SU Dampers

[Badfrog]

Hi all,

 

I have extensively tweaked my SUs, whether the semi-original HS6 or the present HS8.

Among tweakable items, the dashpot dampers are quite difficult to optimize. Basically, if the dashpot moves too fast, the engine chokes on air and if it is too slow, the engine doesn't get enough mixture.

 

For HS6 and HS4, no problem: whether the carb is standard or highly tuned, the 8103 damper works best. Now for H8, it's another story. There are HD8 (damper 8112) and HS8 models. HS8 can have short (Jaguar XJ6, damper 8102 and XJ12 damper 8103) or long (Rover 2000 TC) dashpots necks.

I got a used pair of Rover HS8 equipped with 8119 dampers, both being normally found on .... HS2 carbs (8114 too).

 

By simple trial, I found that 8103 were OK for a pair of HS8 on a 2187 cc TR4 with sprint 88 cam.

 

Does anybody have a better idea?

[Dazzer]

Hi all,

 

I have extensively tweaked my SUs, whether the semi-original HS6 or the present HS8.

Among tweakable items, the dashpot dampers are quite difficult to optimize. Basically, if the dashpot moves too fast, the engine chokes on air and if it is too slow, the engine doesn't get enough mixture.

 

For HS6 and HS4, no problem: whether the carb is standard or highly tuned, the 8103 damper works best. Now for H8, it's another story. There are HD8 (damper 8112) and HS8 models. HS8 can have short (Jaguar XJ6, damper 8102 and XJ12 damper 8103) or long (Rover 2000 TC) dashpots necks.

I got a used pair of Rover HS8 equipped with 8119 dampers, both being normally found on .... HS2 carbs (8114 too).

 

By simple trial, I found that 8103 were OK for a pair of HS8 on a 2187 cc TR4 with sprint 88 cam.

 

Does anybody have a better idea?

 

You certainly know your dampers Badfrog!

 

Do you use 20/50 or 20 oil?

 

Used to always use 20/50 in all SU/Stromberg's, ironed out any flat spots.

 

I can remember taking the air filters off an early XJ12 coupe, fitted with Strombies, didn't go any faster (didn't need to) but made a fantastic noise.

 

How does the TR go with the HS8s?

 

Cheers

 

Dazzer

[stuart]

Hi all,

 

I have extensively tweaked my SUs, whether the semi-original HS6 or the present HS8.

Among tweakable items, the dashpot dampers are quite difficult to optimize. Basically, if the dashpot moves too fast, the engine chokes on air and if it is too slow, the engine doesn't get enough mixture.

 

For HS6 and HS4, no problem: whether the carb is standard or highly tuned, the 8103 damper works best. Now for H8, it's another story. There are HD8 (damper 8112) and HS8 models. HS8 can have short (Jaguar XJ6, damper 8102 and XJ12 damper 8103) or long (Rover 2000 TC) dashpots necks.

I got a used pair of Rover HS8 equipped with 8119 dampers, both being normally found on .... HS2 carbs (8114 too).

 

By simple trial, I found that 8103 were OK for a pair of HS8 on a 2187 cc TR4 with sprint 88 cam.

 

Does anybody have a better idea?

The only other alternative I could come up with is LZX 1507 as fitted to late 2300/2600 Rover SDI albeit on HS6. but it also depends on wether you have vented dashpots or dampers with holes in the caps.

Mostly trial and error as you have probably already found!

Stuart.

[Badfrog]

You certainly know your dampers Badfrog!

Do you use 20/50 or 20 oil?

I can remember taking the air filters off an early XJ12 coupe, fitted with Strombies, didn't go any faster (didn't need to) but made a fantastic noise.

How does the TR go with the HS8s?

Cheers

Dazzer

 

Hi Dazzer,

 

True, I'm quite bent on carbs as it's the easiest way to go fast(er). I use 30 monograde as initally recommended by Triumph. Easier to find than 20 monograde. I never use engine oil as it takes too much time to warm up to correct viscosity in cold weather.

Coupled to a 2" Phoenix exhaust with single silencer, the TR makes a great noise, a real head turner when going deliberately slow in 2nd gear in villages.

 

Seriously, I had two good reasons to step up to HS8.

First, the style. I don't like webers, they should stay on Alfas, or on Gurney-Eagle manifolds for US muscle. Strombergs make great flower pots. SU are truly THE carbs when dealing in british motoring. They were good enough for Wally "Pacey" Hassan and other Bentley boys, they're good enough for me.

 

Second, the improvement. HS6 or H6 carbs have a dead spot on frank acceleration due to an insufficient amount of readily available mixture, even if you use the long bodies of the H6's with the long manifold of the TR4IRS. This causes fast starts to be ... not so fast. In contrast, HS8's with the usual dashpot and venturi tuning, coupled to the long manifold rebored to 2" produce a great instantaneous acceleration without delay.

This system requires 0.100 jets and TS needles for optimal function.

 

Cheers,

Edited December 1, 2008 by Badfrog

[Badfrog]

The only other alternative I could come up with is LZX 1507 as fitted to late 2300/2600 Rover SDI albeit on HS6. but it also depends on wether you have vented dashpots or dampers with holes in the caps.

Mostly trial and error as you have probably already found!

Stuart.

 

Hi Stuart,

 

I have vented dashpots AND dampers with holes in the cap AND fiber spacers. The latter being really necessary if you don't want the dashpot to hit the damper repeatedly and unscrew it. There was another thread on this not long ago.

 

Just found out that LZX and WZX dampers are for HIF SU's (HIF 7 or HIF 44)

 

Cheers,

Edited December 1, 2008 by Badfrog

[67_gt6]

I never use engine oil as it takes too much time to warm up to correct viscosity in cold weather.

 

Hi, I'm inclined to agree that things change with the cold air - there seems to be a point where the benefit of the denser charge of air is lost to the effect of the cold on the carbs. But, with 20w50 oil wouldn't the oil - in theory - start out as thin (or thinner) than a straight 30 oil...?

 

andy

[Badfrog]

Hi, I'm inclined to agree that things change with the cold air - there seems to be a point where the benefit of the denser charge of air is lost to the effect of the cold on the carbs. But, with 20w50 oil wouldn't the oil - in theory - start out as thin (or thinner) than a straight 30 oil...?

 

andy

 

Andy,

 

You do make sense. I never thought of that, but I observed that at normal temp 20/50 SAE engine oil appears more viscous to the finger touch than 30 SAE chainsaw oil. Could be an illusion.

 

Opinion anyone ?

Edited December 1, 2008 by Badfrog

[stuart]

Hi Stuart,

 

I have vented dashpots AND dampers with holes in the cap AND fiber spacers. The latter being really necessary if you don't want the dashpot to hit the damper repeatedly and unscrew it. There was another thread on this not long ago.

 

Just found out that LZX and WZX dampers are for HIF SU's (HIF 7 or HIF 44)

 

Cheers,

According to the SU reference manual (Burlens) I have they are quoted as being for HS6 although some dampers are used for multiple different applications (and engine sizes) across the full range of carb sizes from H2s to HiF and HS8s. Dashpot springs can also make a difference as well.

Stuart.

[johnny250]

In HS6's I use SAE 10 motorcycle fork oil... (readily available down to SAE 5 at least if you need it) no sign of any flat spots on a six cyl. anyway,

 

john

Edited December 2, 2008 by johnny250

[Badfrog]

In HS6's I use SAE 10 motorcycle fork oil... (readily available down to SAE 5 at least if you need it) no sign of any flat spots on a six cyl. anyway,

john

 

John,

 

The fork oil as well as ATF oil are often used. I tried them myself and found that they are correct in viscosity but by a mysterious way (micro-splash?) they tend to disappear very fast from the dashpot. Some years ago, I mixed ATF with SAE 30, it worked fine but I got lazy about it. Chainsaw oil is nice.

 

Besides it comes as a pint container which finds its place it the boot, by the Lockheed canister, extra electric pump, extra coil, spare belts, tool box, jack, picnic box, travel cigar humidor, and the Missus' complete w-e apparel. I have a personal spot in the glove box for spare undies.

[North London Mike]

Andy,

 

You do make sense. I never thought of that, but I observed that at normal temp 20/50 SAE engine oil appears more viscous to the finger touch than 30 SAE chainsaw oil. Could be an illusion.

 

Opinion anyone ?

 

 

Hi Guys

 

Can't contribute constructively to the debate on the actual dampers as mine came with the car and 'if it ant broke don't fix it' riules apply

 

However, I do top them up and use the Penrite damper oil, neat little bottle, works realy well and easier to pour than from a 1 gallon can

 

http://www.penriteoil.net/files/WB34N3WFNJ/SUDAMP-PIS.pdf

 

I know you die hards all like to use engine oil and think this stuff is a con but I've tried both and think the Petrite stuff works better however, I do find myself topping up quite often, every other week/ 500 miles. How often do you top up

 

Comment: Think it works better but wastes quicker ! Could be that the overflow top up just blows off (bit like the first quarter of an inch of the dipstick, never top up to the full line as I'm sure you all know)

 

Pays your money and takes your choice

[Badfrog]

Hi Guys

 

Can't contribute constructively to the debate on the actual dampers as mine came with the car and 'if it ant broke don't fix it' rules apply

 

Sho'nuff, but what's yer number, pal?

[tthomson]

...... I have a personal spot in the glove box for spare undies.

 

Having never been in a position that needed me to replace my undies whilst in a moving TR, I would suggest these are 'extra' rather than 'spare' undies!! However, the imagination does boggle!

 

TT

[Badfrog]

Having never been in a position that needed me to replace my undies whilst in a moving TR, I would suggest these are 'extra' rather than 'spare' undies!! However, the imagination does boggle!

TT

 

Spares, trust me TT. French wimmen, they don't just boggle your imagination....

[Rhodri]

Badfrog, there is a website for SUs that says that you should not have vented dashpots and vented dampers- just one or the other as it destroys the vacuum. http://www.jcna.com/library/tech/tech0006.html . See part 1. Although if yours are working well then that disproves the theory!

 

Rod

[Badfrog]

Badfrog, there is a website for SUs that says that you should not have vented dashpots and vented dampers- just one or the other as it destroys the vacuum.

Rod

 

Rod,

 

Jim Taylor is perfectly right. I do have vented dampers but the vents I was referring to for the dashpot are the two large holes down in the flat base of the piston. I don't have upper venting in the small shoulder of the dashpot . The theory is safe. Whatta relief...

 

Cheers,

[Badfrog]

Hullo, Inspecteur Finicky talking on ze forum,

 

I was kinda puzzled by this airvent story. I checked my secret library for the "BMC S.U. carburetter service parts list" (an original cum fingerprints, mind you). Sez here that 8112 dampers are for HD8 carbs while HS8 require 8102.

Now, the bad part: 8102 is identical in size to 8103 but without a hole in the cap, and the HS8 dashpot has no internal airvent. The only carbs where I could identify dashpot airvents were the H series.

H6 and HS6, usually found as replacement on TR4s for original H6 have no airvent and 8103 holed dampers.

 

So, if Jim Taylor is right, how come HS8 have no venting at all (no airvent, no hole in damper) and still are supposed to work? Should they require a degree of constant depression? Guess it's up to me to try HS8 with 8102 and 8103 in a radarless zone. I'll let you know.

 

PS: if anybody needs info from the BMC book, I'd be happy to oblige.

 

Cheers,

Edited December 6, 2008 by Badfrog

[Badfrog]

Hullo, Inspecteur Finicky talking on ze forum again,

 

I just got a pair of new 8102 dampers from Burlen. They came without holes in the cap and a plastic shoulder in lieu of fiber washer . OK so far.

The weird thing is that the steel axis is not firmly set in the cap but moves around a bit. The axis ends with a little "ball" that rotates in a casing molded in the cap. Just like a human hip joint.

Anybody knows about these new things?

 

Vicious little mutant thingies....

[john.r.davies]

Badfrog,

I don't know different dampers for original carbs from a hole in the engine, but I fear you have a basic misapprehension.

Unless you misspoke yourself:

 

Basically, if the dashpot moves too fast, the engine chokes on air and if it is too slow, the engine doesn't get enough mixture.

 

The purpose of the damper is to slow the piston as you accelerate. That makes the air through the throat go faster for the same volume, so that more fuel is sucked out into the flow. The mixture richens to assist the acceleration. So slower, more damped piston=richer mixture, not as you wrote.

 

'Tuning' a damper is more to do (IMHO) with one's driving style than absolute performance. One keen for economy could use paraffin to match their feather footed action on the throttle - well, maybe not. A hot shoe like you should choose a thicker oil. But also IMHO, the damper, let alone the oil in the damper matters very little in the rather larger question of squeezing more perfomance out of an engine.

 

JOhn

Edited December 14, 2008 by john.r.davies

[Rhodri]

My personal views-

 

I think that if you are a hotshoe, you will use a very thin oil, to allow the dashpots to rise quickly thus opening the jet and allowing more fuel out quickly. If you are an economy driver, then use thicker oil to damp the dashpot more, thus controlling the mixture quantity. The viscosity of the oil controls the reaction to throttle movement.

 

The mixture will not vary if the dashpot rises quickly, or slowly, as it is governed by the needle profile ( fuel ) and the dashpot obstructing the intake, ( air ).

 

Obviously it is not as simple as that!

[67_gt6]

My personal views-

 

to allow the dashpots to rise quickly thus opening the jet and allowing more fuel out quickly.

 

I don't think this is what you are trying to achieve. In theory, with a perfect profile needle, at any given throttle opening the fuel/air drawn in is always the same. So, when the dashpot raises you do get more fuel but there is also more air - the ratio doesn't change. During acceleration you want it to change - richer - before it settles back down to normal cruising mixture.

 

Let's say your carb needles have 8 "stations", and each station gives you a perfect 14.7:1 air fuel mixture for a constant velocity of air. However, for acceleration, you need it to be more like a 13:1 ratio during the acceleration period. You can only achieve this by slowing the rate at which the piston moves between the stations so that, briefly, you are getting a richer mixture because the rate at which the fuel is drawn in is higher than would normally be the case because you have changed the velocity, due to the disparity between piston position and throttle opening eg normally if your throttle is open 30%, the piston/needle is at position X = 14.7:1. But, with damping, when the throttle is first opened to 30% it is held slightly at position W rather than jumping straight to position X - if it moved quickly between stations you would always be getting 14.7:1 ie no acceleration. This leads to a change in the velocity at the venturi - effectively an accelerator pump. Normally the SU is operating at constant velocity - fuel metering is achieved by maintaining the velocity of air at the venturi point and thus the profile of the needle determines the amount of fuel drawn at any given piston position. By damping the piston you interrupt this.

 

Andy

Edited December 15, 2008 by 67_gt6

[Badfrog]

Hi guys,

 

Thanks for your comments. It's not easy to answer to three persons at the same time but I'll try.

 

First, I'm not such a hotshoe anymore. Well, then, sometimes...

My problem is to upgrade my car in the most thorough and comprehensive way. I don't want to modify the damper, I want the best original one for my carb setting. The inital problem was the lag in acceleration with HS6 carbs and the original short intake manifold. I learned from Kas Kastner that this was a classic and that both parts had to be separately improved. The manifold is the easiest: just use the long one from TR4IRS and improve the passages through polishing (not too much) and angle redesign with a grinder.

 

A short parenthesis: air filters are incredibly important in this matter. Paul Tegler reports on the same story on his website and all he had to do to stop the choking was discard his K&N filters and go back to original filters for his spitfire.

( http://www.teglerizer.com/triumphstuff/index.html )

 

Now for the carbs. Many people go for Webers, I don't. I love SU's. So I had three choices: One, reprofile the pistons of my HS6 (front and rear redesign), it was nice but I wanted more. Two, a pair of double SU's as in the Sabrina engine (whoa, that much?). Three, two HS8, ... yummy.

This is where the problem started. I initially tried a pair of HS8 from a very modified and very destroyed Dolomite that had the original 0.125 jets (UJ needles). I was constantly too rich and unable to get a nice idle. The mileage was ludicrous (plus 30 % consumption).

So I fitted 0.100" jets fitted in lieu of the original 0.125". I knew the mix would be automatically leaner and I expected excess air problems. I initially tried KD and RH needles but consumption was truly excessive again, with poor idle. I finally solved the air/mix problem rather nicely in terms of acceleration and consumption with TS needles and NGK BP6HRIX plugs.

Unfortunately, this setting resulted in severe choking above 4500 rpm, a problem that already occured with KD needles, although much less pronounced and almost acceptable. Intuitively, the car was getting too much air as the "shsssss" noise was easily recognizable and when I relieved my foot, the car would start again after a few seconds and go further up. Pumping the pedal got me to 5500 rpm. So the piston was going to high, too fast.

 

John wrote :

"The purpose of the damper is to slow the piston as you accelerate. That makes the air through the throat go faster for the same volume, so that more fuel is sucked out into the flow. The mixture richens to assist the acceleration. So slower, more damped piston=richer mixture, not as you wrote."

 

John, maybe I miswrote somewhere but I totally agree with you: the piston must be slowed during acceleration and must not be pushed too high at full speed to maintain richness.

So I don't think we disagree when I say:

"Basically, if the dashpot (sorry I meant piston) moves too fast, the engine chokes on air and if it is too slow, the engine doesn't get enough mixture.". Slow is not too slow: slow is right speed, too slow is not enough fuel coming up through the jet.

 

Rhodri wrote:

"I think that if you are a hotshoe, you will use a very thin oil, to allow the dashpots to rise quickly thus opening the jet and allowing more fuel out quickly. If you are an economy driver, then use thicker oil to damp the dashpot more, thus controlling the mixture quantity. The viscosity of the oil controls the reaction to throttle movement. The mixture will not vary if the dashpot rises quickly, or slowly, as it is governed by the needle profile ( fuel ) and the dashpot obstructing the intake, ( air )."

 

There I disagree. It's true the needle and the venturi obstruction are the only parameters, but air will come in faster than fuel (viscosity plus duct diameter), hence my car's momentary choke. You HAVE to control the travel speed of the piston.

 

And that's why I fully agree with Andy "67_GT6" when he writes:

"But, with damping, when the throttle is first opened to 30% it is held slightly at position W rather than jumping straight to position X - if it moved quickly between stations you would always be getting 14.7:1 ie no acceleration. This leads to a change in the velocity at the venturi - effectively an accelerator pump. Normally the SU is operating at constant velocity - fuel metering is achieved by maintaining the velocity of air at the venturi point and thus the profile of the needle determines the amount of fuel drawn at any given piston position. By damping the piston you interrupt this."

 

Finally, where do we stand?

 

1) It is possible to find the right damper in my setting : I have to recheck the dashpot/piston adjustment which controls the inner depression in the dashpot assembly and get the right damper and oil.

2) It is not possible and I have to return to 0.125 jets and work on fuel consumption with leaner needles. This I don't believe because HS8 have been equipped with 0.090" and 0.100" in various Rover cars with engines of a displacement similar to mine.

 

Conclusion: Stay tuned for more testing and ultimate glorious success with La Marseillaise and Champagne for all.

 

Cheers,

Edited December 15, 2008 by Badfrog

[stuart]

Of course the other variable is how worn are the dash pots with regard to the clearance between them and the pistons. They were manufactured as a matched pair and it would be just what you need if some DPO has swopped them

Stuart.

[Badfrog]

Of course the other variable is how worn are the dash pots with regard to the clearance between them and the pistons. They were manufactured as a matched pair and it would be just what you need if some DPO has swopped them

Stuart.

 

Absolutely right, that's what I meant by checking the dashpot/piston adjustment. I'm afraid I had this repeatedly postponed lately. Lucky enough, I found the figures for a perfect match in th haynes book. Test is easy: empty oil, remove spring, push the piston up max, invert (piston facing ground) and count seconds for slide to separation.

 

Not stupid to catch piston with the hand rather than let it hit concrete.

 

Cheers,

Edited December 15, 2008 by Badfrog

[Rhodri]

Badfrog, I stick to my thoughts. If the dashpot goes up quickly, i.e. thin oil, then more fuel and air will go into the engine quickly and vice versa, with thick oil. The dashpot controls the fuel as well as the air.

 

An easy way to find out is to fill the dashpots with EP 90 or more and drive the car, then try it with paraffin!

 

Rod