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Cornwallav8r
Samba Member
Joined: April 26, 2021
Posts: 39
Location: Central PA
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 Posted: Sat Jul 02, 2022 3:02 am Post subject: Separate throttle bodies ok? |
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I am installing a set of throttle bodies and EI/FI Speeduino based ECU into a 1600 dp I am restoring in a 75 Bug. A mechanic buddy tells me that I will have trouble getting the engine to run well or efficiently using the 4 separate throttle intakes, since they're not in any way connected. (2 double intake pairs, one each side with short vertical intake tubes). If any of you has ventured this path and has an opinion, as I set this up, it would be very helpful. Is there a problem with 4 separate intake paths?
The guy is extremely knowledgeable, and I very seldom catch him being wrong, so I want to explore this a bit. Thoughts? |
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mikedjames
Samba Member
Joined: July 02, 2012
Posts: 2736
Location: Hamble, Hampshire, UK
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| Posted: Sat Jul 02, 2022 6:21 am Post subject: Re: Separate throttle bodies ok? |
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Your EFI needs to know air flow fairly accurately. You will have to balance the throtlte bodies and butterfly opening carefully if you are using a single throttle position sensor.
Or you have a single air box with a MAF sensor...
If the TB you are measuring from is not precisely representative of the other three it will cause issues.
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Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.
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Chickensoup
Samba Member
Joined: January 06, 2018
Posts: 5368
Location: Good Hope, GA
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| Posted: Sat Jul 02, 2022 6:57 am Post subject: Re: Separate throttle bodies ok? |
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Pics of throttle bodies? Do they have a idle circuit? I assume your tuning by speed density
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Lingwendil
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Joined: February 25, 2009
Posts: 3988
Location: Antioch, California, a block from the hood
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Chip 
Samba Member
Joined: July 19, 2008
Posts: 969
Location: Utah
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| Posted: Sat Jul 02, 2022 10:58 am Post subject: Re: Separate throttle bodies ok? |
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| Cornwallav8r wrote: |
I am installing a set of throttle bodies and EI/FI Speeduino based ECU into a 1600 dp I am restoring in a 75 Bug. A mechanic buddy tells me that I will have trouble getting the engine to run well or efficiently using the 4 separate throttle intakes, since they're not in any way connected. (2 double intake pairs, one each side with short vertical intake tubes). If any of you has ventured this path and has an opinion, as I set this up, it would be very helpful. Is there a problem with 4 separate intake paths?
The guy is extremely knowledgeable, and I very seldom catch him being wrong, so I want to explore this a bit. Thoughts? |
Your mechanic is wrong. ITBs are used all over in the naturally aspirated high performance EFI world. As others have said, make sure your linkage is good, and you will either need a decent map signal, OR run the throttle bodies in an Alpha-N mode where the tps is used to determine fueling rather than the map sensor. Either method can deliver good results. The other thing to make sure you do is don't over do it with the bore on the throttle bodies. Too much and you'll reach the maximum flow of that 1600 long before you reach full throttle. The generic 48mm IDF throttle bodies that you see available from CB performance are too big. Vwspeedshop.com in the UK has a nice setup and sells them in as small as 38mm. The right set of ITBs will deliver good throttle control and fast throttle response. OEMs don't do single throttles because they work better than individual units, they do it because it's easy(ultra reliable) and cheap.
As others have asked, what units are you planning to use? Something off of a bike maybe? |
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modok
Samba Member
Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Sat Jul 02, 2022 11:46 am Post subject: Re: Separate throttle bodies ok? |
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It can work very well.
Most high performance motorcycles are built this way.
Your mechanic never has seen any of those?  |
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DeathBySnuSnu
Samba Member
Joined: August 25, 2012
Posts: 1183
Location: MS
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| Posted: Sat Jul 02, 2022 3:32 pm Post subject: Re: Separate throttle bodies ok? |
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Uhhhhh yeah.
And these are just the ones I own.
Loads of more examples on internet.
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Paul.H
Samba Member
Joined: April 03, 2015
Posts: 613
Location: England
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| Posted: Sun Jul 03, 2022 1:13 am Post subject: Re: Separate throttle bodies ok? |
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| Chip wrote: |
| Cornwallav8r wrote: |
I am installing a set of throttle bodies and EI/FI Speeduino based ECU into a 1600 dp I am restoring in a 75 Bug. A mechanic buddy tells me that I will have trouble getting the engine to run well or efficiently using the 4 separate throttle intakes, since they're not in any way connected. (2 double intake pairs, one each side with short vertical intake tubes). If any of you has ventured this path and has an opinion, as I set this up, it would be very helpful. Is there a problem with 4 separate intake paths?
The guy is extremely knowledgeable, and I very seldom catch him being wrong, so I want to explore this a bit. Thoughts? |
Your mechanic is wrong. ITBs are used all over in the naturally aspirated high performance EFI world. As others have said, make sure your linkage is good, and you will either need a decent map signal, OR run the throttle bodies in an Alpha-N mode where the tps is used to determine fueling rather than the map sensor. Either method can deliver good results. The other thing to make sure you do is don't over do it with the bore on the throttle bodies. Too much and you'll reach the maximum flow of that 1600 long before you reach full throttle. The generic 48mm IDF throttle bodies that you see available from CB performance are too big. Vwspeedshop.com in the UK has a nice setup and sells them in as small as 38mm. The right set of ITBs will deliver good throttle control and fast throttle response. OEMs don't do single throttles because they work better than individual units, they do it because it's easy(ultra reliable) and cheap.
As others have asked, what units are you planning to use? Something off of a bike maybe? |
I've actually gone down to 36mm with fully machined tapered bores.on the new IDF throttles
Individual throttles can work so long as the coupling between the two is good |
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Cornwallav8r
Samba Member
Joined: April 26, 2021
Posts: 39
Location: Central PA
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| Posted: Tue Jul 19, 2022 5:51 pm Post subject: Re: Separate throttle bodies ok? |
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| DeathBySnuSnu wrote: |
Uhhhhh yeah.
And these are just the ones I own.
Loads of more examples on internet.
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Super. THANKS guys. I am using a set of 42mm i think, got them on Alibaba. Really nice hardware and cheap price. Couldn't resist. I did just add 1/2" hose barbs to a central machined housing with an idle air stepper, I will pull map from there. |
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Cornwallav8r
Samba Member
Joined: April 26, 2021
Posts: 39
Location: Central PA
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| Posted: Tue Jul 19, 2022 6:03 pm Post subject: Re: Separate throttle bodies ok? |
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[quote="DeathBySnuSnu"]Uhhhhh yeah.
And these are just the ones I own.
Like this: https://www.amazon.com/SherryBerg-45-dcoe-45mmDCOE...&psc=1
I don't think the mechanic meant it couldn't work, he just said I would need the combined vacuum lines as discussed. For throttle linkage I put together something basically same as the $120 kit using chrome holy tubes, a hex aluminum extrusion for standoff, and some rod ends, all left from some aircraft builds. It appears to be rock solid, no slop in the works. Though I think I need to adjust the throw angle to reduce the initial throw right above idle, for smoother acceleration.
Last edited by Cornwallav8r on Tue Jul 19, 2022 6:30 pm; edited 2 times in total |
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Cornwallav8r
Samba Member
Joined: April 26, 2021
Posts: 39
Location: Central PA
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| Posted: Tue Jul 19, 2022 6:35 pm Post subject: Re: Separate throttle bodies ok? |
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| modok wrote: |
So what he meant is that he or you would not be smart enough to make it work. Just kidding.
Manifold pressure is over rated for sure. Any GOOD MAP based system, also relies heavily on referencing current ambient pressure and using a throttle position sensor also.
A lot of people have BIG struggle synchronizing two throttles.
IMO this is because these days electricity and computers is cool and mechanical things are not cool.
But really the mechanical things are NOT that hard, so, you can do it if you try. |
I will take your word on the map versus tps , I currently set for map based, I have an ambient pressure sensor, a cht and ambient air temp sensor.
I learned on an old Russian bike to balance carbs by blocking off one side, noting the rpm drop off, and adjusting other side to match the 2 sides. Dunno if possible here, I would think so, maybe just block one cylinder each side to compare. Does 42mm seem about right for a stock 1600 dp? What i ordered. |
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modok
Samba Member
Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Tue Jul 19, 2022 6:57 pm Post subject: Re: Separate throttle bodies ok? |
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42mm should be OK 
Synchronizing two throttles can be done several different ways, and they all work!
Pull the plug wire, short the plug wire, TWEAK it one way or another and listen, measure flow, or measure vacuum.
I'm confident we can solve any mechanical problems one can run into. |
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mark tucker
Samba Member
Joined: April 08, 2009
Posts: 23937
Location: SHALIMAR ,FLORIDA
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| Posted: Thu Jul 21, 2022 7:12 am Post subject: Re: Separate throttle bodies ok? |
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| WHY WOULD YOU PUL THE PLUG WIRE? JUST PUT A SNAIL ON EACH ONE AND GET THEM THE SAME, THEN GET THEM ALL TO OPEN THE SAME TIME. |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12714
Location: Western Canada
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| Posted: Thu Jul 21, 2022 7:27 am Post subject: Re: Separate throttle bodies ok? |
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There are applications where there is not enough room to use a snail. That is where other methods shine.
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Cornwallav8r
Samba Member
Joined: April 26, 2021
Posts: 39
Location: Central PA
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| Posted: Tue Jul 26, 2022 5:18 am Post subject: Re: Separate throttle bodies ok? |
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| oprn wrote: |
| There are applications where there is not enough room to use a snail. That is where other methods shine. |
Um, what's a snail? Besides a Slimy critter? |
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modok
Samba Member
Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Tue Jul 26, 2022 2:02 pm Post subject: Re: Separate throttle bodies ok? |
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A flowmeter
Googled carburetor snail, comes right up, for now at least |
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Cornwallav8r
Samba Member
Joined: April 26, 2021
Posts: 39
Location: Central PA
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| Posted: Fri Jul 29, 2022 8:02 pm Post subject: Re: Separate throttle bodies ok? |
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Deleted
Last edited by Cornwallav8r on Fri Jul 29, 2022 8:11 pm; edited 1 time in total |
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modok
Samba Member
Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Fri Jul 29, 2022 8:10 pm Post subject: Re: Separate throttle bodies ok? |
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"flowmeter"?
Last edited by modok on Fri Jul 29, 2022 8:13 pm; edited 1 time in total |
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Cornwallav8r
Samba Member
Joined: April 26, 2021
Posts: 39
Location: Central PA
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| Posted: Fri Jul 29, 2022 8:12 pm Post subject: Re: Separate throttle bodies ok? |
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| modok wrote: |
| What kind of an engineer doesn't understand the word "flowmeter"? |
I didn't see the post. On my ipad. |
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modok
Samba Member
Joined: October 30, 2009
Posts: 26785
Location: Colorado Springs
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| Posted: Fri Jul 29, 2022 8:14 pm Post subject: Re: Separate throttle bodies ok? |
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| Oh, sorry |
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