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Rb30Det Pistons Or Rods?


Daboss
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Hey forum I am back once again for the advice of the pros. I have not posted in awhile but been doing a lot of reading and topic watching, been a member for awhile and I must say this forum has helped me out tremendously. Had running a built rb25 in a 95 R33 with extensive mods for years and only recently cause of my negligence :/ I have broken it. Sad :( sad day :( very sad :down: , had an oil leak that i neglected and spun the rod bearing which messed up the crank and I said long ago if I ever had to go back into the engine it was rb30 or nothing. So guess what :woot: its rb30 time.

I really only have one major question that I need advice on and it is as the topic says, what would be the better choice to go with if you ultimately had to make a choice between pistons or rods for a rb30 build? Car will be a daily driver and only looking for 400 to 500 wheel hp for now. If I decide to go any higher which will be awhile from now I will take it down and install the part/parts I need. I looked through all the threads and no real definitive answer thats why i decided to make a topic.

Car is a 95 R33 gtst and I basically have everything I need for the install and with the budget I have opted to focus more on oil flow, oil return, block and head tidy up.

For build I have sourced:

N/A rb30 with oil and coolant holes already drilled

Acl bearings main and rod

1.3mm MLS head gasket

Reimax oil gears

N1 oil pump

N1 water pump

Crank collar

Head drain mod

Vct external feed

Valve stem seals

Using hx40 turbo, meth injection, velocity stack intake mani, ss t4 twin scroll exhaust mani, 850cc injectors, walbro e85 400lph intank fuel pump, pfc, etc.... from cars previous setup.

After all of this from what is left of the budget I have a choice to make between rods or pistons and do not know which to chose that's why I am calling on you to help me chose the better of the two that suits my build. All suggestions are welcome.

I was thinking pistons as i can strengthen the rods up a little by replacing the rod bolts. What do you guys think?

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Excellent cause that's exactly what I was leaning towards. Thank you for the quick and informative responses, I think that is exactly what I will do.

Now do you have any suggestions on what piston and gasket combination to use to get a 9:1 compression ratio?

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Go higher if you want a nicer streeter with better fuel consumption. You can buy 9:1's off the shelf if not. If you're not in a great hurry you'll get a set off custom CP's with what ever comp you like. I ordered mine with oversized wrist pins, teflon coated skirts and ceramic coated crowns for about $1200. Took about 5 weeks to arrive which wasn't too bad.

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Some excellent information guys, thanks. One question that I cant seem to find the answer for that I have been wondering is what compression ratio would a set of rb25det piston get in a rb30 block that is not decked and running a 1.3mm headgasket? Also is it ok to run a 87mm headgasket with stock bore 86mm pistons?

Edited by Daboss
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Pretty sure the pin height is heaps different between 30 and 25 pistons, can't remember which way but is a big issue. Actually I think if you deck heaps off the block it is workable, but as you mentioned undecked, it would be a massive fail :) is not like the 25 pistons are much cheaper so not worth it, get the correct pistons and boost on. (at least 9:1 comp)

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Pretty sure the pin height is heaps different between 30 and 25 pistons, can't remember which way but is a big issue. Actually I think if you deck heaps off the block it is workable, but as you mentioned undecked, it would be a massive fail :) is not like the 25 pistons are much cheaper so not worth it, get the correct pistons and boost on. (at least 9:1 comp)

Oh noo wasn't being cheap with pistons, just had a set of forged rb25det pistons already and wanted to know if they were usable. That way I could get a set of rods and have the best of both worlds.

Any head gasket will be fine. It's only 1.5mm between biggest and smallest bore sizes.

Thank you sir.

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Wasn't accusing you of being cheap! Seeing as you already have the pistons I would look into using them. I am pretty sure its a matter of decking the block to use them. I think you will find you will be able to achieve a decent comp (at least 9:1] by using them. Obviously most people just get the proper pistons so I don't think you will find much info, Best bet would be take the measurements yourself to be sure.

Edited by superben
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Hey there have another question for you guys can the rb30 piston rings interchange with the rb25 piston rings seeing as they are both the same bore?

Nobody knows if standard rb25det piston rings fit the standard rb30 pistons?

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Provided they're the same bore size and the same thickness rings then it should be fine. I think from memory standard is 1.2, 1.2 for the compression rings. Can't remember oil control.

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  • 6 years later...

Thread revival..

I'm thinking of getting RB25 Tomei pistons and fitting to some forged RB30 Rods in the RB30 block. I prefer tomei pistons as the piston clearance is tighter and Jap is better.

My last experience was i fitted cast oem 25 r33 pistons to RB30 rods with r33 head and contradictory to what people beleive, the comp was high not low.. comp test showed 200psi

Although the 25piston sat lower it has more meat ontop so actually was fine, correct me if im wrong.

 Now with a neo head  im guessing comp maybe too high but its using E85 anyway and the tomei 260 cams lowers comp at low revs and comp test anyway so would 10.5-11 :1         ( guessing) comp be ok with a 3076 and E85???

Or maybe a thick head gasket will help out too...

The cars still going strong, just preparing as cylinder 6 is slowly going down..

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