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998 Rebuild


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#1 detroitmini

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Posted 08 January 2020 - 04:46 PM

Hey all,

 

As it is my first engine build, thought I would share my thinking and gain others input.

 

My engine was leaking oil and coolant, so I decided to tear it down, replace the seals, and repaint for a fresher looking engine bay (pics of starting point to come). The engine is starting as what I believe to be a stock 998 with a HS4 single carb and pancake filter. As with most projects, I hit the slippery slope and started debating engine upgrading. I currently have a 12G202 head laying around (got in the purchase of the car) and what I believe to be a pressed steel exhaust for a mini (see attached. may be for a b series). My buddy happens to have a 266 cam laying around. 

 

So the final plan would be to have:

FDR: See below in questions

Stock block and crank

266 Cam

Stock pistons

12G202 head skimmed for 10:1 CR and ported

Stock Rockers

HS4 with stock intake (cut from exhaust)

Pressed Steel Exhaust

 

Questions:

- Will the upgrades give me enough power to drop to a FDR of 3.1:1? Would love to get some higher top end speed as here in Michigan there is a lot of highway driving.

- Is the HS4 big enough? i also have twin HS2s I could switch to but I like the simplicity of single carb.

- Will I need the Aldon Yellow Dizzy? i have seen most people upgrading convert to these.

- Any experience with the pressed steel exhaust? or should I got for LCB?

 

End note:

I do have the Vizard book and reading as I go along.

 

 



#2 Moke Spider

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Posted 08 January 2020 - 06:35 PM

Sounds like a nice project.

 

On your proposed CR, without running the numbers, I'm pretty sure with that Cam, 10:1 will be too high.

 

Personally, I've found on most builds, a Final Drive taller than 3.44:1 takes a lot of the nippiness from them, even for highway motoring. Others run FDs of 3.2 and 3.1 on 998s and like them, but, as mentioned, I find it takes the life right out of them. Try it and keep an open mind about it, you might like it, then again, you may wish to swap back. These engines I find don't suffer in any way from running at high revs for extended periods, ie, 4000 to 4500 all day isn't a problem as long as you use quality oil and change it when the book suggests (ie, 3 000 miles). I am frequently doing very long runs and sitting on these rpms all day for weeks on end and been doing these sort of runs for over 30 years.



#3 detroitmini

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Posted 08 January 2020 - 07:00 PM

Awesome. Thank you! I think I will stick with the 3.44:1.

 

If you think 10:1 is too high, what CR would you recommend?



#4 Moke Spider

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Posted 08 January 2020 - 08:38 PM

Awesome. Thank you! I think I will stick with the 3.44:1.

 

If you think 10:1 is too high, what CR would you recommend?

 

Just to be sure we are on the same page, is this the 266 you are contemplating ?

http://www.minispare...sic/MDM266.aspx

 



#5 detroitmini

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Posted 08 January 2020 - 09:12 PM

I do believe. I currently have a cam marked on the end:

 

KC

MD266MB



#6 Moke Spider

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Posted 08 January 2020 - 11:41 PM

I do believe. I currently have a cam marked on the end:

 

KC

MD266MB

Sounds like it.

 

When I ran the numbers you can bump the static CR up to 9.9:1 on the basis that you timing the Cam in as per Kent's recommendations and that you are using 97 RON Fuels.



#7 detroitmini

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Posted 09 January 2020 - 01:09 AM

 

I do believe. I currently have a cam marked on the end:

 

KC

MD266MB

Sounds like it.

 

When I ran the numbers you can bump the static CR up to 9.9:1 on the basis that you timing the Cam in as per Kent's recommendations and that you are using 97 RON Fuels.

 

 

Is this place you were running the numbers in a common place? Would love to learn.

 

Also, where would I get Kent's timing recommendations?

 

I did plan on switching to 97 RON Fuels. Figured it would be worth it for the performance increase.



#8 Moke Spider

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Posted 09 January 2020 - 09:40 AM

The numbers I 'run' through a calculator and write down on paper. I work them out using the Dynamic Compression Ratio method.

 

You can get the basic data on the cam here;-  https://www.kentcams.com/part/MD266

 






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