MX5 V8

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southernd
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MX5 V8

Post by southernd »

Hey,

I bought Andy's old MX5 V8 last October and after a couple of running issues Andy told me about this forum.

The car is a mk1 MX5 which a JRV8 3.5 Rover engine. Just had it on the rolling road today and it made a measly 164bhp. Every fuelling/ignition reading was perfect, any suggestions will be really welcome!


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DaveEFI
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Re: MX5 V8

Post by DaveEFI »

southernd wrote:Hey,

I bought Andy's old MX5 V8 last October and after a couple of running issues Andy told me about this forum.

The car is a mk1 MX5 which a JRV8 3.5 Rover engine. Just had it on the rolling road today and it made a measly 164bhp. Every fuelling/ignition reading was perfect, any suggestions will be really welcome!
What is the spec of the engine? 164 bhp is more than many, but less than some. :D

Note that RV8 cams - especially 'wild' ones - can have a pretty short life. And the engine can appear to run ok, but be well down on maximum power.
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southernd
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Post by southernd »

Hey Dave,

It was option 3:

http://www.jrv8.co.uk/engines/

285 cams if I remember and a pretty extensive rebuild. Built for around the 200bhp mark. It's done very few miles since rebuild, less than 10k from what I can see. I've yet to do a compression check but there's zero that sticks out as an issue. Torque wasn't that high either.
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southernd
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Post by southernd »

Here's a short vid on the rolling road:



This was after the ignition was advanced a little too much but gives an idea of the running :)
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v8250
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Post by v8250 »

If engine built for 200bhp at fly, I'd expect to see 168bhp at rear wheels c/o transmission losses. So may be the engine/car is on tap at originally planned?

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Post by southernd »

Pretty sure he said flywheel, I'll post a pic in a second.
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Post by southernd »

MX5 4.6 V8
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Post by v8250 »

southernd wrote:Pretty sure he said flywheel, I'll post a pic in a second.
what was their engine correction set up factor? or, could they have a print out error where the reading is at rear wheels?

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Post by southernd »

To be honest I don't know, it's the first rolling road I've been too. I did try and get to Austec but 3 phone calls not returned I gave up with them!
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Post by southernd »

Most likely I'll try and get hold of an experienced Rover V8 mechanic. If the engine proves no good I'll look at getting a 4.6 short block, a bit of work but more powerful from the start :D
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Post by ChrisJC »

What's the tolerance on that reading? They are 'compensating' for the transmission losses somehow, and although they always reckon they are spot-on, I would hope they could give you a +/- on the reading.

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Post by DaveEFI »

southernd wrote:Most likely I'll try and get hold of an experienced Rover V8 mechanic. If the engine proves no good I'll look at getting a 4.6 short block, a bit of work but more powerful from the start :D
Does it really feel short of power on such a light vehicle? I know we all want more. :D
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Post by Darkspeed »

If the heads are stock and unmodified you can put as much cam, carb and compression as you like on it - It will not do 200BHP - for stock heads 168BHP is about as much as you could ever expect.

ETA

Graph shows as expected with stock deads - flow stops after 5500. Lift the valve as much as you like and put as much carb behind it as you please - the air will not get past the restriction in the throat.

Spend £4-500 having the throats opened up and some decent seat cut and it should see 225BHP.

ETA +

The torque increase from 2500 would be what you would notice most with the head works.

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Post by southernd »

They didn't tell me much to be honest, I got the print out you see :)

If anyone remembers the MG Maestro, it feels like that. Yes it's nippy, it will move if you spank it but nothing like a V8 should. I'm not a BHP snob, it's not something I normally chase but for a V8 it just doesn't have much umph.

They are Vitesse cylinder heads, I'll Google them in a mo. Looking at the invoice/list of work the compression was raised to 9.75:1 and a hurricane camshaft, the rest was pretty much a full rebuild.
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Post by southernd »

Thanks for the head info, that makes sense. The Vitesse do seem to have bigger valves etc, would they be classed as performance?
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