some of you might have seen my recent dyno post.

just a base run yesterday, no tuning. spoke to the engine builder and another tuner buddy today and lots of discussion aroun jets

here is the dyno print ; 117.4kw (157.4hp) and 166.4nm torque



the setup is as follows :

s5tii motor (ex turbo), street port, full rb system, 48 IDA

now the carb is jetted as follows :

200 main, 150 air, F11 tube
36mm choke

our collective view is that the 36mm choke is too small and we are going to up this to 38mm

secondly, the 200 main is too large and 150 air too small, so going to reduce main to say 160 and increase air to say 190

will post the dyno run once we've done this....a week or two

but in the interim, can some of you please offer some comments on (1) the current jetting and (2) our intended plan of action

given the bucks i've laid into this i'm not too unhappy about 157hp at the wheels but not ecstatic either. Sure, its a trade off between driveability, etc hence going for a street port. I'd be quite happy if we can get 185hp out of this baby in its current form. I think 200rwhp is going to be a long shot from the 157 i'm at now.

thanks guys

 

I do know you need at least 40mm chokes. 36mm is choking that poor engine to death. Custom 41's may be good...some around here even run 42's (Wackyracer the guru.)
I have a similar setup (carb, porting wise) and run 210 main, 180 airs with 40mm chokes. 70 idles. Still needs some fine tuning, but is not too far off. I may go 210/190 or 215/195...rotaries do like slightly bigger air jets to make it a bit more crisp. Timing is 20L/10T at 4000rpm. NGK B9EGV or stocker 4 prong plugs.

 

I think your on the right track. Looks to me like your porting is conservative. The racers around here are putting down near or in the low 200 rwhp with the 12a. That is with 38mm venturies. Also figure none of these IDA's are as they came from weber. The intake of choice is the Mazdacomp. The others need porting/polishing.

FWIW I put down 153 rwhp with a DCOE weber carb. As best as I can recall, mains 195, ac's 165, with F11's.

Also search for some old threads. I think I posted on some of them.

 

yep, you're right, the porting is conservative

you see, when I started out with this project the dominant issue for me was driveability. Power was of secondary concern.

I did not want something idling at 1700rpm, only hitting the power band from 5000rpm to 9000rpm but then I could show a dyno sheet showing 240rwhp

So hence we went with a mild street port, more for driveability and reliability point of view.

So yeah...this is what has come out. quite respectable. But lets see what happens when the carb is rejetted.

 

here are the racing beat guidelines for jetting. maybe we should archive this ?

 

Unfortunately, those jettings are for track cars. For street, you will LOOSE!!! You have to go with at least a 42 venturies for a large streetport.

 

wackyracer, how much hp you think i'm losing with only 36mm venturi's ?

 

I cant tell you but with that small of venturies, you will gain lots of low-end but sucky on mid-to-top end. In other words, you are choking it down to bare minimum. Since I live near a freeway entrance that at least 1 mile long, Im able to do test runs.

There are no two engines that are alike so dont be afraid to try different jettings and be sure to log it. I recommend starting it with 42 venturies, 150 air and 210 main. idle jet is 70+. Also, junk the carb's built-in filter, mod the fuel inlet and use 300 needle/seat or grose jet. Thats in addition to having an unrestrictive 2.25 dual or 2.5 single exhaust.

 

dp

 

will keep you posted of results

we will def start by first opening up that chokes.

 

Depending on which side of carb you have, OMP inlet located @ fuel bowl & modded fuel inlet



Modded fuel bowl (an extra ounce of gas)


OMP lines (GSL-SE reduced to 2 lines)

 

wackyracer is there a flotbowl adjustment on these carbs??

 

Unlike holleys, there isnt except for float tabs. If its a new float, no need to adjust it unless its flooding. And when it floods, check the needle and seat for debris.

 

buy cb preformance weber handbook full breakdowns on the carb and some tuning info (but applies to vw's). it is money well spent and only about $15

 

http://www.aircooled.net/gnrlsite/re...idarebuild.htm

http://www.piercemanifolds.com/48IDA.pdf
http://www.piercemanifolds.com/48IDApl.pdf


http://www.vwtrendsweb.com/tech/0308...ce_weber_carb/

 

Glad this got dragged up, as I'll be fighting this battle myself soon. I'm thinking the original poster's low power numbers are more to do with his low compression (ex- Tii) motor?

 

yeah good point re lower comp rotors. speaking to different tuners they undecided about how much extra power it will give, but they all agree there will be extra torque. The turbo rotors i'm currently using are the 9.0 comp ones. the s5 n/a luckily are the same weights so swapping shouldn't be a problem and their comps are 9.7

apologies for not providing feedback on this, but we upped the chokes to 38, upped the airs to 160 and downed the main to 190. Then got 125kw on the wheels (168hp) which is a 7% increase over the previous readings. Again, not shooting the lights out but quite a reasonable number anyways.

here is the comparative chart. numbers pretty even up until around 5500rpm onwards where the extra kicked in

 

There's nothing low about those numbers at all. Even with 38mm chokes you're probably losing a bit on the top end. Also remember that Dyno results vary. Americans are used to their Dynojets which read significantly higher.