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RS Motorsport :: Classic Speed Restored
Carrying on from "The Works Escorts" forums of years past, RS Motorsport is dedicated to those small Fords from the Golden Era of Motorsport, namely the 60's, 70's and 80's.
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Roger Miller
Course Official
Joined: 21 Dec 2005
Posts: 2034
Location: Adelaide, South Australia
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Roger Miller
Course Official
Joined: 21 Dec 2005
Posts: 2034
Location: Adelaide, South Australia
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Roger Miller
Course Official
Joined: 21 Dec 2005
Posts: 2034
Location: Adelaide, South Australia
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Shaun Timmerman
P Plater - C3 License
Joined: 31 Oct 2006
Posts: 78
Location: Victoria, AUSTRALIA
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Roger Miller
Course Official
Joined: 21 Dec 2005
Posts: 2034
Location: Adelaide, South Australia
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 Posted: Wed Jul 25, 2007 1:43 pm Post subject: |
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Well...........
In a crossflow I recon u pretty much wasting your time.
In a 15 to 1 ..........say........ pinto with super raised pistons, there could be some merit.
I feel at this point, the pistons would be better grooved to accomodate combustion.
http://www.popularhotrodding.com/tech/0604phr_508cube_big_block_chevy_build/index.html
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Last edited by Roger Miller on Wed Jul 25, 2007 3:09 pm; edited 1 time in total |
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Roger Miller
Course Official
Joined: 21 Dec 2005
Posts: 2034
Location: Adelaide, South Australia
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| Posted: Wed Jul 25, 2007 1:50 pm Post subject: |
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Well said.
| Quote: | Quench Clearance and Deck-Height
Although a quench-type chamber is not very desirable from a performance standpoint, nearly all production cylinder heads have quench areas. Actually, the term “quench” is a misleading description. The quench portion of the chamber is that area where a flat portion of the head and a matching flat portion of the piston close together at top-dead center, significantly reducing the volume of the chamber.
From the name, it sounds as if the quench area is supposed to restrict combustion, but in fact, the quench design is used to enhance combustion in a chamber that has a relatively large diameter. When the piston and head quench surfaces come together during the compression-ignition changeover, the combustion gases in this area are pushed over into the open part of the chamber, creating turbulence that improves the combustion process.
For maximum performance with a quench-type cylinder head, the quench clearance should be as tight as possible, but there must be sufficient clearance between the two surfaces to prevent any contact at top-dead center.
The desired quench clearance is actually a figure selected as random by the engine builder, and once it is selected, the builder must calculate a corresponding piston deck-height (the distance from the deck of the piston to the deck of the block). The total quench clearance will include the piston deck-height and the compressed thickness of the head gasket (the thickness after the cylinder head is clamped down with the recommended fastener torque). Therefore, the thickness of the compressed gasket – which is normally supplied by the gasket manufacturer – is subtracted from the quench clearance, and the resulting dimension is the required deck-height.
It is hard to recommend a desired quench clearance that will be correct for all engines, but I think 0.038-inch of clearance between the quench surfaces is an absolute minimum in an engine with a 4.00-inch bore and about 0.007-inch of piston-to-wall clearance. However, if the piston clearance is greater, say 0.009- to 0.010-inch, this may not be enough. A safe figure for all-around performance is 0.040-inch. Anything up to about 0.045-inch is probably okay, and I wouldn’t worry about a little extra clearance as long as it was close to these recommendations.
But remember, if you let the quench clearance open too much – to 0.060-inch or more – you’re going to lose power. This much opening at the quench will allow excessive amounts of the intake charge to remain in the quench area as the piston reaches top-dead center, and especially if the piston has a high dome to obstruct the spread of the flame front, these gases may not be properly combusted during the ignition phase. This significantly reduces combustion efficiency.
I’ve also heard there are some builders who claim an engine will make more power if you let the piston “smack the heads a little.” I think this sort of talk is mechanical nonsense, and I would not recommend it under any circumstances. When you disassemble an engine for inspection, always check the piston and head decks on the right bank for signs of contact. Because of the crank rotation and piston sway in a conventional V8, the pistons in the right bank tend to show signs of contact before those on the left, and if you see signs of contact, I think you should open the quench clearance a little bit or you’re going to bread some parts.
Another important thing to watch in the quench area is to make certain that when the piston is at top-dead center the quench area is exposed to the open part of the chamber. If the quench decks are not parallel or angled slightly toward the valves, the quench area may be closed off from the rest of the chamber as the piston dwells near the top of the stroke, and gases trapped in the quench will not be combusted properly, this can lead to secondary combustion and detonation problems. |
Smokey Yunick's Chevy Engine Guide
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Roger Miller
Course Official
Joined: 21 Dec 2005
Posts: 2034
Location: Adelaide, South Australia
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| Posted: Wed Jul 25, 2007 3:02 pm Post subject: |
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More ............
Magnificent Quench
What is the most, exact precisely defined occurrence in all piston engines? It isn’t ignition timing, combustion, crank indexing, or valve events. It is Top Dead Center. You can’t build an engine with an error at Top Dead Center because TDC is what everything else is measured from. Spark scatter, crank flex and cam timing can move, but TDC is when the piston is closest to the cylinder head in any one cylinder. The combustion process gets serious at Top Dead Center and about 12 degrees after TDC, most engines want to have maximum cylinder pressure. If maximum cylinder pressure occurs 10 degrees earlier or later, power goes away. Normal ignition timing is adjusted to achieve max cylinder pressure at 12 degrees after TDC. If your timing was set at 36 degrees before TDC that is a 48 degree head start on our 12 degree ATDC target. A lot of things can happen in 48 degrees and since different cylinders burn at different rates and don’t even burn at the same rate cycle to cycle, each cylinder would likely benefit from custom timing for each cylinder and each cycle. Special tailored timing is possible but there is an easier way—“Magnificent Quench”. Take a coffee can ½ full of gasoline burning with slow flicking flame. Strike the can with a baseball bat and you have what I would call a “fast burn”, much like what we want in the combustion chamber. The fast burn idea helps our performance engine by shortening the overall burn time and the amount of spark lead (negative torque) dialed in with the distributor. If you go from 36 degrees total to 32 degrees total and power increases, you either shortened the burn time or just had too much timing dialed-in in the first place. If you have really shortened the burn time, you won’t need so much burning going on before Top Dead Center. Now you can retard timing and increase HP. Did you ever have an engine that didn’t seem to care what timing it had? This is not the usual case with a fast burn combustion but an old style engine with big differences in optimum timing cylinder to cylinder will need 40 degrees of timing on some and others only need 26 degrees. If you set the distributor at 34 degrees, it is likely that 4 cylinders will want more timing and 4 cylinders will want less ( V- . Moving the timing just changes, which cylinders are doing most of the work. Go too far and some cylinders may take a vacation. Now what does quench really do? First, it kicks the burning flame front across and around the cylinder at exactly TDC in all cylinders. Even with spark scatter, the big fire happens as the tight quench blasts the 32 degree old flame around the chamber. Just as with the coffee can, big flame or small flame, hit it with a baseball bat and they are all big instantly. The need for custom cylinder-to-cylinder timing gets minimized with a good quench. The more air activity in a cylinder you have the less ignition timing you are likely to need. When you add extra head gaskets to lower compression you usually lose enough quench that it is like striking the burning coffee can with a pencil. No fire ball here and that .070-.090 quench distance acts like a shock absorber for flame travel by slowing down any naturally occurring chamber activity. A slow burn means you need more timing and you will have more burn variation cycle-to-cycle and cylinder-to-cylinder, result more ping. Our step and step dish pistons are designed not only to maximize quench but to allow the flame to travel to the opposite side of the cylinder at TDC. The further the flame is driven, the faster the burn rate and the less timing is required. The step design also reduces the piston surface area and helps the piston top stay below 600 degree f (necessary to keep out of detonation). All of our forged pistons that are lower compression than a flat-top are step or step dish design. A nice thing about the step design is that it allows us to make a lighter piston. Our hypereutectic AMC, Buick, Chrysler, Ford, Oldsmobile and Pontiac all offer step designs. We cannot design a 302 Chevy step dish piston at 12:1 compression ratio but a lot of engines can use it to generate good pump gas compression ratio. Supercharging with a quench has always been difficult. A step dish is generally friendly to supercharging because you can have increased dish volume while maintaining a quench and cool top land temperatures. You may want to read our new design article for more information. ".
By John Erb
Chief Engineer
KB Performance Pistons
http://kb-silvolite.com/article.php?action=read&A_id=39
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chris pfeiffer
P Plater - C3 License
Joined: 19 Jun 2006
Posts: 105
Location: Melbourne
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| Posted: Wed Jul 25, 2007 10:15 pm Post subject: |
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You mean all i had to do was hacksaw a few slots and not even
remove the valves while i did it ?
I've wasted a lot of time and effort
Chris
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Shaun Timmerman
P Plater - C3 License
Joined: 31 Oct 2006
Posts: 78
Location: Victoria, AUSTRALIA
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| Posted: Wed Jul 25, 2007 10:35 pm Post subject: |
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Chris,
Yes, it appears so...... lol  
P.S. The datsun rods are on hold, as with the rest of th N/A bottom end.
I have since purchased an ems for the turbo motor so concentrating on finishing that first.... Decided I needed to finish some projects before starting more...lol
Shaun.
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Tom Murphy
P Plater - C3 License
Joined: 15 Jan 2007
Posts: 84
Location: Ireland
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| Posted: Thu Jul 26, 2007 12:05 am Post subject: |
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Hello Shaun,
Did you notice any improvement with the slots?
Regards
Tom
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Shaun Timmerman
P Plater - C3 License
Joined: 31 Oct 2006
Posts: 78
Location: Victoria, AUSTRALIA
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| Posted: Thu Jul 26, 2007 11:02 am Post subject: |
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Tom,
My motor is no where near refined enough to notice the improvements... Neither is my testing...... It was also done with additional porting, so there was no benchmark. Was more a case of practicing porting control at the time...... I have read a lot on this subject as I found it quite interesting... Some swear by it, some think it is a load of shite... Some reproduced figures to match, others found no measureable gains.....
Each to there own I guess....
Shaun.
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Danny M
Seasoned Racer
Joined: 07 Jan 2006
Posts: 1483
Location: Brisbane, Qld
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| Posted: Fri Jul 27, 2007 7:31 am Post subject: |
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I haven't got time at the moment to go through all the text as I'm assembling my engine again but the idea of grinding flame slots is an extremely old one which came out of aircraft in the 2nd world war to promote flame propogation and stop detonation when you increase the compression as all the gain you will see in drivability and power is coming from the compression increase and not the slot as the slot is promoting an even fire
The best example would be the use of lumpy top pistons in a pinto when you have to fire the spark around the corner of a lump if you were to mill a slot through the middle you are accomplishing the same thing but you still can't beat using a smaller chamber and a flat or dished piston
Danny
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Roger Miller
Course Official
Joined: 21 Dec 2005
Posts: 2034
Location: Adelaide, South Australia
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| Posted: Sat Aug 04, 2007 10:23 am Post subject: |
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More
| Description: |
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Download |
| Filename: |
The Bottom End.pdf |
| Filesize: |
14 KB |
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230 Time(s) |
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Tom Murphy
P Plater - C3 License
Joined: 15 Jan 2007
Posts: 84
Location: Ireland
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| Posted: Sun Aug 05, 2007 1:14 am Post subject: |
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Roger,
Good to see you are keeping up with your reading 
I am not saying that I think the flame grooves are a great thing but photos I have seen on the net indicate that the flame burns into the squish area more than without the grooves.
This can only be a good thing?
Regards
Tom
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