SR Rebuild advice... help me think about this please

[s14unimog]

So I just finally laid eyes on what happened with my last setup and its about expected. The car ran great for about a year and half with good track use and always under a heavy right foot. Since this break down its time to rethink things and see where I want to change. Here is the setup I was running and my thoughts for the future.


Current:
OEM pistons (stock CR)
OEM rings
Eagle H-Beam Rods
ACL bearings
ARP main studs
ARP head studs
Cosworth 1.5mm head gasket
HKS 264's (I/E)
BC retainers
BC springs
RAS
FP TD0620G turbo
Tomei Expreme manifold / Greddy dump / 82mm to the back
Freddy intake manifold
Nismo side feed 740's
Nistune computer


Considering the car made good power and did so for as long as it did, it seems to me that I just met the limit of the stock pistons. I'm not a professional engine builder but I do know the SR was healthy and feel it would be a waste to not revise/rebuild. What I noticed from this last setup that I did not like was the lack of TQ and absence of bottom end power. The motor was a turd outside of boost but ran like a scalded ape under boost; pretty much expected with the setup. My thoughts for moving forward obviously included aftermarket pistons but I'm weary about increasing the CR too much. I still want the car to be a 93 car but would love to have some bottom end back. Aside from that I'm pretty sure the 20G is leaving.

So my questions are as follows:

How do you define an ideal CR for an application? Is it just fuel type concern? A give/take with reliability?

Is the 2871R my best comparable turbo change? I miss my 2860RS but really enjoyed the power range of the 20G. Given my exhaust manifold its probably the best "bolt on" solution; yea?

For those who are interested, here is the latter. I'm assuming the erosion was from the blow by gases.

http://img.photobucket.com/albums/v721/s14unimog/BreakDown04-22-11016.jpg
http://img.photobucket.com/albums/v721/s14unimog/BreakDown04-22-11019.jpg
http://img.photobucket.com/albums/v721/s14unimog/BreakDown04-22-11021.jpg

[Leetfade]

There are a lot of options. It just depends on your budget and overall goal.

I would definitely look towards some machine shop work. Maybe +1.0mm valves, new valve sleeves, etc. The valvetrain is a big part of that longevity.

The 1.5mm head gasket definitely lowered your CR which would attribute to your turbo lag issues. The flip side is it probably helped the longevity. Less compression on boost = less stress.

Maybe look towards getting a spring set up closer geared to the HKS 264s. Those BCs will work ok but there are definitely better options. Not knocking them as they are a good, inexpensive option, they just don't seem to go through some of the rigor and tolerances that other companies do.

My suggestions, Apex'i 1.1mm head gasket, Z32 or Ford MAF(if you don't already have it), some new, slightly oversized pistons (JE, CP, plenty of good options), Supertech +1.0mm valves / seals, and any number of spring / retainer combinations.

The turbo just comes down to what you're really going for. The GT2871r is a nice, fast spool with good potential and is proven over and over again. While you can make 400 whp on it, I would probably keep it around 350 to keep it in it's better efficiency range. The new Borg Warner EFRs show a lot of promise as well.

Good luck!

[s14unimog]

^ thanks for the advice. I'm pretty much in the same mind as you're thinking.

I just got the head back from the machine shop this morning. Before using this head last time I had it decked and new guides and seals installed on stock valves. This time they checked each zones for leaks and it's still doing well. The deck was within spec so they just ended up cleaning it up and buffed the cam journals.

The idea/drive behind the 1.5mm head gasket was exactly that. Give up some CR for longevity but we definitely didn't help the lag issue; the 20G wasn't much help there either though.

The valve springs are a stiffer rate and with RAS's I never had any issues, although I made sure the lifters were bled really well before they went in last time.

I'm currently running an N62, I just forgot to list it above. Can't exactly support 740's without it... I'm also running a Z32 fuel pump and have never had fuel pressure issues. This setup had close to 10hrs on the dyno over two visits and always looked/ran reliably.

I'll check into the Borg Warner turbo's. I always seem to forget about them. I did notice there is an Australian company producing BB center sections for the 20G so that might be an option as well. I followed the "2871R users" thread for a while and your comments about the efficiency range seemed to be the case if you reviewed the compressor maps and members experiences. I wonder how much more enjoyable it would be if I came into boost sooner even if the peak power was lower.

[mct3351]

That was definitely caused by knock, not "over stressing". Not going to speculate what caused the knock but something wasn't right in your setup that let to the broken ring lands and pitting/erosion.

Guessing thats from the #3 cylinder? And the broken ring lands/knock damage is almost always on the intake side. .

[s14unimog]

^ yeah I suspect my timing might have been a little too much for the winter months and higher boost pressures. That's actually the #1 but yeah intake side.

[mct3351]

Do you write your own tunes?

If so how much boost were you running and what did your timing look like in the corresponding load column/row?

[4x4le]

Sorry to hear B.
I got pistons for ya, and you should give me a go at tuning this one. I vote detenation too.

[fliprayzin240sx]

Cheap alternative would be boring out the block and running stock Z32 Pistons. 87mm forged goodies for cheap.

[s14unimog]

Do you write your own tunes? If so how much boost were you running and what did your timing look like in the corresponding load column/row?

Na, I don't right my own tunes. The car had a total of maybe 10hrs over a couple sessions.

Sorry to hear B.
I got pistons for ya, and you should give me a go at tuning this one. I vote detenation too.

Ya well the tune should have been fine. I've run this setup for over a year and half now. I really think this winter just brought me too high of boost pressure and that damn 20G just pisses me off. I can't get it to stabilize worth shit.

Cheap alternative would be boring out the block and running stock Z32 Pistons. 87mm forged goodies for cheap.

Oh that's cool, I've never heard of people running those. What's the CR with them in an SR? Any experience with them?

[4x4le]

I was thinking I read of people putting them in na sr's due to them raising the compression. I believe the rods need machined some too.