BSR GTU E31 Head Images

[z-ya]

Here are some photos of a Bob Sharp GTU head I picked up with a bunch of other BSR stuff. It's and E31, and was most likely used on this car:

 

 

I also have the port matched intake and Mikunis.

 

 

 

 

 

 

 

 

Here is a piston that I believe was setup for this head:

 

 

 

 

[josh817]

I don't like that you have that. LOL

 

Can you measure the entrance to the intake and exhaust ports. Whats the diameter of the intake and then whats the height and width of the exhaust port square. I've got a head I just bought but don't know if its mildly ported or outrageously ported.

 

Thanks!

 

Edited September 28, 2010 by josh817

[z-ya]

I don't like that you have that. LOL

 

Aren't you glad I shared the images?

 

Intake ports are around 1 9/16"

Middle exhaust ports are 1 1/2" x 1 5/8"

Outer exhaust ports are 1 1/2" x 1 1/4"

Edited September 30, 2010 by z-ya

[josh817]

 

Our intake entrances match. I'll need to look into on the flow numbers of my head. Perhaps I have a gem. I was thinking "meh its ported but we don't know if it flows well". I'm not going to get my hopes up just yet.

[Tony D]

Definately looks ported for carburetion...

[z-ya]

Definately looks ported for carburetion...

 

These are the carbs that were used on that head.

 

 

The manifold runners have been enlarged and the ports match the head.

 

Now, I don't know crap about these carburetors, but I am starting to learn. Todd at Wolfcreek says they are 44mm that were modified back in the day so that now they are essentially 50mm.

Edited October 5, 2010 by z-ya

[josh817]

These are the carbs that were used on that head.

 

 

The manifold runners have been enlarged and the ports match the head.

 

Now, I don't know crap about these carburetors, but I am starting to learn. Todd at Wolfcreek says they are 44mm that were modified back in the day so that now they are essentially 50mm.

Probably drilled out. I wanted to do that but was told to just purchase the proper carbs. I wonder if 50's are necessary to breathe with this sort of port. Perhaps at high RPM's, like 7000 and up to make power. I was hoping to go for Weber 45's as they should be the same bodies as the 40's and not a special body like the 50's, I think. Hopefully I can get away with 45's and just not choke them down as much...

 

By the way:

http://www.311s.org/PDFs/U20Eng_TrnService%20Manual40.pdf

 

Go to page 80 on the PDF file (not page 80 in the document), should have a service manual for the Solex 44PHH.

[z-ya]

Probably drilled out. I wanted to do that but was told to just purchase the proper carbs. I wonder if 50's are necessary to breathe with this sort of port. Perhaps at high RPM's, like 7000 and up to make power. I was hoping to go for Weber 45's as they should be the same bodies as the 40's and not a special body like the 50's, I think. Hopefully I can get away with 45's and just not choke them down as much...

 

By the way:

http://www.311s.org/PDFs/U20Eng_TrnService%20Manual40.pdf

 

Go to page 80 on the PDF file (not page 80 in the document), should have a service manual for the Solex 44PHH.

 

 

They modified the 44mm to cheat. They look like 44s on the outside, but are really 50mm. You need and engine that has at a 250WHP potential to use 50mm carbs.

[josh817]

They modified the 44mm to cheat. They look like 44s on the outside, but are really 50mm. You need and engine that has at a 250WHP potential to use 50mm carbs.

Hm I never knew that. I always thought it was a budget or availability thing but that wouldn't make sense for BSR I guess. I wonder what the rules called for. I know the 1972 SCCA GCR says 44mm Mikuni's but 45mm Weber's are allowed in substitute, then again thats not C Production otherwise it wouldn't have the big fenders.

 

Well I guess that's bad news. I don't want to run 50's. :[ What is your application, like displacement and stuff? I'm doing another 3.1L. I blew off my idea of running Vintage because I have so much stuff that wouldn't be allowed.

 

Final question. I stated that the Weber 50mm carb is a "special" body, that being different from a 40 or 45. I wonder if the bolt spacing is wider, meaning I can't use the manifold I have now. If so then perhaps someone can shed some light on drilling out carbs, pro's and con's.

 

Sigh.... You sure I can't just run a 45mm with a 40mm-43mm choke?! Grrrr

[Gollum]

Definately looks ported for carburetion...

 

(please don't kill me)

 

Do you say that because the ports aren't raised as much as they could have been for that port size?

[d3c0y]

Sigh.... You sure I can't just run a 45mm with a 40mm-43mm choke?! Grrrr

 

You can run Mikuni/Solex 44s with 41mm chokes (biggest they make) or just run no chokes at all?

[josh817]

You can run Mikuni/Solex 44s with 41mm chokes (biggest they make) or just run no chokes at all?

I'm just having trouble seeing how a 50mm would work better. If the intake port is 39.5mm then a 45mm with a 40mm choke sounds reasonable. I'm figuring as long as the choke isn't smaller than the port. Hmm... Running no choke was an option I first read in that How To Modify your Datsun Book:

 

Running with no chokes doesn't sound like a super idea to me though. I think that with a 3.1L displacement that and around a 7000-8000 max RPM 50mm seems needed. Now I'm wondering how much it would cost me, how will it mess with jetting, and will Webermm chokes and aux. chokes bolt in/fit/work properly if I were to drill out. I can't find anything on Google about it except for motorcycle carbs.

Edited October 8, 2010 by josh817

[Tony D]

I've seen 44's run with no chokes. Not a street application for sure.

 

I said 'looks like carburetion' because of the size of the ports. Running 50mm carbs makes for BIG runners to get the taper you need.

 

You get the same power from 45mm ITB's as you do from 50 Carbs, but with much smaller ports, and higher port velocities.

[josh817]

Whats the reasoning behind 45mm ITB's making more power, other than velocity? I know you speak well of fuel injection, if thats the type of ITB you are talking about.

 

What I'm getting at is could a 45mm ITB be comparable to a 45mm Weber? I don't know how ITB's are setup but do I would assume they don't even use chokes. From what I've seen its strictly a body with a throttle and an injector. Natural taper to the body itself when machine? Is there a point where although its a higher velocity it chokes the motor? Peak power would be at a lower RPM than a 50mm carb?

 

Tony, you've seen a lot. So far you have said you've seen no chokes. What about bored out bodies. Obviously Z-Ya's carbs are bored out but I want to know if it is as simple as sending it to the machine shop and having them bore it out and then fitting chokes for that bore and rejetting? If I can get away with boring a carb body out to lets just say 50mm, and I'm able to fit 50mm Weber chokes no problem, along with rejetting, I'd be thrilled. Something about just seems fishy though. I'm curious how thin the bore walls are AKA bore it to 50mm and find pitting and cracks from breaking through into who knows what. I also worry that jets which are needles, like the idle jet, would be protruding into the bore and somehow prevent me from continuing on. I have all these nightmares of me destroying a carb body.

 

 

You see my logic though, right Tony? If a book says 50mm-55mm carbs are needed for 8000-9000 RPM (what did they spin up to in SCCA and IMSA?) on a 2.4-2.8L then if I'm wanting to do 7000-8000 but with 3.1L I'd need a 50mm, like them?

 

 

EDIT:

Tomorrow I'm going to take some measurements. We have an extra set of 45mm carbs. I want to see if 50mm would even fit within the bolt holes. Also on the front of Webers is like a breather hole or something, right about the left barrel. That sits close the the throat too. 45mm to 50mm would be 5mm difference so 2.5mm on either side of the barrel. Supposedly a 40mm is the same body as a 45mm so if drilling a 45mm works, then drilling a 40 should work. Sounds make believe in my head, to do it cheaply.

 

I actually can't even find chokes or horns for the 50mm Weber. Best second option would be get a set of Mikuni's or Solex's and rape them or just settle with 48mm bore size which I can find stuff for. 48mm sounds like a happy medium between 45mm and 50mm when I think about it.

Edited October 13, 2010 by josh817

[RIP260Z]

Josh817,

If 48mm sound like a happy medium, what about 48mm Dellortos? A bit hard to find in the US (I think). I am running this size on my Rebello built 3.2l

[josh817]

The fact is that I could buy 45mm 48mm or 50mm Webers, I'm just a cheap ass. I'd have to get a price quote from my machine shop and then see how much throttle shafts, chokes (main and aux), and horns are. Sounds like a lot of money and its probably better to just buy the proper version. Whats your Rebello application? Street track? I've heard of Dellortos but I don't know whats available for them. I'd really like to stick to Webers, since that's what my father taught me. If I have any questions he can answer. Solex/Mikuni/Dellorto he will be like uhhhh I don't know for sure. He could make assumption but wouldn't be positive unless they are truly exactly the same.

 

Also he does British cars. Every British car that has come in with something other than SU's or Stromburgs has a Weber DGV or DCOE. Point being, Dad is a distributor for that stuff so I wouldn't have to order online. Just tell him what I need. Yay.

[z-ya]

What are your HP goals? Build the long block to support those goals, and then choose carb/venturi based on that. When you say the chokes are removed, you really mean venturi, right? When you remove the venturis from 44PHH carbs, it makes them approximately 50mm. That's why they were illegal at the time.

[JMortensen]

When you say the chokes are removed, you really mean venturi, right? When you remove the venturis from 44PHH carbs, it makes them approximately 50mm. That's why they were illegal at the time.

Choke tubes = venturis. If you remove the venturis from 44s they become 44s, which is the diameter at the exit hole of the carb. No change you make to the venturi is going to change the size of the exit hole. The venturis neck down the opening to speed airflow through the carb at low engine speeds. I believe Mikuni shipped most street bound 44s with 34mm venturis.

[josh817]

Choke tubes = venturis. If you remove the venturis from 44s they become 44s, which is the diameter at the exit hole of the carb. No change you make to the venturi is going to change the size of the exit hole. The venturis neck down the opening to speed airflow through the carb at low engine speeds. I believe Mikuni shipped most street bound 44s with 34mm venturis.

That is correct. I just measured our 45mm Webers and its 45mm at the back where the throttle plates are but at the front its actually 48mm. There is a little step/bevel which is 50mm but that is where an airhorn would insert (to make up for the thickness of the airhorn walls which is 1mm). The body/barrel itself has a natural taper of 3mm.

 

If I wanted to go 50mm then the front of the carb would have to be 55mm for the airhorn to slide in and then step down to 53mm for the barrel. I'd show pictures but my computer is broken so I can't upload.

 

EDIT

Here is a 40mm from the front. You can see the step, at first I thought it was a liner or the end of the choke tube.

 

Also note the vent hole for the float bowls. The hole tricks you into thinking its a certain thickness but actually when you look into it, it opens up bigger. Point being if you see 5mm of material on the outside and gouge it out, you're going to break through the other side after you get about 3mm in.

Edited October 13, 2010 by josh817

[Tony D]

Choke tubes = venturis. If you remove the venturis from 44s they become 44s, which is the diameter at the exit hole of the carb. No change you make to the venturi is going to change the size of the exit hole. The venturis neck down the opening to speed airflow through the carb at low engine speeds. I believe Mikuni shipped most street bound 44s with 34mm venturis.

 

John's right. When you remove aux venturis, you get a 44 mm hole for all your air to pass through.

That would be equivalent to a common venturi size in a 50mm setup.

 

It's the diameter of the hole the air has to pass through. Carburettors necessarily work on RESTRICTION to airflow to put fuel into the airstream, and therfore never will flow as well as possible unless you m ake a VERY big carb (hence 50's and 55's.)

 

There are 40PHH's that have 44 mm bores to the throttle plates and when you remove the outer neck-down the characteristic of the carb changes necessitating new jets. Toyotas used them on early TG motors. Sleeved down 44's to 40. The part from the aux venturi to the throttle plate was 40mm, everything else was 44mm.

 

Generally there are larger airbox side bores simply to allow for aux components like venturis to be matched properly on their exit side to the throttle plate diameter. Due to this alone, removing them effectively gives you a 47mm bore with a 44mm venturi for main jet draw-in. Normally 36mm or 38mm is the largest 44mm choke you will see.

 

Compare this to even a 40mm ITB with a straight 40mm bore and you will see it will flow better than any 44 or 45 with a standard venturi in it.

A 45mm ITB will flow more through it's 45mm hole than any 44mm carb will as there is no restriction to flow at all. You might flow that will on 44's with the venturis taken out, but the drivability will be nowhere near as good.

 

And to put it straight, the venturis are not to speed airflow through at lower engine speeds. They are there to create a physical low pressure area to SIPHON FUEL FROM THE BOWL. The fuel must be lifted from the jet well UP to the bore where it is introduced. Differing the size of the venturi will change the ammount of depression you get and the resultant booster action. Generally a carb will not work without a booster venturi (10 or 12mm in the main bore, in front of the 36-38mm choke in the body. Without the main venturi, there would be no physical low pressure area to make the idle and progression circuit work.

 

And this is why carbs will never flow as well as comparably sized ITB's. They depend on pressure differential to introduce fuel to the airstream. EFI does not need this. CFM determination for Carbs is at 9" HG. For EFI it is FAR lower since that kind of pumping loss is not required to get atomization and fuel introduction to the airstream.