[kuya]

Completely missed the gear changes they don’t match to the z3 stock ratios bc they are the tsx ratios should this be fine for boost

 

[kuya]

I gotta be stupid or something answered my own questions the gear ratio is better in the tsx will hold better and it has the lsd from the z3 in there so best of both world’s apologies for the spam

 

[Lotus]

EP3 used a different selector mechanism (switch block) on top than a z3 gearbox. They can be swapped. The difference is in the direction of the throw.
For you 500 to 600HP, the stock ratios don't matter as you need a stronger gearset anyhow. Gear-X, PPG, MFactroy, etc.
Or go down to 400HP. Then they will just about work if you are symphatetic while shifting and launching.
That power is also about all you manage to get on the tarmac anyhow unless you go really wide and low on super sticky tries at the front. Boost by gear is your friend.
Who cares about power that only spins the wheels in 1st to 4th gear?

 

[kuya]

Hello! Quick couple-month check-in — haven’t picked up much since last time. I did end up getting a transmission: the one I posted before turned out to be a scammer and wasn’t any good. I ended up with another RSX Type-S 6-speed with a Z3 LSD and new syncros. From what the seller said it came from Shawn K20 — I didn’t know who he was, but he has a following on Insta. The seller just never got around to using it. I also got K-Tuned cables.

A couple things I’ve decided: I’m going to go with new rods and pistons. Since I’m replacing piston rings and bearings, might as well replace everything, right? (My wallet is crying.) I’m looking at Nippon Racing turbo pistons and SCAT rods. I’ll still run 87 mm — the walls are good but need a proper clean. I also picked up a 4-piston oil pump with the K24 install kit for a good price.

Now the questions — and anyone is more than welcome to add input, ask questions, or tell me to shut up. I’m very open and enjoy the conversation and learning.

From what I’ve read and been told, the transmission and power goals are still going to be an issue: unless I upgrade gears, I’m not going to be able to put this power down without breaking something or just spinning all the time. So — is it worth upgrading rods and pistons without a gear upgrade? Current pistons are fine and just need some loving, or should I do the new rods/pistons now to be safe and avoid sending a rod into orbit later?

About the 4-piston oil pump: I called 4-Piston and asked about oil pans. They said most pans work but pointed me toward what they offer, like their 4P race pan and Moroso pan with baffles — but those are extremely expensive ($500–$800). I’ve seen conversations here about other options like Unit2Fab but couldn’t find what would work with the 4-piston pump without spending a fortune. I understand the reasoning behind the prices, but I’m wondering if there’s a budget option or a DIY route that would work.

Using Lotus and other posts from a while back to find comp ratios, I came to ~10.4:1 with the pistons and rods I mentioned and a stock-sized head gasket on E85. Should I shoot for a lower ratio and change to a thicker head gasket to bring comp down? I’ve also read that in this turbo application a slightly higher comp (10.4 vs something like 9.8) can help with E85 and "longevity" but need a good tune — so I’m on the fence.

Don’t be afraid to tell me what you think or what I should do — very open to opinions. I still have a lot to buy and do to get this thing running, or I could just slap it together, run it NA, and see what happens from there.

Cheers — thanks again for all the help and for taking the time to read. Truly the best car community in and out of the forums.

 

[Lotus]

10.5 CR is good for any boost a stock gearbox can take even on 93 octane gas.
e85 runs great on a turbo. Just use a OEM headgasket. Thicker ones reduce squish, something you don’t want if you can avoid it.
if you rebore the block, I‘d go for Mahle 4032 alloy pistons. If not, the Nippon pistons will be gone for some 400HP as well. both will last much longer than 2618 alloy pistons, will clapper less and use less oil.
if this is a street build and you got a PRB k20a2 style oil pump, why not just get a k20a2 oil pan and a baffle kit?
Doing a swap and a turbo build is already complex. I’d keep it as simple as possible on the engine and gearbox side and get it to run properly, heat managed well, 2.75” to 3” drone free exhaust etc. running for a season.
Then build an engine and a gearbox if that power you got is not enough. This is unless you start to track the car.