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Opinion Twin 1.25" Vs 1.5" Su's Mild Tune 1275?

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#1 InnoCOOPER

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Posted 12 January 2018 - 04:01 PM

Would like opinions please.

 

Currently running rebuilt engine with

 

Brett Sims modified S Cylinder Head 35.7x29

Kent 266 Cam

Aldon Yellow with vacuum advance

Lightened Flywheel

3.44.1 Diff 

C/R Gearbox

Currently running Twin 1.25" SU's on standard manifold but tweaked as per Vizards instructions.  

Maniflow LCB / RC40  Twin Box

 

Question.  Is it worth putting twin 1.5" SU's on?  Reading the forums i get the feeling that twin 1.25" will suffice.  Current thinking is a nice maniflow inlet manifold and MED Stub stack and filter system.

 

If anyone has any experience in similar setup let me know. 

 

Cheers

 

 



#2 Cooperman

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Posted 12 January 2018 - 04:34 PM

Twin 1.25's will be fine. Your peak power is at 5700 rpm so you won't be using over 6000 rpm and at 6000 those carbs can supply ample volume of fuel/air mix.

#3 carbon

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Posted 12 January 2018 - 08:47 PM

I'm running almost exactly the same spec on my 1293, using twin HS2s.

 

It's really not worth changing to the Maniflow inlet manifold if you have standard lift rockers, as the MD266 is a bit short on lift and this is the main restriction for the breathing at higher rpm. But if you would like a bit more pep then I would recommend a change to 1.5 ratio rockers along with something like a 32mm bore maniflow inlet manifold.

 

Be aware that if you change from standard to 1.5 rockers chances are the distributor advance curve will need tweaked to give best results at low to mid rpm.

 

Can't comment about the MED Stub stack and filter system, I am using K&Ns with the BMC HS2 alloy elbows and this seems to work well enough.


Edited by carbon, 12 January 2018 - 08:48 PM.


#4 Retroman

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Posted 13 January 2018 - 02:03 AM

As per Cooperman and Carbon above the Vizarded HS2's and manifold will supply plenty of air, for your spec. You would see no benefits from twin HS4.

I have used the MED stub stacks on twin HS6's and 1 1/2's, and they are good. I use my own CNC design based on Vizards.

 

I never really like the twin HS2's in standard form, yes they do look good and should certainly have their place on a standard Cooper or S. To get the best performance they need the DV treatment, manifold included, and even then are still pretty asthmatic.

 

A single HIF 38 and MG manifold both to DV spec is a better flowing simpler setup.



#5 InnoCOOPER

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Posted 13 January 2018 - 12:45 PM

I'm running almost exactly the same spec on my 1293, using twin HS2s.

 

It's really not worth changing to the Maniflow inlet manifold if you have standard lift rockers, as the MD266 is a bit short on lift and this is the main restriction for the breathing at higher rpm. But if you would like a bit more pep then I would recommend a change to 1.5 ratio rockers along with something like a 32mm bore maniflow inlet manifold.

 

Be aware that if you change from standard to 1.5 rockers chances are the distributor advance curve will need tweaked to give best results at low to mid rpm.

 

Can't comment about the MED Stub stack and filter system, I am using K&Ns with the BMC HS2 alloy elbows and this seems to work well enough.

I have a pair of cone K&N Filters and some stub stacks that go inside (i have smoothed them and shaped them so they a have a bit of radius on the lip) but you mention BMC HS2 Alloy Elbows?  what are they?   I also have a set of minispares 1.5 rockers which could be added at a later date.  Will try the K&Ns (with updated needle) and see if that helps.  Happy with the car though and drives well, very smooth, progressive and fast enough for what i want out of a 1974 Mini which is why i went for the 266 Cam.



#6 InnoCOOPER

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Posted 13 January 2018 - 12:48 PM

As per Cooperman and Carbon above the Vizarded HS2's and manifold will supply plenty of air, for your spec. You would see no benefits from twin HS4.

I have used the MED stub stacks on twin HS6's and 1 1/2's, and they are good. I use my own CNC design based on Vizards.

 

I never really like the twin HS2's in standard form, yes they do look good and should certainly have their place on a standard Cooper or S. To get the best performance they need the DV treatment, manifold included, and even then are still pretty asthmatic.

 

A single HIF 38 and MG manifold both to DV spec is a better flowing simpler setup.

Thanks for the advice. agree the Single HIF and MG Manifold would be just as good but i am trying to keep it looking fairly original and to be honest i am happy with the way the car drives.. i might just put the K&N Cone filters on and leave it at that.  The standard airbox is a little restrictiive.



#7 carbon

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Posted 13 January 2018 - 01:29 PM

 

I'm running almost exactly the same spec on my 1293, using twin HS2s.

 

It's really not worth changing to the Maniflow inlet manifold if you have standard lift rockers, as the MD266 is a bit short on lift and this is the main restriction for the breathing at higher rpm. But if you would like a bit more pep then I would recommend a change to 1.5 ratio rockers along with something like a 32mm bore maniflow inlet manifold.

 

Be aware that if you change from standard to 1.5 rockers chances are the distributor advance curve will need tweaked to give best results at low to mid rpm.

 

Can't comment about the MED Stub stack and filter system, I am using K&Ns with the BMC HS2 alloy elbows and this seems to work well enough.

I have a pair of cone K&N Filters and some stub stacks that go inside (i have smoothed them and shaped them so they a have a bit of radius on the lip) but you mention BMC HS2 Alloy Elbows?  what are they?   I also have a set of minispares 1.5 rockers which could be added at a later date.  Will try the K&Ns (with updated needle) and see if that helps.  Happy with the car though and drives well, very smooth, progressive and fast enough for what i want out of a 1974 Mini which is why i went for the 266 Cam.

 

If you're happy with the way the car drives at the moment then would not recommend changing to '1.5' Minispares rockers (are yours forged or roller?). I'm using the forged ones and this set-up gives about 10.5mm lift at the valve. If you have A+ rockers I would suggest changing these for pressed steel rockers (wide pad type).

 

The HS2 alloy elbows I an using are the ones used on standard BMC twin set-up between carbs inlet and filter box. I'm also using K&N cones but fitted 'upside down' onto the alloy elbows with the top cover of the air filter box holding it all together.

 

With K&Ns I would suggest AH2 needles with red springs as starting point. If the inside of the carbs have been fully vizarded then you may find QA needles give more suitable mixture at top end.



#8 InnoCOOPER

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Posted 13 January 2018 - 02:15 PM

 

 

I'm running almost exactly the same spec on my 1293, using twin HS2s.

 

It's really not worth changing to the Maniflow inlet manifold if you have standard lift rockers, as the MD266 is a bit short on lift and this is the main restriction for the breathing at higher rpm. But if you would like a bit more pep then I would recommend a change to 1.5 ratio rockers along with something like a 32mm bore maniflow inlet manifold.

 

Be aware that if you change from standard to 1.5 rockers chances are the distributor advance curve will need tweaked to give best results at low to mid rpm.

 

Can't comment about the MED Stub stack and filter system, I am using K&Ns with the BMC HS2 alloy elbows and this seems to work well enough.

I have a pair of cone K&N Filters and some stub stacks that go inside (i have smoothed them and shaped them so they a have a bit of radius on the lip) but you mention BMC HS2 Alloy Elbows?  what are they?   I also have a set of minispares 1.5 rockers which could be added at a later date.  Will try the K&Ns (with updated needle) and see if that helps.  Happy with the car though and drives well, very smooth, progressive and fast enough for what i want out of a 1974 Mini which is why i went for the 266 Cam.

 

If you're happy with the way the car drives at the moment then would not recommend changing to '1.5' Minispares rockers (are yours forged or roller?). I'm using the forged ones and this set-up gives about 10.5mm lift at the valve. If you have A+ rockers I would suggest changing these for pressed steel rockers (wide pad type).

 

The HS2 alloy elbows I an using are the ones used on standard BMC twin set-up between carbs inlet and filter box. I'm also using K&N cones but fitted 'upside down' onto the alloy elbows with the top cover of the air filter box holding it all together.

 

With K&Ns I would suggest AH2 needles with red springs as starting point. If the inside of the carbs have been fully vizarded then you may find QA needles give more suitable mixture at top end.

 

Ahh get it.  Ive done the same in the past with just the replacement K&N Filters on the elbows and the lid of the box holding them on... seemed to be ok.   I am using Minispares Forged rockers. i think you mentioned before about the Calver ones (1.4)?  Currently running AAQ needles which follow a similar curve but just richer than my original AAP (Innocenti).  Also has blue springs in.   I think that i will try the K&Ns...  that should be better than the standard airbox.   I haven't done the inside of the carbs but when i do then will get it on the rolling road to get right.  The needle suggestions are helpful as you are running a similar spec.  Cheers



#9 Retroman

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Posted 13 January 2018 - 04:41 PM

 

 

 

I'm running almost exactly the same spec on my 1293, using twin HS2s.

 

It's really not worth changing to the Maniflow inlet manifold if you have standard lift rockers, as the MD266 is a bit short on lift and this is the main restriction for the breathing at higher rpm. But if you would like a bit more pep then I would recommend a change to 1.5 ratio rockers along with something like a 32mm bore maniflow inlet manifold.

 

Be aware that if you change from standard to 1.5 rockers chances are the distributor advance curve will need tweaked to give best results at low to mid rpm.

 

Can't comment about the MED Stub stack and filter system, I am using K&Ns with the BMC HS2 alloy elbows and this seems to work well enough.

I have a pair of cone K&N Filters and some stub stacks that go inside (i have smoothed them and shaped them so they a have a bit of radius on the lip) but you mention BMC HS2 Alloy Elbows?  what are they?   I also have a set of minispares 1.5 rockers which could be added at a later date.  Will try the K&Ns (with updated needle) and see if that helps.  Happy with the car though and drives well, very smooth, progressive and fast enough for what i want out of a 1974 Mini which is why i went for the 266 Cam.

 

If you're happy with the way the car drives at the moment then would not recommend changing to '1.5' Minispares rockers (are yours forged or roller?). I'm using the forged ones and this set-up gives about 10.5mm lift at the valve. If you have A+ rockers I would suggest changing these for pressed steel rockers (wide pad type).

 

The HS2 alloy elbows I an using are the ones used on standard BMC twin set-up between carbs inlet and filter box. I'm also using K&N cones but fitted 'upside down' onto the alloy elbows with the top cover of the air filter box holding it all together.

 

With K&Ns I would suggest AH2 needles with red springs as starting point. If the inside of the carbs have been fully vizarded then you may find QA needles give more suitable mixture at top end.

 

Ahh get it.  Ive done the same in the past with just the replacement K&N Filters on the elbows and the lid of the box holding them on... seemed to be ok.   I am using Minispares Forged rockers. i think you mentioned before about the Calver ones (1.4)?  Currently running AAQ needles which follow a similar curve but just richer than my original AAP (Innocenti).  Also has blue springs in.   I think that i will try the K&Ns...  that should be better than the standard airbox.   I haven't done the inside of the carbs but when i do then will get it on the rolling road to get right.  The needle suggestions are helpful as you are running a similar spec.  Cheers

 

Sounds like a decent plan, you will need to rolling road it, especially after doing the carbs inside they make a good difference and with stubstacks and K&N's is as good as it gets. Keiths 1.4 forged rockers are a better option than 1.5's too I have used them a few times on various builds, they look pretty similar to S type.







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