That is very interesting. Can I ask how long your stacks and complete runner lengths are? See post 150 for correlation btw intake runner length and harmonics.

Not sure what on the complete runner length (I’m using Triumph Speed Triple throttle bodies on PMO risers with Al’s mating plate).

The velocity stacks are ~5.25” from top of the stack to the top of the top lip on the Triumph throttle body. They are very tall.


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Mine are 4.5''. Should be very interesting when I get it on a dyno.

Good info here: Blog - Emerald Adjustable Length Intake Trumpet Development

Velocity stacks. :D

http://forums.pelicanparts.com/uploa...1511623263.jpg

Still running strong!

http://i35.photobucket.com/albums/d1...psehnr9vcr.jpg

http://i35.photobucket.com/albums/d1...psy8lpbsk1.jpg

http://i35.photobucket.com/albums/d1...psxen85aqt.jpg

http://i35.photobucket.com/albums/d1...psvqfgvuez.jpg

How does the bar mount? The flush look, looks great :)

Which bar?

Bumper = Bar in Australia ;)

I took my car for the first drive yesterday. My build is: 3.2SS single plug 9.3CR, DC20 cams (113 lobe), 43mm Triumph ITB's (thanks Clay!), Megasquirt EFI, classic retrofit CDI, straight headers and Dansk 2 out.

I've balanced the ITB (maybe it needs a little more), set timing and a very standard first AFR tune.
OMG she pulls like a train!!! And the roar from the stacks is amazing!

I few questions: Even though I have an extra spring on the linkage, I have a bit trouble getting all the way back to idle. I can manually press it back. Any good ideas?

And: I noticed during my short frist drive, that MAP seems significantly higher with ITB's than with plenum? It's maybe a stupid question but: Is the value in tunerstudio (20 - 100) a percentage or real value?

I'm working on the lower rpm's as I get backfires trough the ITB's and the throttle response is not too good. It pulls VERY hard from 4000-7000.

Short video:

https://youtu.be/9dfqiRvUgJ0

tuning
 

Nux,
Greetings and excellent work on your part. You may need more return spring, but, one thing I've found with the Speed Triples is that you may need to loosen the two screws that fasten the butterflies to the shaft and then let the spring force close the butterflies. this tends to help to self-center the butterflies in the ITB to minimize any rubbing/friction caused by them not being perfectly centered in the throttle body.

Make sure you have the ITBs balanced well. Follow Clay's guide to getting them balanced. The next thing is to datalog and review what is happening to your AFRs ...backfires thru the stacks typically indicate,,unbalanced ITBs, bad timing and/or lean conditions...while popping thru thru the exhaust is often a rich condition.
MAP readings are in kPa and not in % and can be higher with ITBs than common plenum.

regards,
al

Thanks Al - I'll try that. I did set the ITB's up according to Clay's guide, and it runs quite well. It seems that MAP is way over 100, which may in part explain why my tune is somewhat off. At idle I'm seing MAP 40-60, whereas with plenum it was more like 20-40. So my initial AFR ratios are currently not correct.

If you become terribly frustrated with MAP, I have seen (not with 911 yet) ITBs tuned entirely by throttle position sensor as well.

del

I suspect that your MAP calibration is incorrect. 40-60 at idle is ok, but wide open throttle (low/no vacuum) with normally aspirated engines (no turbo) would only be at local atmosphere or so...i.E. 100kPa.. have you been data-logging to review the areas where you are going lean/rich?

I've had excellent results using Speed Density (MAP) tuning, but, as has been mentioned, you can try alternative methods of tuning. I've also had excellent results with Alpha-N (TPS) tuning. There is also the ITB method that is a blend of MAP & TPS. (MAP has better resolution at low RPMs and TPS better at higher RPMs)

regards,a
l

regards,
al

I hope to stay with MAP for now. The engine responds very well at WOT. I'm still using Tony's Bitz kit with MS1, but I have a MS2 on the shelf and may change this winter and ad ignition as well.

No data logging yet, this was just a quick spin of a few miles to see how it felt. I'll make sure to log next time.

Hi nux,
I had similar issues with the return to idle. I ended up having to adjust the linkages so that they had just a little bit of dead pedal looseness. Just a touch. Also make sure that all the joints are free to moveand the hardware isn't too tight.

Some general thoughts on tuning ITBs -
The map signal will be **** compared to common plenum. I tried to tune my maps off the map values but found much more success going off throttle % instead. I did this for timing and VE in the end and you couldn't pay me to go back to MAP based.

As Al said, if you get some pops thru the intakes when you open the throttles you probably need more Accel Enrichment. My itb setup required much more enrichment for tip in
and throttle stabs than others running Carrera intake manifolds needed.
Ive heard that many tuners can listen to the way a motor revs in neutral and can tell how good the enrichment is. If it's good, it'll rev up very fast and smoothly when you stab the pedal fast. No pops, no missing. With a 3.2 ss with ITBs it should rev quickly! Mine is close to my cb900f now that I've spent hours fine tuning it. The 2.7L crank and rods don't hurt either!

nice - thanks! How much accel enrichment do you have now ? This is my current setup:
http://forums.pelicanparts.com/uploa...1534179525.png

So you are basing the maps only on throttle position then (alpha-n)? If so, are you happy with engine behavior at small throttle openings?

I'm not familiar with that software. I notice at cold start and tip in (wall wetting), 911s like a ton more fuel.

After a bit of reading, I'm now pretty sure that the popping on accelleration is due to lack of accel enrichment. Makes perfectly sense that the ITB's let in a lot more air then plenum does when opening up the throttle.