1.9 Gti On 40's

[taffycrook 2]

longun,

 

If you ignore the actual power outputs for now. The two graphs show how much the 40's strangle the engine in the upper rev range.

The power seems to be down on what was expected but this does not alter the fact that the 40's flow less than the 45's and in this test this reduces performance.

 

The fact your engine made 6 bhp more with 40's than this one means nothing. It certainly does not mean that there is something wrong with the carbs or the way they were set up.

If you consider a 1.9 flows around 1.19 times the air of a similar 1.6.

max power was made at 5370 rpm in this test which would mean a 1.6 would be at 6400 rpm. Not far off what yours was at similar power outputs.

considering the tests were done on different rollers this shows that the set up isnt performing different to yours.............is your set up wrong too?

[taffycrook 2]

@taffy: I think the jetting of your 40s carbs was just plain wrong.

 

Mine had 145bhp on the rollers, was setup great and flew to 6750 without hesitation.

 

Now you've put 45s on just proves one thing: they have the right jetting for this engine.

 

Hilgie both sets of carbs were set up to similar AFR's using a wide band lambda the 40's were further trimmed on the rollers to try and fingd the missing power.

The jetting is pretty close to ideal for the engine, the 45's have not been altered from the basic set up.

[Longun 1]

longun,

 

If you ignore the actual power outputs for now. The two graphs show how much the 40's strangle the engine in the upper rev range.

The power seems to be down on what was expected but this does not alter the fact that the 40's flow less than the 45's and in this test this reduces performance.

 

The fact your engine made 6 bhp more with 40's than this one means nothing. It certainly does not mean that there is something wrong with the carbs or the way they were set up.

If you consider a 1.9 flows around 1.19 times the air of a similar 1.6.

max power was made at 5370 rpm in this test which would mean a 1.6 would be at 6400 rpm. Not far off what yours was at similar power outputs.

considering the tests were done on different rollers this shows that the set up isnt performing different to yours.............is your set up wrong too?

 

 

No need to be so defensive. I don't pretend to know much about engines and I was not starting a I've got more power than you argument, all I wanted get get across was the power on my car is higher up the rev range, I didn't know the gear box made such a difference. I'll just go with 40's work beter on 1.6 engines then because they suit the gearbox and flow rate.

Edited April 23, 2007 by Longun

[taffycrook 2]

I don't mean to come across as defensive, I am just trying to point out in this test that the 40's came out 2nd best.

Must be something wrong with the results as they dont match what people were expecting is the typical reaction.

My post has nothing to do with the gearbox, it is about capacity the 1.9 is simply bigger than the 1.6 therefore taken simply it needs more air.

The heads are the same so in the interest of brievity we can say they flow similar quanities of air, so a 1.9 is 1.19 times bigger so flows that much more at any given rpm.

Not true as the flow rates depend on soooooo many things but it can be used as a guide therefore the set up I used performed very close to your 40's.

The point of the thread is to open debate I have posted a set of results, they show that 40's can be used on a 1.9 but in this case they are holding it back in the upper rev range.

[mfield 20]

The point of the thread is to open debate I have posted a set of results, they show that 40's can be used on a 1.9 but in this case they are holding it back in the upper rev range.

 

I found the above statement to be true when testing 40's and 45's back to back. My 40's had 30mm chokes which gave a nice load of low down power but it lacked flow badly when hitting 5.5k+. When 45's were fitted with 36mm chokes the 50-70mph time was about 1 possibly 2 secs slower (in fifth on a 1.9 box), the top end however came alive and pulled past 7k with ease. The top speed went from about 120-125 to 130-135. I must add i had a tuned head and longer duration cam (no extra lift though). I also tried 40mm chokes in the 45's which killed all low down power, i presume due to slow air speed . It gave a small amount more on the top end but not much, once again i presume the head didn't flow enough to take advatage of the increase. I always wanted to try and get some 34mm chokes made to go in the 45's because i felt that the maxium flow would be ample for a 1.9 and still have a fast pickup low down.

 

Please don't flame me people for being honest with what ive tried out, im not a pro and never will be so there is a strong chance there's people out that can set 40's up better than i can do 45's

[christopher 5 1 Cars]

Am I missing something here? I'm hearing a lot about 40's vs 45's but what about the choke sizes.

 

Surely the only possible comparison can he drawn from say using a 40 with 36mm chokes and a 45 with 36mm chokes.

 

I can't see how any other comparison can be valid when we are talking about different choke sizes.

 

Does a 45 with 36mm chokes actually flow more then a 40 with 36mm chokes?

 

 

(I'm actually using a 34mm choke in my 1294cc engine)

Edited April 24, 2007 by christopher

[taffycrook 2]

Does a 45 with 36mm chokes actually flow more then a 40 with 36mm chokes?

(I'm actually using a 34mm choke in my 1294cc engine)

 

YES!

Edited April 24, 2007 by taffycrook

[Sam 4]

I always wondered if 45s would have been better on my TU 8v. I ran 36mm chokes in 40s and it never seemed to rev well. The 36mm chokes have very marginal flow over 34mm ones in a DCOE40.

 

I went through it all with carbs