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Old 30 Jun 2007, 17:05 (Ref:1950661)   #26
SidewaysFeltham
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Surely, aren't you confusing cylinder temp with gas temp?

The main reason some cylinders run hotter than others is because of compromises in the block design, siting of bores, one to another and wall thickness: as well as less effecient coolant flow. Bearing in mind the whole thing 's a compromise.

If the swept volume of each cylinder is the same: the compression ratio is identical, cylinder by cylinder, since the combustion chamber siszes are identical and the gasflow has been correctly sorted to ensure that the same weight of charge is received by each cylinder, then the combustion process should be pretty much the same.

One cylinder normally runs hotter than another because the mixture it's receiving is too lean; which means the jet for that cylinder needs sorting (if carbs) or the injection/injector needs looking at.

The whole point about the process is balance: balance of reciprocating bits: balance of gasflow; balance of BMEP, cylinder by cylinder.

If the Air:Fuel ratio delivered to each cylinder is identical (within whatever tolerances have been set), then the combustion temp should be pretty much identical. Unless there is something wrong with a plug, or the chamber or the squish design, which has caused an uneven flame front, for example.

And this will introduce precisely the sort of imbalance one is seeking to avoid, since it will make the engine rev lumpily (even if this isn't detectable, bearing in mind the revs and time/rev at say 9,000 RPM), and limit the engine's own acceleration, life, power output and rev potential.

Thats why blueprinting is so critical for classes which use standard engine bases.
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Old 2 Jul 2007, 14:44 (Ref:1952400)   #27
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I've had off centre crank, blew my engine up ! nothing to do with maniufacture, just badly ground giving different strokes!

I deck blocks so pistons are flush, they're flat topped so its all in the head . . . . I used to just use water and syringes courtesy of the HEad of PAthology at my local Hospital !
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Old 2 Jul 2007, 18:00 (Ref:1952615)   #28
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Amazed that a crank could be so off spec?

Of course, even if you ensure that all pistons are flush to the top of the block, if one or more webs of the crank gives a different stroke, then the swept volume would be different: as would the compression ratio!

Since CR= Swept Volume : TDC Volume i.e. combustion chamber (Including any space in the piston crown and above the piston in the bore).

Back to blueprinting!
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Old 2 Jul 2007, 18:01 (Ref:1952618)   #29
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Thats exactly how i did it zefarelly and it seemed ok but i will try diesel next time as gordon stated as that made sence with the air bubbles and all...
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Old 2 Jul 2007, 20:45 (Ref:1952807)   #30
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I use to use engine oil mixed with parrafin. Dunno why must have picked it up from someone.
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Old 2 Jul 2007, 21:18 (Ref:1952842)   #31
SidewaysFeltham
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Doesn't matter what you use, provided there are no air bubbles!

And the liquid is not given to rapid evaporation.

Most tuners traditionally used some form of oil, as it would not encourage rust on highly polished surfaces. Paraffin and Diesel do, of course!

I also used to use a mixture of Paraffin and SAE 30.

For the record, Bill Blydenstein, the ace engine tweaker of the Vauxhalls for the late Gerry "Ginger" Marshall, used to run his home-made gasflow rig by dumping a measured amount of gallons of water through each port and timing the flow with an accurate stopwatch!

If it works...............................
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Old 2 Jul 2007, 21:23 (Ref:1952848)   #32
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Off topic but Gerry and Ginger are two different people surely? Ginger drove the Kitten did'nt he?
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Old 3 Jul 2007, 06:42 (Ref:1953053)   #33
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Quite correct!

A Total Systems (Brain!) Failure!

Add tiredness to age.
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Old 3 Jul 2007, 08:36 (Ref:1953134)   #34
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Mind you I can remember Gerry with "gingerish" hair a long time ago !
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Old 3 Jul 2007, 08:57 (Ref:1953160)   #35
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Back on topic In the days when I could get the old non crossflow heads by the vanloads and for nothing , I would keep skimming more off the head untill it would "pink" on 5 star and then put in the next cam up the range. It was a bit time consuming to say the least ! But in the 60s it was the only way I could find out how far I could push C R . Now you can Google it .
Also I used to build up engines in the kitchen (but I bet I'm not the only one)
I used to find that I could use about 9,5 to 1 cr from when the inlet valve closed .

Last edited by GORDON STREETER; 3 Jul 2007 at 09:03.
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Old 3 Jul 2007, 09:14 (Ref:1953179)   #36
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thats Dynamic Gordon . . . not that I've ever seen you static!

interesting point though as I calculated just over 8:1 dynamic on one of my old engines, but 11:1 static with an A6 cam

CR coupled with cam timing is another debate is it not ? I've got 3 precrossflow heads to go on the flow bench this week ( you can still find them pretty cheap) and then they'll be skimmed and fetled to achieve desired CR ( hopefully!)
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Old 3 Jul 2007, 09:41 (Ref:1953214)   #37
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Mind you I can remember Gerry with "gingerish" hair a long time ago !
So can I! hence the confusion. At that time he was a Wrench for Team Lotus, I seem to recall? And much lighter too!
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Old 3 Jul 2007, 10:23 (Ref:1953255)   #38
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Originally Posted by GORDON STREETER
Also I used to build up engines in the kitchen (but I bet I'm not the only one)
So did George Bevan with his RAC Touring Car Championship (Thrice) winning Imps, driven by Bill McGovern (Whom memory nags me used to drive a furniture pantech when not racing!).
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Old 3 Jul 2007, 10:36 (Ref:1953273)   #39
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Wahts wrong with the living room ? I remember rebuilding a Lambretta engine layed out in a line on newspaper on the carpet in front of the fire

Kitchens tables are good for cleaning Twin 40's up though !
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Old 3 Jul 2007, 10:40 (Ref:1953278)   #40
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Some useful stuff on effective (Dynamic) CRs here:

http://www.empirenet.com/pkelley2/DynamicCR.html

And now, of course, with variable cam timing a reality (I thought of this in the mid 60s, discussed it with some of my colleagues at Ford Europe, but at that time we couldn't see a reliable way to achieve it!).

As you say, Zef, that's another topic.

The problem then becomes awfully dynamic and interactive. For example, if you use Blow Down Scavenge with either supercharging or turbocharging for optimum power (since the incoming charge "Blows" the spent gases out through the exhaust valve and ensures the cylinder is totally filled with fresh charge), then the overlap is nightmarish! So is the fuel consumption!

And the effective or dynamic CR would be quite small: which you need for forced induction, anyway!

And so it goes on..........................
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Old 3 Jul 2007, 13:29 (Ref:1953408)   #41
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interesting stuff, so Gordons got it right, and I'm not far off . . . aiming for 9:1 DCR and a static 12:1 CR

I'm going to ask my cam man what he reckons for a static CR as well, just for reference like !

my new cam is this


VALVE LIFT : 11.30 mm
DURATION @ 0.1mm Valve lift : 322 °
DURATION @ 1.0mm Valve lift : 274 °
PEAK DIFF.: maxlift @:106 ° ATDC
Valve lift at TDC w/o clearance:4.61 mm
1. w/o clearance at:0.45 mm valve lift

Valve opens : 54 ° BTDC 86 ° BBDC
Valve closes : 88 ° ABDC 56 ° ATDC

2. w/o clearance at : 1.35 mm valve lift 1.35 mm valve lift
Valve opens : 31 ° BTDC 63 ° BBDC
Valve closes : 63 ° ABDC 31 ° ATDC
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Old 3 Jul 2007, 15:11 (Ref:1953475)   #42
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Hi Zef

Compression starts when flow through the inlet valve ceases, which is around the time the valve reaches the seat or just before. Can you measure how many degrees before TDC that occurs with the clearance you are running on the inlet Zef?

Computing dynamic CR with the figures given reveals the problem:

With the valve timing of 31 63 63 31 the inlet valve closes at 117 degrees before TDC - although of course you state there is 1.35mm valve lift less the running clearance so compression cannot start at this point. If it did, you would need a static CR of 11.5:1 to give a dynamic CR of 9.07:1 with your rods and crank.

Taking the timing at 54 88 86 56 the inlet valve does not close until 92 degrees before TDC. Of course this isn't a true figure either as this timing is with zero clearance so the valve would have closed some degrees earlier. If this was the valve closing point a 12:1 static CR would give a dynamic CR of only 7.44:1.

If I was guessing I would say the valve closed 10-15 degrees earlier than this - in the range of 102-107 degrees before TDC.

My rough calculations show that to meet the dynamic CR target of 9:1 you would need a static CR of 13.4:1 if the inlet valve did not close until 102 degrees BTDC and 12.6:1 static would be required if the inlet valve closes at 107 degrees BTDC.

I'd be interested to see how my figures compare with the figures you get from your cam man and anyone else.

Phoenix
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Old 3 Jul 2007, 17:06 (Ref:1953555)   #43
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How can you arrive at the answer without access to the bore, stroke and other critical measurements, Phoenix?
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Old 3 Jul 2007, 18:03 (Ref:1953591)   #44
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Michael In the dim and distant past there was an aftermarket device called a VARICAM, I would have thought that it was a sort of mechanism like a dizzy advance and retard although I never saw one. I have read some very old mechanical books going back to the 1920s and its all there, but at the time the modern materials weren't availible. Even an adjustable C R engine. Although things have moved on the engine as we know it is still a compromise even F1 (ticking over at silly speeds) and has never been very efficient at producing power for the heat it generates.
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Old 3 Jul 2007, 18:11 (Ref:1953599)   #45
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Yes, Gordon, I very much agree about the inefficiency of the IC engine!

In fact, it's the sheer set of compromises that make engine tuning such fun! provided one is a professional masochist!

Varicam: that rings a bell here too??

Do you remember when 100 bhp/Litre was the Rubicon?

In fact with a normally aspirated engines that was reckoned to be pretty much the maximum theoretical output!

As were certain low cornering G levels!

How things advance.
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Old 3 Jul 2007, 18:32 (Ref:1953609)   #46
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Originally Posted by Michael C Felth
Do you remember when 100 bhp/Litre was the Rubicon?
.
it still is in my little world

and its widely regarded as the max without cheating or getting unreliable with legal guts!

I know its now been bettered, but . . . in period I think it was more like 80-85 per litre

just got back from an interesting afternoon on the flow bench . . . CFM vs CR seems to be the battle, and thanks to QEP for letting me use the kit, trouble is I come back with as many questions as answers
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Old 3 Jul 2007, 19:03 (Ref:1953635)   #47
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What engine are you running, Zef? And in which class?

How tight are the regs?
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Old 3 Jul 2007, 19:42 (Ref:1953673)   #48
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How can you arrive at the answer without access to the bore, stroke and other critical measurements, Phoenix?
Because Zef has told me those before!
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Old 3 Jul 2007, 21:39 (Ref:1953741)   #49
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fia period spec, 82mm bore, 72.75 stroke, 4.83 rod, 39.6 inlet vv, 34.5 ex, precrossflow, twin 40's 34 chokes

so fairly relaxed !

gordon has ran similar (ish!) with no restrictions and had 161 english shire horses, I've yet to break 140 with my shopping cams!
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Old 4 Jul 2007, 07:41 (Ref:1953950)   #50
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Phoenix: OK, thanks, All is now clear!

Zef: What class do you race in?
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