Stromberg uprated Carb needles and springs

[Guest]

Does the installation of uprated needles and springs really make that much of a difference? Would be interested to know.

2 x 175 on a 3L are UNDERCARBED, it's only ideal size for a 2L engine.
it needs 2 x 2" Su really.

175 pairs max out and start to do their usual thing at 150-160bhp (massive stand off - over-rich and all that stuff)
+ I really don't like those late CD carb non fixed needles.....they only did it cos people were incapable of centring the fixed needles properly.

The only reason 175 work on the Stag is because the engine is so detuned the A-F mix simply can't get in there.
Try making an engine run right at 4-5:1 CR it's a miracle it works at all!

[tractorjames]

I put uprated needles and springs in my car, and it majorly overfuelled it at high revs causing a flat spot and black smoke. Cant remeber afr but it was rich. Actually went the otherway and put thicker than standard needles in.

[mike@thenook]

Maybe I should just qualify this by saying that my engine is standard apart from tubular manifolds.

For me, the uprated needles and springs made a positive difference - not oodles of extra power but enough for me to think the £60 I spent on them worth it

Out of interest, did you use the same ones James..?


Cheers

[Guest]

If you change the exhaust manifolds you will have to change needle And advance curve.
most people never look at ignition advance at all.

Btw the only advantage the ZF box has is 4th gear lockup.
This drops the losses by quite a bit but it's still overdriven

[new to this]

2 x 175 on a 3L are UNDERCARBED, it's only ideal size for a 2L engine.
it needs 2 x 2" Su really.

175 pairs max out and start to do their usual thing at 150-160bhp (massive stand off - over-rich and all that stuff)
+ I really don't like those late CD carb non fixed needles.....they only did it cos people were incapable of centring the fixed needles properly.

The only reason 175 work on the Stag is because the engine is so detuned the A-F mix simply can't get in there.
Try making an engine run right at 4-5:1 CR it's a miracle it works at all!

When i bought my sprint it came with 2 inch carbs HS 8 think they came from a jag

Dave

[mike@thenook]

[QUOTE=down_the_plug_hole;387475]If you change the exhaust manifolds you will have to change needle And advance curve.
most people never look at ignition advance at all.

Must admit, never fiddled with that - runs on 14btdc

[mike@thenook]

When i bought my sprint it came with 2 inch carbs HS 8 think they came from a jag

Dave

Think my Sprint had Hs6 SU’s - 175’s as standard?

Being a bit simplistic here the Sprint had a 16 valve head which has same number of valves as a Stag but half as many Pots so I can see that it would make sense maybe for bigger carbs to work on the bigger engine.
Only thing with that is that I would therefore seem right that a 600 Holley might work better than a 390 but never heard of anyone trying that option..

Maybe I’m just not thinking straight..?

[flying farmer]

Think my Sprint had Hs6 SU’s - 175’s as standard?

Being a bit simplistic here the Sprint had a 16 valve head which has same number of valves as a Stag but half as many Pots so I can see that it would make sense maybe for bigger carbs to work on the bigger engine.
Only thing with that is that I would therefore seem right that a 600 Holley might work better than a 390 but never heard of anyone trying that option..

Maybe I’m just not thinking straight..?

The box my Holley came in (about 30 years ago) had a size chart for different engine capacities and rpm. IIRC a 3 litre engine needed about 300cfm, so the 390 is actually oversized for the Stag.
Don't know just what a pair of 175 Strombergs actually flow, but I only got a fraction more power with the Holley due to the manifold being so restrictive, but it was easier to set the jetting.
Trouble is, every change from standard will require different jetting, manifolds, exhaust system and even compression ratio will affect how the carbs work.

Neil

[new to this]

Think my Sprint had Hs6 SU’s - 175’s as standard?

Being a bit simplistic here the Sprint had a 16 valve head which has same number of valves as a Stag but half as many Pots so I can see that it would make sense maybe for bigger carbs to work on the bigger engine.
Only thing with that is that I would therefore seem right that a 600 Holley might work better than a 390 but never heard of anyone trying that option..

Maybe I’m just not thinking straight..?

Mike

The sprint did come with 1.75s carbs as standard,mine were an upgrade,done before i bought it

Dave

[mike@thenook]

The box my Holley came in (about 30 years ago) had a size chart for different engine capacities and rpm. IIRC a 3 litre engine needed about 300cfm, so the 390 is actually oversized for the Stag.
Don't know just what a pair of 175 Strombergs actually flow, but I only got a fraction more power with the Holley due to the manifold being so restrictive, but it was easier to set the jetting.
Trouble is, every change from standard will require different jetting, manifolds, exhaust system and even compression ratio will affect how the carbs work.

Neil

Hi Neil,

yep, still got the box for mine and it has that size chart on it which does suggest that for a normal road car, the 390 is the one.
I didn’t get any more noticeable power with mine “out of the box” but fiddling with the jest it did get a bit better but only at the top end at the expense of the bottom - thereby removing a Stag benefit I felt.
I think you’re right on the manifold restriction, plus the way the Holley sits on the manifold the primary butterflies are out of centre which i’d Have thought may present another hurdle on flow. at least the stroms both flow into the centre of the manifold inlet.

[Kithmo]

[QUOTE=mike@thenook;387480]

If you change the exhaust manifolds you will have to change needle And advance curve.
most people never look at ignition advance at all.

Must admit, never fiddled with that - runs on 14btdc

It's a bit more complicated than that, 14 deg btdc is the initial timing. To change the advance curve you have to change the springs and weights in the distributor. If it's electronic ignition the map needs re-programming/changing in the unit.

[Guest]

Think my Sprint had Hs6 SU’s - 175’s as standard?
Being a bit simplistic here the Sprint had a 16 valve head which has same number of valves as a Stag but half as many Pots so I can see that it would make sense maybe for bigger carbs to work on the bigger engine.

The sprint is also a severely detuned engine.
I tested the head from the Lotus 907 and it flowed worse than the STD sprint head did.

It's fairly well proven the STD sprint motor was supposed to make 135bhp but it totally failed the grade in prod. (127 only)
Spen reported a well sorted blueprinted one was showing 150bhp on their Heenan dyno.

That would be the point the carbs totally maxxed out as the competing Lotus 907 (sunbeam lotus) from over in Ryton was making 160bhp officially in prod, from twin Dellortos with albeit a twin cam head, better exhaust, 2.2L and a commercial van slant 4 bottom end!



Stands to reason the STAG which is easily capable of 180bhp from 3litres is WAY WAY DETUNED.
In a few days I can start playing around with my prototype head again then attempt the impossible on the "hampton court maze" inlet manifold!

result expected thurs for at least the head.

[tractorjames]

Yes i used to tony hart springs and needles. Mine has tubular manifolds and straight piped front to back so that might have affected it

James

[Guest]

Basically if your engine has tubular manifolds the CR drops at low revs.....you a need a shed load more advance there.
Forget hearsay, static anything and received wisdom it's a fact.

If it's got a major restriction in the inlet ports it's gonna need loads of advance at the top end too.....easy 36 total.
If you're not working in this ball park the engine will feel sluggish and asthmatic.

I get this all the time, people assuming all sorts of stuff, then when you run it on the rolling road and show them the transformed torque curve and how much better it drives....they go ooohhh errrr....then usually forget to pay the bill....

Funny it's usually the kind of ppl that say F off at christmas when everyone is having their nice fun and I'm not..
..remember Bruce from Bristol...how I got him an extra 60bhp and a GT6 cabrio that drives like a dream?

That's why I sold my rolling road and don't work in xxxx country any more.

[mike@thenook]

Thanks for this, interesting stuff as always.
im running a normal distributor with the LD magnetic contacts (can’t remember the make) but not programmable.
Maybe one day i’ll go electronic but I’d love to find a way of making the inlet manifold more friendly, it’s really not designed for transportin air/fuel efficiently!