Supercharging Questions And Confirmations!
#1
Posted 25 June 2022 - 12:31 AM
Looking to achieve a fast punchy road car not a race car, few questions!
1275 metro engine in need of rebore to 1293.
Blow through or suck through which is best?
Whats the sweet spot for CR?
What power can a good condition metro bottom end and gearbox handle in standard form, I would love to see around 130hp 130ftlbs but thats just an imagination figure in my head!!
I have restored and rebuilt many many but I have never dealt with forced induction, eaton m45 seems to be most likely, im happy to spend money on whatever I have to however I don't really want to throw cash at things I don't need to, I'm currently down a piston rabbit hole, there's a few sets for £150, some at £700 and I don't know which are good bad or completely useless 😅
I have been advised x pin diff, drop to 8.5CR and 2.7 final drive. If I go suck through I will go with a vmaxscart kit with the 40dcoe, if I go blow through I will be able to draw and machine the parts needed via my work, but thats as far as I have got.
Always wanted a 1293 supercharged mini since I was a kid, not sure why, but now its time to finally make it a reality!
Thanks for all your help, love this forum!!
#2
Posted 25 June 2022 - 08:47 AM
Your gearbox will be fine. Currently X pin diffs are not available as the planet gears are stuck somewhere.
#3
Posted 25 June 2022 - 11:54 AM
A 2.7 FD is not going to increase punchiness, but will put more stress on your gears. I'd only go that low if you want quiet(er) & slightly more economical cruising. That'd be contrary to a CR as low as 8.5 too. But I'd go for a turbo over a mechanical blower anyway.
#4
Posted 25 June 2022 - 07:29 PM
I want to go supercharged, I've always wanted one, not saying I may end up changing to turbo later down the line!
I'm wondering if the pistons currently on ebay for about 150 quid will be okay? Also is it worth fitting oil squirters? I will dry deck and get the compression down to somewhere near 8.5 as that should allow me some wiggle room on the boost once run in.
286 cam a good choice?
Thanks for all your advise I really appreciate it!!
#5
Posted 25 June 2022 - 07:47 PM
#6
Posted 25 June 2022 - 08:11 PM
Thanks, is it likely the crank and rods will hold together? I will fit a centre strap and oil pickup. Not sure what to do about a diff as I currently don't have one!
I want to go supercharged, I've always wanted one, not saying I may end up changing to turbo later down the line!
I'm wondering if the pistons currently on ebay for about 150 quid will be okay? Also is it worth fitting oil squirters? I will dry deck and get the compression down to somewhere near 8.5 as that should allow me some wiggle room on the boost once run in.
286 cam a good choice?
Thanks for all your advise I really appreciate it!!
I would not be using that cam.
if it is well built the rods and crank are fine.
squirters talk to your engine builder.
why dry deck? What are you looking to get from it?
#7
Posted 25 June 2022 - 08:12 PM
What sort of power can a metro engine in standard form handle before things start breaking? It's only a road car but just so I have a rough idea.
More than you are talking about.
#8
Posted 25 June 2022 - 08:40 PM
#9
Posted 25 June 2022 - 08:41 PM
#10
Posted 25 June 2022 - 10:45 PM
You want minimal overlap with forced induction or you'll just be blowing your induction charge through in to the exhaust manifold. MG Metro, 266, SW5 are all good choices. They're essentially road engines that just happen to be fed on denser air. You don't need a lot of the exotic stuff that high revving race engines need. Standard rods, cranks & bearing caps are fine to a good way beyond what you're after. Pistons don't have to be that special either 21253's were a popular choice.
#11
Posted 25 June 2022 - 10:49 PM
#12
Posted 26 June 2022 - 09:21 AM
Standard A+ rods will take north of 200bhp. Oil squirters are not required unless you're going high boosts and require an under crown cooling due to excess chamber pressures.
#13
Posted 26 June 2022 - 02:27 PM
#14
Posted 25 July 2022 - 08:22 PM
@Torqu-E-Cycles. A bit late to the discussion but thought I would share my own build on the off-chance it might help.
After cooking my 1275 pistons due to running lean I paid much more attention to the rebuild;
supercharger - opcon twin screw kit (once sold by minispeed uk)
engine block - rebore and face +20 to suit new pistons.
Pistons - Omega cast +20 with 10cc dish with new rings etc. (MED)
rods - standard
crank - standard
head - bought ported and modified as part of supercharger kit - chambers measured at 27cc +/- 0.2cc
This gives me a CR of 8.51
camshaft - ST RE13 from calverST tuning - designed for forced induction use. timed in at 109.5 deg after TDC
Carb - HIFF44, BCA needle, red spring.
Minispares Molybdenum cross pin diff
Standard metro gearbox 3.44:1 (??)
The supercharger looks to be giving roughly 7 psi
I also fitted an AEM air/fuel gauge to make sure I could avoid crispy pistons and so far the readings give me some confidence in my setup so far.
Still putting miles on it and hopefully one of the local clubs will have a dyno day where I can find out what the power might be.
Butt dyno suggests somewhere into three figures with enough torque for safe overtaking
.
Hope this helps.
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