Hernj65

I'm beginning to plan out a build for my motor. Its a bp4w with a hotside mp62.
I want to make as much as I can without having to spend big money on transmission upgrade, so whatever the 6 speed can handle. I think with this power goal I can get away with rods only? This will be an e85 only car as well which decreases my chances of detonation. Stock pistons can do this I have read but I'm actually thinking of swapping the bp4w pistons for vvt pistons because the e85 and little extra compression I think would pair nice. This is a street car and I might do some local track events but that is a big maybe.
I do not want to increase rev limit to something crazy at most ill do 7200rpm.

I know this is pretty noob post but I was hoping to get some advice on what would be ideal for this goal. In my mind I am thinking I can just do a rods only build but I'm unsure of the other parts that will help the motor last a while. I don't want to spend a lot of money on parts that aren't needed. Any advice is appreciated on what I should include. TIA

der_vierte

Rods only and E85 is probably okay. If you have the money, put some forged pistons in it. If you don't, carry on.
Maybe look into a Fluidampr instead. Keeps the oil pump happy.
Just freshen up your head, no need for anything fancy there. New bearings, gaskets, head gasket, ARP head studs while you're in there and you have a nice engine.

Jumpster74

iTrader: (1)

This thread answers that question in a different sense, but you'll get some good info from reading. There's some good build lists/references of things you do/dont need for 300hp+ in there. I think general consensus is its fine to send it with rods only ~300hp.

https://www.miataturbo.net/diy-turbo...d-cost-105444/

Kboi12

I would not spend the time to remove an engine to tear it down to just change the rods. You go that far you do the whole thing. Time is money. Just my opinion.

Hernj65

decent thread. I looked through that spreadsheet and a lot of those items on the list I have done. At first I was surprised but the list tallies out everything he's spent. I don't mind what I've spent up to date on my car. Also I already have a supercharger which I'd only need I spend $125-$250 in pulleys and tensioner for it to be capable to make that amount of power.


In regards to pistons the other person that commented that's a good point but I'm still on the fence of doing them. From what I understand is if you get forged pistons it increases cost quite a bit for parts and more engine work. I've read many examples of people using oem pistons and are just fine and they weren't even using e85. To me that is the determining factor if I was keeping pistons. If I had planned at all on using regular pump gas to make my goal I'd definitely get forged pistons but right now I'm just not seeing it necessary. I'll have to do more reading if course and make a decision.

der_vierte

This. Going forged pistons is going to cost more than your complete rods only engine. You'll be fine, don't worry.

Fireindc

iTrader: (13)

A good reason to keep stock pistons is if you drive the car often in winter. I DD mine and it sees a lot of <20* cold starts and is nice and quiet. Still made 310whp and has held it down for many track days (and 2 season podiums!). On e85.

Hernj65

yeah I like the idea if being able to drive in cooler weather and keeping stock tolerances if possible. Im pretty confident I can just go oem pistons probably think about 10.5:1 pistons to get a little bit more compression.

Hernj65

@der_vierte I see that most end up going with a boundary pump and a better damper. I wanted to ask you if it's a dumb idea to just get the boundary oil pump and then maybe add a damper later on? I'm not sure if that is backwards thinking. My thought is I'll have the engine apart and then later on its easier to just swap the damper. If you can only choose one of these parts which is preferred in a power range I'm targeting (300hp)

LeoNA

It is difficult to change the pump after the engine is installed. Aftermarket forged pistons will make more power and have a higher capacity.

Fireindc

iTrader: (13)

Personally, I went the other way. Stock VVT oil pump (higher pressure than bp4w pump), and Fluidampr to keep it happy.

Not saying this is the right way. Just what I did. YMMV

LeoNA

Higher volume because of the 10mm thick pump gears vs 9.5mm.