TeamCapri
Tech, Repairs, Upgrades => Capri XR-2 89-94 => Topic started by: Gaz on January 24, 2017, 08:40:16 PM
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So, go out and start the Capri. But idling for about 2 minutes, then I look on the side of the block to see a little bit of bubbling happening around the head gasket area. Great news, I know. So I'm thinking arp head studs, Cometic gasket. Besides the obvious full engine seal set, if it only has a hundred and fifty thousand on it, would it be worth it to rebuild it, maybe put in forged pistons? Does anybody know if this thing came with forged pistons from the factory? If not, can somebody list part numbers that I will need for the head studs and the head gasket?
Also, a recommendation of Manufacturers on con rod bearings, would be nice. I was thinking King.
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IIRC the pistons arent forged but the conrods are. Ill post part numbers when I get home im at work right now so I dont have the time to search for them.
If you have the cash laying around id rebuild it, no use to put that much money in and then have to kill for a bad rod or something 10k later. From what ive heard King is the recommended brand as is Cometic. If you do the full gaskets just use Mazda brand gaskets the aftermarkets are generally worse then OEM. Really it all just depends on your goals if you want to keep or increase HP drastically id do a performance rebuild but otherwise id say youd be fine to leave it alone.
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The B6t short blocks are tough as nails. If anything have the head freshened up. Honestly you can do that yourself. Get a spring compressor, like for motorcycle, I got one on Ebay cheap, a set of Super Tech valve seals and you want to just lap the valves back into the seats. Do not have them ground. Have the head cleaned and milled, go get some Miata head studs from ARP and your choice of gasket and slap it back together. The pistons are not forged but squeeze cast but plenty good with enough fueling.
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IIRC the pistons arent forged but the conrods are. Ill post part numbers when I get home im at work right now so I dont have the time to search for them.
If you have the cash laying around id rebuild it, no use to put that much money in and then have to kill for a bad rod or something 10k later. From what ive heard King is the recommended brand as is Cometic. If you do the full gaskets just use Mazda brand gaskets the aftermarkets are generally worse then OEM. Really it all just depends on your goals if you want to keep or increase HP drastically id do a performance rebuild but otherwise id say youd be fine to leave it alone.
Any luck on that hg number?
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Sorry Gaz I've been really busy last few nights, completely forgot. A few of my friends run this head gasket.
HG: https://www.flyinmiata.com/1-6-cometic-head-gasket.html
ARP Headstuds: https://www.flyinmiata.com/arp-head-studs.html
Those both should fit Flying Miata also carries other HG Incase you want to drop compression or anything. They both will fit as there isn't much of a difference in the head other then cam profiles and the intake manifold.
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Now, on Keystone, I'm listing several cometic head gaskets for an xr2. Varying from .098 to .027 thickness. Stock is one millimeter or .040. Should I go with something smaller to raise compression? Or will I have to worry about valve Clash?
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I think its a non-interference engine, so you don't have to worry about that.
Jack Byrd
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Well...should I go thinner to raise compression, then? What y'all think?
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I dont see any reason why you couldnt/shouldnt go thinner. Youd gain a small horsepower increase and the car would be happier off boost.
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Stick with the OEM thickness gasket. The compression increase won't be appreciable on such a small engine.
Changing the relation of the head to the block either through gasket thickness or block/head decking will change the valve timing ever so slightly, because it changes the effective length of the timing belt.
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I would think that the tensioner would take up that slack in the effective length of the belt couldn't possibly physically change.
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I've thought of putting these T203a cams in it as well. https://jmautosports.com/kelford/kelford-racecams/t203a/i-222482.aspx
What other mild cams have been used for better grunt?
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Ive heard of people using Auto Miata cams for better lower end power.
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The auto cam can be sourced from the n/a capri, too. It's the exhaust cam. Intake cams are all the same, I believe.
It does move the powerband down, at the cost of top end power. I ran one for a while thinking it would help the turbo spool faster, ended up putting a stock XR2 cam back in. I like the better top end power.
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+1 on Matts comment. I took that sucker out real quick. There is a reason Mazda used the cam that they did.
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+1 on Matts comment. I took that sucker out real quick. There is a reason Mazda used the cam that they did.
I see. Pistons, then?
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I would think that the tensioner would take up that slack in the effective length of the belt couldn't possibly physically change.
The tensioner pulley only adjusts on the intake side of the timing belt.
When you deck the head or put a thinner head gasket on, you shorten the distance between the crank and exhaust sprocket. The length of belt is still the same and causes the intake and exhaust cams to retard counter-clockwise.
All lot of the Miata folks due this cuz they found retarding the cams shifts the power band slightly higher in the rpm range to make more hp. The small bump in compressing helps keep the low end power, while also increasing the power in the mid and upper rpms too.
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Good thought Chris.
Jack Byrd
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If it really has all those benefits it sounds worth doing.
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A lot easier to just add some boost isn't it?
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A lot easier to just add some boost isn't it?
This, times 10.
Decking the head can also have other negative side effects - you're removing material. It may be easier to warp, the valves will run closer to the pistons - I personally wouldn't mess with it.
Yeah, grab some proper forged pistons with a higher CR if you want to bump the CR.
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A lot easier to just add some boost isn't it?
This, times 10.
Decking the head can also have other negative side effects - you're removing material. It may be easier to warp, the valves will run closer to the pistons - I personally wouldn't mess with it.
Yeah, grab some proper forged pistons with a higher CR if you want to bump the CR.
Well, yeah. I was only going to have it decked if the block was warped, but that doesn't seem like a common occurrence on these. What's the farthest bore you can go with on this? . 20?
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.20 would be really pushing it to fo it right youd have to get the block sonic tested. Only a few select b6 blocks havd enough wall to do .20 overbore
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.20 would be really pushing it to fo it right youd have to get the block sonic tested. Only a few select b6 blocks havd enough wall to do .20 overbore
How far did you overbore yours?
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I was speaking out of thought. My thought process was that the b6 itself allready is a stroker motor. I believe IRCC that Mazda developed it by taking another 4cylinder and then boring it out, that being said I didnt think that it would have to room for that overbore. Ive never once said, or implied I was a expert, and Id like to say that I was probably wrong. Im not a trained mechanic, im just a 20 year old whos hobby is working on his Capri. Id like to think my knowledge has increased greatly over the last year. That being said I get your point Matt and ill shut up about things that I have no real clue on.
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IMHO… forged pistons don’t make sense in a b6t unless your goal is 300hp+ and even then, I’d say you would be better off spending the money on a BPT instead.
I’ve seen b6’s with their heads decked over .08 which in turn bumped the compression nearly 2 full points. I personally would never going that far though, cuz once you go beyond .04 or so, you’ll be turning the motor into an interference type engine and requiring adjustable cams too.
Whenever I’m doing a head gasket job now a days, I just take the head to the local machine shop and have them shaved regardless. Nothings more irritating then having to redo a HG job a month latter because you were too cheap/lazy to do it right the first time.
Overall I have to agree with azgtx, If the block isn’t leaking or knocking, then just freshen up the heads.
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I was speaking out of thought. My thought process was that the b6 itself allready is a stroker motor. I believe IRCC that Mazda developed it by taking another 4cylinder and then boring it out, that being said I didnt think that it would have to room for that overbore. Ive never once said, or implied I was a expert, and Id like to say that I was probably wrong. Im not a trained mechanic, im just a 20 year old whos hobby is working on his Capri. Id like to think my knowledge has increased greatly over the last year. That being said I get your point Matt and ill shut up about things that I have no real clue on.
The 1.6L is an overbored 1.3L
A .2 overbore is easy….. just go to your local junkyard and pick up a BP engine cuz that’s what a .2 overbore is (and a tad bit more stroke too).
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I did a B6 single cam .03.
Jck Byrd