Esprit Turbo project car - part3 - the further continuation

[Lotusfab]

Static Compression ratio

I used perspex and a syringe. Heres my calcs. I couldn’t find the manufacturers gasket spec, so I used figures I have seen else where. When I went through it with the expert we calculated 7.7 CR. Heres what I got after measuring.

 

[Lotusfab]

So if this is correct the CR has increased to half way between the HC and standard Turbo. The question now ( I’m not qualified to answer) what would be the effect of this and is it necessary to adjust the boost pressure? 
remember standard Turbo    7.5.1    
                    HC.                           8.1

Fabians Bond car.                7.76.

assuming the gasket thickness is correct? 

[CHANGES]

At 7.76:1 you would probably be fine..   You could also just tweak  boost back a fraction to get spot on ..  You can use one of the on line calculators to give boost for required final C/R.     

I have to take my hat off to how quick you did all the measurements..   well done .  

[Lotusfab]

10 minutes ago, CHANGES said:

At 7.76:1 you would probably be fine..   You could also just tweak  boost back a fraction to get spot on ..  You can use one of the on line calculators to give boost for required final C/R.     

I have to take my hat off to how quick you did all the measurements..   well done .  

Thanks Dave, I’m glad you brought this up its nice to know exactly what the CR is and I would not have measured it without your input. I will look into the boost correction and modify it as required.

[Lotusfab]

I am thinking using this graph to stay within the original engine parameters I should reduce the boost from 8 to 6 psi?

[jonwat]

3 hours ago, Lotusfab said:

Static Compression ratio

I used perspex and a syringe. 

Out of interest did you balance the combustion chamber volumes? 😀

[Lotusfab]

Combustion chamber volumes, of course! 😄😄😄Heres my piston check, little grease on the edges to hold the water. Same  for the head with the spark plug in.I think the wastegate will have to start to operate at 5.5 PSI to achieve 6psi max. I don’t have any practicle experience of this, its entirely theoretical.  I know the other engines are running standard wastegates. I think the spring length will have to be shortened to achieve reduced psi  or a shim made for the casing. The HC has uprated cooling and I’m not racing, I want reliability, so it might be wise to reduce the boost to give the same final compression as the stock Turbo.

Now I really must get on with the build!😄😄😄😄

[Lotusfab]

This time I have dotted the I’s and crossed the T’s twice!

[Lotusfab]

Error

 

[Lotusfab]

I have fitted a short spindle for the oil filterIn order to do an oil pressure test without the sandwich plate. I will test it with and without the cam towers fitted. I hope oil goes everywhere! 

[drdoom]

Not to tread on Dave's turf by any means but I'd suggest less focus on CR, more on fuel delivery, ignition timing and overall soundness of build. Assuming high grade fuel will be used and the car is not to be wrung out hard in general it would seem the marginal change of SCR should be of little consequence. Turbo engines will not long tolerate hard running with either lean mixture or undue advance, in my limited experience. Good work so far!

[Lotusfab]

I suppose if I reduce the boost to match the same final compression ratio the power output will reduce to that of a standard Turbo, but my engine will be far more robust. Ina, guessing the ignition timing and fuel wont change much if the final compression is stock. Anything else and the jetting and ignition timing might have to change slightly?

[drdoom]

If the minute change in SCR is what you inquire about , then no, there is no need to fuss about creatively with regard to tune. It takes considerably more to affect power output of an engine than a small change in SCR. There is a good case however in having the lot checked out by a competent professional to ensure that fuel mixture and spark timing are indeed where the engine is happy, once it's up and running with things bedded in. You owe yourself that peace of mind after all this.

[Lotusfab]

 Yep I will investigate it to the Nth degree until I am satisfied its running as well as it can be. I hope to progress the engine a bit more today. I only have 16 shims,  so there will be a delay. I really love doing shimming, its my favourite! 😜😜😜Just like the gearbox adjustments if you don’t have a wide selection it takes ages to get it correct, as you have to wait for new shims to make the corrections. I am on a eal mission to get this running again ASAP. More importantly I want to get onto the ski rack mechanism and install them and the skis on my car. I reckon about four weeks before its finished with the skis, unless I run into issues which we all know happens quite a lot with these cars! 

[CHANGES]

16 hours ago, drdoom said:

Not to tread on Dave's turf by any means but I'd suggest less focus on CR, more on fuel delivery, ignition timing and overall soundness of build. Assuming high grade fuel will be used and the car is not to be wrung out hard in general it would seem the marginal change of SCR should be of little consequence. Turbo engines will not long tolerate hard running with either lean mixture or undue advance, in my limited experience. Good work so far!

What I was trying to bring attention to,  is that the focus should be on ALL points, nothing should be overlooked as they are interlinked..   With the component changes made  and the work that was done on the head , there was high possibility static C/R would increase significantly ..  I am not sure  how much Fabian was aware this tied into the boosted final C/R and the influences it could have  ..  You are quite correct in saying fuel delivery and ignition timing need close attention .  However by maintaining the final boosted C/R,  the fuel delivery and ignition should be able to remain within the factory settings ..   It is far easier to gather this sort of data during the build , even if it takes time .  By doing so it make you aware of any compensatory adjustments that will be needed , as in this case boost level..  

I must be honest when i say, the SCR Fabian has is a lot lower than i expected with the work done..   Not sure how an 8.0:1 piston set up with a well skimmed head can end up a 7.76 :1  ..    I did notice the piston bowl volume was measured in the bore , this is quite normal and easier to do with the forged piston crown shape.  However this measurement will include the deck height volume as part of..  Fabian listed this separately in his data at 3.45 mm .   This is 0.136'' which also seem a bit high , i normally expect forged piston deck height at between .0.010'' and 0.040'' depending on build spec.   However there are several spec changes in this build , with machining and a cross over of parts ie early block late pistons etc which will mix up the norm .. If all the data is correct then this has all worked out for the good ..    I would just ask Fabian to re check data content and reaffirm .  As i say , the SCR is not an issue , these all vary when machined , its just the adjustment to the boost level that is needed to keep things within the ignition and fueling window..     

[Lotusfab]

Hi Dave thanks for all the input I needed help with this, as its out of my experience. I calculated the piston to deck clearance from the first piston ring top. I measured to the top of the liner from the ring and then made a correction for the liner nip to work out the height of the deck relative to the first ring. Is there something I missed using this method? The only other error might be if the gasket figures I used are wrong?

[Lotusfab]

The only gasket data I can find is the original was 0.5 mm thinner. Look what happens to the calc with a thinner gasket, I just tried this but have never calculated it.can’t be a coincidence. I measured my head gasket and compressed about 1.7 mm I think is about right.

[jonwat]

On 23/05/2020 at 14:00, Lotusfab said:

Combustion chamber volumes, of course! 😄😄😄

What about gas flowing the ports & manifolds or reprofiling the valves & seats?

Extra oomph for very little effort. 😀

[CHANGES]

3 hours ago, Lotusfab said:

I measured my head gasket and compressed about 1.7 mm I think is about right.

Yes , that is close enough .., I use 0.065''  which is a near as dam it 1.7mm ..  

4 hours ago, Lotusfab said:

Hi Dave thanks for all the input I needed help with this, as its out of my experience. I calculated the piston to deck clearance from the first piston ring top. I measured to the top of the liner from the ring and then made a correction for the liner nip to work out the height of the deck relative to the first ring. Is there something I missed using this method? The only other error might be if the gasket figures I used are wrong?

unfortunately you have made slight error here ...  The deck height is from the top of the piston crown , to the top edge on the liner.   Because the piston can rock in the bore when checking, i always take a couple of measures..  1 from the piston edge directly over the wrist pin..  2 and 3 from 90' of wrist pin .. with 2 and 3 , I rock the piston taking two measurements on both and then the average will give me measurement when piston flat. This should be the same or close to #1 measurement if different i take the average of the two .   But because you measured the piston in the bore at TDC , the volume you will have come up with will be the piston bowl and deck height together in one ..   In this case you only need to add it on to the gasket and the combustion chamber volume  along with the swept volume, to give total volume , then calculate from there .. 

hope that helps .    

[Lotusfab]

Mmm I am confused! I took an average of your expected piston deck height from the previous post 0.003 inch and put it into the calculator. Heres the result.

 

[Lotusfab]

The head is on so I cant measure any more. I can reverse the calculation. Assuming the HC head is the same. I take out the nip correction. So top of ring to liner top. Heres the result. This all might be a result of the calculator type  being used.

[Lotusfab]

I suppose it makes sense as my volume measurement was taken from the piston ring edge top the top of the liner. So presumably the volume calc correction must start at the piston ring edge as well?

[snowrx]

Fabian, if you measured the volume of the cylinder above the piston with the plate and pipette, than you're miles ahead of any fiddly calculations of the deck height. What was that measure for you?

Static CR =(swept volume +unswept volume)/swept volume,   with the swept volume being bore & stroke and the un-swept being cylinder volume + gasket volume + combustion chamber volume

 

With the OEM Goetze gasket, I also saw ~1.7mm compressed measure. There are some aftermarket ones out there that compress to 1.5mm though.

[drdoom]

Nope, as Dave says the measurement is to be taken from top of crown so do lose the focus on the top ring in this. This reflects the fact that the volume of the annular crevice between upper piston and bore wall is comparatively small. Good methodology otherwise in using a smear of grease to seal when taking liquid measurement of both the crown volume and the that of the head, beyond which all that should be required for a correct SCR is a reasonably correct figure for the height of the compressed head gasket. With these 3 volumes correctly determined the math is dead simple.  

[drdoom]

Bore area for a 95mm cylinder = 70.88 cm squared. Gasket height @ 1.5mm results in 10.6 cc,  gasket at 1.7mm results in 12.0 cc. Reversing into this as a cross-checking exercise, for 8.0 SCR with 550 cc swept volume ( i.e. displacement ) we should expect the sum of crown, head, and gasket volumes to be about 78 cc, as my dusty old synapses would reckon.