Esprit Turbo project car - part3 - the further continuation

[Lotusfab]

I can work it all out manually but I decided to use the calculator. If we reverse the calculation form a SCR of 8 using the calculator it gives a piston to deck height of almost exactly what I measured. The definitions may not be correct, but I believe the SCR calculated for my car is correct. At roughly 7.7 to 1. I did it manually just now as below.

so unswept volume = piston crown Volume + head gasket + combustion chamber + volume to deck 
so unswept = 33( piston crown and volume to deck measured) + 37( combustion chamber measured) + 13 head gasket= 83 cc
swept volume = 544 cc 

SCR = (544 + 83)/ 83 = 7.55.1

[Lotusfab]

Would be interesting to see what the SCR is with this gasket on a Turbo with standard pistons. Probably not where it was designed to be at. As they seem to run ok maybe small changes in compression are not that critical? I will still mod the boost as Dave suggested for all the reasons mentioned.

In fact I just calculated it I am guessing a standard Turbo SCR is about 6.79.1.  Due to the thicker gasket.

[Lotusfab]

In order to get the correct final CR I estimate you have to increase the boost pressure by over 1 psi! 

[Lotusfab]

Stainless exhaust studs. Manifold is back on now, whilst I wait for new cam tower bolts and shims.

[Paul Coleman]

Here you go @Lotusfab    

 

[Lotusfab]

Thanks Paul, thats excellent and didn’t know he went to Cortina as well! He’s wrong though you can’t have a white one with skis! Incidentally there is a one owner S3 in Copper fire and Lotus Gold leather. Its all original and is being restored by Lotusbits  Stunning one owner car! More importantly the trim and colour is identical to my car. Would be interesting to park them next to each other! 

[jonwat]

1 hour ago, Lotusfab said:

In order to get the correct final CR I estimate you have to increase the boost pressure by over 1 psi! 

The boost won't effect the compression ratio, only the compression pressure.

[drdoom]

Intrigued by those core plugs, exhaust side of the head. Of what material, where sourced?

Cheers 

[Lotusfab]

35 minutes ago, jonwat said:

The boost won't effect the compression ratio, only the compression pressure.

Thanks yes final pressure as per the graph earlier.

8 minutes ago, drdoom said:

Intrigued by those core plugs, exhaust side of the head. Of what material, where sourced?

Cheers 

Not sure Lotusbits specified them. I will find out and let you know.

[Lotusfab]

Harry has already done my Cortina trip, only problem he had the wrong colour car and skis! At least I know where to go now! Once the engine is built I will rack up the miles. Then I’ll test the skis at high speed on a track and head off to Cortina!  

[Lex Templar]

11 hours ago, Lotusfab said:

Thanks Paul, thats excellent and didn’t know he went to Cortina as well! He’s wrong though you can’t have a white one with skis! Incidentally there is a one owner S3 in Copper fire and Lotus Gold leather. Its all original and is being restored by Lotusbits  Stunning one owner car! More importantly the trim and colour is identical to my car. Would be interesting to park them next to each other! 

Is that a dry sump Fabian?

[Lotusfab]

No its an S3, but stunning!

[Lex Templar]

3 hours ago, Lotusfab said:

No its an S3, but stunning!

Ah an S3 N/A gotcha. 

[Lotusfab]

Yep with 30 HP more than a Turbo! New stainless cam followers.

[CHANGES]

18 hours ago, Lotusfab said:

I can work it all out manually but I decided to use the calculator. If we reverse the calculation form a SCR of 8 using the calculator it gives a piston to deck height of almost exactly what I measured. The definitions may not be correct, but I believe the SCR calculated for my car is correct. At roughly 7.7 to 1. I did it manually just now as below.

so unswept volume = piston crown Volume + head gasket + combustion chamber + volume to deck 
so unswept = 33( piston crown and volume to deck measured) + 37( combustion chamber measured) + 13 head gasket= 83 cc
swept volume = 544 cc 

SCR = (544 + 83)/ 83 = 7.55.1

Sorry to bring this up again ,  but i can not help feel there is something amiss ..  I base this on logic of 8.0:1 pistons with skimmed head will be higher than 8.0:1  not 7.7:1 .. 

To get an idea of where i am coming from .. lets put some base figures we normally find on a stock engine with 8.0:1 pistons into the calculator..  

Bore at 95.27... stroke at 76.2... cylinder head chamber at 40cc... H/gasket 'crushed' 1.651... H/gasket 'crushed' bore...97.3...  deck height 0.25... piston bowl 23.5... 

The result we get is  8.001:1    ...  This is what we would expect to see..  Some may vary but only slight.. 

I can only assume the piston bowl and deck height measurement you made has at 33  may be wrong..  I work out the combined figure should be around 23.75..  This would be an easy misread to make ..

Now if we Add in other measurements you made ,  like  cylinder head volume @  37 , and make allowances for the 33 figure being misread ..   we end up with 8.283:1    This would be a more what we would expect to see.  

However looking at the picture of the head , it has been machined down to the inlet valve seats , I usually see a volume of just below 35  when  skimmed to this , even with cut back valve seats .. .. This would give a SCR of 8.483:1     

So it may be safe to assume the SCR is somewhere between the two or at least the lower of 8.283:1 .. 

To be on the safe side and get the best timing and fueling , I would set the turbo waste gate to account for this in your final boosted CR. 

On the up side , it will be a bit more responsive off boost low down .  You may need to very slightly adjust you timing and low down jets ,  but a dyno technician will fix that very easy.  It will only be slight tweaking to refine and get the best from all that you have done ..  

Hope this helps clear up any doubts .. 

Dave 

 

 

[Lotusfab]

I’m still not sure whats going on here. Was the original gasket on the HC 1.2 mm thick? 
I would have to half the boost to 4 PSI if the compression ratio is 8 psi. Using the old style wastegate That would mean a different spring or mod to the wastegate body. 

[Lotusfab]

Just found this on the internet. Should your calc have a gasket thickness of 1.2 mm? According to this article the Goetze gasket came.in in 1993 and effectively detuned the HC. Interesting in the article it states the thicker gasket reduces the compression ration by 0.5. That would be inline with my figures???

[snowrx]

Running your numbers through my spread sheet gives a static CR of 7.56:1 with a 1.7mm (compressed) gasket and 7.68:1 with a 1.5mm one. 

My '85 LC engine with JE 8:1 95.5mm pistons has a cylinder volume over the piston of 27cc, and a combustion chamber of 37cc, FFIW. 

I think later blocks had a lower deck height to work with the thicker gasket, so there's another variable in the mix. 

CompressionCalculation.xls

[Lotusfab]

Well at least the combustion chamber figure is the same! Despite of possible errors in measuring the only differences really are the piston design and skimming. The Increased gasket thickness reduces the compression ratio on the HC by 0.5 according to the Lotus Marques article. Making it 7.5.1 . Would it not be reasonable to assume the SCR is somewhere between 7,5 and 8 to 1? Skimming we are talking very small numbers compared with the 0.5 mm gasket thickness change? 
 

[CHANGES]

1 hour ago, Lotusfab said:

Just found this on the internet. Should your calc have a gasket thickness of 1.2 mm? According to this article the Goetze gasket came.in in 1993 and effectively detuned the HC. Interesting in the article it states the thicker gasket reduces the compression ration by 0.5. That would be inline with my figures???

With the greatest respect Fabian  , what went on with gaskets in 1993 etc has nothing to do with what you have now..  Fact.. You now  have a 1.7 gasket , you now have a 8.0:1 set of pistons with a 23.5 bowl , You say have a combustion chamber of 37 cc ,  you have a a 95.27 mm bore , you have a 76.2 mm stroke,   and a deck height of circa 0.25 mm ...  The rest is just math.   You really need to concentrate on what you have in front of you , instead of looking for it fit what you would like it to be ..  The fact is , even if you had left in your original pistons , grinding the head and reducing the cc to 37 would increase your CR by 0.25 to 7.75:1 .   It really comes down to when you make changes , things WILL be different..    This is what i was trying to make you aware of when i pointed out the volume / CR checks to be made..    None of this is a real problem , what you have is very serviceable .  You are running the forged pistons that can take extra final CR , which is just more in line with the injection charge cooled cars than your original spec.  The reason for making you aware is so you can adjust you tuning parameters to suit.  If you want to maintain your existing carb jetting and  dizzy set up , then you would need to control your boost accordingly..  BUT... If you want to run original boost and higher final CR that is also fine , you will gain more BHP , But you would need to get it all set up on a dyno with re-jetting/choke and dizzy re-formatting.    Running std boost level with higher final CR on std tuning set up will cause detonation at higher revs from running advanced and lean ,  it would feel really quick like that but be damaging the combustion area at the same time ..   These are the sort of changes people make and don't address properly , then moan like hell when it all goes south...   Now you have been there once , none of us want to see you go there again..  The advise on how to deal with what spec you have arrived at is simple...  Please don't over complicate or over think this.....  Just move forward and do one of the two options to facilitate the build spec you have..           

[Lotusfab]

Dave, any idea what the operating pressure of the old Wastegate is and the tolerance please?

[Lotusfab]

I have decided to replace the new stainless cam followers and use Arrow ones. They are more expensive, but I think its worth the extra investment. What I don’t ever want again is a cam follower failure. Lotusbits can do a good deal on these.

[Lotusfab]

“what went on with gaskets in 1993 etc has nothing to do with what you have now”. I have to disagree with you here Dave. The whole point is the original 8.1 HC Turbo as it left the factory was reduced to 7.5.1 buy the fitting of the Thicker  Goetze gasket, this is a fact from all the research I have done. I have found data from Lotus that says the new gasket was 0.5 mm thicker. Two experts and Lotus Marques confirm this Compression reduction info is correct and its confirmed by the maths. Its relevant to my car insofar as a calculation cross check. I think the calc you produced earlier on to derive 8.1 should have been done with 1.2 mm gasket thickness to confirm the other figures. If you were able to achieve  8.1 with stock car setup and a 1.7 mm gasket some of the other figures used must be wrong? 
I am glad you pointed the effects of changes as I have had an opportunity to think about and address them. I never would have even thought about measuring the SCR until you mentioned it as the other experts guiding this project had already dismissed it as irrelevant  with my current set up. I am learning a lot here which is great, so are some of the people reading all of this thread. Thats all part of the hobby.
Your correct though I have what I have In front of me and will continue the engine build to the highest standard I can. With that in mind I have upgraded the cam followers and am replacing all of the cam tower bolts,  even though in reality the new cam followers I already had probably would have been fine for my application. 
The shimming is taking a while, especially now I have changed the thickness of the cam followers. Back to square one - but I will get there soon! 

[Lotusfab]

On 24/05/2020 at 21:53, Lotusfab said:

Thanks yes final pressure as per the graph earlier.

Not sure Lotusbits specified them. I will find out and let you know.

Core plugs were cnc machined from solid block. If anyone  wants Some contact Mike at Lotusbits.

[Lotusfab]

Sorry to bore everyone, but anyone following this thread must realise I never give up no matter what the setback! So I have reverse calculated the compression ration.

The Mahle piston dome volume and deck clearance are stock on my car within a margin of acceptable error. I am confident the combustion chamber volume is 37 cc. 
we know the stock car had a 1.2 mm thick gasket and a compression ratio of 8.1. The calculator is simply a volume adding spread sheet. So I adjusted the piston volume and deck ht to give a compression ration of exactly 8.1. I then changed the gasket thickness to 1.7. The result 7.7.1. This is the figure to be expected from Daves estimate of skimming effects (0.25) and 0.5 drop due to a thicker gasket. Its also the same as the figure that was guesstimated by the expert.  So 8 - 0.5(gasket) + 0.25 (skim) = 7.75.1. 

Thats it on this Honestly! Those people who turned off can now switch back on! Heres some help!