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ITB's vacuum ports necessity question


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Borla (formerly TWM's) have my ITB's for a rebuild.

 

Besides all the other things that are wrong they mentioned to my surprise that there is an issue with "my" vacuum ports and asked me if I'd like their machine shop to try to replicate them on the new housing.

 

This was surprising because I'm fairly certain these were OEM from the dealer, which caused me to look into it a bit deeper.

 

I've found some 7's that have them cut like mine and capped and others that use them.

 

Here is one on BaT that had them capped

 

image.png.9dfcc35446810f8dcc15b6c2b1cf1c8b.png

 

Here is another that has them connected

 

image.png.bf8238fb7fa3d7ab21a88f5165de0e2f.png

 

These are also capped

 

 

 

image.png

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Here are mine

 

 

So the question is, what purpose do they serve if they aren't necessary?

 

Should I not have them machined and just run it as is?

 

I assumed that it allows for IAC to work. So how do they ones with the capped work? Do the butterflies have a small gap and never close all the way?

 

 

IMG_20210310_140854286.jpg

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In my experience they are used for balancing the throttles. I suspect yours were being used to try and pull a smooth vacuum signal, possibly for the FPR.

 

I'd just cap them and map the car with no vacuum signal to the FPR.

 

Where were they connected?

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59 minutes ago, ashyers said:

In my experience they are used for balancing the throttles. I suspect yours were being used to try and pull a smooth vacuum signal, possibly for the FPR.

 

I'd just cap them and map the car with no vacuum signal to the FPR.

 

Where were they connected?

 

Straight to the IAC. Looks like IAC fed the air to the runners past the butterflies when those closed.

 

Which poses question as to how the cars above run with these capped if they don't use the IAC like the green one from BaT

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My car does not have the vacuum ports. The engine is tuned on throttle position and RPM only. The throttles are tuned so they pull equal vacuum at idle. It works fine for me. I wouldn't bother to change it. The idle is higher than if it used a vacuum signal and it runs richer under acceleration. I don't have big cams, but no vacuum works the better than including a vacuum signal if you are running long duration cams.  

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6 minutes ago, CarlB said:

My car does not have the vacuum ports. The engine is tuned on throttle position and RPM only. The throttles are tuned so they pull equal vacuum at idle. It works fine for me. I wouldn't bother to change it. The idle is higher than if it used a vacuum signal and it runs richer under acceleration. I don't have big cams, but no vacuum works the better than including a vacuum signal if you are running long duration cams.  

 

Thanks. Trying to understand.

 

So you don't have an IAC valve and your butterflies stay partially open to take air at idle? You also have TWM's?

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I have TWM throttles. I do not have a IAC. I do not remember the size, but they make two sizes for Zetecs and I have the bigger ones. They were installed by Quicksilver, they were not installed by Caterham or a dealer. Each butterfly has a throttle stop and a idle adjustment. The throttles are partially open at idle. Each butterfly has to be adjusted with a tool used to tune SU carburetors called a Unisyn. You can probably tune yours the same way motorcycle guys do it with four vacuum gauges because you have the ports for vacuum.. The vacuum needs to equal on all four throttles. A Unisyn goes over the opening for all the air. My car has a Pectel ECU. I do not know what Caterham used. Quicksilver builds Zetec engines for Formula Continental SCCA race cars and a lot of the parts for my engine are the same as they use in the race cars.  

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29 minutes ago, CarlB said:

I have TWM throttles. I do not have a IAC. I do not remember the size, but they make two sizes for Zetecs and I have the bigger ones. They were installed by Quicksilver, they were not installed by Caterham or a dealer. Each butterfly has a throttle stop and a idle adjustment. The throttles are partially open at idle. Each butterfly has to be adjusted with a tool used to tune SU carburetors called a Unisyn. You can probably tune yours the same way motorcycle guys do it with four vacuum gauges because you have the ports for vacuum.. The vacuum needs to equal on all four throttles. A Unisyn goes over the opening for all the air. My car has a Pectel ECU. I do not know what Caterham used. Quicksilver builds Zetec engines for Formula Continental SCCA race cars and a lot of the parts for my engine are the same as they use in the race cars.  

 

Interesting. TWM (Borla) lists only one set on their website for ITB's. My build also uses a Pectel. 

 

I do not have Unisyn but I have the other meter. Not sure on accuracy or application differences but it gives me a ballpark when I was testing things

 https://www.amazon.com/dp/B00CMC57R0/ref=cm_sw_em_r_mt_dp_46RPF4HEHTBZR2V97TXZ?_encoding=UTF8&psc=1

 

I'm not going to fix at at this moment while it's not broken but thanks for the feedback. I wasn't sure how some people ran without these vacuum ports being drilled or with them sealed. Your setup helped answer that question. Seems like your setup is better due to having less parts involved. I'm not sure if my model even has an option to keep each butterfly partially open at idle but there might have been an adjustment screw on the back of one that controlled all at the same time. 

 

Have you ever dyno'ed your setup?

 

 

The parts list that I got for "$100 rebuild" so far has ran about 10x that and I'm getting practically a brand new unit in return (actually had to get a new body among along with everything in it), but I'm expecting the car to behave quite different and hopefully for the better once the unit is back. 

 

In a less than ideal world, it won't run right after the return and I'll have a lot more troubleshooting and tuning to do with the rebuilt setup. 

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If you look at the Amazon page. The other sync listed that they are suggesting you purchase is a Unisyn. They are very accurate from reading to reading, not a specific number. They go against the trumpet like yours and there is a plate in the middle of the hole on top of the throttle. The plate screws in and out and there is a small ball in a tube that goes up and down depending on the vacuum. I can't remember the correct name for the tube with the ball, but they are cheap and accurate.   

Amazon.com: Uni-Syn Carburetor Synchronizer/Carb Synchronizing/Balancing Tool Weber Su Type: Automotive

I was looking at your pictures a little closer and it appears your throttle shaft runs through all four individual manifold runners (in the same plane as the camshafts). One throttle shaft for all four butterflies and cylinders. My unit has 4 throttle shafts one for each cylinder or butterfly. The shafts are vertical or run in the same plane as the engine cylinders. I will ask Quicksilver, but this might be something made for them. When the Formula Continental car came out Quicksilver was contracted to take the Zetec engine and engineer the parts necessary to get in the car (Dry-sump, front drive and alternator, engine mounts, manifolds, headers, etc) They had a power level they wanted out of the cars and they came up with a reliable repeatable combination. I think they built about 40 cars and all were delivered with Quicksilver engines. My engine is not all out. It makes 188 HP. It could be tuned up to make 200, but it was intentionally not optimized. It is a little rich and could be a little more aggressive with the timing. The car is much better than me. It runs on regular high test from the pump and only has 10 to 1 compression. The head has been work on but not a lot and it has mild cams. The prior owner built this engine after throwing a rod from a bad down shift. I believe the motor that lost a rod had bigger cams and more compression. They spun it to 7800 and made 220 HP. My motor is intended to live and the ECU cuts off at 7200.     

The use of a vacuum signal in addition to the throttle position sensor and RPM makes the engine run better at part throttle. Not having a vacuum signal makes so you have to run real rich on throttle tip in to accelerate. It still accelerates as well but it burns more gas and is terrible for emissions.     

 

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