What WHP?
DavidhMX5 - 25/12/18 at 07:40 AM
Work starts on the engine this week. 
First problem, what power to aim for. Original thoughts where 300+ but having never driven or experienced one of these cars I'm starting to
wonder if it's possible to use more than 300 if that.
Engine is a 1.8 NB (mx5) which is having a full strip and rebuild. Rods will be changed for forged plus stud kit for main and head. That setup with
standard pistons will be good for around the 300 mark (FI), any more and I will need to replace pistons with forged and consider gearbox strength.
So what WHP does your car make and how usable is the power?
rusty nuts - 25/12/18 at 08:17 AM
Thes cars can bite even with just 100 BHP , perhaps before deciding what you need it might be worth finding out what you can handle ? A days driving
tuition in a locost type car could save you loads of money and embarresment ? Whatever you do decide take it very carefully initially until you get
used to it .
big_wasa - 25/12/18 at 08:44 AM
Haven driven the summer in a 7 with sub 85bhp I can honestly say it was great fun on the road. It was hard to get into trouble in the dry and it
topped out around 90 and that was plenty fast enough for me .
Around Cadwell I could just keep it planted.
But I am a Zetec nut and I’ve probaly now wrecked it with a 220~250 bhp turbo transplant. But I am aiming for a small turbo low boost setup.
We all like to think we are Casanova in the bedroom, Rocky in a confrontation and Ken Block behind the wheel.
Truth is often a little differant.
[Edited on 25/12/18 by big_wasa]
froggy - 25/12/18 at 10:44 AM
The higher you aim the more savage the delivery with a small engine .
Ugg10 - 25/12/18 at 12:26 PM
For road use I would go for around 175hp flywheel (140-150whp) with a decent amount of torque, normally aspirated. I think this suits the 600kg (and
below) sevenesque/fury/Phoenix the best (250ish bhp/ton is where I would aim for, less power less weight is good). You are better spending money on
balanced brakes (don’t over brake), an atb diff and a geometry set up with you in the car. For track use you,can go another 50% but IMO this then
becomes pretty much unusable on the road (or only use 50% of the capability). Much better to b able to use 80% of the performance then trying to wr
stl an overpowered car.
So a 1.8 mx5 an with decent exhaust and a throttle body setup up and a bit of head work would be my choice if you are stuck with the mx5.
Just my 2p worth.
DavidhMX5 - 25/12/18 at 12:56 PM
Ok so the impression I'm getting from answers so far is don't over power.
Bit of additional info if it helps.
Firstly I'm late 50's and don't have any unrealistic expectations of my ability (road, track, bedroom or bar brawl). 
Car will have multi map ECU set up for sensible road, fun and track.
I do have a fair bit of driving experience including some more exotic cars plus a tame race driver for tuition.
Brakes will not be standard MX5 but haven't decided what yet.
Suspension set up will be done by a pro, diff will match power.
For me the build is as much about seeing what I can produce as using the car once complete. Mix of road and track
Only track experience is on two wheels but getting past my prime for that.
Probably best direction at this stage is to build the engine to allow high boost but not set it up for max output until I know how much I want or can
handle.
Back to the original question, how much power do these cars generally have?
ianhurley20 - 25/12/18 at 02:03 PM
Mine was an almost bog standard 1.6 Mk2 MX5 engined car. 115bhp. My intention was to swap the engine for a 1.8 MX5 unit after a year or so but decided
against change. I had more grip than power so the car was very driveable in the dry and easy to control through bends etc. In the wet it was a problem
with its lack of weight to grip the roads. You had to be very careful indeed. I really enjoyed the cornering and braking ability of the car together
with reasonable performance - and - a decent range on one fuel fill. I've been in cars with LOTS more power but not really any extra fun so my
advice would be to get as many rides in other cars as you can, don't ignore the lower powered cars and then make a decision. You may be surprised
by your own final decision
froggy - 25/12/18 at 02:44 PM
If we’re talking about an mx5 my mate runs a turbo 1.8 with a td04 and 270hp at 12lb which is as far as it goes on a stock engine , we’ve been
fettling it with better tyres brakes this yr and after several track days it now feels like it’s ready for more power. Std diff broke last time out at
oulton so fitting a black line atb over the break .
Charlie C - 25/12/18 at 05:50 PM
The 5 speed gearbox has been know to fail (strip gears) at 250+ whp, it would abvisable to use a 6 speed box as they are much stronger. Also on mx5
race/track cars some are using gearbox oil coolers at high bhp.
The other thing to concider is cooling your limited on space for alarge enough rad intercooler and oil cooler for a 300 whp engine.
hobbsy - 25/12/18 at 06:42 PM
quote:
Originally posted by wasa
Ken Block behind the wheel.
Truth is often a little differant.
[Edited on 25/12/18 by big_wasa]
If you had to aspire to be a driver for me it wouldn't be Ken "Cock" Block, having seen his exploits first hand. Although the YouTube
vids with infinite takes do flatter....
As for the OP query, if its a turbo charged engine you could build it for 300 but then restrict boost until you get used to it. Or if a good boost
controller boost by gear and rpm etc.
Then when you want more turn crank it up!
ian locostzx9rc2 - 25/12/18 at 06:52 PM
I correctly set up car with 140/160 bhp is more than enough for the road and will embarrass cars with a lot more grunt on trackdays don’t get to hung
up with big bhp figures it will spoil the car . ( just my opinion) and if you can get some tuition by an expert .
[Edited on 25/12/18 by ian locostzx9rc2]
hobbsy - 25/12/18 at 06:55 PM
Guess a lot of it is also how the power is delivered. As someone said small displacement big power tends to mean big boost and narrower powerband and
and it comes in a lump. Good for drag but not so good for road or circuit use
Careful boost control and mapping could make all the difference.
jeffw - 26/12/18 at 08:05 AM
Or but a Rotrex on it instead of a turbo.
DavidhMX5 - 26/12/18 at 08:54 AM
quote:
Originally posted by hobbsy
Careful boost control and mapping could make all the difference.
Plan to use a dual port wastegate and 4 port electronic boost control linked to Emerald ECU.
This should allow me to set max boost at different values across the 3 maps (switchable from dash) and set max boost based on gear selected.
DavidhMX5 - 26/12/18 at 08:59 AM
quote:
Originally posted by jeffw
Or but a Rotrex on it instead of a turbo.
I did consider that but there does seem to be a reliability issue with the turbine shaft. Not sure if this is still the case?
Also potentially more expensive than a small Garrett turbo (half the initial cost) as still need intercooler etc. The exhaust manifold is often a very
expensive (if built well) part of a turbo set up but that I can do myself.
[Edited on 26/12/18 by DavidhMX5]
adithorp - 26/12/18 at 08:42 PM
Personal opinion 200bhp in a 500kg because or 300 in a 600kg CEC and after that the gains are marginal. I challenge anyone to try and keep up with
hobbsy when he's got 135.
Gord - 26/12/18 at 09:57 PM
quote:
Originally posted by DavidhMX5
Work starts on the engine this week.
First problem, what power to aim for. Original thoughts where 300+ but having never driven or experienced one of these cars I'm starting to
wonder if it's possible to use more than 300 if that.
Engine is a 1.8 NB (mx5) which is having a full strip and rebuild. Rods will be changed for forged plus stud kit for main and head. That setup with
standard pistons will be good for around the 300 mark (FI), any more and I will need to replace pistons with forged and consider gearbox strength.
So what WHP does your car make and how usable is the power?
I’m about 80% into turboing my 1.6 MX5 engine, hoping to see around 200-230 WHP, it’s road legal but mostly driven on the track. Have you started your
build yet, fitting everything in is challenging.
There’s a massive difference in cost between 230WHP and 300WHP and to be fair your probably not going to be able to use much more of that extra power
in such a light weight car.
[Edited on 26/12/18 by Gord]
DavidhMX5 - 27/12/18 at 08:18 AM
Just starting the build this week.
Cars ability to use the power is a concern I have.
From what has been said on this thread I think I will do the initial build with just rods and a 2554 turbo. Should get me to around the 240whp mark
with some head porting.
I can always upgrade the engine once I've driven the car for a while if I think it needs or could use it. Need something to do in the winter
months.
Thanks for all the responses. Very helpful.
jeffw - 27/12/18 at 02:59 PM
quote:
Originally posted by DavidhMX5
quote:
Originally posted by jeffw
Or but a Rotrex on it instead of a turbo.
I did consider that but there does seem to be a reliability issue with the turbine shaft. Not sure if this is still the case?
Also potentially more expensive than a small Garrett turbo (half the initial cost) as still need intercooler etc. The exhaust manifold is often a very
expensive (if built well) part of a turbo set up but that I can do myself.
[Edited on 26/12/18 by DavidhMX5]
No issue with the turbine shafts at all.
jossey - 28/12/18 at 10:07 AM
300 isn't usable. Loads of people I know including myself have reduced power to make them work better. Mine was 300 and we reduced to 269hp at
the flywheel too not wheels. 220 to 230 at wheels is enough for me. Having only done around 30 trackdays but I've had kit cars for 8 years or
so.
Its a totally different monster. I've had m3, 540i, 435i, AMG merc, vr6 and many other fast cars and non are anything like the westfield even
with 269hp. I have mates with 200 who can chase me down on the road as the turbo power is not linear enough.
Aim for a nice linear power line and 220 and you will be blown away.
David
froggy - 28/12/18 at 12:26 PM
Power delivery is the key , my heavy roadster at 830kg has just over 400whp but having a very flat torque curve from 2200-6000rpm is easy to drive as
your never really asking for a lot of boost compared to a 4 pot . I’ve just bought an mx5 for winter and wet track days but will be concentrating on
the suspension and brakes instead of adding power
DavidhMX5 - 29/12/18 at 08:26 AM
Advice noted
Will do a stock rebuild with just new rods and some minor porting to smooth airflow coupled to a small turbo.
That saves some money.
Thanks.
Gord - 29/12/18 at 11:39 AM
You won’t need new rods, just decent quality new rings and shells, hone the block, change the water pump, oil pump, lap the valances, new valve stem
oil seals, new decent quality head gasket and change all oil seals etc and you will have a nearly new engine which will give you between 200-240bho
easily.
DavidhMX5 - 29/12/18 at 02:30 PM
Gord - Agree with everything on your list except not changing rods. While in there I want to remove the weak point in the engine as rods at limit
around 250. I anticipate the car will see a fair amount of track action and rebuilding after a thrown rod would be expensive. Worth it for peace of
mind to me. Pistons should be good for 300 so a good margin of safety there and can stay as long as I don't find any horrors in the bores when I
get in there.
BaileyPerformance - 31/12/18 at 05:52 PM
Personally, i wouldn't put stock pistons to 300hp, 280 max.
You'll need a TD05 turbo, or something that sized.
550cc or bigger injectors
Walbro pump
Can we offer to map it? we have mapped over 100 mx5s
www.facebook.com/baileyperformance
jossey - 31/12/18 at 10:26 PM
Bailey built my zetec turbo engine. Can highly recommend.
I will use them again.
jeffw - 1/1/19 at 07:29 AM
quote:
Originally posted by jossey
300 isn't usable. Loads of people I know including myself have reduced power to make them work better. Mine was 300 and we reduced to 269hp at
the flywheel too not wheels. 220 to 230 at wheels is enough for me. Having only done around 30 trackdays but I've had kit cars for 8 years or
so.
Its a totally different monster. I've had m3, 540i, 435i, AMG merc, vr6 and many other fast cars and non are anything like the westfield even
with 269hp. I have mates with 200 who can chase me down on the road as the turbo power is not linear enough.
Aim for a nice linear power line and 220 and you will be blown away.
David
400BHP produced by a Rotrex is perfectly usable.
jossey - 1/1/19 at 10:48 AM
Jeffw.
I can't comment on that sorry I've not driven one. What I know is from caterham and westfield drivers who either race or do fast trackdays
say the sweet spot is around 220 to 240. Don't get me wrong in the dry my westfield was great fun and after Bailey improved the progressive power
it was OK.
Then there is the damage to the body. I had to strengthen mine to take 269 on boost. Chassis twisted. Then the crown wheel on the diff rounded so new
lsd. Then the prop shaft broke which was from D and f in Leeds so new landy one made. Then a half shaft broke so put standard ones back on then other
went. So 2 new at 800 quid a pair for rs ones made up. Then the clutch started to go. Then the rear diff mounts twisted. Then the rear arms of the
axle ripped off. So after fixing all that it was fine.
I guess this is the same as a lot of discussions here it's about driver skill which I've only done 60 or 70 in my life so can't say I
have good experience and 400hp would likely kill me haha.
I had a busa mk car on loan for a day think that was 220hp
and 500kg ish that was great fun best car I've driven.
That said I want an ecoboost with 350hp haha
[Edited on 1/1/19 by jossey]
Gord - 6/10/19 at 09:38 PM
quote:
Originally posted by DavidhMX5
Gord - Agree with everything on your list except not changing rods. While in there I want to remove the weak point in the engine as rods at limit
around 250. I anticipate the car will see a fair amount of track action and rebuilding after a thrown rod would be expensive. Worth it for peace of
mind to me. Pistons should be good for 300 so a good margin of safety there and can stay as long as I don't find any horrors in the bores when I
get in there.
Dave, did you get around to fitting a turbo, if so how did it go?
DavidhMX5 - 8/10/19 at 06:49 PM
No, complete change of direction.
I now have a GBS Zero sat in my garage being built (Gen 2 chassis).
Decided fabricating all the parts was just too much like my day job.
Zero has all the upgrades including front end wishbones, calipers and discs. Rear fully adjustable rose joint. Unique atm as the rear upgrade
hasn't been released yet.
Engine will be with me in a couple of weeks, Duratec I4 2.5ltr mated to mx5 mk3 gearbox (both new).
Diff has a J3 Driveline plate type LSD.
Everything on the car other than the diff casing is new so will be a new reg.
Initially will be using TBs normally aspirated but have plans to add a rotrex supercharger if I need more ponies.
Should be on the road middle of next summer.
I haven't written about in on here as definitely not a lowcost option. 
