v8ian
Posted a lot
Posts: 3,763
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Lots of reasons why rods exit blocks, I have had an engine demolish it self when a ported head burst the water jacket, filling the bore with water at 7k, the only thing useable was the injection, that was a 383 Donovan SBC, Neither do you know how the engine was abused or for that matter how well it was built.
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Atmo V8 Power . No slicks , No gas + No bits missing . Doing it in style. Austin A35van, very different------- but still doing it in style, going to be a funmoble
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3point141
Yorkshire and The Humber
Posts: 106
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Hi,
just to be clear on the issue of "squish", as pointed out, it does aid in turbulence, mixing charge to achieve a better (and more efficient) combustion, but think for a minute what this might mean. Mixing the charge to achieve better, more homogenous properties implies that during the compression stroke, there are still regions of charge with high and low fuel ratio which have yet not mixed. should these regions remain un-mixed could result in "detonation" (self-ignition due to compressive heat) of the lean regions, this going on outside of the propagating flame front. I know from experience in high-compression engines how one engine can run higher compression and not experience "pinging" than a different one which has not had its squish gap set (blueprinted) and cannot adequately exploit this phenomena.
Although, now you mention running almost 1-bar boost, you might be completely outside what the engine might be able to run by following the advise above. In this case.. run a compression lowering plate, please don't mill your pistons. Assuming they're cast (hyper-eutectic, probably) that's really a bad idea as the material is really fragile and will likely fail due to fatigue effects. Any piston is designed to be as light as possible, so don't carry anything in the way of "spare material", aside from milling to achieve valve clearance on a "cammer", I would in no way expect a piston to endure machining to achieve compression lowering.
Have you thought of fuel additives?
If you're not going to be doing mega-mileage, just mix toluene (or cellulose thinners) in with your fuel & not bother with modifying the engine at all! This will help with the engine life in two ways; principally by increasing the octane rating of the fuel such that pre-detonation will not occur, secondly, toluene is a slow burning fuel so will help reduce maximum combustion pressures and help the system extract higher average combustion pressure over a larger crank stroke angle. This will help keep your rods inside the block... where they belong.
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goldnrust
West Midlands
Minimalist
Posts: 1,872
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I generally agree with 3point141, that is the correct and proper theory and way to do things, and for most engines that is the route I'd follow. However…. You're talking about an mx5 engine to turbo here, which is a relatively specific case. As MDH says, the original mx5 1.6 was literally a 323 turbo engine with the turbo removed, it has a number of features specifically designed for turbo use, such as oil jets that cool the underside of the piston CROWN. The 1.8 is an evolution of the 1.6, and carries forward many of the features. On an entirely standard mx5 engine, you should be safe to ~250hp. This is normally achieved with ~12-15psi of boost, an appropriate intercooler, ECU, injectors, etc. The amount of power a stock mx5 engine can take in turbo form is limited by the rods, past 250hp you are on borrowed time before they bend or snap. Very few people bother building an uprated bottom end for the mx5 engines, because once you pass this 250hp, you'll find at 270-280 you start shearing teeth off 5th gear, and at 300hp you run the risk of killing the diff. Basically it starts getting mega expensive once you pass the 250hp area. Obviously there are failed engines on much lower boost/power loads than this, but they are usually the result of some other form of failure, such as incorrect tuning causing detonation. I daily drove my mx5 1.6 turbo with 14psi boost for 2 years / 30,000 miles without real incident. The best thing you can do is get on some of the mx5 specific forums, where theres larges amounts of info about which turbos suit the engine well, which mods you need at which power level (you'll want a clutch past 7psi!) and lots of 2nd hand parts for sale. www.mx5nutz.com is a popular UK site, www.miataturbo.net is an American site that's got a lot of good info, sadly they are not a friendly bunch, but their FAQs are very very useful.
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Last Edit: May 5, 2015 8:01:06 GMT by goldnrust
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froggy
Posted a lot
Posts: 1,099
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The plug and play megasquirt for the mx5 is very good value for the money .
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Yeah the whole "not a good idea machining the pistons" malark was why I thought aboutaking new ones from billets but since researching forging that's not a good idea either
So I'll leave the pistons as they are, replace the rings, add a decompression plate and tune it properly... I've got a mounting point ready for an intercooler, just funding really haha
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No need for a decomp plate on the mx5 lump....
Have you thought about a supercharger instead of a turbo? A nice eaton m45 will boost you up to 200hp ish.
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Koos
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I've already bought a turbo, just welding up a manifold ATM...
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hario
Part of things
S202 C300STD
Posts: 421
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Jun 17, 2015 15:09:31 GMT
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For A-series turbo builds we had to burette the cylinder head to measure the combustion chamber volume, then die grind (polish & smooth) the wall material & re-burette until the calculated lower volume was achieved. Perhaps not enough easily cuttable metal within a 4-valve pent-roof head chamber though?
As above I read pistons are manufactured ovaloid such that they are narrowest perpendicular to the gudgeon pin axis, as material expansion is most in that plane.
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Last Edit: Jun 17, 2015 15:11:02 GMT by hario
*S202 C300TD Wagon* Installed: OM606 & 722.6, Evo6 IC, S600AMG callipers & 345mm rotors. No catz. Leatherish seats.. Rust.. Future: DIY manifolds & turbo compound build. Built IP, & some kind of software. Less rust..
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