6 replies to this topic

[LC-GTR-1969]

Gday everyone,

 

I have a few questions relating to my 202... 

 

I currently am running 45dcoe webers with 9 port head, webers are running 40mm chokes... Running pump 98 fuel.

 

Basically I have a few queries...

 

1) It was dyno tuned and made best power at the wheels running a 165 main jet, 200 air correctors. However AFR was about 11.8:1. We did not have much time to test, as it was moresoe on the dyno to help diagnose a fault (which is now solved)... We set the timing for max power- noticed that the engine was running quite rich (11.2:1) and so we changed the air corrector from the 165 that was in it, to 200s. The engine did not gain any extra power- in fact it dropped 1hp by doing so... The AFR was still rich though...

 

I presume that the engine is wanting a richer mix due to detonation. The spark timing is set at 27 degrees as this is where it made the most power- it also 'feels' very crisp at 27 degrees. 

 

I am thinking that the plugs could be too hot, pushing the detonation- I am currently running BP6ES ngk. What are others running with the more 'wild' 202's?

 

2) I decided to whack some 160 mains in to see whether the seat of my pants feel was quicker, and it certainly was... Engine definitely pulled harder with one step smaller mains, however in third gear at about 6k it started to pink (from what I could tell)... So I brought it home to re-assess...

 

What I did notice, however, is that the engine pulled really (really) hard in the powerband with the 160 mains, however the progression was crap from about 2500rpm to 4000rpm. This is basically where the engine is out of the cam but progressing onto the mains (from what I understand). The progression is much, much better running the 165 mains. 

 

I do not quite understand why the progression is effected so much at 2500-4000rpm just by running 1 step smaller mains... Do you think it is that because of the 40mm chokes, that the engine needs a bigger jet to pull across fuel due to the relatively weak signal that the carbs would have? Would I be better putting in even bigger Air correctors ( say 220) and keeping the 165 main jet?

 

I have considered dropping the choke size, but for the moment I want to retain the 40mm chokes.

 

Any help would be much appreciated. I know that i really should invest in more dyno time but cash is gooone (haha) so self-tune is my friend right now lol...

[71Ranger]

Hi,

 

Im not a weber guy so I can't  help you, but there is a heap of info on this forum

 

Go to this link

 

http://www.google.com/advanced_search

 

in the all these words box put in weber tuning

 

in the site or domain put in http://www.gmh-torana.com.au/forums/

 

Loads of good links

 

Cheers Brian

[jd lj]

The air corrector size will only make a difference at the upper end of the rpm's, so they will have no impact on the progression.
Richer idle jets and main jets may fill in the lean spot during progression but may be too rich during their own circuit.
What size auxiliary ventruis are you running? If you're using 5.0's you could try using 4.5's to get the mains to engage earlier.

My opinion is that even though 40mm chokes will give outstanding performance if you keep the revs up but the bottom end of the revs isn't going to be good. 36mm chokes are more suitable for a street car. It depends on what you're using the car for though and what you want to get out of it.

What series are your carbs, 9's, 13's, 152 G's?

[LC-GTR-1969]

The air corrector size will only make a difference at the upper end of the rpm's, so they will have no impact on the progression. 
Richer idle jets and main jets may fill in the lean spot during progression but may be too rich during their own circuit.
What size auxiliary ventruis are you running? If you're using 5.0's you could try using 4.5's to get the mains to engage earlier.

My opinion is that even though 40mm chokes will give outstanding performance if you keep the revs up but the bottom end of the revs isn't going to be good. 36mm chokes are more suitable for a street car. It depends on what you're using the car for though and what you want to get out of it.

What series are your carbs, 9's, 13's, 152 G's?

 

Thanks for you reply...

 

I would rather stick with the 40mm chokes for the moment- I know I am sacrificing driveability, but at the moment I am working on the car for purely max performance (1/4 mile).

 

From memory the carbs are 152gs.

 

The 'issue' with progression exists when using the 160 main jet as opposed to the 165 main jet. As you mentioned, the air corrector had no effect on progression. 

 

What do you think regarding plug heat range? 

[jd lj]

I know other people are using the same plugs with good results.

Do you know what size the auxiliaries are?

I assume your problem with the progression is a flat spot /hesitation. The richer main jets would be compensating for the leanness during progression but is probably too rich when working in its own circuit. If it's too rich then the power will drop off. An AFR of 12.5 will give maximum power.

[LC-GTR-1969]

Excellent point- I had not considered that one or more of the jets may not be sized correctly... I was surprised at the difference in the progression myself... It was a very conservative drop/ one step smaller which I did not at all expect to influence the bottom end progression as much as it did..

 

I will try to size up the jets and check them all...

 

Thanks again for all the advice everyone, much appreciated.

Something doesn't add up - the flow difference between 160 and 165 main jets is only something like 2.5% (Weber jets are sized by "equivalent diameter"). There's no way that such a tiny change should make such a noticeable difference by the seat of the pants. Makes me think at least one set of jets isn't what it appears to be.

 

For plugs I'd be running 7s, though I doubt very much the 6s would be getting hot enough to cause problems.