4.6 V8 swap to MX5

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southernd
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4.6 V8 swap to MX5

Post by southernd »

I was on here a bit last year looking for advice on Andy's old MX5 V8 so I thought I'd update you on what's happened since then to help anyone else.

Despite many hours and some increase in performance I just couldn't get the 3.5 to run properly. The car stank of fuel a lot of the time and the horsepower just simply wasn't there. I took decision to bin the engine and start again.

I sourced a 4.6 Range Rover V8 with all ancillaries from a breakers in Kent. For a little over £500 delivered it was a bit of a gamble but my intention was to focus on putting in fuel injection.

I went with MS from ExtraEFI in the end. The Rover loom, connectors and turnaround time was very good. It came with a map for the RV8.

Once the old engine was removed we found a number of problems. Broken engine mounts, gearbox being bolted into the bodywork and some other issues which probably took the longest to fix. I probably have been very focused on a good job so no corners have been cut.

The exhaust manifolds were stainless steel from the MGBV8, with some hammering they fitted. The old exhaust was also seperate for each side on the old setup, we merged the two branches into one and fitted a wide band lambda. At the rear the twin tail box from mx5parts fitted perfectly which kept costs down and reduced the noise.

A new all alloy radiator was fitted with twin 10" revotech fans and a RS Turbo fan controller with manual override. The standard RRv8 thermostat was binned and a 75C one from a TVR put in. The exhaust has been wrapped and as much to keep heat away from the engine bay as possible. The 4.6 is slightly shorter than the 3.5 so air flow is a little better.

The brakes have been upgraded to Wilwood 4 pot calipers and the suspension lowered by 13mm and shocks replaced.

Gearbox was untouched, no work was needed as was the diff, the E36 323i diff is capable of 300 ft/lb of torque, a good choice.

Only bodywork has been a new bonnet bulge, made from two roasting tins which has gone off to be sprayed up next week.

The rolling road results today showed:

190BHP at the wheels.

250 ft/lb torque at the wheels.

The engine proved in very good condition and sounds very sweet, a gamble worth taking. Being completely stock those figures are spot on.

In credit to ExtraEFI the map was only 10 ft/lb of torque out, it really does work almost of of the box.

I will get a video done once it's on the road.

Image


MX5 4.6 V8
Previous of many SD1's back in the day!

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Rossco
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Post by Rossco »

I've always fncied an MX5 with a V8

Nice work

southernd
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Post by southernd »

Thank you, can't wait to get it finished, a bonnet respray and that's it!
MX5 4.6 V8
Previous of many SD1's back in the day!

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ChrisJC
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Post by ChrisJC »

Nice work - well done.

Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8

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