MPG with throttle bodies ? Your experiences

Fuel atomisation, uniformity of fuel vapour achieved within cylinder, correct or ideal fuel/air ratio (AFR), uniformity of AFR to each cylinder, and uniformity of volume of air delivered to each cylinder, ignition timing. That's assuming all other factors equal, eg same weight of car, gearing, rpm, speed, etc.

 

No doubt Toyotec can list a few more I've missed!!!

 

Ah yes, good point. That would be a very good reason why stoppy-starty airflow is bad.

 

wow what a productive evening - not only have I lie about my fuel consumption, I've also been told I don't know how to 'ballance' carbs up and that I don't understand injection! spot on!

 

if you understood injection properly then why did you swap to carbs? in no way, shape or form are they better than injection.

worse on fuel consumption, less reliable, harder to set up and will give no apretiable powergain over an equivelant injection setup... oh and if you manage to get the fueling right for peak power it'll be well out across the rest of the rev range...

also bear in mind there have been people on here running nearly 200bhp on k-jet (wasn't it hotgolf???) which means that its up to the job regardless of how modified or not your engine is... unless your going for over 200bhp in which case for not much more money you could have throttlebodies and stand alone management like mega squirt. if you have the money to build a 200bhp+ motor then you can aford to manage it right.

not saying you're telling porkies about the fuel consumption etc or that you dont know how to set them up its just that from my expieriences with carbs I cant really see how you've achieved it.

will admit however that from what I've seen and read of bike carbs they are normally far better designed than carbs for cars as injection has only been a recent thing for bikes.

 

I think this is going to be my last post on this thread as I think this is getting a bit out of hand. We could all argue til the end of time about the pro's and con's of carbs vs injection.

Theres been some very valid interesting points made particularly coming from pete and paul, for example I'd never even thought about carbs releasing fuel into the inlets even when the valves are actually closed.

I run a modern fuel injected car as a daily and my carbed mk1 for a bit of fun so the best of both worlds perhaps? Only the audi has cost me 600 in 6 months in sensors and coilpacks whereas the golf has cost me circa 20 in idle jets.

btw hotgolf created a high reving 2.1 16v mk1 (my fav mk1) which produced 209bhp.............. running twin 45 webers.

 

for what its worth, i run a mk2 9a 16v with bike carbs. been on a run to sleaford and back this weekend. 30 of petrol got me 200 miles of 50/60 mph A roads and 30 mph through all the towns. there were a few 'spirited' moments and also alot of stop start traffic over the weekend. if some one wants to work out the mpg i think it would give a good realistic average??

for reference car is running mappable ignition and makes 170 bhp and 160 lb-ft.

 

Assuming 1/litre and accepting the inaccuracy in the amount of petrol added (brim to brim?) that's 30mpg. Based on previous measurements brim-brim I've achieved around 35-36mpg in my Mk1 2.0 16V (K-jet injection) on that type of journey, although you'd also need to add in that its lighter. Its about the same power output. If I try to drive economically on a long run I can achieve 40+mpg, and if its a track day or race weekend or something, can drop to 10-15mpg although often there will be a lot of warming up the engine stationery, waiting, then do a 1/4 mile run, then queuing, etc. so its really unfair to compare like that.

 

thanks for working that out Paul. i know the number cant be exact but it does give a ruff idea what this set up will achieve. I know mine will aslo do more on the motorway at a steady 70 mph but thought the example above was a bit more 'real world'. i also know that when you give it the beans it does drop drasticly!!

 

Seems that someone in this thread has a real issue with carbs think they need to get out and do abit more research, there are reasons carbs are still popular and its not down to lack on knowledge with injection.

gunit I remember your thread when you had the carbs set up, is your engine just a standard 9a with a KR head and cams? The torque figure is great and I doubt it could be achieved on that engine with kjet. My main reason for swaping to carbs is to hope to improve my torque figure and curve, my engine was RR prior to the change so once back together I can see what gains/losses the carbs have given me.

 

Hotgolfs mk1 was on carbs true, the mk2 he had prior to the mk1 ran Kjet and was running somewhere near the 180bhp mark, however he did say tthat it was struggling for fuel at the top end. it was a 2.1 16v like the mk1

personally i have never heard anyone rave about high mpg figures from carbs, but high power is a different story.

 

2dubnick, i'd be intrested in seeing what your carbs do over standard i never had chance for the comparrison on mine as it was an 1.8 8v originaly.

as for my engin, its all standard exept the cams which are piper 274/276.

 

9A, stage 2 head, 4 branch
R1 carbs, 2.1 mains.

can do 30mpg on a run nicely.
is around half when nailing it.

 

I dont see why this is not obtainable if they are set up correctly on a decent lump...

 

Small block uses less fuel right?

 

I had a 9A with ported head, 4 branch, running R1 carbs and regularly got 25mpg.

They can be quite economical (Compared to Webbers) if they have been set up correctly

 

R1 or bike carbs in general?

 

bike carbs.

 

The carbs need to be set up properly and shouldn't get you below 20mpg driving on the road... There are people that swear bike carbs can be set up to achieve above 30mpg all the time.