twin carb manifold - need heating?

[Dave]

Hi,

Would anyone be able to tell me as to whether a twin manifold for a grey motor would need to have a water heating pipe through the base of it.

ive been advised by a carb expert who raced grey motors in the 60's that if it is not heated, the horsepower will be dramatically reduced and it is not worth touching...however, i dont believe that the stardard manifold is heated anyway!?

any help would be great.  American auto pasts stocks some sort of alloy intake manifold for grey motors, but i dont think it is heated.  Is there a way to make a heating duct underneath it?

It would be running extractors, so would have less heat than a normal manifold anyway.

Cheers
Dave

[Fast_Eddie]

Dave,

I am not an expert, but I believe that the standard grey inlet manifold is heated via the exhaust. You may note that the exhaust manifold and inlet manifold are bolted together.

Further, I think the heating is contolled by a spring which shuts off the exhaust gas as the manifold reaches operating temperature.

When you fit extractors to a grey and retain the standard inlet manifold, you loose the functionality of the heating process but I do not know the effect on horsepower.

My understanding is that the water heated manifold found in later red motors was to assist in cold starting and idle, rather than normal operating conditions, but others may confirm or refute this.

Finally, I haven't seen a twin stromberg manifold for a grey with a water jacket, but they could be out there. The one I am preparing for my car does not.

Regards

Ed

[ChrisB]

Hi Dave,
I have one of those manifolds for twins on a grey with a water tube. I got it from "Slims Auto Spares". I will get a photo over the weekend and post it here for you. I grabbed it at the time for a long term project, as it gets cold here in ACT and the old girls dont like it until they warm up. There was a recent thread re this trouble on EJ Daves car having trouble in the cold. Dr Terry gave a good suggestion, worth looking for


ChrisB  

[Dave]

Thanks fellas,

I'm in Brisbane, so its obviously not so bad except for a couple of days here and there in winter.

The bloke at the carby centre claimed that they tested some grey motors on a dyno many decades back and there was far better horsepower with the heater - better vapourisatoin i guess.

You would think an intake manifold is bound to heat up being bolted onto a block though? He is the expert i guess.

Another option - does a two barrel stromberg (like an in the HD X2 or whatever it was called) bolt onto a standard grey motor manifold - or would it be too big for an unworked grey?

Cheers
Dave

[ChrisB]

Dave here is a picture of the manifold as promised. It is a Klienig manifold.


Cheers ChrisB  

[EJ_Dave]

Chris,

good to see the photo. Now I won't have to trek all the way over to your place to see it!

Dave- I did what Dr Terry suggested and for the Canberra winter it worked very well. I think that either heating the manifold or the incoming air would have a similar effect. I've never put my car on a dyno but before I rigged up the warm air intake my car performed very smoothly ONCE IT WAS WARM. It seemed to have more power after swapping the standard manifold and exhaust for extractors and a 2 inch system. The only downside was it was much more temperamental when cold.

I'm not sure how warm the inlet manifold will get due to heat from the head. Mine always seems to stay pretty cool (lukewarm or less after a reasonably long run- 10ks +?) under the carby so effectively the carby doesn't get heated at all. Vaporisation of fuel from the jet in the carbies would have a cooling effect that would counteract any heat coming from the head. This effect might be greater with two carbies or a dual throat carby (I have a single standard carb).

Regarding a dual throat carby, I have wondered about this myself. I think it may be possible if you modified the standard manifold by making the hole bigger and relocating the studs to suit the bigger carby. There looks to be plenty of room to do this on a standard manifold. I don't think a WW stromberg would be too big for a grey but it would need to be re-jetted.

Another carby option is to use a single stromberg from an HQ. This is something I have seen Dr Terry (and probably others) suggest. Apparently the venturi or something is larger, they flow better and produce worthwhile power increases. They will also bolt on with no changes to the manifold and accept the standard air cleaner (even and oil bath if you choose). Again, re-jetting would be required.

Hope this helps.

David

[Leon (FCCOOL)]

Maybe that guy you were talking to raced his grey out of the garage in the morning up to the end of his street becuase the reason that most perfomance manifolds have no heating is becuase it reduces horsepower.
the manifold is heated to warm the mix up when the motor is cold. this is sacrificed in perfomance manifolds to allow max performance once it is warm buy allowing a more dense air mix. just about all twin or triple carb manifolds, red or grey dont have any water jacket even 2 barrel single holley manifolds dont suffer from water heating.
remember that a colder mix will give you power, it affects the combustion the same way nitrous does but in a much milder dose, this is why some people have cool cans, heat wrapped headers and turbos use intercoolers.
When I was 19 I tried a 202 carb on the base of a grey carb, it seemed to go harder but I think part of it was psychalogical as this also gave it a louder throaty sound when I punched the gas, I dont know why it was like this but I got asked a few times if I was running multiple sidedrafts.
If your losing performance it may be running to cold so dont drive it like a girl, twin and triple carbs usually have their peak in a higher rev range than the single.
There used to be a guy around here with a shit hot FE running triple webbers off the side of a Duggan alloy crossflow head on a red and he had a heat sheild that sealed the carbs & manifold from the heat of the engine bay, this sheild went all the way up to the bonnet with foam to seal it, it was doing 13's but he reckoned it should be capable of 11's

[Dave]

G'day,

I will stand corrected as i'm no expert, however in terms of heat shielding, i think basically you want the air to be cool and dense when it is enhaled by the carbie or induction system.  This dense air is mixed with the fuel - yet the hotter the combustion chamber the better.  

Norm Beechey's yellow HT monaro had extensive aluminium shields around the filterless webbers that helped scoop cool air from the bonnet scoop.  The intake manifold however, is rarely shielded.

If you imagine squirting a jet of fuel onto a mildy warm hotplate, rather than a real hot one - the combustion will be smaller.  The density of the air needs to be changed before it hits the combustion chamber - as it will already be sealed off by the valve by the time the combustion takes places.

At the end of the day a grey motor is still going to be the slowest thing on the road - i just thought if you go to the trouble of setting up twins, it may as well be done properly.


Could someone explain the physics better? Dr Terry...?

Cheers
Dave

[Ed]

I think what ur trying to do is vapourise the fuel efficiently.

Heating the manifold will assist in vapourising the fuel making a better fuel/air mix.

Heavy droplets of fuel wont make a good fuel/air mix.

Intake air on the other hand is better if cool. ie denser.

There's a compromise on both counts though, and if it's driveability on the street you're after I would think a heated manifold is better.

my 2 cents.

Ed