Turbo weber 32/36 questions(blow through)

Engine, Transmission and related drivetrain.
stanis82
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Re: Turbo weber 32/36 questions(blow through)

Post by stanis82 »

bertvorgon wrote: 18 Jun 2020 08:58 Not sure what to say about the balance pipe, I would maybe leave it in as first test. Boost overcomes a lot of flow variability.

What I meant about the secondary is that we milled the secondary bore to a larger diameter, at the venturi point, then, we did a backcut under what is now a very minimal venturi, to give MORE of the venturi effect.

So, we basically made the 32/36 which is the throttle plate size, the actual venturi size is 26/27 MM, so we made the secondary about 34 MM+, really increasing airflow when the secondary is open.

I wish I could remember how much of a cut we did, it is so long ago and I never wrote it down in my log book. Too hard to measure now with the carb in place and booster venturi blocking a measuring tool.

That mod, coupled with my larger cam at the time, really let my engine breath past 6,000-6,500 RPM and 8,000 RPM was easily achieved in 5th gear.

Possibly in this attached picture you can see how much bigger the secondary venturi is, almost same size as throttle.

Another trick for flow is you can mill the throttle shafts a bit flat. All these type of tricks really do increase flow.
Wow it has been a while!!
Well i am up and running with the twin weber turbo setup!!
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stanis82
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Re: Turbo weber 32/36 questions(blow through)

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510rob
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Re: Turbo weber 32/36 questions(blow through)

Post by 510rob »

What specific turbo is that? A T61 or a T70, or a hybrid?
stanis82
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Re: Turbo weber 32/36 questions(blow through)

Post by stanis82 »

510rob wrote: 23 Feb 2021 15:45 What specific turbo is that? A T61 or a T70, or a hybrid?
It's a T70 MasterPower Turbo with a T4 flanged, 0.68 A/R turbine housing
stanis82
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Re: Turbo weber 32/36 questions(blow through)

Post by stanis82 »

bertvorgon wrote: 16 Jun 2020 09:51 Hey Teran, welcome back!

Wow, time has flown since this post started. You are on the right path for sure, don't know if I can help much as you are on a path the is a new frontier, blowing through 2 carbs in a drag application.

First thing for sure is make sure fuel delivery lines can deliver the VOLUME required. As mentioned, at one point I had that 3.0 MM needle and seat, which I ultimately did not need and went to a 2.5 MM needle. It turned out that was my learning curve to have enough VOLUME of fuel.

I too milled the top choke plate area down, to increase air flow in my air box. You can see in the picture the amount taken off.

Only testing will tell if sealing off the secondary air is a good idea or not. Do you have a wide band to monitor the A/F ratio? I know at one point my main fuel secondary jet was just over 3.MM. Many, Many years ago, a fellow showed up with a turbo Fiat X19, running a 32/36 and he ran it with NO FUEL JET in the secondary!

We did bore out the secondary, enough meat to take a good cut, then do a back cut to regain a "venturi" effect. That really increased the air flow.

Make sure you are using the right top gasket of course. Picture attached of the 2 available. For what it is worth I put the bearing kit in also, makes the carb very smooth in actuation.

Make sure, if you can with your compressor bypass valve, that it does NOT pull open till at least 16" or more of vacuum, as that keeps the boost up when shifting as much as possible.

Float change for sure.

I had a 1982 SR5 with the 3TC motor, I loved it as that was a torquey motor!

Not much else I can add at this point...keep us posted on progress.
Keith, when you ran the 3.0 MM needle valve what issues did you have ?
I already bought two of the 3.00 MM needle valves but won't use them if they would cause issues. Should i try them out or just get the 2.5 MM ?
Thanks!
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bertvorgon
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Re: Turbo weber 32/36 questions(blow through)

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Morning, good to hear from you. I hope it is warm and sunny for you, still cold in Canada.

I had no problems with 3.0 Mm grose jet that I can remember.

As I said, I was chasing the WRONG problem at the time, I figured the carb was the issue when in fact it was that my FUEL LINE was too small. I had LOTS of pressure but inadequate VOLUME of fuel.

Once I upped my fuel line size, I went back to a 2.5 MM needle, with no problem for the motor to pull sustained 5th gear to 8,000 RPM.

Funny you should send this note today, last night I was thinking of going BACK to my Non-bored out, modified carb and then put a 2.5 needle in just to ensure adequate flow for the odd top end blast.

With our Draconian speeding laws here now, I really don't need the top end like I used to and would rather have "crisper" acceleration down low and mid range when jumping on the secondary
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer
stanis82
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Re: Turbo weber 32/36 questions(blow through)

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bertvorgon wrote: 02 Mar 2021 06:57 Morning, good to hear from you. I hope it is warm and sunny for you, still cold in Canada.

I had no problems with 3.0 Mm grose jet that I can remember.

As I said, I was chasing the WRONG problem at the time, I figured the carb was the issue when in fact it was that my FUEL LINE was too small. I had LOTS of pressure but inadequate VOLUME of fuel.

Once I upped my fuel line size, I went back to a 2.5 MM needle, with no problem for the motor to pull sustained 5th gear to 8,000 RPM.

Funny you should send this note today, last night I was thinking of going BACK to my Non-bored out, modified carb and then put a 2.5 needle in just to ensure adequate flow for the odd top end blast.

With our Draconian speeding laws here now, I really don't need the top end like I used to and would rather have "crisper" acceleration down low and mid range when jumping on the secondary
Yes Keith it is more or less warm and sunny for us!!
Thanks for your reply!!

Thanks for the clarification!!

The twin 32/36 weber setup feels great/no flat spot so far at just 5 psi boost on the carbs with stock jettings but my AFR is showing in the 12's at WOT. So definitely I have to start with upsizing my secondary fuel and downsizing secondary air jets before I can increase the boost. The launch from 1st gear at this low boost level is out of this world and surprised me I must say, but I can do with more boost in the other gears..

Low rpm operation while not in boost is very torquey given there are two 32mm primary butterflies opening simultaneously.. It is equivalent to the operation/torque effect of a 38/38 carb and luckily for me so far boost starts to come in smack when the secondary 36mm butterflies open.
As far as setting lean best idle, my idle jets are as expected too big as only one turn out on the air mixture screw per carb gets me best idle but I may just leave it that way depending on how things go with the increase in boost... But would this affect carb performance if the lean best idle is not right per Weber's specifications?

My fuel feed line is 3/8" ( and my return is 1/2" ) so we shall see how it goes as well with adequate fuel VOLUME as you explained for the two carbs and I will keep the 2.0MM stock needle valves in for the while...

But all in all, I am very happy I went with this twin 32/36 weber experiment so far! Hope things get better as I go up in boost!!
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Re: Turbo weber 32/36 questions(blow through)

Post by bertvorgon »

I run mine, at W/O into the 10's and have seen into the 9's depending on air density.

Lean best idle...once off the idle....they are not in play, only the transition. It goes through it so fast I have never worried about it being "perfect".

I do watch my exhaust gas temp, as at part throttle, at almost the point of the secondary opening, I get quite lean and the EGT temp goes very high, 1,400 - 1,500 F. My problem here is our mountain climbs, where I can just see maybe 1" of vacuum, or zero manifold pressure, I can maintain any speed up a long climb. Then the A/F on the primary top end is too lean and the EGT tries to go off the gauge..NOT GOOD. I sometimes have to blast into the secondary to cool things down. Kind of funny really.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
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1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer
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Re: Turbo weber 32/36 questions(blow through)

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stanis82 wrote: 02 Mar 2021 06:20
510rob wrote: 23 Feb 2021 15:45 What specific turbo is that? A T61 or a T70, or a hybrid?
It's a T70 MasterPower Turbo with a T4 flanged, 0.68 A/R turbine housing
When does it start to spool on that motor? I'm assuming you have a P-trim turbine in there.
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Re: Turbo weber 32/36 questions(blow through)

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Not sure of course about that turbo, but I only ran the .68 for solo.

Is that the same relationship for area ratio Rob?
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
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1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer
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Re: Turbo weber 32/36 questions(blow through)

Post by 510rob »

The Schwitzer rating used just the single-point minimum cross sectional area of the nozzle right where it exits the reduction cone and points at the turbine. The later AiResearch ratings use the area:radius ratio measurement with a constant A:R relationship as the gas travels around the turbine housing. Both get the same job done, but each does it slightly different. The quoted values are a bit apples/oranges, but net the same result.
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Re: Turbo weber 32/36 questions(blow through)

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Got it.

I used to love the response with that small housing but it sure needed the race slicks to even begin to control the boost traction at lower RPM.

When Dave Christie and Sam O'Young/Mike Boyle came along, I needed all the bottom end I could get. Best competition ever!
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer
stanis82
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Re: Turbo weber 32/36 questions(blow through)

Post by stanis82 »

510rob wrote: 02 Mar 2021 16:53
stanis82 wrote: 02 Mar 2021 06:20
510rob wrote: 23 Feb 2021 15:45 What specific turbo is that? A T61 or a T70, or a hybrid?
It's a T70 MasterPower Turbo with a T4 flanged, 0.68 A/R turbine housing
When does it start to spool on that motor? I'm assuming you have a P-trim turbine in there.
Sorry for the very late reply! It starts to spool at around 4500 rpm and makes full boost by about 7000 rpm and then i shift at 7500 rpm. I don't like it!!
So i went with another turbo just weekend with the same size compressor housing but a smaller turbine T3 flanged with 0.64 A/R and smaller compressor and turbime wheeels. Feels great in 1st gear so far..
Boost still starts kinda late like 4000 rpm but reached full boost by 6000 rpm which is still late but did feel more aggressive vs the bigger turbo..
Will see how it feels in the other gears when i take a spin today...
stanis82
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Re: Turbo weber 32/36 questions(blow through)

Post by stanis82 »

bertvorgon wrote: 03 Mar 2021 09:51 Got it.

I used to love the response with that small housing but it sure needed the race slicks to even begin to control the boost traction at lower RPM.

When Dave Christie and Sam O'Young/Mike Boyle came along, I needed all the bottom end I could get. Best competition ever!
Hello Keith.. it has been some months!
Got a question for you:

Did you ever have to mess with your emulsion tubes or are you running stock ?
My 32/36's came with F50 in primary and F6 in secondary.
I am finding some difficulty in that if i step on at at say 3000rpm, i am drowning in fuel until boost hits at 4500 rpm or so then it cleans up..
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Re: Turbo weber 32/36 questions(blow through)

Post by bertvorgon »

hey, hope your doing ok!

No, I never felt I had to mess with the emulsion tubes, just the air corrector jets.

I would maybe say your fuel jet in the primary is maybe too rich to start with ?

That is the one problem with our blow through systems is that the carb does NOT sense AIR DENSITY CHANGE, as air pressure builds above the throttle(s)

Maybe try going down on the primary jet, then see what it does...then decrease the air corrector jet, as that starts to effect as RPM builds and the top end richens just before the secondary opens.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer
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