what you are doing and make your own springs and stops etc and have a vacuum advance that you can tailor, again ive owned/driven setups where it has worked well, although i dont for a second doubt it would have still been better on mappable, just like the fuelling would be.

steviep

Don't know how relevant it is to what you're trying to find out Steve but my brother runs 2 4 barrel Holleys on his drag car and is nudging 850bhp. Will be no use at all if you're just talking forced induction but if there's anything you need to know I can find out.

Ade

My Capri is great to drive, not really big power but 150BHP from 2.0 pinto is not bad compared to other cars with the same engine.

Pretty flat low down (mega long duration rally cam too) but still easy enoug to drive around town and plenty fun over 3000RPM. Used to do 30k a year in it!
Just on a maxed out single 38 DGAS now, 45's soon though which should give another 20-30 brake.

Oh yeah it idles at 1500RPM which would probably not be needed with EFi, or even just mapped ignition.... and its thirsty, 15MPG usually, single figures on track

Stavros

Chip- As you say, AFRs will often not be optimal, but acceptable is ok, and emissions/economy wasnt a consideration.
My old GTT was like that, technically it was rich everywhere, but the reality was it drove lovely.

Basically although getting the same peak power is never a problem, it was if it drives perfectly fine which was the thing.
Ie itd be no good if running a carb would give noticably less low down power, boost threshold, part throttle drivability, etc etc.

Chip

iTrader: (3)

It depends on the carb setups used, on the SU carbs used on metro turbos for example, its surprising quite how accurate you can get it, but ONLY if you understand how to viscosity tune the oil in the damper, and machine the needle (please god dont actually anyone file it like mentioned above, im sure he wasnt speaking literally, as thats the biggest cause of bad runing SU engines ever, as it doesnt give an even profile and then when the needle rotates it all changes, lol) EFI is far easier to get right, just like mappable ignition is, but its perfectly possible to get decent driveability without either, HOWEVER the more BHP per litre you are trying to cram out of it, the harder it becomes as the more resolution you need, if you are trying to get a streetable 350bhp per litre out of an engine like is common in competitive evo's now, its just not going to be possible on carbs without feeeling the compromise, like its not going to be possible on a mechanical distributor without doing so, although Im guilty there for the first time in this thread of not talking from EXPERIENCE, as ive never made a carbed 800bhp evo of course, lol.

Garage19

I have run blow through CV carbs on quite a few turbo bikes. I can tune them so that they are very drive-able but.......

If i didn't have the carbs bolted on the bike in the first place and had to decide from scratch i would go EFI every time. Sooo much easier to set up.

And with an EFI system be doable for under Ł300 DIY it is cheaper than new carbs.

Stavros

Thats not direct experience Chip, but its reality at least, was just worried about people talking utter arse they heard.

Ive seen carb fed turbo and s/c cars in the states, countless amounts of them, pushing 300bhp per litre with claimed great drivability tho, but with big capacity I doubt its a big issue.

Chip

iTrader: (3)

Well to a certain extent I guess that at 10 litres even if its WAY down on off boost torque, you are still going to make it to the shops and back without stalling.