Will it Blow?

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FarnhamStag
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Will it Blow?

Post by FarnhamStag »

Hi guys,
I'm slowly getting more confident whilst testing my car but I'm now concerned about the longevity of the engine. Drawing on all your experience I would appreciate your opinion.
The MS3 log is showing boost of 195kpa (14psi) at 6K rpm, MAT peak of 28C, Engine is 1986 3.5 block bored/stroked to 4.3 by tvr, BV heads, V8 tuner turbo cam, MS handling fuel and ignition, Rotrex C38-81 charger.
Car weight is 1200kg, 280 hp before charger.

The engine seems to run well, no detonation, but the question is will it hold together if it has so far or does there generally have a gradual weakening of components leading to a bang?
It only hits 14PSI just before a gear change for a very short period of time,
10psi at 5k, 7psi at 4krpm and on the road boost can't be held for long anyway. Not Sure if I'm brave enough for a track day!
I'm also running a fairly conservative timing of 15 degrees advance over 4700rpm so does this reduce some of the stresses or is it better to get it optimized on a dyno?

I appreciate this is a very open question but I guess some of you have learned the hard way and I'm really trying to avoid that right now.

Any advice is welcome, thanks Dorian


4.3 Big Valve V8, Rotrex C38-81, Intercooled, MS3X Triumph Stag.

JJMclure
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Post by JJMclure »

reading 'mercan forums the longevity of blown engines does owe a lot to the tune. ive no experience of a blown engine myself but being too aggressive with the timing seems the path to carnage.
good luck with it
don't nibble on the barrel, pull the trigger!

SuperV8
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Post by SuperV8 »

What's your compression ratio?
I don't know what the mechanical limits as regards maximum boost and there are a lot of variables which will affect this.
Have you got an intercooler as this will help? seems like you have as your air temps seems good.
I have a similar setup to you although using 4.6 cross bolted engine with Procharger. I was thinking of aiming towards 10-12 psi in the inlet manifold so my supercharger will have to make a little more due to losses in pipework/intercooler.
I would keep an eye on your plugs for any signs of detonation and yes running a conservative timing will help, but there will be a limit and a need to balance having to reduce timing and maximise boost, there are diminishing returns with increasing boost levels and reducing timing.
If you're seeing 14psi that must be making a fair amount of power! Do you want more or just concerned with having it reliable?

Tom.
Dax Rush 4.6 supercharged V8 MSII

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Blown v8
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Post by Blown v8 »

Have you got forged pistons ? Arp studs ?
Standard pistons won't take a lot of abuse,you will end up melting one !
The next weak spot is head gaskets,arp studs help,I ended up O ringing my heads,never had any trouble since

r2d2hp
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Post by r2d2hp »

Hi Dorian, my setup sounds similar to yours but max boost I see is about 6psi but my IAT is hitting 50 degrees which worries me. Are you running an inter-cooler?

Out of interest where do you measure your IAT temps as mine is taken from inside the plenum

regards
Reg

FarnhamStag
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Post by FarnhamStag »

Sorry forgot some rather basic info! Compression is 9.8:1 but has not been meaured, heads and block have been skimmed but I'm using composite gaskets so hopefully this will mean its around 9.5 at a guess.
Running shell 98 ron V power, big intercooler with about a 6 degree increase over ambient on full boost, and the crank and head are fixed with ARP studs. 1 5/8 primaries on exhaust and Bosch green giant injectors which are close to maxing out!
IAT temperatures are taken about 400mm before the throttle housing and the map values from the Plenum.

I'm really not looking for more power, its a road car primarily but I don't want to lose the low end boost/ torque I have now either.
It may at some point go on a track day if I'm brave enough!
4.3 Big Valve V8, Rotrex C38-81, Intercooled, MS3X Triumph Stag.

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