SP and SE bottom end question.

by **bear2230** » Sun Mar 04, 2012 5:32 pm

Hi all,

I have been hearing of late a bit of talk regarding the strength of the SP's internals. In particular the SE's have stronger Internals making them better for more boost.
My question is what did they change exactly? If anything at all.
Different rods? Forged pistons? What?
I'm not having a dig at SE's, just waying up my options with how many RW Killerwasps I can safely aim for when we do the Adaptronic. On Manias dyno it has 142 at present. Could 160 cause engine failure?
Car won't be tracked and has 25,000km with stock internals.

Richard.

by **Hjt** » Sun Mar 04, 2012 6:30 pm

Your car is a lot faster than mine mate

I always was under the impression ours wasn't as stable purely because the higher compression and vvt on the head.

by **NitroDann** » Sun Mar 04, 2012 7:35 pm

The answer is 250rw/ft-lbs. Which is impossible at mania because they do not calculate torque.

IF you have stock internals, then its about 250rwhp also, just happens to be.

Both are 100% equally as strong. B6, VVT, NA8, NB8a, SE, and SP are all identical in this regard.

Dann

by **Tedsmx5** » Sun Mar 04, 2012 8:42 pm

Thanks Dann I have always wondered if there was any difference, and you have answered my question without me asking. Must make it up to Mt Sugarloaf, I worked up there for 3 year in the 1990s.
Ted

by **bear2230** » Tue Mar 06, 2012 5:23 pm

Thanks Hayden & Dann, I will go for 165atw on the highest setting and 125atw for rainy or grandma days. I'm too much of a pusspuss to even go for anything higher ATM.
Bring on the Adaptronic and bigger injectors.(calling BadBong)

Richard.

by **greenMachine** » Tue Mar 06, 2012 9:41 pm

NitroDann wrote:
Both are 100% equally as strong. B6, VVT, NA8, NB8a, SE, and SP are all identical in this regard.

Dann

That goes against a lot of internet 'wisdom' I have seen, both here and on the big board, the gist of which is that the BP rods are more susceptible to bending under load (not necessarily boost) than the earlier ones.

Not saying you are wrong Dann, but if you are right there are a lot of people changing rods for no reason ...

:mrgreen:

by **NitroDann** » Tue Mar 06, 2012 9:46 pm

Theres lots of talk about how '1.6s seem to take the boost better'.

And it may have to do with the shorter stroke, and therefore better rod ratio, but the rods are identical. And the rods are what breaks first, making the rod breaking power the max power on stock bottom end. 250rwhp ish.

Dann

by **NitroDann** » Tue Mar 06, 2012 10:14 pm

I hope wazzah comes in and tells me how wrong I am

Dann

by **wozzah1975** » Tue Mar 06, 2012 10:33 pm

This is an interesting topic.

I watch in interest with people chasing B6 turbo rods and fitting them to BP engines (as Dann stated they are dimensionally identical).

Here is a good comparison of some different castings.
http://www.clubprotege.com/forum/showth ... 6T-ConRods

I had a heated discussion with a person about the rods because I couldn't see what all the fuss was about. In the Ford/Mazda spare parts listing, the B6T, BP and BPT connecting rods are ALL listed as the SAME part number, and I didn't have a set to compare at the time.

I found out though that the B6T rod is definately beefier (I have now seen them first hand), BUT it is also beefy in alot of the wrong areas adding unnecessary weight. There are also different rod bolts used, and different machining/cast marks. Bottom line, they are probably marginally stronger.

In regard to the part numbers, it is possible that the part number listed them all the same due to supersessions in the spare parts system (in other words they all now use the same rods if you need to repalce them OE)

In my opinion, there is not enough difference in them to bother sourcing the B6T rods (unless you had a spare set, in which case you may use them). With the availability of good aftermarket rods its hardly worth thrying to source set, you would just buy some Spools or Eagles etc and be done with it and know they won't break.

Cheers
Woz

by **wozzah1975** » Tue Mar 06, 2012 10:34 pm

NitroDann wrote:I hope wazzah comes in and tells me how wrong I am

Dann

I completely agree with you in regard to the stroke and rod ratio! There are different castings though

Cheers
Woz

by **NitroDann** » Tue Mar 06, 2012 10:36 pm

As usual, legend.

Cheers mate.

Dann

by **Sean** » Wed Mar 07, 2012 12:31 am

wozzah is correct, B6T rod were beefier back in the turbo familia/TX3 etc. They have a thicker beam, thicker small end and larger bolts. Factory specs the weight at 580g with nuts and bolts compares to 540 for the MX5 ones. As wozzah though Mazda did discontinue the B6T rods - if you order a replacement set for a B6T you'll get the same as if you order a replacement set for an MX5 B6 or early BP mx5.

I cannot speak with any authority on an SE etc, but I'm almost certain Dann and wozzah are correct in stating all MX5 B6/BP rods are the same, like I said, they were in early BP engines, and no-one has shown me real or even internet evidence to suggest they changed at any time.

Again as wozzah said, B6 and BP rods ordered from mazda all share the same part numbers these days.

B6 has a slightly shorter crank, which may as one of those pair mentioned relate to the boost handling capabilities, as would the various compression ratios offered.

The stroke is longer in a BP as Dann suggested and the BP also has longer bore spacing to fit it's larger pistons (83mm?).

Both engines share the same block deck height and head height, as well as functionality like oil squiters, oil passages etc as well as similar head and crank design - I believe very late BPs maybe the VVT ones also had a crank girdle or support of some sort, but again, I'm not particularly cluey on the late ones...

So to paraphase, Dann and wozzah are right in what they say.

I'd add that in my expereince, I've seen a lot more of these fail from broken rod bolts than broken rods or pistons.

by **geofiz** » Wed Mar 07, 2012 12:48 am

The SE has a crank 'girdle' or Main Bearing Support Plate

I am unsure if these are fitted to all late model NB's or not.

by **wozzah1975** » Wed Mar 07, 2012 9:08 am

geofiz wrote:The SE has a crank 'girdle' or Main Bearing Support Plate

mbsp.jpg

I am unsure if these are fitted to all late model NB's or not.

The front wheel drive engines use a girdle almost identicle to this, I fitted it with some slight mods to my conversion as I already had it.

Cheers
Woz

by **sailaholic** » Wed Mar 07, 2012 9:35 am

The sump is different to suit the girdle. from memory all nbc have the right sump. Early sumps can be modified to suit. Details, along with factory and upspeced bearing support plates can be found on the miataroadster website.

Can someone please explain how with the same block height a different stroke is achieved? I'm imagining that the piston is pulled further down into the block at the bottom of the stroke? Hence more bending load on the rods?

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