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1275 SPi - Rockers, Extractors, Intakes - More Power!
https://www.ausmini.com/forums/viewtopic.php?f=5&t=85497		 Page 1 of 1
Author:  BKozan [ Wed Apr 30, 2014 2:24 pm ]
Post subject:  1275 SPi - Rockers, Extractors, Intakes - More Power!
So, the long and short of it is that I'm ready to spend some money and get a bit more "oomph" from my little Rover. She is super reliable, runs great, and really has no issues to speak of.

This car is my daily driver, and I will autocross / trackday on the weekends. It must remain reliable.
I am aware that the best gains can be had by converting it to carbs, but I am going to keep the SPi.
I am not interested in making my own parts, adapting parts from other cars, or pinching pennies at every corner. I simply want to do it right, the first time.
I would prefer mods that favour low to mid range torque / power. I don't need to "squeeze every drop", but just want the favourite bolt-ons that a tried and true.
I am not going to increase the displacement of this engine - it will remain 1275.

Intake / Exhaust
  • It seems there really aren't any throttle body / intake manifold upgrades, just a plain old K&N Filter. Is this true? If there are options above the K&N, are they worth looking at?
  • From all of my reading, LCB extractors are the way to go. I need to keep my Cat and sensors, and am not concerned about appearance. Am I correct in assuming that some steel LCB extractors are worth my time and money? (It seems this forum is against posting to specific products, but I would love to know which companies make the best and worst).
  • I've read that many people believe in only replacing the back portion of the exhaust (from Cat back), instead of the full system (including extractors). Any truth to this? Better low-end from the back half only?

Rockers
  • It seems that 1.5 Hi-Lift rockers really only make a difference in the top RPM range, and even then, not much. Is this worth considering? I don't imagine I'll ever change the cam on this engine.
  • Many people seem weary of the roller rockers, because they flat-spot after X,000 kilometres. For my daily driver, would standard (non-roller) be preferred?

So before posting this thread my plan was to simply purchase a K&N filter, a full exhaust system (LCB Extractor-Downpipe-Connecting Pipe-Cat Conv.-Rear Pipe-Muffler), and a full forged 1.5 rocker assembly (non-roller). Of course I thought I should run it by the gurus here first, to ensure I'm not wasting my money.

What say you? If I replace the above mentioned bits, will I actually feel a difference in my "pants dyno"?

Thanks guys!
Author:  Harley [ Wed Apr 30, 2014 3:09 pm ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
BKozan wrote:
Intake / Exhaust
  • It seems there really aren't any throttle body / intake manifold upgrades, just a plain old K&N Filter. Is this true? If there are options above the K&N, are they worth looking at? K&N filter in the stock airbox is the best solution for power. The replacement filter without the box just makes noise.
  • From all of my reading, LCB extractors are the way to go. I need to keep my Cat and sensors, and am not concerned about appearance. Am I correct in assuming that some steel LCB extractors are worth my time and money? (It seems this forum is against posting to specific products, but I would love to know which companies make the best and worst). Getting any old LCBs wont work because they interfere with the inlet manifold - so get the proper set - besides, it needs the oxy sensor hole anyway.
  • I've read that many people believe in only replacing the back portion of the exhaust (from Cat back), instead of the full system (including extractors). Any truth to this? Better low-end from the back half only?
Get a sports exhaust with extractors specifically for your engine, if it was good enough for John Cooper garages to upgrade the lot, there must have been a reason. Cat back only will do a small amount, but mostly just make more noise.

Rockers
  • It seems that 1.5 Hi-Lift rockers really only make a difference in the top RPM range, and even then, not much. Is this worth considering? I don't imagine I'll ever change the cam on this engine.
  • Many people seem weary of the roller rockers, because they flat-spot after X,000 kilometres. For my daily driver, would standard (non-roller) be preferred?
As good as pointless without changing the cam too.

So before posting this thread my plan was to simply purchase a K&N filter, a full exhaust system (LCB Extractor-Downpipe-Connecting Pipe-Cat Conv.-Rear Pipe-Muffler), and a full forged 1.5 rocker assembly (non-roller). Of course I thought I should run it by the gurus here first, to ensure I'm not wasting my money.

What say you? If I replace the above mentioned bits, will I actually feel a difference in my "pants dyno"? Nope, but depends how sensitive your pants are. The above might get you 5-10 hp combined. Headwork, cam and compression could get you 15-20.

Thanks guys!



If you want more power from a stock SPI engine, this is what you need to do: Full exhaust, cam, raise compression, 1.5 rockers, rework head for bigger inlet / exhaust valves, K&N filter. Throttle body can be modified ever so slightly for more 'free flowing', but it has to be done right and not by old mate barry with a dremel.
Without the head work - lots of other stuff won't have as much of an effect.
Author:  KLAS [ Thu May 01, 2014 3:30 am ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
if it's an option for you, you can help the engine a lot by modifying the existing parts. the intake manifold is cast quite rough inside, the exhaust manifold should be matched to the gaskets.
the injection exhaust system is basicaly a LCB system. don't need an upgrade if you don't modify the engine by much.
a bigger throttlebody is only needed if you reach 85+ HP.
i would stick with 1.3 rockers, or the factory ones. much less stress on springs and lobes. the factory cams are known to chip at the lobes with 1.5 rockers fitted.
Author:  BKozan [ Thu May 01, 2014 10:23 am ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
Harley wrote:
Without the head work - lots of other stuff won't have as much of an effect.
This is exactly what I was afraid of hearing.

KLAS wrote:
the injection exhaust system is basicaly a LCB system. don't need an upgrade if you don't modify the engine by much.
So you're saying I can simply get out my dremel, and open up the inside of the existing extractor to match the exhaust ports on the head, and I can expect similar gains as buying a new LCB extractor?

Thanks again for the advice guys!
Author:  Harley [ Thu May 01, 2014 10:45 am ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
At the end of the day the injection system was designed for fuel efficiency and lower emissions - not power.
On an SPI engine - you won't get more than 85hp with the stock ECU and injector - they just can't put enough fuel in to make more power.
MPIs are good for 90hp NA and theres a supercharger kit that gets more - but not much.

Going to bigger bore helps a lot, as does the headwork, alternately if you must stay with injection, then look at aftermarket computers or go to 7 port head.
Author:  timmy201 [ Thu May 01, 2014 11:45 am ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
There is a few 5 port injection kits here:
http://www.twinkam.co.uk/shop/category_ ... Parts.html

Some of them sound very interesting too!
Author:  KLAS [ Fri May 02, 2014 3:36 am ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
BKozan wrote:
KLAS wrote:
the injection exhaust system is basicaly a LCB system. don't need an upgrade if you don't modify the engine by much.
So you're saying I can simply get out my dremel, and open up the inside of the existing extractor to match the exhaust ports on the head, and I can expect similar gains as buying a new LCB extractor?

yes, because if you don't change any major part like the head or camshaft you won't feed the engine with so much more air/fuel to make a "real LCB" necessary.

i guess you can never kill the myth that the injection is made to meet emissions only. thats why the 60HP Austin Metro engine is putting out 63HP with the EFI system in the Mini :wink:
i have never seen a NA MPi with more than 75HP without reprogramming the ECU. thats about the point where it starts to run lean with the factory full throttle map.
Author:  BKozan [ Fri May 02, 2014 9:11 am ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
Well, thanks for the information everyone. It's always a good idea to get some crowd knowledge.

Sadly, I think for now I'll just throw on a K&N Filter and keep enjoying the crap out of my little Rover. I'm keen to do the headwork (and more), but I want to do as much as possible in my own garage. At the very least I want to disassemble, clean, and reassemble - which is fairly new territory for me - so I want to really, really take my time and learn as much as possible, and do everything right, As this is my daily driver, I was hoping to find a little more power from a quick weekend project. Oh well.

Thanks everyone!
Author:  timmy201 [ Fri May 02, 2014 9:50 am ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
Or make it louder, lower and firmer. It'll feel faster, and that's the important bit!
Author:  Harley [ Fri May 02, 2014 10:32 am ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
Make it lighter - same as adding power! :D
Author:  MiniBob [ Fri May 02, 2014 9:14 pm ]
Post subject:  Re: 1275 SPi - Rockers, Extractors, Intakes - More Power!
Harley wrote:
Make it lighter - same as adding power! :D


Colin Chapman said "if you want to go faster, add a little lightness" !!
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