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Really cheap piston and rods

 
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Goldwolf  



Joined: 25 Jun 2017
Posts: 92
Location: Athens,GA

PostPosted: Tue Nov 28, 2017 5:10 am    Post subject: Really cheap piston and rods Reply with quote

After learning the news that I may need an engine rebuild I got to pricing all the replacement hardware. $285 for some rod bolts made me start looking at different rod/piston combo's.

Now my goal here is to just rebuild the stock NA motor, stock NA head.
Thanks to Dan's thread and work http://924board.org/viewtopic.php?t=36293&postdays=0&postorder=asc&highlight=cheap+stroker&start=0

and this old thread from Peter http://924board.org/viewtopic.php?t=14027&highlight=gti+rods

It got me looking at the rod specs on the early Mitsubishi 4G63 rods. They are wider than the later rods, which if I read correctly is better to be wider. These are available from a lot of aftermarket companies. 150mm length, 21mm wrist pin, 48mm big end bore, 1.116 big end width. Manley's are $350 from Amazon. I think this part# is correct Manley 14021-4. You would have to widen the journal right? the 4G63 width is 1.116 compared to stock of 1.098.

So the pistons that would work with our block are from the Mitsubishi 4G64 block, they used the same rods too. Now Peter said this in his post (He bought different pistons that what I am getting at):
Quote:
They are for a Toyota 2Y motor and are 40thou over which makes them 87.0mm, have a compression height of 34.7mm and a pin diameter of 22mm. If I team them up with later Mitsubishi 4G63 rods which are 150mm long I'll end up with the same overall length as the NA 924 rods and pistons.

One nice plus with the mitsu rods is that the bore is 3.6mm smaller than the 924 rods so I can get the crank offset ground and pick up an extra 3.6mm of stroke. Remember, this is a NA motor I'm building so every little bit counts.

Just did the numbers and 87mm pistons with an extra 3.6mm stroke (taking it to 88mm) gives a capacity of 2092.5cc an extra 109cc. Woo Hoo.


So the closest off the shelf piston I could find is the Wiseco K564M87
Quote:
WISECO 4G64 w/ 4G63 HEAD PISTONS: 21MM PIN (1988-1992) (8.5:1 - 8.7:1)
Dedicated 2618 alloy forgings, offset wrist pins, Nitrided/Napier Steel rings, skirt coatings, complex dish and dome designs, special skirt profiles, and other features insure longevity and power with boosted and nitrous engines.

- Stroke: 3.937" (100mm)
- Rod Length: 5.906" (150mm)
- Compression Height: 1.378" (35mm)
- Head cc's: 47
- Dome Dish: -22cc
- Gasket Thickness: .042" (1.1mm)
- Deck Clearance: .0" (0mm)
- Block Height: 9.251: (235mm)
- Compression Ratio: 8.5:1 - 8.7:1
- Pin Diameter: .827" (21mm)


Now I think we can ignore the stroke measurement as its for the Mitsu head right? I'm still learning.

So the pistons Peter bought are 34.7mm compression height the Wiseco has a 35mm compression height. Would this cause interference on the NA head? Or could it be made up with gasket?

Also what about the head shape/dish etc..? Is there a way to figure that?
the Wiseco also says 8.5-8.7:1 Compression, does that apply?

Now I'm not done. I went and found the OEM for the Mitsubishi piston is Nippon. The part#'s are not that easy to locate but I believe I have found them here: http://www.dashzracing.com/84-86-Mitsubishi-Galant-2-4-Sohc-G64B-Piston-Rings-Set.html for $180!!

I think this is the correct part, the details are not clear with the Nippon stuff. http://www.apaengineering.net/nprcatalog/Searches/ProductDetails_New.aspx?Partno=DISC-11-537&PartDescription=Engine%20Piston

I do think these are cast pistons, which would probably be fine for a stock NA motor.

One last thing to really cheapen out. Find a used set of 4G63 rods est~$100 and get new ARP bolts for $50

Pistons, rings, rods and bolts for the cheapo $420!
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motormouth  



Joined: 28 Feb 2010
Posts: 107
Location: Canton

PostPosted: Wed Nov 29, 2017 2:36 am    Post subject: Reply with quote

Check this out.

http://garage.ideola.com/top-DL-CompressionRatioCalc.html


I have a long-term stalled out project that I was going to use the Mitsu rods for. I have a set of Crower billet rods I got in a cyber Monday sale several years back and had a local machine shop regrind the crank to match the rods. They ended up widening slightly and when they ground the crank down, did an offset grind for more stroke.

Does a negative dish means the pistons are concave or convex? I haven't purchased pistons yet for my build, so I haven't done a lot of research there yet.
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Goldwolf  



Joined: 25 Jun 2017
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Location: Athens,GA

PostPosted: Wed Nov 29, 2017 6:51 am    Post subject: Reply with quote

Thanks, saw that the other day but brain was full. I plugged in the #'s and it looks like compression ratio would be too high with stock head gasket.



With the bigger gasket can get it down to 10:1 or 10.5:1



Any risks with running those thicker gaskets? Is 10.5:1 too high? I want to run regular gas.
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motormouth  



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PostPosted: Wed Nov 29, 2017 7:02 am    Post subject: Reply with quote

12.1 CR isn't that high. It would be pretty good for running on race gas. You might get away with running on 93, but my guess is the combustion chamber isn't designed well enough to keep temperatures low enough to avoid knock.

I believe there are several forum members that run high CRs in NA engines. Remember, the higher the CR is, the higher thermal efficiency is in the Otto Cycle. Its proportional to the heat ratio in the thermal efficiency equation.


Last edited by motormouth on Wed Nov 29, 2017 7:33 am; edited 1 time in total
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morghen  



Joined: 21 Jan 2005
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PostPosted: Wed Nov 29, 2017 7:15 am    Post subject: Reply with quote

12:1 is not high at all, high performance street hondas run 13:1 or even higher.
This is clearly not a modern high revving engine but it will run great at 12:1 on premium gas.
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motormouth  



Joined: 28 Feb 2010
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Location: Canton

PostPosted: Wed Nov 29, 2017 8:28 am    Post subject: Reply with quote

Out of curiosity, could you run the later 4G63 rods on a 924 crank? My impression when I was collecting parts was that the later rods were narrower on the big end than stock 924 rods. You would end up having slop, but it looks like Peter was talking about doing that.
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Goldwolf  



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PostPosted: Wed Nov 29, 2017 9:32 am    Post subject: Reply with quote

The difference in width is small. In Dan's thread about the cheap stroker his machinist recommend the wider so that's what I figured.

With my 12:1 scenario above I still have valve clearance right? Non-interference.
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motormouth  



Joined: 28 Feb 2010
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PostPosted: Thu Nov 30, 2017 3:03 am    Post subject: Reply with quote

Most modern engines are interference, it isn't a big deal if your engine is an interference engine.

Anyone else have any insight on using a narrower rod such as the second gen Mitsu rod like Peter said he was planning to?
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MikeJinCO  



Joined: 08 Jun 2010
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PostPosted: Thu Nov 30, 2017 10:24 am    Post subject: Reply with quote

The problem with pistons isn't the interference, it is the pistons chasing the valves particularly at overlap as exhaust valve is opening when the piston is coming up to it. On my 931S2 pistons that come out flush to the deck I had to cut valve pockets that are 6mm deep which leaves room for exhaust valve growth due to heat.
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Goldwolf  



Joined: 25 Jun 2017
Posts: 92
Location: Athens,GA

PostPosted: Sat Dec 02, 2017 6:43 am    Post subject: Reply with quote

Found some cast pistons at summit that will work. $75 set, no rings though.
https://www.summitracing.com/parts/UEM-3221-5MM/
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Raceboy  



Joined: 01 Mar 2004
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PostPosted: Sun Dec 03, 2017 6:19 am    Post subject: Reply with quote

I bought cheap H-profile rods with bolts from Aliexpress, they make both 944 and 924 rods.

https://www.aliexpress.com/item/924-928-944-H-beam-forged-4340-connecting-rod-without-bolts-for-Porsche-with-high-quality/32782381728.html?spm=2114.search0104.3.1.TXY3lF&ws_ab_test=searchweb0_0,searchweb201602_3_10152_5000015_10151_10065_10344_10068_10345_10342_10343_10340_10341_5130015_10541_10084_10083_10307_10303_10302_10539_5080015_10312_10313_10059_10314_10534_100031_10604_10603_10103_10605_5060015_10596_10107_10142,searchweb201603_14,ppcSwitch_5&algo_expid=c99a30a3-e283-4548-b15a-b39d8717afbf-0&algo_pvid=c99a30a3-e283-4548-b15a-b39d8717afbf&rmStoreLevelAB=2

Just received them yesterday and at first glance they look very high quality, they also sent me the drawing, I will perform measurements next week and have them x-rayed. For 45 usd per rod I can do extra step
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