Change of ITB leads to change of engine characteristics?

[Nux]

Some of you may have noticed the new JSR ITB project. It's been a long road, but we're finally ready with the first few kits.

These are Elliptical roller barrel ITBs, which means that there are absolutely zero obstructions in the air flow at WOT. Its just a straight tube directly to the intake valve.

Test Engine is:

Stock 3.0L short block.
Wössner 10.5 pistons
Twin plug dizzy
Cams: DC 24/21, 114LS (was actually made for plenum - not ITBs).
Heads ported to 42mm.
SSI and Dansk two out.
Stock valve train.


The first real engine test occurred a month ago. We were stressed for time unfortunately and I found out that we had an issue with a faulty lamda probe which caused a lot of trouble with my mapping. In the end the engine ran AFR 11-11.5 at WOT which of course is far too rich. Still - we gained 10hp compared to the old Triumph ITB setup, but lost some torque (probably due to the very rich condition).

This will be corrected next time.

My questions is: with the old ITBs peak HP was at 6300rpm. The only thing we changed was the ITBs (and the tune of course) and we now have max HP at 7100rpm?!?! Same dyno, same temperature, same engine.

What may be the cause? Is that the consequence of better air flow alone really (these flow 20% better than the old ITBs)? Or does the change in runner length account as well? Also the change from unequal runner length to exactly the same may account as well as a change of the injector placement (lower placement in the new JSR).

what are your thoughts on this?

[Mixed76]

Runner length and diameter affect intake resonance and air velocity vs rpm, should change the shape of the HP and torque curves.

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[dannobee]

Yup, the length of the intake tract from the back of the valve to the top of the stack length and the diameter of the tubes change everything about where the engine will peak. Shorter tract length=higher peak rpm. Bigger diameter=higher peak rpm.

[Bigtoe32067]

Those look pretty sweet. Hope it all works out.
Tony

[Lyle O]

It would be interesting to see the "before" and "after" curves side-by-side, so we could see if other characteristics change as well (slope and/ or shape of the curves, etc., and where they change).

I, too, love your new ITB valve concept. Best of luck.

[winders]

I think those stacks are too short as most people, even those building race engines, want to improve midrange power. Here are the stacks on my 3.6L race engine:



These are the AT Power ITBs. They use a shaftless butterfly with the butterfly real close to the intake valve. They are 45mm in size but act more like 50mm ITBs due to the shaftless design and the proximity of the butterfly to the valve. With these, my peak power is at 7400 RPM and peak torque is at 5900 RPM. The engine is designed to rev to 8000 RPM.

What does you filter setup look like?

[winders]

Originally Posted by Nux

]

By the way, if those are MSD Blaster coils, they are oil filled and designed to be mounted upright. They will likely fail mounted as they are now. If you want to mount coils that way, you need to get the black MSD Blaster "High Vibration" coils (PN 8222).

[Walt Fricke]

Scott - what do you use for air filtration on those very tall horns? All tracks have some dust, but the CA tracks are all pretty dry without much that is green off the pavement.

[faapgar]

Hey Nux.I love what you are doing.Love to be one of your 1st US CUSTOMERS.Ciao Fred

[winders]

Originally Posted by Walt Fricke

Scott - what do you use for air filtration on those very tall horns? All tracks have some dust, but the CA tracks are all pretty dry without much that is green off the pavement.

[Nux]

Originally Posted by winders

I think those stacks are too short as most people, even those building race engines, want to improve midrange power. Here are the stacks on my 3.6L race engine:



These are the AT Power ITBs. They use a shaftless butterfly with the butterfly real close to the intake valve. They are 45mm in size but act more like 50mm ITBs due to the shaftless design and the proximity of the butterfly to the valve. With these, my peak power is at 7400 RPM and peak torque is at 5900 RPM. The engine is designed to rev to 8000 RPM.

What does you filter setup look like?

You're right Scott - they're too short. This car is a 3.0L SC but has a 964 decklid, which compromises the space for the stacks. This is max we could get in there.

But part of the problem is that they are probably too big for this application. They move air a little too good - which I believe is part of the lost torque. A hotter cam should correct this.

[Nux]

Originally Posted by dannobee

Yup, the length of the intake tract from the back of the valve to the top of the stack length and the diameter of the tubes change everything about where the engine will peak. Shorter tract length=higher peak rpm. Bigger diameter=higher peak rpm.

Still, I'm surprised that the cam keps up to 7000. It's 1000rpm difference. But it certainly demonstrates that these ITBs move a lot more air.

Car feels fantastic by the way - quite a change when it suddenly pulls ALL the way to redline.

[Nux]

Originally Posted by faapgar

Hey Nux.I love what you are doing.Love to be one of your 1st US CUSTOMERS.Ciao Fred

Thanks!!

I think I need to take a Tour d' US with our ITBs when we are allowed to travel again!

[safe]

Originally Posted by Nux

Still, I'm surprised that the cam keps up to 7000. It's 1000rpm difference. But it certainly demonstrates that these ITBs move a lot more air.

Car feels fantastic by the way - quite a change when it suddenly pulls ALL the way to redline.

When I dynoed my 3.2 with ITBs for the first time it made peak power at 6900-7000 something, with STOCK cams. ITBs with lots of flow keeps the engine spinnin.

I learned that quite small changes to the cam timing can alter this more than you think.

[winders]

Originally Posted by Nux

You're right Scott - they're too short. This car is a 3.0L SC but has a 964 decklid, which compromises the space for the stacks. This is max we could get in there.

But part of the problem is that they are probably too big for this application. They move air a little too good - which I believe is part of the lost torque. A hotter cam should correct this.

I do sometimes forget that I am using a fiberglass 3.8 RSR-style deck lid which does provide me with some extra room.

What are you using for air filters and how are they attached?

Your ITBs are 45mm, right? If that is the case and they flow like or better than 50mm conventional butterfly ITBs, yes, I would say they are way too big for a 3.0 liter. Even with hot cams.

[911 SLANT]

Do you think you might be leaving some Horsepower on the table with SSIs? I'm assuming your pushing 250hp or more. Headers would seem to flow better at the higher RPM your getting.

[Nux]

Originally Posted by 911 SLANT

Do you think you might be leaving some Horsepower on the table with SSIs? I'm assuming your pushing 250hp or more. Headers would seem to flow better at the higher RPM your getting.

absolutely - but the owner insisted on SSI's.

We might change the muffler though. I have a sweet Dynomax setup (came recommended from William Knight) that will add another 10hp or so.

[Nux]

Originally Posted by winders

I do sometimes forget that I am using a fiberglass 3.8 RSR-style deck lid which does provide me with some extra room.

What are you using for air filters and how are they attached?

Your ITBs are 45mm, right? If that is the case and they flow like or better than 50mm conventional butterfly ITBs, yes, I would say they are way too big for a 3.0 liter. Even with hot cams.

Correct - the 3.0 setup flows equal to 51mm conventional ITBs. So yes - way too big.

The 3.6 set flows equal to 53.5mm conventional ITBs. So now we are thinking about downscaling a bit. They actually flow too good. You can see why here, its just a straight shot to the intake valve (here on a ported 2.7):



Current filter setup on the 2.7:



But we are working on a better solution which will sit higher up and closer to the decklid (as cold as possible). Also working on a plenum solution for the boosted guys

[Walt Fricke]

I was introduced to the concept of volumetric efficiency some 35 years ago by a guy named Grady Clay (RIP)at his shop in Denver with a twin cam 356 motor he had on a stand for a tech session. He said every bend in the path of the intake air reduced VE. Makes sense. About the only way you could do better that way might have been to angle these intakes outward? Being able to see as much of the valve head as is shown here is pretty impressive.

[manbridge 74]

https://www.sae.org/publications/technical-papers/content/2017-01-1078/

Below is a quote from the above SAE document that might help with your VE calculations

“The model predictions showed a smaller pumping loss associated with the butterfly valve until 30˚ throttle opening. Between 30˚and 70˚ throttle openings, both designs have shown similar performance. However, beyond 70˚ throttle opening, a significant performance enhancement is observed with the proposed barrel type. Specifically, an increase of 34% in mass flow rate at WOT is observed as an indication of better engine performance with the proposed throttle valve design. This is particularly important for racing vehicles.”