Soliciting thoughts & opinions - power upgrades to a 998

[MPlayle]

As the title implies, I am looking for thoughts/opinions on methods for getting a bit more power out of my 998 engine.  I find running with highway traffic at 4K rpm for much time is tiring on me, though necessary for getting in/out of San Antonio.  There are also a few hills that Bruce and I go over on our drives to area C&C events where I still lose significant momentum on the uphill.

The engine currently runs very nicely: has good oil pressure, does not overheat, gets me 30 - 33 mpg regularly.  The transmission/differential is currently set up such that 4K rpm is 70 mph (3.1 final drive, but non-standard drop gears make it act like a 3.2 final drive)

The engine spec as it is currently: stock pistons and cam; alloy intake manifold supporting a single HS-4 carb with a K&N filter in a modified stock air box; LCB exhaust; Mini Sport "Stage-3" 998 head with mild porting and bigger valves; forged 1.4:1 ratio rocker arm set.  The head and rockers were done to boost the power slightly from stock when I changed the final drive to the current setup.

What I would like to do is add more power so I can change the final drive again to either a 2.95 or 2.76 to lower the rpm more when doing highway speeds while still having sufficient power/torque for the winding hill country backroads.

The approaches I know of are: 1) upgrade to a 1275 based engine; 2) overbore and change the cam in the current 998; or 3) add a turbo kit to the existing spec.

Please chime in with your thoughts, pros/cons of the above approaches, any other alternative approaches.

[MiniDave]

1275 motor/gearbox would be my first choice because it's all bolt in. Turbo to the existing engine would be second choice because kits exist that again are (supposedly) bolt on stuff, but spendy ($5K+).

I run a 2:76 in my green Mini, 70 mph is about 3300 rpm, 75-80 is 34-3600 rpm. I only have to downshift to 3rd if it's a really steep hill or if I'm at altitude (Colorado Mtns)

I like turbo motors in general, don't know what to expect from the Jet motors kit on a 998, but the mods you've already done will help quite a bit, I would call Jeremy and see what he says.

[MPlayle]

I had planned on trying to speak with Jeremy at Jet Motors about their kit on a 998.

The 1275 option is at least as spendy as the turbo kit and it leaves me with the 998 still sitting around.  Being in an apartment with detached garage makes storing things like an extra motor a bit iffy.

[cstudep]

With all the work you have already done to the 998 engine I think I'd lean toward adding the turbo. Expensive but a 1275 upgrade will be as well. I suppose the advantage of the 1275 upgrade is the potential to sell the 998 to recoup some cost, but I don't know what the demand is for such things. Generally speaking if someone is going to buy an entire engine, its likely going to be of the 1275 variety.

[MPlayle]

With all the work you have already done to the 998 engine I think I'd lean toward adding the turbo. Expensive but a 1275 upgrade will be as well. I suppose the advantage of the 1275 upgrade is the potential to sell the 998 to recoup some cost, but I don't know what the demand is for such things. Generally speaking if someone is going to buy an entire engine, its likely going to be of the 1275 variety.

Those were some of my thoughts as well.  I am also inclined to think the cost of rebuilding/enhancing the 998 (non-turbo approach) will likely be about the same as the turbo kit (pistons, rings, bearings, cam, machine shop work).  I am not really into the Honda engine swaps and those tend to be spendy as well.

[cstudep]

Yeah the Honda swaps are pretty spendy these days, probably the most expensive option actually. Just a worn out v-tec with transmission is getting pretty costly these days.

[94touring]

If you have a small bore stage 3 head with bigger valves you really need the cam to go with it. You might actually be a bit soggy down low with a stock cam on a performance head with bigger valves, though the 1.4s will help a little.  Adding a nice street cam like a 266 or evo1, both would work great with 1.4 rockers, simultaneously going taller on the gears will make it feel equally "slow".  You'll utilize 3rd gear a lot to pull hills.  3.1 or your 3.2 is a great compromise as is for doing highway speeds.  To run a 2.76 in my humble opinion takes a large bore with power or better yet a turbo.  I'm not a fan of taller gears because it's just lazy feeling to me in a mini.  I still want a 5 speed for the best of both worlds.  Also what's your compression ratio?  Bump it up to about 10:1 with the cams listed above. If you're running low compression right now that alone will liven it up. 

[MPlayle]

I am trying to keep cost effectiveness and ease of implementation in mind with this latest effort.

The goal is to have an engine that will confidently pull hills while providing decent highway capability/comfort and retain reasonable reliability.

One of the current issues is the non-standard drop gears.  They shift the effective behavior of the final drive down one rating.  Examples: the originally installed 3.44 set acted like a 3.76; the currently installed 3.105 set acts like a 3.2.  If I install a 2.95, it will act like a 3.1 and installing a 2.76 will act like a 2.95.

I did not know it had the non-standard drop gears until after the change to the 3.1 final drive when I did not get the expected 3.1 behavior I really wanted.  The performance of the current setup is basically adequate, but really needs just a little more "grunt" for the hills based on having the current configuration for a few years.  The better highway behavior would be a nice addition.

To get the originally desired 3.1 behavior, I need to either change the drop gears to standard (1:1), or put in a 2.95.  Either of which will mean the extra "grunt" will become more necessary.  Thus this discussion for reasoable ways to achieve the desired results ("grunt" for hills and comfort for highways).

All that said, as far as I know it is still the factory 9.4 compression of the latter series 998s.

Is it possible to just change the cam without totally gutting the insides of the block?

[94touring]

To get what you want will take time and money is all. Dropping in a turn key 1275+ power house with a 2.95 or 3.10 would be the easiest way. 

[94touring]

If you do tear down what you have, get the 1098 crank, add the cam, measure measure and triple measure deck heights, chamber volumes, piston dish volume, ect to know exactly what your compression ratio is. If you do a basic compression test you'll have a rough idea what you currently have.  Tosssing on a stage 3 head may have a radically different chamber volume than stock.  These details matter.

[MPlayle]

Are the connecting rods the same between a 998 and 1098?

[94touring]

Yes it's the stroker crank for a 998, so there may need to be thicker gasket and or block decking required to get proper deck height for piston to head clearance. Or you figure out what rods make it perfect without needing thicker head gaskets or block decking.  Benefits are low end torque increase where you want it.

[MPlayle]

So I would have to tear it all apart in order to determine what may be needed before ordering parts?

Kind of something I was hoping to avoid if possible.  But, that is why I started this thread - to get input and find out what sort of effort I would be facing.

[94touring]

You'd mock it up and see where the pistons top out at. Same as what I'm doing on a vw type 1 motor build with stroker crank, C height pistons, and 5.7" rods. You need to re-ring and dingle ball hone at minimum.  If there is a lip/ledge on the cylinder wall then you're looking at a bore up at that point. But this is all part of the process.

[MiniDave]

No matter what you do with the gearing you're still only going to make about 40-45 hp with a 998, it's not enough to pull hills in 4th. A 1275 will make more torque and with a 3.0 will be in the sweet spot at highway speeds.

Dan's version with the 1098 crank will give it good torque, but you're talking about a total rebuild.

If you can find a guy with a Vtec removed 1275 you'd be in good shape.

Either that or go turbo - that will give you the torque to pull hills and the taller gears.

[94touring]

It's been forever since I read this but should explain it.

https://www.calverst.com/technical-info/engine-1098-initial-tuning-potential/