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Do I need axle upgrades if im running 250+hp?

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dherr2 Avatar
dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
Yes, been in the car since 2004. See Rover V8 swap for more details on the swap. Have not updated my site forever, but the details are on the old site.

After successfully doing an R160 Subaru diff in my Spitfire (with a turbo miata engine and 6 speed), are now working on getting all the parts to convert my TR4A to IRS, Nissan R200 LSD and CV axles.

In reply to # 1589172 by Dsavoie47 You are running a rover v8?

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dherr2 Avatar
dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
Dsavoie47 Daniel Savoie
Granite falls, Waahington, USA   USA
1964 Triumph TR4 "Jennifer"
Looking good! The rover v8 should be producing at least 60 ft/lb more torque than the engine I'm going to run. So I might try it and see if I can het away with it.

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dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
So 250 HP but 150 pounds of torque means you are looking at an S2000 motor, correct cool smiley

Dsavoie47 Daniel Savoie
Granite falls, Waahington, USA   USA
1964 Triumph TR4 "Jennifer"
Yes. Hopefully. Might go with mx-5 motor. Depends on what my options are come engine time

dherr2 Avatar
dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
I went back and forth on my Spitfire project. I really wanted an S2000 engine and 6 speed, but had trouble justifying double the cost for only 150 ft pounds of torque. Would have been great in a Spitfire since they are so light, so probably would be fine, but I got a BP4W with a 6 speed for half the price. Added a Turbo and ECU so total cost was similar, but now I have a much more powerful engine with 220HP but more like 200+ foot pounds of torque and a 7,000 redline, so still high reving. Stock a 99-00 MX5 engine has 140 HP and 119 ft/pounds of torque so with some mild boost (10 pounds) you can easily achieve similar results.

ducbsa Bruce Metcalf
Berryville, VA, USA   USA
What is a BP4W engine?

dherr2 Avatar
dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
The BP4W is generally accepted as the best version of the NA/NB Miata engine. It was used in the 1999-2000 version of the 2nd generation NB model. It is a 1.8 with higher compression, a dual plane intake, higher red line and makes 140 HP. This was also the version that was factory turbocharged for the Mazdspeed Miata. It costs more than the earlier 1.8 engines, but is a good 20 HP stronger. With a 6 speed, it makes for a pretty sweet engine for swapping into our cars.


Dsavoie47 Daniel Savoie
Granite falls, Waahington, USA   USA
1964 Triumph TR4 "Jennifer"
Its definitely a possibility for my build. The s2000 engine is more money but bone stock its one of the best performing I4 engines. And probably the best performing naturally aspirated I4s of all time

dherr2 Avatar
dherr2 David Herr
Adamstown, MD, USA   USA
1972 Triumph Spitfire MkIV "Rat Rod"
No argument there, the S2000 motor is pretty much a modern motorcycle style engine. Apparently the K Series is even better, but you have to secure all the parts to make it RWD. If you are seriously considering the S2000, check out this as a possible alternative Kmiata web site as they have put together the pieces to build a pretty high performance RWD platform for miatas and other similar swaps.

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