Cam Timing and Lowered Compression - Miata Turbo Forum - Boost cars, acquire cats.

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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 02-03-2014, 07:52 PM   #1
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Default Cam Timing and Lowered Compression

OK Usually i can use the seek and ye shall find option for all my amatuer woes but on this occasion it has failed me.

I have a 91 1.6 that originally had a Greddy turbo set up on it, i removed almost all off its nasty parts and fitted MSPNP, new EV14 injectors (670cc) and an intercooler kit.

When we replaced the timing belt we found the inlet cam was out by one tooth and the idler pulley had been machined to have an elongated hole instead of the usual round hole.

The timing belt was uber tight and impossible to fit with a std idler pulley so I fitted a second adjustable at max out setting on both the timing belt fitted but is snug. Further investigation has revealed a thick metal head gasket has been installed.

Am i correct in thinking this would be why the cam timing had been adjusted? on the dyno day it wouldn't pull more than 135bhp but was achieving 200nm TQ. then at 4500rpm it just lost all gains.

If the compression has been dropped by the thick head gasket, am i right in thinking the timing on the cams will need adjusted now?


as a side bar, the greddy kit has now been ditched in favour of an ARTech manifold and T25 Turbo.
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Old 02-03-2014, 11:33 PM   #2
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It sucks, but you need to pull the head gasket and replace it with a .030" OEM unit. Reducing the squish area on these motors makes them even more prone to detonation than they already are.

Advancing the intake cam will also make the car prone to detonation by increasing dynamic compression across the rev range.
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Old 02-04-2014, 05:30 AM   #3
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The answer i feared most, sigh
I really do wonder what this cars original Turbo installer was thinking, i have now and will no have removed every single component of his work

It was supposed to be so easy!
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Old 02-04-2014, 10:28 AM   #4
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At least you picked an awesome username for the forum here. :]
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Old 02-04-2014, 04:18 PM   #5
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The name was no accident =)

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Old 03-19-2014, 09:50 PM   #6
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To Savington

It was worse than we thought, when we got the head off



a 4.5mm steel plate with a headgasket on either side, not to mention the RTV covering some of the oil ways

further issue were found when i got the head off that the rubber blank from the very back of the inlet manifold for a vacuum takeoff was absent compounding my tuning woes,

Now reassembled with genuine mazda gasket, and everything associated with the Greddy kit now in a box, she fired up and runs nicely.

10 internet points for you sir!
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Old 03-19-2014, 11:05 PM   #7
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Wow, that is ghetto. Good job manning up and taking care of it.
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Old 03-20-2014, 12:09 AM   #8
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That is quite possibly the most ghetto thing I've ever seen done to a Miata. Props for doing the right thing and getting it running correctly.
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Old 03-20-2014, 12:23 AM   #9
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Quote:
Originally Posted by Savington View Post
That is quite possibly the most ghetto thing I've ever seen done to a Miata. Props for doing the right thing and getting it running correctly.
I personally think that OP should have just JB welded some quarters onto the pistons and left the spacer.
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Old 03-21-2014, 07:56 AM   #10
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This whole car has been about trying to "do it once, do it right"
My stepfather was an engineer building race bikes and all i have in my head is his words about "if a jobs worth doing.."

Sorry i am not one for posting too often, i tend to prefer to spend my time tinkering. I will dig out the cars thread somewhere and update it.

short version is

91 J LTD, formerly Ghetto Greddy set up, with cams out by teeth to adjust timing, vortec FPR jack through the roof, Tan injectors. running std plastic pipe with gaffa tape to pass the boost from turbit to inlet mani.

Now fitted with
ARTech manifold and T25 Turbo, Custom stainless downpipe, Front mounted intercooler, MSPNP2 with EBC, Bosch EV14 670cc injectors, VTPS, MTXL WIdeband, SVT Big Brakes waiting in the shed to go on after running is sorted,
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