Reversion - Page 2

zefarelly · 15 Apr 2008, 10:01 (Ref:2177873)

having read more, and more again, and re read what I read beforehand, I'm not a million miles off optimising what an ancient inefficient old iron 2valve motor will achieve, without cheating that is, but that last 10% is the hardest bit to get.

theres no doubt that the theories say most of the numbers people tell me they have are rubbish.

phoenix · 15 Apr 2008, 10:23 (Ref:2177893)

Quote:

Originally Posted by zefarelly

having read more, and more again, and re read what I read beforehand, I'm not a million miles off optimising what an ancient inefficient old iron 2valve motor will achieve, without cheating that is, but that last 10% is the hardest bit to get.

theres no doubt that the theories say most of the numbers people tell me they have are rubbish.

You know what they say Zeff (or said, now they use lights!) "When the start flag drops, the BS stops"

zefarelly · 15 Apr 2008, 11:34 (Ref:2177946)

indded Phoenix, not all the 180 bhp twin cams can beat a 125 bhp GT !

BoT . . . .1.5mm shims made . . .90lb on the nose . . . .we'll see what happens . . . more soon

terence · 15 Apr 2008, 11:53 (Ref:2177964)

Quote:

Originally Posted by zefarelly

indded Phoenix, not all the 180 bhp twin cams can beat a 125 bhp GT !

BoT . . . .1.5mm shims made . . .90lb on the nose . . . .we'll see what happens . . . more soon

125 BHP! Did you forget to fit the cam last time?

zefarelly · 15 Apr 2008, 13:22 (Ref:2178035)

it was just a 1" rod in the block with some blobs welded on randomly, I read about it in an MG tuning book

terence · 15 Apr 2008, 13:54 (Ref:2178056)

Quote:

Originally Posted by zefarelly

it was just a 1" rod in the block with some blobs welded on randomly, I read about it in an MG tuning book

Touche!. Was it Dave Vizards.

zefarelly · 15 Apr 2008, 14:17 (Ref:2178078)

no, but it had the same effect as a scatter cam, or was it scatter cushion

I think we'd better leave it there before we get banned from the race tech forum, its the only part of ten tenths I can take seriously ( usually).

Q: IF I go over 90lb on the nose, to say 100lb to avoid valve bounce etc, I'd probably have to change tappets every race, is there a general limit ? I'd assume its directly related to lobe and tappet size . . .

terence · 15 Apr 2008, 15:36 (Ref:2178131)

Yes quite agree Zef. The extra springing will inevitably mean more ware in all of the valve gear,not just rockers,if you have a few hours spare,how about polishing them just to remove any stress raisers.As for the tappet faces,they will take a fair pounding if your a little generous on clearances,otherwise they should be up to it.Why would you need to go so high though?

GORDON STREETER · 15 Apr 2008, 16:46 (Ref:2178173)

I went through a season fitting new springs between qualifying and race before I started to use BDA ones. As I don't use silly lift there is a window that is usable. Yes I do know you want to open the valves immediately but you would need a "square" cam !!!!!

zefarelly · 15 Apr 2008, 18:50 (Ref:2178247)

Quote:

Originally Posted by GORDON STREETER

. Yes I do know you want to open the valves immediately but you would need a "square" cam !!!!!

I was speaking hypathetically really, I don't lift a huge amount, 11.5mm or thereabouts, but if one was to get carried away in a certain direction . . .

at the end of the day the budgets of money and time come into it all anyway, I can probably only afford to go so far every time I retune, then if it goes pop I have to revert to afoordable/reliable until I can have another go

changing springs sounds a bit extreme . . . but I suppose you do rev a little bit higher than the average 105E

AU N EGL · 17 Apr 2008, 20:57 (Ref:2180172)

Quote:

Originally Posted by zefarelly

I was speaking hypathetically really, I don't lift a huge amount, 11.5mm or thereabouts, but if one was to get carried away in a certain direction . . .

at the end of the day the budgets of money and time come into it all anyway, I can probably only afford to go so far every time I retune, then if it goes pop I have to revert to afoordable/reliable until I can have another go

changing springs sounds a bit extreme . . . but I suppose you do rev a little bit higher than the average 105E

I think every race mechanic knows this one:

1- Power
2- Reliability
3- Affordablity

You can only have two.

ian_w · 19 Apr 2008, 10:38 (Ref:2181266)

Quote:

Originally Posted by zefarelly

Q: IF I go over 90lb on the nose, to say 100lb to avoid valve bounce etc, I'd probably have to change tappets every race, is there a general limit ? I'd assume its directly related to lobe and tappet size . . .

What you are looking at is something called Hertz stress - its a complex thing but basically the surface stress on the cam is a function of the Load divided by the radius of the cam.

The lowest cam radius is on the nose and you would imagine that the highest load is at maximum lift - this is not however true. At very low speeds, i.e. cranking then the spring force is dominant and the max load is over the cam nose.

However, at higher speeds the maximum load is during the valve opening phase as the cam has to accelerate the mass of the valve, remember Force = mass * acceleration. Over the nose of the cam the load is actually quite low as the valve is deceleration and therefore the spring force is offset by the negative acceleration force of the valve.

Overall, I would not have thought a 10% increase in spring load would cause you a major wear problem.

I was unsure from your previous posts whether the cam you are now running is a new design. If it is then this could be the cause of your problems. Cam dynamics is a hugely complex subject particularly with pushrod engines. If your new cam has too fast an opening acceleration, this can cause the spring to start surging at a high speeds. What happens is that the opening rate of the cam matches the natural frequency of the springs and the spring goes out of control causing the valve to 'float'. I have seen it before where the surge is someway short of the max rpm and as the speed increases further then the valvetrain comes back under control as the cam frequency no longer matches the spring frequency.

Adding spring load by shimming is unlikely to fix this, you really need to change the cam profile. Alternatively you can do such things as fit dual springs and vary the interference between them to create damping. You can also run close to coil bind as this 'destroys' the surge wave as the valve reaches full lift. You can also get around it by fitting springs with a higher natural frequency as well as playing about with pushrod stiffnesses. All of these will require considerable development time and money, may be easier to switch back to a known 'good' cam profile.

zefarelly · 20 Apr 2008, 07:26 (Ref:2181809)

we ran a smaller capacity engine yesterday with the same set up, 60 thou shims gave 90lbs on the nose, revved to 7800 quite happily, amazingly flat torque curve from 5-7k ( within 5lb/ft ) and peak power at 7050, in short it produved 7% more power per litre than my engine, and its pretty much standard Ford inside

I'll finish reworking my 'new' cylinder head and fit it this coming week, we'll be back on the dyno when theres a beggars slot!

R59 · 20 Apr 2008, 08:54 (Ref:2181885)

No, they weren't welded on randomly, they ended up like that due to the wear and tear in the machining equipment at the factory.

I remember Pete Baldwin used to get his 649 cams from BL, then send them off to be re-machined as per the drawing because the lobes used to be all over the place caused by knackered equipment at BL.

Did someone mention guitars?

zefarelly · 20 Apr 2008, 13:48 (Ref:2182127)

I don't have the right equipment to check cams that accurately, but its amazing how bad some are!

Just got all my guitars hanging on the wall in the music room . . . an acoustic, and just the half dozen

**dtype38** · 20 Apr 2008, 16:45 (Ref:2182223)

Quote:

Originally Posted by R59

Did someone mention guitars?

Perhaps you chould use a lower frequency one. How about mine

phoenix · 20 Apr 2008, 17:18 (Ref:2182235)

Quote:

Originally Posted by zefarelly

we ran a smaller capacity engine yesterday with the same set up, 60 thou shims gave 90lbs on the nose, revved to 7800 quite happily, amazingly flat torque curve from 5-7k ( within 5lb/ft ) and peak power at 7050, in short it produved 7% more power per litre than my engine, and its pretty much standard Ford inside

I'll finish reworking my 'new' cylinder head and fit it this coming week, we'll be back on the dyno when theres a beggars slot!

Zeff, I'm intrigued. Was it running the same cam profile - lift, duration and timing - that you had on your engine?
Was it a 1498 cc? And what size inlet valves was it running?

Thanks

Phoenix

zefarelly · 20 Apr 2008, 19:02 (Ref:2182277)

excuse the quality, but if we're talking axes . . .heres mine

oh, BoT . . .same cam, 1300 had contactless ignition and 37/31 valves, 1500 39.6/34.5 and points, both on 40's 32/34 chokes, otherwise the same

**dtype38** · 20 Apr 2008, 21:58 (Ref:2182401)

I consider myself fully out-axed

jerryk · 25 Apr 2008, 11:04 (Ref:2186414)

excuse me, but apart from 1 on the wall they all seem to be broken . they all have 2 strings missing!

terence · 25 Apr 2008, 11:23 (Ref:2186430)

Thats because Zef only has two fingers on his playing hand

zefarelly · 25 Apr 2008, 18:45 (Ref:2186879)

4 actually

one for each string, and a thumb to hang on with

its a far superior persuit to strumming

I'm sure you can all play the one string banjo though

Robyn Slater · 26 Apr 2008, 14:45 (Ref:2187469)

[QUOTE][/I've just spent 4 hours on the old head ( Goodwood one) re porting to get to 80% port/valve size . . QUOTE]

Anyone know where this theory comes from?

I,m intending to fit twink valves in a 1300 pre-xflow head.
The std. inlet throats are already larger than the 80% rule!!!!!!

So it seems i,d be fitting valves which are going to cause more shrouding and also weigh more.

Any thoughts?

phoenix · 27 Apr 2008, 17:10 (Ref:2188389)

[QUOTE=Robyn Slater]

Quote:

[/I've just spent 4 hours on the old head ( Goodwood one) re porting to get to 80% port/valve size . . QUOTE]

Anyone know where this theory comes from?

I,m intending to fit twink valves in a 1300 pre-xflow head.
The std. inlet throats are already larger than the 80% rule!!!!!!

So it seems i,d be fitting valves which are going to cause more shrouding and also weigh more.

Any thoughts?

The theory comes from the velocity at which the air coming through the inlet tract is stable - i.e. there are no losses due to turbulence etc. - and refers the ration between the valve diameter and the port diameter - note NOT the valve diameter and port throat diameter.

I believe these values have largely been found by experiment and are only a guide, because each port and each valve in individual engine designs will behave slightly differently, because of interference to the flow from things like valve guides and stems, port geometry, the proximity of valves to the cylinder wall or head (shrouding) etc.

Even in the most perfect aerodynamic environment, airflow become turbulent at about mach 0.6. As ports tend to fall short of perfection, because they have things like vale guides and valves in the way and bends in them - all of which do their best to cause disruption to the airflow - turbulence sets in at a lower speed - usually somewhere around mach 0.5 in a 'good' port.

Air flow exiting a poppet valve becomes turbulent at an even lower speed - somewhere between mach 0.29 and mach 0.32 depending on the shape of the valve, valve seat, port angle, port throat and the proximity of the valve to the cylinder wall or the combustion chamber.

If you check the ratio between speed in a 'good' port and a 'good' valve, given above, you will see that the port can be 64% of the area of the valve area (or the port 80% the diameter of the valve) though on some engines the port can be stable at only 60% of the area of the valve (about 77.5% of the valve diameter).

Large valves definitely give the possibility of making more power, so I think you should not dismiss them too readily. I think standard Lotus TC valves are 38.862 mm diameter and the 'Big Valve' ones are 39.751 mm. Ports for these would need to be 30-31 mm and 31-32 mm respectively. Surely your ports are not that large already?

zefarelly · 28 Apr 2008, 07:52 (Ref:2188893)

I know people have tried massive valves, but shrouding is the next issue with precrossflow heads with a legal bore size (82mm)

I'f I overbore to 1650 and run 85mm I can deshroud easily, and maintain compression far more readily without skimming the head until its paper thin and blowing head gaskets . . .its all a bit of a compromise

TC sprint valves are about the best compromise I think, I'm pretty sure the heads won't take much more than a 32mm port without breaking through, and I've already spent over 2 days getting that far . . . I need to try a few gash heads for experimentation.

re flow . . . .32mm port, no valve 143 cfm, with valve ( std stem diameter ) I lost 10 cfm up the top end but its better right through the mid range with a bigger port . . . .lets hope it works when its actually on the engine.

BoT . .reversion appears to be solved byt 60 thou spring shims, my balls up on installation basically