19 replies to this topic

[grumpy xu1]

Hi All, I'm interested to know if anyone has measured the CFM flow through 1 of these carburettors, just like how you could pick a Holley for example ? It would be good for working out overall CFM. Gary.

[warrenm]

At a rough calculation, because I can't remember the exact measurement over the bridge(where the jet is, but will measure tomorrow) about [email protected]" or 294cfm@3".

[warrenm]

Correction, my guess at the bridge measurement was way off. Figures should be [email protected]" & 264cfm@3".

[jd lj]

Has anyone played with fitting a short ram tube inside the air filter to improve air flow into the carb. With the existing 90 degree edge with no radius that would restrict the effective throat size below the actual size due to the way air flows around a 90 degree corner.

[grumpy xu1]

That's true James, apart from the air that doesn't go into the ram, it would be better to run a spacer with a ram inside it & the element on top of the spacer, therefore removing the 90° U turn !

[grumpy xu1]

Correction, my guess at the bridge measurement was way off. Figures should be [email protected]" & 264cfm@3".

So if you had a std bore 202, good internals, ported cylinder head, graphed distributor, headers, correct camshaft, decent ve & top rpm of 6500 for instance, those carburettors should provide enough CFM no problem ? I can't see how they couldn't.

[grumpy xu1]

I hope that doesn't sound like I'm doubting you Warren, I'm actually impressed with your feedback & very interested in your thoughts ! At worst case scenario that's 500 CFM, which including the percentage difference in port flow, should be more than what's needed. So if it had problems at that rpm, is that an air cleaner problem or a camshaft problem ? 6500 & under i can't see how the carburettors could max out.

[claysummers]

Remember that multiple carbs don't multiply the flow. You can't compare low ratings for multiple carbs on individual runners to a single jug on an ordinary manifold.

Sent from my SM-G781B using Tapatalk

[jd lj]

So what would be the max hp achievable with triple 175 Strombergs? Sorry I'm not familiar with converting cfm to hp potential.

[warrenm]

I hope that doesn't sound like I'm doubting you Warren, I'm actually impressed with your feedback & very interested in your thoughts ! At worst case scenario that's 500 CFM, which including the percentage difference in port flow, should be more than what's needed. So if it had problems at that rpm, is that an air cleaner problem or a camshaft problem ? 6500 & under i can't see how the carburettors could max out.

I haven't used Strombergs in many moons & it would be 17 years since I had 1 3/4" SU's on, but I know when I changed to 2" SU's it increased the engine's response through out the rev range. 

[grumpy xu1]

I haven't used Strombergs in many moons & it would be 17 years since I had 1 3/4" SU's on, but I know when I changed to 2" SU's it increased the engine's response through out the rev range. 

I understand, but there's no choice when you're trying to stay xu1, but up the power level. It has to look factory correct.

[grumpy xu1]

It's probably going to need 400 CFM to not have any dramas. Do you think that is going to happen running the factory 1.75,s Warren ?

[warrenm]

Without knowing the your engine specs, it's hard to know. The 175's will be ok, they will become a restriction if your going to push the revs to 7000 or 8000, which I'm sure you wont be if it has an authentic block. I made these air cleaner bases up for the 1 3/4"s which worked well, I also smoothed the bridge down(removed the sharp edges)which also helped, the times were quicker from memory, but also better throttle response.

 20220112_063434 (600 x 450).jpg   57.69K   6 downloads  20220112_063514 (600 x 450).jpg   68.74K   6 downloads

[rodomo]

Stop me at anytime cos I'm no buff on this.

 

The 73 Brock Torana ran triple 45mm webers with 1 throat each blocked.

 

Am I right so far?

 

45mm is bugger all bigger than 1 & 3/4"

 

This is measured at the butterfly?

 

The CD 175 = 1 & 3/4" at the butterfly, not the bridge.?

 

Am I still right?

 

Would it be fair to say that HDT opted for the webers to delete the restriction of the bridge?

[warrenm]

Stop me at anytime cos I'm no buff on this.

 

The 73 Brock Torana ran triple 45mm webers with 1 throat each blocked.

 

Am I right so far?

 

45mm is bugger all bigger than 1 & 3/4"

 

This is measured at the butterfly?

 

The CD 175 = 1 & 3/4" at the butterfly, not the bridge.?

 

Am I still right?

 

Would it be fair to say that HDT opted for the webers to delete the restriction of the bridge?

Probably, or to get more adjustments, or both. 73 was the start of Group C, if I'm not mistaken.

[grumpy xu1]

Yep, 6000, possibly 6500, it's not going to set the world on fire, bit i don't want to be reving at a point where the torque is over & these engines of ours need to run externally a factory looking component. Those carburettor transition devices look like a good idea to me, they would help. I might try for a similar design. Thanks for the photos of them. Gary.

[caterham2]

Stop me at anytime cos I'm no buff on this.

 

The 73 Brock Torana ran triple 45mm webers with 1 throat each blocked.

 

Am I right so far?

 

45mm is bugger all bigger than 1 & 3/4"

 

This is measured at the butterfly?

 

The CD 175 = 1 & 3/4" at the butterfly, not the bridge.?

 

Am I still right?

 

Would it be fair to say that HDT opted for the webers to delete the restriction of the bridge?

58 mm Webers actually. I have a manifold from my XU1 in its group C days that also has the 58 mm setup. Brock had this, Bond had 2" SU on his car

[warrenm]

I got the idea from an item called a "Stub Stack".

[jd lj]

Brock ran 58mm Webers as stated above but I've never heard what size chokes they used.
With any carb the throat size doesn't equal the actual opening size as you have to subtract the area of the throttle shaft from that size. For example on a 45 DCOE Weber there's nothing to gain by machining a choke out to anything over 40.5mm because that extra 4.5mm (45-40.5=4.5) is the area squared of the throttle shaft.

[warrenm]

Brock ran 58mm Webers as stated above but I've never heard what size chokes they used.
With any carb the throat size doesn't equal the actual opening size as you have to subtract the area of the throttle shaft from that size. For example on a 45 DCOE Weber there's nothing to gain by machining a choke out to anything over 40.5mm because that extra 4.5mm (45-40.5=4.5) is the area squared of the throttle shaft.

A bit like the bridge in an SU.