High Milage Motor + More Boost

[biasword]

Hey Guys, i have a high milage sr20det (250k + miles). Its currently bone stock and drives well.

I am not trying to make any type of ridiculous power. Think ~300hp s15 turbo build. MY question for the brain trust, before swapping the turbo and upping the boost a little, should I refresh the motor / rebuild the head or can a motor of this milage take the extra power.

Fwiw, its a babied street car that gets driven literally as a grocery getter and on the weekends.


Apologies for the elementary question, but appreciate the responses

[burnsauto]

If it were me, I'd refresh things. Before that, a compression check and a leak down test would be recommended, just to get an idea of the condition of rings/headgasket/valves. If you run into any trouble with that, you'll have a better idea of how deep you need to go with your rebuild.

Budget wise, keep in mind you'll go over budget. You'll find things that you weren't planning on, or you'll get into the "might as well" mindset when getting elbow deep into the project.

[Kingtal0n]

You can perform an FSM 'rebuild' (not really a rebuild) if you are a highly experienced mechanic with a ton of experience, it should not be any issue. But the fact you asking on a forum means you may not be so experienced.

If it was MY engine, I would set up a clean room, let it clear out and run a particulate meter to ensure less than 1ug/m^3 of PM2.5 is in the air. Then, extremely cleanly using surgical procedures, open the engine and dismantle as little as possible to expose the parts in need of service. usually this means a light hone for cylinder walls and re-ring on factory pistons. Keep everything in order. Inspect every wear surface. have spare rockers/shims/piston/bearings/etc... to install as needed to keep the process going with zero down time. You want to open it, perform the service the same day, and close it back up, just like a surgery patient. Measure everything the way the FSM explains. Use ONLY fsm procedures for bottom end. Do not use plastigauge use a proper dial bore and micrometer and triple check everything using OEM hardware. There is more to it but I will stop there I think you get the point.,,,

For people who may not be so experienced or confident, here is what I recommend
1. compression test make sure they all reading 123PSI or higher and all about the same compression. Don't worry about the service limit for compression because after you clean everything in the head and service the valvetrain stuff it will likely perk up a bit.
2. keep everything in order dissemble the valvetrain and inspect guides and journals for wear. If the engine is in great shape everything could be looking new still I've seen them come apart 250k looking mint. Synthetic oil, High quality air filtering and good maintenance and factory PCV is what keeps the engine alive, FWIW
3. Leave the bottom end alone, dont remove main caps or rod bearings or anything like that. Dont even look at them. If it was running fine: leave it alone down there.
Just clean it up. Clean out any dark residues, clean the deposits or sludge or anything you see. If you use brake cleaner its fine, but quickly re-oil anywhere you spray or wipe brake cleaner because it could start to oxidize, even aluminum is at risk.
4. Now is a good time to replace valve springs and upgrade cams. I recommend match the cam to spring manufacturer and use a low lift cam ,like tomei poncam and matching spring. Do these install yourself- don't trust anybody. Follow the FSM to the 'T'. Remember it says to torque the front of the cam first and then follow some bolt pattern and using a very nice properly calibrated torque wrench 1/4" Drive you can carefully incrementally re-install the new cams from tomei. Do not use BC cams or comp cam springs or anything like that- stick to japanese "JDM" such as S3 JWT and Tomei and HKS and only use low lift stuff.
5. Replace the timing chain stuff, and oil pump use a high quality NISSAN oil pump straight from the dealer. Inspect it carefully. You may also wish to smooth it anyplace you might see some burr in the pump or engine, run your finger along mating surfaces and make sure its smooth and O-ring can slide smoothly, make sure the pickup is bolted to the engine. You need a bolt-on oil pickup if you don't have one get it.
6. Check the valve guides, lash adjustment as needed, be ready with new shims assorted shims. I've never had to do this but I suspect it worth the effort. Once the springs are out you can gently wobble the valves and see how the guides feel tight or now, you MIGHT need to have some new guides put in, but I would avoid it at all costs if at all possible do not let a machine shop touch any of your parts.

What the 'refresh' really boils down to is a new oil pump, new timing stuff, cam/spring if possible, and mostly the rest is just cleaning. Get it done quickly and do it somewhere that the air is free from debris, Try to setup a clean room if you can which just means setup a fan with a filter in an enclosure and have the fan run through the filter and a filter for incoming air and let it go overnight. You can buy a PM2.5 + PM10 meter from "temtop" for like $90 its worth every penny IMO.

the piston and bore stuff is where I draw the line, I would do it but I don't recommend it for anyone that lacks the experience. Its better to keep on using reliable high mileage internals than to fuck up a perfectly good running engine bottom end trying to do something without the proper experience or knowledge. $.02