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998 Compression Ratio


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#1 Ghostrider

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Posted 08 January 2019 - 11:25 AM

Fear not, I'm not going to ask how to calculate the CR, I am just having second thoughts about the compression ratio I have chosen.

Setup is a 998 std bore pre a plus with dished pistons, evo001 cam, lightened flywheel and 12g202 head.
I wanted to opt for a 10:1 CR however as the head is unskimmed, a lot of material will need to come off to get this CR with dished pistons on a 998. The machine shop would charge me a fortune to remove probably somthing like 80 thou, and I simply don't think my wallet can take a punch like that. I haven't got the head yet so I can't exactly check how much yet, but it will be a lot.

So would dropping the CR to somthing in the 9 region be okay? I'm aware obviously it'll be slightly less power but it'll mean less to skim.

#2 Lucas1988

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Posted 08 January 2019 - 01:57 PM

small question why did you opt for a evo001 cam and not go for a sw5 which is great for this engine from memory.



#3 Ghostrider

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Posted 08 January 2019 - 03:37 PM

small question why did you opt for a evo001 cam and not go for a sw5 which is great for this engine from memory.


To be honest I originally was going to put the sw5 in but in the end after talking to a few people on here I opted to go for the evo001 as it seemed to suit my setup and mainly what the car was used for, driving style etc. Plus it’s much cheaper!

#4 Ghostrider

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Posted 08 January 2019 - 03:38 PM

small question why did you opt for a evo001 cam and not go for a sw5 which is great for this engine from memory.


To be honest I originally was going to put the sw5 in but in the end after talking to a few people on here I opted to go for the evo001 as it seemed to suit my setup and mainly what the car was used for, driving style etc. Plus it’s much cheaper!

But don’t get me wrong the sw5 is a fantastic little cam

#5 cooperd70

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Posted 08 January 2019 - 03:49 PM

I had heard that the sw5 is a little noisy. Is this the case? Had initially been thinking to have one fitted to my 998 (along with some other mods) - already modded stage 3head/twin 1/4 SU's/lcb, but hearing that it's noisy have started to look at Kent options.

#6 Cooperman

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Posted 08 January 2019 - 04:14 PM

The Evo001 is absolutely great in a 998. Of course you need a good inlet and exhaust system to make it work at its best. It has excellent mid-range torque.

Because you have fitted dished pistons you are going to have to accept a lower CR. Ideally a 998 needs flat top pistons and, remember, the 998 Cooper had raised D-top pistons to get the CR to a good figure. Ideally the pistons should come right to the top of the bores and not sit slightly down the bores at TDC. The block needs to be 'decked' to suit.

Obviously quite a lot is going to have to be skimmed from a 202 head, especially if the chambers have been enlarged as part of the gas flowing process, just to get to around 9:1.



#7 Ghostrider

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Posted 08 January 2019 - 04:57 PM

The Evo001 is absolutely great in a 998. Of course you need a good inlet and exhaust system to make it work at its best. It has excellent mid-range torque.
Because you have fitted dished pistons you are going to have to accept a lower CR. Ideally a 998 needs flat top pistons and, remember, the 998 Cooper had raised D-top pistons to get the CR to a good figure. Ideally the pistons should come right to the top of the bores and not sit slightly down the bores at TDC. The block needs to be 'decked' to suit.
Obviously quite a lot is going to have to be skimmed from a 202 head, especially if the chambers have been enlarged as part of the gas flowing process, just to get to around 9:1.

Thanks Cooperman, I had a feeling I might have to accept a lower CR. I believe the chambers are still standard size. I know it would be greatly beneficial to gas flow the head but i think that’ll have to wait for the time being. Saving at university is hard let alone throwing money at my mini all the time!
Would a CR of around 9:1 still be good? It should still be a good improvement over the standard head so long as it gets some material removed. Of course once I’m able to do my CR calculations I can see what is going to be realistic as to how much can be skimmed etc.

#8 Cooperman

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Posted 08 January 2019 - 05:32 PM

The BIG limiting factor will be the head. When trying to get a bit more from any car with an A-series engine the limiting factor is always the head. It is seriously bad at flowing mixture in and exhaust out.

I suggest you get a copy of David Vizard's book 'Tuning the A-Series Engine' and read up on head improvements. There is a lot you can do yourself which will show a measurable improvement. It needn't cost a lot except a bit of your time and some dirty hands.

Do you have an engineering dep't at your Uni? They would have all the tools you need to get the job done. I know when I was an engineering student (a long time ago) I used to do a lot of work on rally car engines using the college workshops and know-how.



#9 Ghostrider

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Posted 08 January 2019 - 06:59 PM

The BIG limiting factor will be the head. When trying to get a bit more from any car with an A-series engine the limiting factor is always the head. It is seriously bad at flowing mixture in and exhaust out.
I suggest you get a copy of David Vizard's book 'Tuning the A-Series Engine' and read up on head improvements. There is a lot you can do yourself which will show a measurable improvement. It needn't cost a lot except a bit of your time and some dirty hands.
Do you have an engineering dep't at your Uni? They would have all the tools you need to get the job done. I know when I was an engineering student (a long time ago) I used to do a lot of work on rally car engines using the college workshops and know-how.

Yes I’ve been meaning to get a copy of that book, I managed to find a yellow David vizzard book in the library at uni, theory and practice of cylinder head modification, it seems to go over modifying mostly the mini head so I have taken that out and may start do get my hands dirty.
I’m very jealous of you being able to do such jobs in your workshops back in your day. I am actually a aerospace engineering student and we do have a large machine lab and automotive lab. However much to my annoyance they do not allow people to use the workshops for non uni work which I can’t understand. Surely they’d want to encourage you to do things like this rather than say go away, I’d be able to learn so much more. I might try asking nicely again.

#10 Cooperman

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Posted 08 January 2019 - 09:07 PM

I, too, was an aerospace engineering student. In fact I had a 5-year engineering apprenticeship with the old De Havilland Aircraft Company at Hatfield. It used to be a block-release system with full time at the Hatfield College of Technology and then back in the factory.

We always had access to machine tools and could also do projects of our own as part of the course-work.

I got into rallying when I was a week off becoming 19 and my best friend (whom is still my best friend 60 years later and who drove my Cooper 'S' on a revival rally as recently as last October) got a new 850 Mini for his 21st birthday, so we had to prep that for rallying including doing work on the head. That's how I got into Mini rallying and building.

Good luck with your studies. If you have as interesting life as I had as a result of my training you will have a great time with lots of happy memories.



#11 Ghostrider

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Posted 08 January 2019 - 10:35 PM

I, too, was an aerospace engineering student. In fact I had a 5-year engineering apprenticeship with the old De Havilland Aircraft Company at Hatfield. It used to be a block-release system with full time at the Hatfield College of Technology and then back in the factory.

We always had access to machine tools and could also do projects of our own as part of the course-work.

I got into rallying when I was a week off becoming 19 and my best friend (whom is still my best friend 60 years later and who drove my Cooper 'S' on a revival rally as recently as last October) got a new 850 Mini for his 21st birthday, so we had to prep that for rallying including doing work on the head. That's how I got into Mini rallying and building.

Good luck with your studies. If you have as interesting life as I had as a result of my training you will have a great time with lots of happy memories.

Wow, that's quite an adventure. Sometimes I really wish I could have been alive back then, I'd still love to give things like rallying a try. Maybe if my flying career in the RAF crashes thanks to more cuts, I'll have to try motorsport of some kind. Its a shame such companies like De Havilland are long gone, I do enjoy hands on work, maybe that's why I love working on my mini so much.

Also I'd just like to thank you, you're a true credit to forums like this, whenever I have an issue and dig around the forums for answers sure enough you've already answered it. Yourself and plenty of others on here have so much knowledge that is truly priceless not to mention you take the time to help people on here of which I am truly grateful for.



#12 ACDodd

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Posted 08 January 2019 - 11:12 PM

9:1 will work very well.

Ac

#13 gazza82

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Posted 08 January 2019 - 11:19 PM

I, too, was an aerospace engineering student. In fact I had a 5-year engineering apprenticeship with the old De Havilland Aircraft Company at Hatfield.


My late Father is ex De Havilland from late 40s/early 50s. Went to Fairey then Westland. Think I've probably got a couple of DH momentos of his. I know there is a book somewhere and possibly a tie-pin/clip!

Edited by gazza82, 08 January 2019 - 11:19 PM.


#14 Cooperman

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Posted 09 January 2019 - 12:07 AM

The training we got at DH was really second to none. I know it stood me well during my working life and I had my own design and technical support company with CAA design approval. I got to meet a lot of interesting people all over the world in the Aerospace, Automotive and other industries.

 

It was a simpler world back then in the mid-1960's when I was building my career. I was also fortunate that I won an Air Cadet/RAF Flying Scholarship when I was 17 and got a full people before I was 18 and flew ATC gliders as well, becoming an instructor at 20. Please don't think my family were in any way wealthy. My Dad was an aircraft fitter and my mum was as shop manager. They didn't even have a car or own their own house. Was I just very lucky? I am inclined to think so. I certainly was with my rallying as I got to co-drive/navigate some fantastic drivers on top level rallies and I got to drive fairly successfully on more local championship and National rallies.

 

Now I'm retired, so I can play with my Minis, help younger people with theirs Minis, fly my vintage sailplane and teach others to fly gliders. By the way, I was 78 last month. Life in the old dog yet! My goodness, I have had a lot of fun along the way  ;D .



#15 Ghostrider

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Posted 09 January 2019 - 04:58 PM

The training we got at DH was really second to none. I know it stood me well during my working life and I had my own design and technical support company with CAA design approval. I got to meet a lot of interesting people all over the world in the Aerospace, Automotive and other industries.
 
It was a simpler world back then in the mid-1960's when I was building my career. I was also fortunate that I won an Air Cadet/RAF Flying Scholarship when I was 17 and got a full people before I was 18 and flew ATC gliders as well, becoming an instructor at 20. Please don't think my family were in any way wealthy. My Dad was an aircraft fitter and my mum was as shop manager. They didn't even have a car or own their own house. Was I just very lucky? I am inclined to think so. I certainly was with my rallying as I got to co-drive/navigate some fantastic drivers on top level rallies and I got to drive fairly successfully on more local championship and National rallies.
 
Now I'm retired, so I can play with my Minis, help younger people with theirs Minis, fly my vintage sailplane and teach others to fly gliders. By the way, I was 78 last month. Life in the old dog yet! My goodness, I have had a lot of fun along the way  ;D .

78! That is truly impressive and you’re still doing things that people 60 years younger than you are doing, I take my hat off to you. That sounds like a brilliant career and a very enjoyable journey you’ve had so far. I left the ATC a few years ago, now whilst at university I was able to get into a raf university air squadron, being able to do flying training out of RAF Wittering and be at university is unreal. Plus driving a mini on the base is really something, we were able to get 6 people inside the car myself included to drive to the officers mess, good thing the raf police didn’t see! Or the rear suspension colapse!
I’m sure everyone on here hopes you keep up what your doing, it’s truely spectacular and I hope your able to continue having fun for many years to come ;D
Jacob




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