IDA experiences and advice please for jetting purposes.

[Shane Noone]

Hey Guys,

Ok here is my issue with the jetting. I have a set of 51mm IDA's - they were set up with 44mm venturi / chokes and then jetted with 180 mains and 170 airs and F7 tubes.
The idle jet is 60. This was all done on a Stuska dyno and found to give the best overall results keeping the AFR around between 12.8 and 13.0

However since the motor has been fitted to the car and ET's are nowhere near what was expected I have just had the car checked on a rolling road ( dyno dynamics ) and the power is down between 15 - 20 hp and the AFR is too rich for most of the range going from 10 around 4k risingslowly to 12.8 at 5500 then going rich to 12.5 around 6k then the power falls away rapidly as the AFR goes rich to 11.6 by 6500.

I need to get back to the rolling road with a selection of jets and maybe tubes to get this sorted. I am thinking I can get the airs drilled out to lean the top and maybe buy some small mains like 165 - 170 ? to drill out of need to.  Don't know whether to stick with the F7 tubes or switch   Don't know whether to buy smaller idles or stick with the 60.

Appreciate you feedback from tuning experience on IDA's guys.

Thanks, Shane.

[Peter]

I don't know much about carbs,
but if its fat in the higher rpm's, i think you should change the main air correctors? so leaner..
or maybe emulsion tubes that lean out the mixture at high rpm's

the idles shouldn't matter, as these are not in action when dr

[Peter]

...when dragracing...

Please correct me if I am wrong IDA guru's

[Berger]

180 mains and 170 airs "sounds" wrong. I guess air should be 195-210 with 180 main, if anything else is normal. But some more info about the engine might help, bore/stroke combo, valves, compression, exhaust dia etc.

[richie]

180 mains and 170 airs "sounds" wrong. I guess air should be 195-210 with 180 main, if anything else is normal. But some more info about the engine might help, bore/stroke combo, valves, compression, exhaust dia etc.

Agreed,170 air is odd for that main,I would get 170 and 175 mains,along with 200,205 & 210 airs,start with the 175 with a 200 air and see how that runs,the weather is so changable at the moment you proberly are better jetting it at the track using mph as your guide


cheers richie 

[Shane Noone]

180 mains and 170 airs "sounds" wrong. I guess air should be 195-210 with 180 main, if anything else is normal. But some more info about the engine might help, bore/stroke combo, valves, compression, exhaust dia etc.

Agreed,170 air is odd for that main,I would get 170 and 175 mains,along with 200,205 & 210 airs,start with the 175 with a 200 air and see how that runs,the weather is so changable at the moment you proberly are better jetting it at the track using mph as your guide


cheers richie 

Hi Richie and Berger

Thanks for that feedback guys. I know different engine builders tune carbs in different ways and some like to use this "square" jetting with large chokes / venturi.... Berger you asked for more engine spec details. Sure it's on Comp Eliminators witha  46mm intake valve / 38 mm exhaust and CR is 11.2:1 cam is FK87 with Pauter 1.5 rollers. Exhaust is A1 lowdown 1.75 racing header. 2332cc. That enough info ?

Thanks.

[Udo]

I agree with richie , but would go back to the chassis dyno to see what the engine likes

Udo

[Shane Noone]

I agree with richie , but would go back to the chassis dyno to see what the engine likes

Udo

Thanks Udo. Yes, I am going back to the chassis dyno with a selection of jets based on you guys thoughts that can be drilled to the right sizes.

[dragvw2180]

 I am no guru but I would bring some smaller venturies  ( 40, 42), may pick up a little airspeed . Mike McCarthy

[Shane Noone]

I am no guru but I would bring some smaller venturies  ( 40, 42), may pick up a little airspeed . Mike McCarthy

Thanks Mike, Didn't have any smaller than the 44's so worked with them but bet your right about the airspeed pickup. However as the guy that built the motor and originally dyno's on stuska setup tried venturi from 42 to 46 and reported gains in hp with every increase. We decided to start with the 44's and re-jet.

So final results were 44 venturi, 175 main, F2 emulsion tube and 180 air corrector. Idle jets were fine at 60. Final AFR at peak power was 12.8 and much better throughout the range with this jetting than previous. Achieved 212 bhp at the flywheel with the belt attached which was much closer to the original stuska dyno figs of 215 and a good increase from the baseline on the day of 201. The biggest factor that increased power from the re-jetting was the switch of emulsion tubes from F7 to F2. We were amazed that single change increased power straight away by around 6-7 hp with the old main and air jets.

Also back to back tested my A1 drk muffler versus a standard large flange Bugpack stinger so about mid length and the muffler performed better.


Cheers guys for all your thougts and suggestions.

Shane.

[leec]

Hi Shane,

Sounds like you have made some real progress there. Who do you use for rolling road?

I'm still running 40 vents, planning on going to 42's but doing back to back comparisons.

Do you race with the belt on then?

Lee

[Shane Noone]

Hi Shane,

Sounds like you have made some real progress there. Who do you use for rolling road?

I'm still running 40 vents, planning on going to 42's but doing back to back comparisons.

Do you race with the belt on then?

Lee

Hi Lee,


It's really a case of trying to get back to the original figures from JMR's dyno session. As you know after installing the motor in my car and getting some passes in something was amiss as the ET's were nowhere near what I expected with the power I was supposed to have.....I have previously achieved very close ET's with my old 2276 that was supposedly 25 bhp less compared to my current 2332.

So I took the car to the rollers and with the jetting exactly as it left JMR, it was very rich and only making 201 bhp flywheel estimate with belt on and cooling and muffler. This combo at JMR but obviously out of the car and on his Stuska made 215 bhp with the belt and muffler. So had been running at 14 bhp less power.

Yes, I race with the belt on only because to me personally it feels like cheating if you pull the belt off on a motor / car you call a street car. Ie you wouldn't pull up to the traffic lights to race a Porsche then jump out and pull your belt off.....if you see what I mean.

Like I say it's a personal thing. I know most people will remove the belt and free up a good deal more horsepwoer that way. Mine is supposed to make 228 bhp when dyno'd at JMR without the belt.

Lee, if your only racing on 40mm chokes there could be more power to come. Bigger is not always better though as you probably realise and every motor has it's own peculiar set of preferences. I have ports that are really too big and a 46mm inlet valve. A 40mm choke might be just the ticket on smaller port heads with a 42mm inlet valve for example.

Sometimes I use a rolling road in Uxbridge called Power Engineering. The tuner there is Iain Ball.

This last session was a private hire of a facility through a friend and fellow racer and very experienced rolling road tuner as he has worked at several well known in the South East and drag races albeit in a 10 second subaru powered fiesta that will most likely soon be in the 9's if the transmission will hold out 

[Gary Justus]

One thing I didn't see was head configuration....But~~210 on the airs.

[richie]

Shane,thanks for posting the results,I have never tried messing with the emulsion tubes,will give it a try next chance I get,still suprised by the closeness of the main and air size but whatever works


cheers richie

[dannyboy]

good to hear you got more power shane all you have to do now is man up and take the fan belt off 

[H67bug]

I am no guru but I would bring some smaller venturies  ( 40, 42), may pick up a little airspeed . Mike


The biggest factor that increased power from the re-jetting was the switch of emulsion tubes from F7 to F2. We were amazed that single change increased power straight away by around 6-
Shane.

Mine did the same