View Full Version : hehe.... SO, what do I need to do to the bottom end to be able to support 300whp??

05-15-2012, 03:11 AM
Yeah, so I have a JDM st185 motor in my st165 and I wanna know what I need to do to the motor to be able to handle the amount of boost it will take to get me up to 300 horses at the wheels? What precautions I should take, etc. I am addicted to this car and the power in produces out of such a small power plant! But, I've got some oil burning and I want it to be a reliable 300WHP. I've got an oversized turbo, 2.5 inch exhaust (I know 3 would be better, right??) a cold air intake cone filter and that's pretty much it. When we were dialing in the swap we found that the wastegate was stuck and allowing over 20 psi of boost. The car felt like it was being rear ended by a semi truck until the safety cut off kicked on. I want THAT again!! Do I need forged pistons and crap like that or just a basic rebuild, i.e. rings, king bearings, I really know very little but I want to be able to drive it hard often and still have it be a reliable daily driver. Whadduyathink?

05-15-2012, 03:30 AM
I really know very little but I want to be able to drive it hard often and still have it be a reliable daily driver. Whadduyathink?

Take whatever budget you have in mind and double it.

There are several people here running 300+hp, fewer are running it on a DD.

05-15-2012, 05:14 AM
Rod bolts... that's about it for bottom end.

05-15-2012, 06:08 PM
Stock 3S rod bolts are fine to 300hp. In fact the rod bolts dont stretch on HP, they stretch on revs. So it depends on where you want to make your HP at.

05-15-2012, 07:14 PM
What type of HP does he have to be making at the crank to make 300 at the wheels?

I would say take car of maintenance, and head/rod bolts, just for safety and sanity.

What crank hp is the stock fuel system good to?

05-16-2012, 04:26 AM
I'm not really too concerned with, when I make the power. As it sits, it starts really breaking out at around 4k rpms with the turbonetics set up I'm running and just keeps on rocketing until the shaking of my crappy tires makes me slow down in fear of my life! I'm boosting between 12-14 psi but I'd like to be boosting enough to make the 300 HP @ the wheels, so probably 20 psi? The motor burns some oil so that is one of my concerns. My mechanic buddy says to replace the rod bearings to handle more boost and y'all are saying rod bolts, so that sounds like a good place to start. I just really don't want to destroy this motor. I had the car 2 years before it ran and I really am enjoying it, so I'd like to keep down time to a minimum. And I don't really have a budget in mind that kinda what I'm trying to figure out.

05-16-2012, 02:10 PM
$.02 Take this with a grain of salt, but don't spend a dime on the bottom end until you get your car in good enough condition to handle the present hp. If you have to back out of the throttle because you are scared of the way your car shakes it is not ready for any type of upgrades it needs up keep more at this time. Invest every penny into getting your car solid and ready for more hp before you even consider building a bottom end that has to support 350hp+ at the flywheel. If your scared now you will be a memory with that much power in an unsafe car again my $.02

05-16-2012, 09:39 PM
Oh, no worries there. I'm getting all that taken care of within the next few weeks. What I'm doing by asking is just to begin to get an idea of what the engine needs to be a good, solid, reliable, 300 WHP. I have no interest in watching my car disintegrate around me as I fly up to 160 mph! I appreciate the concern but few people I know are as much of a wuss about safety as I am. I'm trying to get research started so I know how much money to get together, what parts to acquire, etc. I'm getting new tires next Tuesday along with a safety inspection. Don't wanna widow my wife and leave my 2 boys fatherless. God bless you for your genuine concern bro.

05-18-2012, 10:00 PM
Honestly, you really dont need to do anything to the bottom end to hold 300whp if you have good intercooling and a turbo capable of making that much HP and not run 20 psi to do it. And of course, fuel to support it.

But the actual bottom end will hold 300whp.

05-18-2012, 11:05 PM
As long as you are running a safe tune, then chances are that you will be just fine with a stock bottom end. The big issue is going to be fuel delivery, stock 440cc injectors simply cannot flow 300hp worth of fuel. Either switch to a gen 3 EFI with 540cc injectors, or upgrade to a standalone ($$$)

Stock 440cc injectors can only get you about 250awhp The 540's might just get you over the 300awhp hump, especially if you go with a meth injection system.

The death of stock bottom ends is almost always blown piston ringlands due to knock. Knock comes from too lean of a fuel mixture under load or boost. So if your injectors start approaching a 100% duty cycle, then you start running the risk of causing detonation damage from running too lean a fuel mixture.

Heed the advice of those above and first get your car into good operating condition. You must have a good boost gauge, and a good wideband. Then tune your boost to not let your AFRs go any higher than about 11.5 under full boost.

A little nugget of information for you: most people consider the 350-400 awhp range the area to start considering bottom end work. But, some of the really good tuners have been able to safely run up to 450-500hp on stock internals before they blow ringlands. The rods are good to about 500, and the crank is good to over 1000. The gen 2 block is good to about 650-700hp, the gen 3 block is only good to like 550, and the gen 4 block is rumored to be ok beyond 800-900hp. The 98+ 5s block is good to well over 1000hp.

05-19-2012, 03:35 AM
stupid question but by the block do you mean the block itself or the internals being good for that kind of horsepower as per generation? Great info, thanks

joe's gt
05-19-2012, 03:54 AM
Nothing to the bottom end, block or internals. But you will need to have 3" turbo back exhaust, new electronics (standalone or gen 3 electronics), new injectors, and better intercooling, since you already say you have the turbo and intake. Keep in mind that having that power is worthless if your suspension feels like a capsizing boat every time you turn, so make sure that is up to the task.

05-21-2012, 02:51 PM
Thanks for the advice! I was wondering about the exhaust system, so that confirms that. I have an st185 RC intercooler on the way, so hopefully that takes care of that but injectors and electronics? Does that mean a stand alone ignition or do I have to replace the entire wiring loom/ ECU?? Also, is the stock fuel pump enough to keep up with the higher fuel demand of new, larger injectors?

05-21-2012, 03:26 PM
Did you get the pump and everything else that comes with the rc wta or just the intercooler?
Pretty sure you will have to upgrade the fuel pump.

05-21-2012, 04:27 PM
Pretty sure it's just the intercooler. I've already got a beefed up pump running constantly. That will still help over the stock st165 intercooler, won't it?

05-21-2012, 07:35 PM
^Yeah, it would help.

05-22-2012, 03:05 AM
install a larger heat exchanger and mount a fan on it

05-22-2012, 03:53 AM
On the intercooler?

05-22-2012, 03:40 PM
I made a bracket and mounted to the strut tower, but doesn't matter so long as you have ~ an inch of clearance around it. Mounting a fan to the secondary exchanger makes a world of difference in city driving.

05-23-2012, 04:44 PM
Good advice. To anyone who cares, I have a bunch of JDM st185 parts, i.e. intake manifold with sensors, ECU, wiring harness, etc. on ebay right now. Just type in st185.... Tried to post them here but couldn't figure it out. Sometimes I amaze myself at how UN-computer suave I am. Thank again folks....