Aluminium windsor block ?
- Thread starter flatchat
- Start date
Hi Colin, that's simply not true.
You are right that one of the primary reasons to use twin plugs is to deal with the shielding issue where there's a pronounced piston crown. But that's only half the story, at best.
Twin plugs, for example, substantially help with pre-detonation in a high CR engine. That's one reason why you can typically run a half point (sometimes a full point) higher CR in a twin plug engine. You'll probably notice that most twin plug engines (porsche, alfa are just two examples) ran 10.5 or even 11.0 CR prior to the advent of detonation sensors. In a small 2.0 ltr engine a half point of CR isn't going to give you a whole lot, whereas in a 5.0+ ltr engine it might be quite meaningful.
There are other material reasons to use twin plugs in certain situations, where performance is meaningfully enhanced, and we can debate those at length. But my point here is simply that the shielding issue is not the full story.
As I understand it you are speeding up the flame front so you require less advance in the timing. However nowadays there are rather more economic ways of achieving the same effect than the complications of twin plugs.
Really, once the flame has been ignited its speed would be a function of what the fuel type was & how much it had been compressed wouldnt it, two plugs firing at the same time would just mean a shorter distance for each flame to travel for both flame fronts to burn the whole or as much as possible of the compressed mixture.
Half the distance equals half the time?
Thats better..
Not really, as one flame front has to pass the other before you get complete burn all you are getting is a better burn in an inefficient / slow, ie hemi type chamber.
We did a lot of dyno work on a Birdcage Maserati we built with a twin plug head and in so doing became, probably , the words expert on '50s Magnetti Marrelli twin plug distributors ( fat lot of good that did us !) They have a beautiful vernier type mechanism, which is a pain to set up, to synch the two sets of points but what it does mean you can adjust them to fire before each other or vice versa. We frigged about for ages with various combos but can honestly say we never saw any differance than firing both plugs together. The pistons did have a wacking great dome on them so probably that had a bearing, compression was about 11.5 - 1
Mike
Interesting stuff guys, for sure.
We can all debate about flame fronts and how they travel and what speed and does it help prevent pre-detonation caused by hot spots in the chamber and such. There's probably multiple reasons and valid theories about it all (I have my own opinion and theories....), but the fact of the matter is that when running a high CR in an old skool (pre pre-detonation sensors) engine, twin plugs in a mainstay in managing that high CR. Obviously, it has to be done with finesse, which includes placement of both plugs, timing of the firing, shape of the cc, valve timing/overlap, etc.
Personally, I believe that twin plugs can help with pre-detonation in a high CR engine due to the fact that the plugs are going to fire a few degrees prior to TDC, help to burn clean and complete (less residual combustible in the chamber to pre-detonate on a hot spot on the next revolution ie. the non-firing stroke in 4 stroke engine), and speed up the burn, particularly where there's some shielding due to a pronounced piston crown. My own (limited) hands on experience with a twin plug alfa engine for a GTA replica confirms this, even if my theory is wrong..... The sad thing about the alfa twin plug engine is that because of the small displacement, when you jack up the CR you get maybe 10 or 15 add'l hp going from 9/9.5 to 10/10.5 CR....and you go through a s-load of hassle to get that to work reasonably well. Perhaps in a 331/347 or 351+ SBF the hp delta could be more meaningful. Just a thought.
We can all debate about flame fronts and how they travel and what speed and does it help prevent pre-detonation caused by hot spots in the chamber and such. There's probably multiple reasons and valid theories about it all (I have my own opinion and theories....), but the fact of the matter is that when running a high CR in an old skool (pre pre-detonation sensors) engine, twin plugs in a mainstay in managing that high CR. Obviously, it has to be done with finesse, which includes placement of both plugs, timing of the firing, shape of the cc, valve timing/overlap, etc.
Personally, I believe that twin plugs can help with pre-detonation in a high CR engine due to the fact that the plugs are going to fire a few degrees prior to TDC, help to burn clean and complete (less residual combustible in the chamber to pre-detonate on a hot spot on the next revolution ie. the non-firing stroke in 4 stroke engine), and speed up the burn, particularly where there's some shielding due to a pronounced piston crown. My own (limited) hands on experience with a twin plug alfa engine for a GTA replica confirms this, even if my theory is wrong..... The sad thing about the alfa twin plug engine is that because of the small displacement, when you jack up the CR you get maybe 10 or 15 add'l hp going from 9/9.5 to 10/10.5 CR....and you go through a s-load of hassle to get that to work reasonably well. Perhaps in a 331/347 or 351+ SBF the hp delta could be more meaningful. Just a thought.
Ron Earp
Admin
I'm not much of a believer in twin plug ignitions as being the solution for problems with high compression motors. Anecdotal for sure, but my friend Ed rebuilt his Porsche 911S (early model, high compression, has been rebuilt a number of times) two years ago and went to a twin plug ignition. Other than lightening his wallet a lot and causing some headaches, Ed reports no difference in the running of the motor. I know that goes against all Porsche lore and knowledge gurus in Porsche land, but Ed is used to that dealing with the Porsche crowd.
Ford evidently does believe in twin plug ignitions, but for certain applications and reason that is a bit different than cited here. I've been researching new trucks and started reading about Ford's new (for 2010) 6.2L gas motor. It uses a twin plug ignition and one of Ford truck forums had the lead engineer for the 6.2L on the board for an open question and answer session.
The thread is long and located here:
Ask the engineer for the new 6.2l gas engine! - Page 4 - Ford Truck Enthusiasts Forums
But some of the posts, like #55 and some later ones, talk about why they went to the twin plug solution.
From Mike the Ford Engineer:
But here goes. It has a large bore. It has a large bore to enable larger valve area and reduced stroke, to be able to increase the engine speed to meet the power objectives.
It needs 2 plugs to burn the charge on a timely basis. You need to burn the charge relatively quickly because the longer it is in the chamber unburned, the more heat the charge picks up from the chamber and the more knock (detonation) limited you are. If you increase charge motion (tumble/swirl) the time to burn the charge reduces but the charge picks up more heat from the chamber (higher charge motion leads to higher heat transfer), so you again end up being more knock limited. Adding charge motion via swirl or tumble also reduces port flow coefficients so horsepower is reduced.
Twin plugs and a high flowing port was a good solution for this engine we feel.
The compression ratio is also a fuel economy compromise between unladen and laden (or towing) driving with regular gasoline. If you go to too high a CR, it's great for city driving, but when towing a trailer the spark needs to be retarded too much to avoid knock, and fuel economy suffers.
The components in the engine are typically designed with an adequate safety factor to the specific application. If there is a redesign to improve performance then all the parts get looked at and re-designed to ensure durability and reliability.
Ford uses the twin plug ignition system to increase knock tolerence, as mentioned, but it also lets them run a bit more timing resulting in a bit more torque (power). This motor only has a 9.8:1 compression ratio, certainly nothing out of the ordinary these days.
So, it may very well be the power increases cited by by the twin plug aficionados is more about maximum timing the motor will withstand, a direct consequence of the twin plug ignition.
I hope they fire more than a few degrees before TDC, more like 30-40 degrees BTDC, otherwise that will be one poor running engine!
Ford evidently does believe in twin plug ignitions, but for certain applications and reason that is a bit different than cited here. I've been researching new trucks and started reading about Ford's new (for 2010) 6.2L gas motor. It uses a twin plug ignition and one of Ford truck forums had the lead engineer for the 6.2L on the board for an open question and answer session.
The thread is long and located here:
Ask the engineer for the new 6.2l gas engine! - Page 4 - Ford Truck Enthusiasts Forums
But some of the posts, like #55 and some later ones, talk about why they went to the twin plug solution.
From Mike the Ford Engineer:
But here goes. It has a large bore. It has a large bore to enable larger valve area and reduced stroke, to be able to increase the engine speed to meet the power objectives.
It needs 2 plugs to burn the charge on a timely basis. You need to burn the charge relatively quickly because the longer it is in the chamber unburned, the more heat the charge picks up from the chamber and the more knock (detonation) limited you are. If you increase charge motion (tumble/swirl) the time to burn the charge reduces but the charge picks up more heat from the chamber (higher charge motion leads to higher heat transfer), so you again end up being more knock limited. Adding charge motion via swirl or tumble also reduces port flow coefficients so horsepower is reduced.
Twin plugs and a high flowing port was a good solution for this engine we feel.
The compression ratio is also a fuel economy compromise between unladen and laden (or towing) driving with regular gasoline. If you go to too high a CR, it's great for city driving, but when towing a trailer the spark needs to be retarded too much to avoid knock, and fuel economy suffers.
The components in the engine are typically designed with an adequate safety factor to the specific application. If there is a redesign to improve performance then all the parts get looked at and re-designed to ensure durability and reliability.
So, it may very well be the power increases cited by by the twin plug aficionados is more about maximum timing the motor will withstand, a direct consequence of the twin plug ignition.
I hope they fire more than a few degrees before TDC, more like 30-40 degrees BTDC, otherwise that will be one poor running engine!
I think for most engines thermal barrier coatings are a more economical route to try.
I would to give a plug since I Do have the d
Dart alloy block heads flywheel Etc..etc. The engine produces over 500 Hp and totally street-able. With the new technology with engine builders today can build pretty much build anything you want and make it street-able. One thing for sure it is costly but well worth it.
Anybody that drives a car with a Alloy engine will notice the difference in weight and performance immediately. Performance = $$$
MerryXmass
Dart alloy block heads flywheel Etc..etc. The engine produces over 500 Hp and totally street-able. With the new technology with engine builders today can build pretty much build anything you want and make it street-able. One thing for sure it is costly but well worth it.
Anybody that drives a car with a Alloy engine will notice the difference in weight and performance immediately. Performance = $$$
MerryXmass
Jim Rosenthal
Supporter
I would think that two plugs per cylinder only make a difference in an engine that was designed that way from the beginning. I'll bet as an add-on they don't make a lot of difference.
Years back I had a BMW R90S, and I remember reading that when those engines were bored out to even larger displacements, they required two plugs per cylinder because the piston top area was so large, just to burn all the fuel mixture going in. This wasn't about performance so much as getting them to run smoothly, from what I remember. Maybe they shouldn't have been bored out in the first place.
Years back I had a BMW R90S, and I remember reading that when those engines were bored out to even larger displacements, they required two plugs per cylinder because the piston top area was so large, just to burn all the fuel mixture going in. This wasn't about performance so much as getting them to run smoothly, from what I remember. Maybe they shouldn't have been bored out in the first place.
Ron Earp
Admin
I think that is a bunch of BMW lore says me who has ridden a early R100 for many a mile using only one spark plug per cylinder. I know guys who did the twin plug conversions on them and the lower plug on the kickstand side would often foul out due to oil pooling in it with the bike on the stand.
In doing more truck research I found that Dodge is using a twin plug ignition in the new (09 or 10) 5.7L motors they have. Reasons cited were the same as Ford, they could run a bit more advance and boost that torque curve ever so slightly to keep up with the competition.
flatchat(Chris)
Supporter
Gotcha number locked in Dodge.
Looks like no arguments for the Dart block --- onto heads, don't know about the twin plug jobs tho?--------
Looks like no arguments for the Dart block --- onto heads, don't know about the twin plug jobs tho?--------
Steve Wood (PANAVIA)
Lifetime Supporter
Dont - forget Shelby Engine Company has been revised under new management and they will have some very nice Shelby blocks in 289 and 351w ( and 427 ) coming out soon.
I saw a prototype of the Aluminum 289 yesterday. -- that will be a nice little motor!
I saw a prototype of the Aluminum 289 yesterday. -- that will be a nice little motor!
flatchat(Chris)
Supporter
'Onya Steve, keep us posted :thumbsup:
We could enter the raffle and "Win" one
We could enter the raffle and "Win" one
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