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Old 09-17-2008, 05:33 PM   #1
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Default Pistons and Rods...winter build

So in March of 2007 I bought my car (99 Miata) and it was bone stock and between oil changes it would take 1 quart of oil. I turbo'd it last winter and since then it takes 2 or more quarts between oil changes. I am planning a block rebuild for this winter, but I have some questions. I was thinkin about going with the wiseco turbo pistons from flyin miata with a +1mm overbore, and possibly the carillo A beam rods. My car has a T25 from an SR20, and right now, I am runnin 7psi until I finish my MS. I think my turbo is limited to 14psi to red line, maybe less, maybe more. Either way, I don't plan on running more than 14psi, so should I just leave my stock rods in there? This is my cheap driver car and I don't want to get all crazy with it, but I figured if it's apart, should I just get new rods right away? What boost have people run sucessfully on stock rods? Since my rings are toast, I'm guessing my cylinder walls might be ok...do they make turbo pistons in stock bore size? If I don't need rods, I'd like to yank the motor, pull the head and pan, swap the pistons and rings, and re-assemble. Give me your feedback guys!
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Old 09-17-2008, 06:06 PM   #2
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From what I've read on the subject so far I can surmise that you'd be better off putting in stronger rods than Pistons. What I've read is that the weakest links are the Rods and rings.

If I were you I'd buy the rods being offered by Marc on the forum. I think those are pretty well priced.
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Old 09-17-2008, 06:59 PM   #3
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Suggested source for affordable H-beam rods: http://m-tuned.com/
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Old 09-17-2008, 07:06 PM   #4
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Hmm, I got a 99 with 143K on it and I'm planning on making 300-350whp on a stock block. Power doesn't break them, it's detonation. Avoid detonation, and it will hold up. Weakest link to power is probably the rods. Anything over 400whp and you could possibly bend one. Weakest link to detonation would be the piston's ring landings, then rods. But max RPM plays a huge roll too. Detonation free and 6800 rev limit, I'm betting 350whp will be a walk in the park.
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Old 09-17-2008, 07:52 PM   #5
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Hmm, I got a 99 with 143K on it and I'm planning on making 300-350whp on a stock block. Power doesn't break them, it's detonation. Avoid detonation, and it will hold up. Weakest link to power is probably the rods. Anything over 400whp and you could possibly bend one. Weakest link to detonation would be the piston's ring landings, then rods. But max RPM plays a huge roll too. Detonation free and 6800 rev limit, I'm betting 350whp will be a walk in the park.
Detonation will also destroy your engine bearings. Everything I have seen is that 300whp is the safe limit for the 1.6l, and 350whp for the 1.8l. Anything beyond that and it's just waiting to blow-up. Using forged internals and you should be able to hit 600whp no problem. If you want over that, go with Pauter rods, and some custom Wiseco pistons (redesigned for strength, compression ratio) and you should be good to 800whp. This is all based on having a good tune.
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Old 09-17-2008, 08:05 PM   #6
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Detonation will also destroy your engine bearings. Everything I have seen is that 300whp is the safe limit for the 1.6l, and 350whp for the 1.8l. Anything beyond that and it's just waiting to blow-up. Using forged internals and you should be able to hit 600whp no problem. If you want over that, go with Pauter rods, and some custom Wiseco pistons (redesigned for strength, compression ratio) and you should be good to 800whp. This is all based on having a good tune.
And it destroys sparkplugs, rings, cylinder walls, head gaskets, etc, etc. Everything sums it up. I was just saying pistons seem to be what dies first from detonation, but was not saying it's limited to that.
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Old 09-17-2008, 09:49 PM   #7
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Yeah.. If you plan on only doing one, I would 10000000% suggest Rods. I've made gobs of power on stock pistons.

Stock Miata Rods are good to 325ish MAX! And not daily beatings (My opinion)
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Old 09-17-2008, 09:55 PM   #8
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I'll attest to the above statement. I really wonder how much power I was making at 15 psi. Too bad I never dynoed it.
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Old 09-18-2008, 01:25 AM   #9
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AT 14 psi and a solid tune you should be fine. I wouldnt worry about it.

If its no thing to spend the money and build it, then build it and should for 20 psi... **** 14 psi with a built engine

I have been rocking 14.5-18.5psi on stock internals running 100 oct fuel with my techIIIr.

Beating the **** out of it. 2 trannies are shattered, 2 turbos rebuilt.

Engine loves it
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Old 09-18-2008, 01:16 PM   #10
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So from what I got out of this thread, I will run Wiseco Turbo pistons with a +1mm overbore. I'll buy the H beam rods on M-turbo.net and run 14psi at max with my MS1 and I will be done. I picked 14psi cause I think I was told that my SR20 T25 will max out at that. Correct me if I'm wrong cause I hope I am. I hope to run at leasst 250whp with 14psi and a good tune. Thanks for your opinions guys...do you think 250whp is possible at 14psi on an SR20 T25?
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Old 09-18-2008, 03:08 PM   #11
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im not that familiar with boosted BP's... but comming from owning a sr20det for a few years and going thru 2 240sx's im going to say no.

250RWHP is BARELY achievable at 15psi on the stock t25 turbo. you can reach it alot easier with the stock (harder to find) s14 or s15 T28's from the sr20

I never dynoed but i was definetly under 250rwhp at 12psi with the t25 and at about 250rwhp at 10 psi with the t28


EDIT:
and yeah, dont bother going over 15 psi. its past the efficiency range and itll just kill the turbo faster
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Old 09-18-2008, 06:04 PM   #12
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I dont see why 14psi is high for that turbo.

I would also take the suggestion above and grab the t28. I dont think they are too hard to find.

14psi will feel nice on your car though, once tuned..
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Old 09-18-2008, 07:10 PM   #13
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Shouldn't he be able to get a yr or 2 out of a good stock motor at 14psi?
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Old 09-19-2008, 07:04 PM   #14
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this is dope.
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Old 09-19-2008, 07:52 PM   #15
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Quote:
Originally Posted by thirdgen View Post
So from what I got out of this thread, I will run Wiseco Turbo pistons with a +1mm overbore. I'll buy the H beam rods on M-turbo.net and run 14psi at max with my MS1 and I will be done. I picked 14psi cause I think I was told that my SR20 T25 will max out at that. Correct me if I'm wrong cause I hope I am. I hope to run at leasst 250whp with 14psi and a good tune. Thanks for your opinions guys...do you think 250whp is possible at 14psi on an SR20 T25?
When I dynoed at 14ish psi on my sr20 turbo I put down about 220hp. I was falling down to 11psi by redline though. I think with a good tune and 15psi you could possibly hit 250hp, but it would be a stretch. I am at 9psi and 195hp right now. That is with DIYAutoTune tuning my car. If you are building the motor I would definately search for a bigger turbo.
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Old 09-23-2008, 12:02 AM   #16
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I have a 90 Miata with a fresh built 1.8 out of a 94. I put Wiesco pistons (.020) over, a used set of Carrillo H Beam Rods (Mag particle inspected and new wrist pin bushings), and it is being fed by a T25 out of a Mitsubishi Eclipse. Also I have MS controlling spark and fuel.

The problem with the T25 is that it cannot deliver the volume of air that the engine demands at high rpm. The T25 I had on my 2.0L Eclipse would huff to 18 PSI up to 4k rpm and then slowly taper off to 14 PSI by 7.5k rpm. I so far have been running 10-12psi on my Miata with no fall off (I just have the waste gate directly connected to the turbo). I believe a solid 14-16 psi is capable on this turbo when attached to a 1.8L. I just got the boost controller parts for my MS and plan on getting it on the car by early October. Then I can let you know what the max psi the turbo can put down before dropping off.

If I had to do this again I would have gotten some new Carrillo knock off rods. I was hitting 12 psi on the stock 1.6 L with 165k on the clock…these motors are almost indestructible. Any forged rod would be better than the stock cast. But if 14 psi is your ceiling I would save your $$$. Yet, boost is fun, and you will probably kick yourself in the butt for not getting good rods for 15 psi and up.

I would also HIGHLY recommend that you ensure the pistons have cut outs or will work with the stock oil squiters. I picked up a set of the 10:1 CR Wisecos, and cut the tops of the pistons in a mill to lower the CR to 9.5:1 (Was shooting for 10-9.8:1 after head and block shave but screwed up the volume calc and took too much off). The problem with the “EXACT” fit pistons I got was the web for the wrist pin landed dead nuts on the stock oil squiters. I tried bending the stock ones to clear the rods and pistons with no luck. I ended cutting reliefs in the skirt and web and then shortened a new set of oil squiters…aka 3 weeks of serious butt pain.

Also FM has nice stuff, and in stock, but shop around. I usualy found stuff much cheaper. These guys had much cheaper prices on everthing with decent customer service: http://www.importperformanceparts.net
For example: ARP Head studs IPP $110, FM $167.

Adam

Last edited by kidrabbit84; 09-23-2008 at 12:16 AM.
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Old 09-27-2008, 05:23 PM   #17
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Anyone have some info on the 600hp motor those M-tuned rods where used on? Link?
Are they the same as the Belfab rods? I've seen those in that price range as well. Either way thats a smoking deal for a set of h-beam rods.

Jorge

Last edited by Georonimo; 09-27-2008 at 05:34 PM.
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Old 10-07-2008, 03:39 PM   #18
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I have seen many people say they will only run 10lbs boost or a 50 shot of N.O.S. 10lbs becomes 12, then 14, then 16... IMO, I say just buy both the pistons and rods and have a peace of mind.... How much can a 4 banger cost? If you think thats bad you should see my V12 costs. I got stuck buying two sets of V8 rods because no one sold just 12 rods + 2 sets of V8 bearings.
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Old 10-07-2008, 03:58 PM   #19
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I would, and did buy rods, if it is a decision between better rods, or better pistons.
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Old 10-08-2008, 02:59 PM   #20
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I would, and did buy rods, if it is a decision between better rods, or better pistons.

Although I dont know what stock miata rods look like, I would still think your chances of bore scoring or ring failure would be more than the chances of a rod bend. My choice would be for pistons since they have a lower top ring location and a higher taper machined into them to allow the crown of the piston to expand more.
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