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Balancing the breathing of all 4 cylinders


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I've been just wondering as I look at my plenum box over my carbs....... how can the air from the chargecooler(or turbo) possibly balance pressure to all four air inlet horns? It comes in a small rectangular inlet right between #2 and #3 cylinders, and there must be a whole lot of turbulence getting to the 2 farther air horns. I wonder if there is a lean/rich imbalance going on...... How many of you all have had burned cylinders/ valves, etc, and which cylinders were they? If enough replies, I will make a graph, and let's see if there is any anectdotal data that can make some light on the question. Just to start things off, I have had (in my first engine) a burned piston(hole burned right through the top) in #4 piston, and also 2 burned valves, both in #1 piston.

Just by looking at the flow dynamics, as best I can guess, it looks like #1 and #4 might be lean, and more power from #2 and #3.... also, another indicator might be burned head gaskets.....

Any data from your records?

All this is leading to that I might be thinking about how to re-design the air distribution from the turbo to the air horns on the carbs..... Improve engine potential power without getting detonation on one or two cylinders, while the other two cylinders are still below threshold.

Paul

94S4

85TE

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As the plenum is effectively pressurised under driving conditions, I wouldn't have thought this would be an issue. I can also think of other cars where the imbalance appears far more assymetrical, wi

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As the plenum is effectively pressurised under driving conditions, I wouldn't have thought this would be an issue. I can also think of other cars where the imbalance appears far more assymetrical, without issue (e.g my TR6 PI is fed from one end of a fairly narrow 'plenum' feeding 6 cylinders.

Seizures on earlier cars, and other piston failures, are almost always associated with cylinders 3 & 4 (especially 4). My understanding is that its a design issue with the LC cooling system. You are especially at risk if your heater circuit is not working.

Looking at the mixture on my car (plug chops again....) There is no obvious indication of different mixture on different cylinders

cheers Steve

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The area that air is drawn into each trumpet is not that great as they sit closer to the closing plate rather than the backplate of the plenum. The air is drawn by all four at different times. I'd have thought these two factors mean the pressure differential between intakes while on the intake stroke would be quite small.

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I agree with Steve...when mine seized it did so on 3 &4 and I had the heater off at the time, so the circulation through the block was restricted for the rear cylinders. I've done some modifications to try to encourage more flow around that corner of the water jacket, but the heater is extremely important to get the flow through the jacket and out at the back of the engine and not simply in at the pump and out at the front of the head, without doing much good for the rearmost cylinders. Admittedly, I had been maintaining 130+ for many minutes.....!

Never noticed any mixture problems, piston crown hassles and suchlike; as long as you set the thing up properly it ought to stay good all the way up the range...as Steve says, it's pressurized by the turbo so the whole of the plenum will be full of air at the same pressure..and the mixture doesn't happen until it gets to the carbs, so that should be good too. HOWever...pressure isn't flow, and you may have something with the idea of turbulence...perhaps some sort of perspex version of the plenum and carb inlets on a flow bench with smoke or something to show the flow, eddies, turbulence etc. ?

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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  • 1 year later...

The "snow plow" director and plenum augmentation may help http://www.thelotusforums.com/forums/garage/vehicle/744-lotus-esprit-turbo/page__tab__mods__mod_id__1590

Edited by MrDangerUS
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Guest WausauLotus

Are you guys saying that there is some sort of cooling problem around # 4 if the heater is not "On/Working"? In an effort several years ago to try and get some heat into my 84T the mechanics took out the heater actuator valve and "manually opened" the system. I now have an engine problem (white smoke and misses) which I'm going to work on this winter. Is my possibility of a blown headgasket or worse in any way associated with this heater acutator issue?

Man this does get complicated!

Thanks.............Dave

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  • 1 month later...

Hi Dave...just picked up on this! On the 910 LC engine, the coolant comes in from the pump at the front of the block, and goes out to the thermostat and radiator from the front of the head. So there's no incentive for the coolant to circulate around the back of the engine, cylinders 3 & 4. However, the heater takeoff comes from the rear of the head.. so, if the heater is "ON", there is coolant flow through the block and head to the heater, which improves the flow around 3 & 4. With the heater "OFF", the coolant tends to stagnate around the rear of the block and temperatures can rise...leading to possible piston/liner seizure. I've modified my engine's internals by smoothing the port where the pump inputs coolant to the block and relieving obstructions to the coolant circulating. I also opened up the holes in the head gasket which obstruct the much larger holes in the head, around the exhaust side of 3 & 4, to try to get more flow in this critical area. So far, it seems to be working.

With your motor, I would think that having the heater permanently "ON" could have no detrimental effect and be irrelevant to whatever other problems you might have. I would recommend a compression check and a check for products of combustion in the coolant..both are simple, given the right equipment, and will aid diagnosis. Disconnecting plug leads in turn can also help to isolate defective cylinders.

Have fun!!!

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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  • 3 weeks later...

John,

Do you have any suggestions how to engineer a heater "bypass" for Summer time driving?

IMO, no one would like to drive w/heater ON in 80+F weather.

On page 18.05A of the Parts List there is a nice diagram showing Heater Matrix, Water Valve& plumbing. Me thinking: If one could install a diverter valve between the hose (5) going to the side nipple of the water Valve and return hose from the matrix, bypassing the water valve, than, coolant would circulate freely with the water valve closed (by passing the matrix). Also, I would add an auxilliary electric pump plumbed into the cyl head-to- chassis hose(#20) to help scavenging of the coolant from the rear of the cyl. head (cyl #4 area).

Wow, I think I answered my own question...

Didn't I?

LOL

What say you?

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Think your suggestions ought to work...one of the hoses comes from the head, the LH one; the other goes into the waterpump, so I don't think you'd need any other pump in circuit. In effect, all you'd need to do is to couple the outlet from the head to the inlet to the waterpump...and that ought to get the water circulating from the rear cylinders to the front; better system might be to route the outlet pipe from the head into the inlet pipe to the thermostat, the big ally pipe across the front of the engine...then, once the thermostat has opened, the water pump should force water out of the heater outlet and into the main cooling system route to the radiator. Some simple manual valve would suffice...divert in sumer, heater in winter. One would need to consider flow rates and relative hose diameters....have fun!

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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I think the simpler solution would be to fit a Tee into the hose sucking hot coolant from the front of the head (the nipple just below the temperature sensor)...page EB. 28 of Lotus Notes (section EB.9)

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  • 1 month later...

I fitted a 5/8" brass barbed "tee" at the horizontal spigot below the thermostat (heater matrix return), routeda 90 deg angled 5/8" hose along the rr bulkhead and rh compartment partition wall to another 5/8" tee fitted into the rr-of-the-head to heater matrix inlet hose. Works fine.

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  • 1 month later...
  • 1 month later...

Rich,

It is difficult to take a good picture, but take look here http://www.thelotusforums.com/forums/garage/vehicle/744-lotus-esprit-turbo/page__mod_id__1616__tab__mods

It shows a plan view of the T at the fuel pump and a view of the other T at the hose from the rear of the head (shotfrom the bottom)

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  • 3 years later...

Just noticed this interesting thread.

I can see the problem, the main water pump circulation into the block and out of the head, both at the front.

There is another path though is there not? There is a hose elbow which comes out the rear of the head and into the black water rail pipe which leads into the large curved pipe with a swept-tee which would assist flow. This path would be present surely if the heater is off?

Yes the other cylinders also route into the water rail, but the inlets along the rail are a quite small diameter so not sure how much these resist the flow of water from the larger rear pipe along the rail. 

One possible change might be to reverse the flow of water along the water rail, so the rear of the rail routes back to the front via a hose into the big curved pipe.

Or am I way off beam here? 

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  • 7 months later...
On 19/02/2018 at 01:00, MrDangerUS said:

On 1989+ cars equipped with a water cooled turbo, some flow is maintained trough the turbo to the header tank. I'm afraid, flow may be not large enough to make a difference.

On my S4s the header tank was cooking up pretty badly. It was so hot that the plastic nipple on the tank cracked and started leaking. It has fallen apart when I removed the turbo hose.  In late Spring, I have added a coolant bypass circuit (as described in my previous posts) and an Aluminium header tank. This Summer, I went for a 1200 miles trip in hot and humid weather (85-90F). I run A/C constantly, so the heater valve was closed all the time. I have had NO problems and my turbo survived Summer heat conditions.

 

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Edited by MrDangerUS
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