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75evo
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Re: 24v headwork - power gains

Post by 75evo »

JK,

You mean like a safety switch? Turn on full speed at say 200F?
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Re: 24v headwork - power gains

Post by MD »

Before the thermosiphon effect has pulled the hot water to your switch the engine is crap.
After 40 years of motoring, I am still waiting for this to happen.
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Re: 24v headwork - power gains

Post by Jim K »

In numbers, if the electric pump thing will operate from, say, 78-82*C, then the 'safety' switch will turn on the fan at ~85-87*C. Modern engines have cooling systems and thermostats operating up to 98*C in the interests of economy and emissions!
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Re: 24v headwork - power gains

Post by Mats »

MD wrote:
Before the thermosiphon effect has pulled the hot water to your switch the engine is crap.
After 40 years of motoring, I am still waiting for this to happen.
So you will run the engine without any pump at all until the thermoswitch in the radiator switches the pump on to full speed? What will make the water in the radiator hot enough to flip the switch except luck?
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Re: 24v headwork - power gains

Post by Giuliettaevo2 »

If he places the thermocontact in the cylinderhead it would work a lot better i guess.
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Re: 24v headwork - power gains

Post by Jim K »

Why go into absurd detail here? Its clear that with a mechanical pump you only have a thermo-switch for the fan on the radiator and with an electric pump, you have two sensing points: one where water exits the engine (which controls pump PWM) and one for the fan on the radiator. For safety and in case the pwm dies, you can have a backup on/off sensor to operate pump (no pwm, just on/off). I believe this is simple enough and all that is required.
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Re: 24v headwork - power gains

Post by Mats »

JimGreek wrote:Why go into absurd detail here? Its clear that with a mechanical pump you only have a thermo-switch for the fan on the radiator and with an electric pump, you have two sensing points: one where water exits the engine (which controls pump PWM) and one for the fan on the radiator. For safety and in case the pwm dies, you can have a backup on/off sensor to operate pump (no pwm, just on/off). I believe this is simple enough and all that is required.
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I concur.

This will keep the engine at the correct temp and use as litte power as possible. Robust like a rock, not like it hasn't workt before I mean... :wink:
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Re: 24v headwork - power gains

Post by 75evo »

Actually JK, GiuliettaEVO2 makes a good point. Probably better to hook it up to a sensor on the thermostat housing.

Imagine if your engine block is already at 230F, PWM controller failed, pump is off, no circulation, and the radiator temp is around 180F, by the time the temp in the radiator reaches 200F for the pump and fan to turn on, the head is warped.

How long does it take for water in the engine to make its way to the radiator? It could take a long time because there is no forced circulation. You're relying on thermosiphon where the water channel is quite small (radiator hose) and long. And the fan switch is usually at the bottom (usually coolest part of the rad).

Or better yet, just have the PWM and a manual override switch like Mats said.
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Re: 24v headwork - power gains

Post by Jim K »

Read my post once more: two sensing points: one where water exits the engine (which controls pump PWM) and one for the fan on the radiator. For safety and in case the pwm dies, you can have a backup on/off sensor to operate pump (no pwm, just on/off).
That's 3 sensors: One for the pwm pump cct, one backup (pump on/off) and one for the fan in the std factory location. I think that covers all cases.
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Re: 24v headwork - power gains

Post by slyalfa »

if I may go back a few pages before a coolant pump thing.
back to the hydraulic lifters

"lifters start pumping up at that particular RPM"
7800 or whatever
I thought they pumped down and you lose lift?

What would happen if if you take a hydraulic and shim it to have the clearance for a flat tappet when all the way pumped down. Then it would only pump it that last tiny bit for a quit idle and low speed. but at hi RPM it would only be able to pump down to the same spec as a flat tappet. so get the best of both worlds. it still would have a bit more mass then the flat tappet but might make for a good compromise.

maybe even modify them so they only work at a max of the biggest lash you would ever want to use. so they could never get too big or too small
in case they do pump up or pump down.
so the only adjustment they can do it take the lash to 0 from the normal flat tappet spec.
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Re: 24v headwork - power gains

Post by Jim K »

There's significant difference between hydraulic and mechanical cam profiles. You can't use both systems with one or the other.
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Re: 24v headwork - power gains

Post by slyalfa »

interesting I did not know that. I know rollers were different to compensate for the rolling contact surface, but I did not know there was any difference for a hydraulic vs mechanical as I thought the valve just followed the lobe and the hydraulic just takes up any slack making for a more or less perfect 0 lash.
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Re: 24v headwork - power gains

Post by Jim K »

The hydraulic lobe is designed taking into account the 'compressibility' of the hyd. follower. If you insist on using a hydraulic lobe with solid followers, you'll end up with a more aggressive lobe, with very high acceleration characteristics and very little necessary clearance (0.05-0.15mm) difficult to control effectively and uniformly for all valves. Running hydraulic cams with solid lifters is considered by many a cheap performance 'trick'... :roll: However, in Alfa-like followers, converting to solid is not so simple and buying solids is very expensive! Given the lack of maintenance/adjustment, I prefer hydraulics, especially after seeing them behave well up to 7800rpm. Keep in mind that conventional-design higher duration lobes will usually extend this rpm limit upward. Lobe acceleration is a most important parameter determining ultimate rpm capability of lifters, maybe more important than rpm itself -I hope you can see what I mean here.
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Re: 24v headwork - power gains

Post by Tim0172 »

JimGreek wrote: On the simpler and more practical side, some guy in the UK is about to try bolting on 2.5liter heads on the 3liter block and that should be a very interesting exercise! Smaller ports mean higher velocity and better low speed performance which is the main detriment of the 24v 3liter.
Jim K.
Hi Jim i am that Guy :D ( by the way from Holland not the uk)
I have been talking to some headport experts asking there opinium About the headports.
So i decided to still go ahead with the 3,0 heads basicly because the exhaust valves on the 2,5 head are to small for the 500 cc cylinder. This would mean also adress the exhaust valves on the 2,5 head incl the intakes wich would become even more expencive.
So 3,0 heads It is for my engine! Along with 38mm intake valves and epoxy the intake Ports to get a Nice shape in the port and reduced csa.
Along with the 9.9mm of lift wich the colombo&bariani Cam Will give this would be a head that would flow enough for 300hp and Redline of 7350 revs/min All things being 100% ofcourse...
Feel Free to give your opinium or thoughts....

Regards,
Tim
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Re: 24v headwork - power gains

Post by Jim K »

I can only convey my own observations here. Surely, 24v 3liter heads have huge ports, a fact reflected on the flowbench, with ~138cfm stock intake flow, in theory good enough for ...350hp! Therefore, there is absolutely no need to work on the heads, except maybe to improve exhaust flow a little. Since we can't increase stroke past the 78mm of the 3.2liter, what this engine needs, is higher compression, cams and revs! I believe I have proven bottom end reliability by repeated use above 7500rpm, but stronger components are really required for serious play. I'm confident that specific power levels of 95hp/liter are easily attainable with our properly built 24v engines, without sacrificing low speed tractability. If you don't care much about putting around town, the sky's the limit as they say. 100-103hp/liter is not extraordinary and you'll still work mostly under 8krpm. Seems that your most important choice is cams... If you have a knowledgeable cam grinder with a broad database (not necessarily Alfa) sit with him and discuss what you can use.
If you have a fwd car, the 156/gta/147 6-speed box has good enough ratios for playing around. If you have rwd... you can only be happy with the TS box, happier with a 10:43 box and happiest with the 9:41 box from the 75 1.6. Of course, you'll have to modify/change various parts like clutch/bellhousing, slave cylinder, LSD, output flanges etc, but these are minor things once you decide to go this way. However, highway cruising will become a distant memory! As a reminder, note that the only official 75 3liter racers (Spain, 1989-91) used the 1.6 gearbox (9:41).
About building up 3liter intake ports... A very good idea but one I would personally not try, for fear of filler chunks detaching and causing lots of damage.
For owners going to 3.5-3.7liters, low speed behavior will be greatly improved but this would be expected.
Don't know if all this helps! :?
Jim K.
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