Couple quirky questions - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Diehardsr20 · 07-06-2014, 01:54 PM

Ok so it's been a while since I posted and I've been searching and haven't really found a definitive answer to some of my questions so by personal experience what does this sound like to you?

I have a stock redtop sr20det, garrett t25, walbro 255 fuel pump, HDI Hi-Lo EBC, Nismo FPR, Wiring specialties harness, Full exhaust/w header, and ecutalk.

I have set the Nismo FPR to 43psi without vacuum and it kicks down to 36psi with vacuum. I run with an in cabin gauge.

Cold start is usually 1200rpms to 1400rpms with a 13afr until it warms up.

I idle sometimes at 600rpms then sometimes I'm lucky to idle at 900rpms, but it never hunts for an idle. it either idles right or falls low then stays at that rpm

My AEM UEGO reads above 18afr (after warmed up) at idle but WOT is 11.2 usually. I'm running 7 lbs of boost on a t25 (I haven't even played with the ebc yet). Cruising AFR (part throttle, highway cruising) is usually 15afr to 17afr.

I've done a compression test recently and saw 80psi across the board on a warm engine, all plugs out, throttle opened. Now I know this isn't a high compression engine but that seems low. I haven't been able to find a definitive answer on this.

Ecutalk shows idle timing at 15 degrees, idle control is 50 percent, I'm getting 31mpg, no codes. It pulls all the way to redline no problem, never any smoke, no hesitation. The only smoke I get is whitish blue and smells like unburnt fuel which this only happens at idle after it's warmed up. Should I trim back my fuel pressure?

It also is hard to start when it's cold, it seems like it floods out because when it does this if I unplug the injectors then crank it, it starts right up, meaning there is too much fuel in the cylinders. During idle at op temps my vacuum/boost reads 15in/hg. In between shifts as the motor de-revs it sits at 20in/hg and engine braking in gear above 1500rpms brings it down to 22in/hg which this seems like a strong vaccuum to me. I've checked the injectors and spray pattern is normal and conical, o-rings also checked out no leaks. I replaced the plugs with new platinum plugs (the local NAPA claimed my NGK bkr6e plugs were lawn mower plugs, and offered these. I agreed against my better judgement) I've replaced the CTS twice (the 2 prong not the 1 prong)

Does any of this sound normal to other sr20det owners? The compression numbers seem way low to me. The smoke bothers me it shouldn't be there. I dont know why it's flooding out at start and if those afrs i'm seeing are normal. Have I missed something?

crash n' burn · 07-06-2014, 03:19 PM

those compression numbers are god awful bro. on that info alone, i'd say you need to pull it apart and check the cylinder walls for ring failure. you should be anywhere from 140's for a motor with a good bit of use on it to 170-180's for a freshly broken in motor.

re-do that compression test, exact conditions as before, crank it over like 4 times. if its still low put a teaspoon of oil into the cyl. and try it again to see if it gains PSI.

Diehardsr20 · 07-07-2014, 12:47 PM

I hear that. I just got done rebuilding a d17 SOHC for a friend after we found 2 dead cylinders. after rebuild was in the ballpark of 160psi across the board. I thought that my numbers were really low even for a turbocharged/low compression engine.

Oil made no difference in psi across the board. I'm leaning more towards headwork then. quick valve job and a new headgasket should tighten it back up

crash n' burn · 07-07-2014, 02:20 PM

It's just odd for every cylinder to be that low. Have you tried a 2nd tester?

Diehardsr20 · 07-08-2014, 12:21 PM

Hmm now that you mention that no I haven't. It is the same compression tester I used on the Honda D17 build recently (1st check was : 90-65-30-30 with a bad head gasket, rings, and 2 bent exhaust valves / after rebuild was : 155-155-150-155), but I will get a second one from my grandfather's shop and double check it before I start pulling it apart.

Diehardsr20 · 07-16-2014, 02:45 PM

Pulled everything apart. Exhaust valves needed a reseat job so I reseated all valves and checked them with a micrometer. Cleaned up the head until it was spotless. Cams, lifters, rocker arms all look great.

Got to the shortblock and found bad blow-by on the pistons. Checked them with a micrometer and they varied 85.0mm thru 85.5mm and piston 4 had a cracked ringland on the compression ring. All bearings were oil starved at one point but not horrible looking. Cylinders are still round. Head isnt warped. Block deck isnt warped either. Im going to do a quick hone and replace the rings and pistons. Fresh gaskets, then put it all back in. Clevitte 77 main and rod bearings, arp headstuds, new clutch and it will be perfect.

Isn't std piston bore size 86mm?

Now I have this question :

If I were to run sr20de pistons as replacements would that bump my compression ratio to 9.5:1? AND

If I went that route would I need a tune from the change in CR?

*anti tyler* · 07-16-2014, 02:52 PM

Quote:

Originally Posted by Diehardsr20

Pulled everything apart. Exhaust valves needed a reseat job so I reseated all valves and checked them with a micrometer. Cleaned up the head until it was spotless. Cams, lifters, rocker arms all look great.

Got to the shortblock and found bad blow-by on the pistons. Checked them with a micrometer and they varied 85.0mm thru 85.5mm and piston 4 had a cracked ringland on the compression ring. All bearings were oil starved at one point but not horrible looking. Cylinders are still round. Im going to do a quick hone and replace the rings and pistons. Fresh gaskets, then put it all back in. Clevitte 77 main and rod bearings, arp headstuds, new clutch and it will be perfect.

Isn't std piston bore size 86mm?

Now I have this question :

If I were to run sr20de pistons as replacements would that bump my compression ratio to 9.5:1? AND

If I went that route would I need a tune from the change in CR?

Not sure on the replacement pistons, I'm SR illiterate.

But if you change the piston size you need to change the tune.

Diehardsr20 · 07-17-2014, 01:56 AM

Ok I went ahead and bought the je forged set 86mm bore 8.5cr. Quick hone job and ill be happy with it.

Diehardsr20 · 07-24-2014, 10:50 AM

So in the the process of building this sr when I realized something about the pistons. Are they original to this sr20det? It looks like someone took a right angle grinder and cleared the oil squirters on all 4 pistons which makes me think they are n/a 86mm 9.5:1 sr pistons (since the n/a fwd sr20de had no oil squirters if I remember right). Cast 54c. Any ideas? I took a pic of one piston and on the intake side skirt its been ground away for clearance. All 4 are like this and it wasnt a machine that did it.

Also are these the correct stock sr20det cams. Since seeing those pistons im not 100 percent of anything being authentic in this engine now. Intake : AA19CB Exhaust : BA29AA

Diehardsr20 · 07-26-2014, 03:43 PM

Well thanks for the help everyone... engine is in and running. JE FSR Asymmetrical pistons 86mm bore 8.5 cr with rings. Arp main studs did not work. Crank began binding after 20ft lbs. The head bolts for arp are a 11mmx1.50mm thread pitch not compatible with fwd sr20. No clearance issues and a vr1 oil for the break in. Thank you everyone

07-06-2014, 01:54 PM	#1
Diehardsr20 Join Date: Jun 2013 Location: Dexter, NM Posts: 37 Trader Rating: (0) Feedback Score: 0 reviews	Couple quirky questions Ok so it's been a while since I posted and I've been searching and haven't really found a definitive answer to some of my questions so by personal experience what does this sound like to you? I have a stock redtop sr20det, garrett t25, walbro 255 fuel pump, HDI Hi-Lo EBC, Nismo FPR, Wiring specialties harness, Full exhaust/w header, and ecutalk. I have set the Nismo FPR to 43psi without vacuum and it kicks down to 36psi with vacuum. I run with an in cabin gauge. Cold start is usually 1200rpms to 1400rpms with a 13afr until it warms up. I idle sometimes at 600rpms then sometimes I'm lucky to idle at 900rpms, but it never hunts for an idle. it either idles right or falls low then stays at that rpm My AEM UEGO reads above 18afr (after warmed up) at idle but WOT is 11.2 usually. I'm running 7 lbs of boost on a t25 (I haven't even played with the ebc yet). Cruising AFR (part throttle, highway cruising) is usually 15afr to 17afr. I've done a compression test recently and saw 80psi across the board on a warm engine, all plugs out, throttle opened. Now I know this isn't a high compression engine but that seems low. I haven't been able to find a definitive answer on this. Ecutalk shows idle timing at 15 degrees, idle control is 50 percent, I'm getting 31mpg, no codes. It pulls all the way to redline no problem, never any smoke, no hesitation. The only smoke I get is whitish blue and smells like unburnt fuel which this only happens at idle after it's warmed up. Should I trim back my fuel pressure? It also is hard to start when it's cold, it seems like it floods out because when it does this if I unplug the injectors then crank it, it starts right up, meaning there is too much fuel in the cylinders. During idle at op temps my vacuum/boost reads 15in/hg. In between shifts as the motor de-revs it sits at 20in/hg and engine braking in gear above 1500rpms brings it down to 22in/hg which this seems like a strong vaccuum to me. I've checked the injectors and spray pattern is normal and conical, o-rings also checked out no leaks. I replaced the plugs with new platinum plugs (the local NAPA claimed my NGK bkr6e plugs were lawn mower plugs, and offered these. I agreed against my better judgement) I've replaced the CTS twice (the 2 prong not the 1 prong) Does any of this sound normal to other sr20det owners? The compression numbers seem way low to me. The smoke bothers me it shouldn't be there. I dont know why it's flooding out at start and if those afrs i'm seeing are normal. Have I missed something?

07-06-2014, 03:19 PM	#2
crash n' burn Zilvia Junkie Join Date: Sep 2012 Location: Colorado Age: 35 Posts: 543 Trader Rating: (12) Feedback Score: 12 reviews	those compression numbers are god awful bro. on that info alone, i'd say you need to pull it apart and check the cylinder walls for ring failure. you should be anywhere from 140's for a motor with a good bit of use on it to 170-180's for a freshly broken in motor. re-do that compression test, exact conditions as before, crank it over like 4 times. if its still low put a teaspoon of oil into the cyl. and try it again to see if it gains PSI.

07-07-2014, 12:47 PM	#3
Diehardsr20 Join Date: Jun 2013 Location: Dexter, NM Posts: 37 Trader Rating: (0) Feedback Score: 0 reviews	I hear that. I just got done rebuilding a d17 SOHC for a friend after we found 2 dead cylinders. after rebuild was in the ballpark of 160psi across the board. I thought that my numbers were really low even for a turbocharged/low compression engine. Oil made no difference in psi across the board. I'm leaning more towards headwork then. quick valve job and a new headgasket should tighten it back up

07-07-2014, 02:20 PM	#4
crash n' burn Zilvia Junkie Join Date: Sep 2012 Location: Colorado Age: 35 Posts: 543 Trader Rating: (12) Feedback Score: 12 reviews	It's just odd for every cylinder to be that low. Have you tried a 2nd tester?

07-08-2014, 12:21 PM	#5
Diehardsr20 Join Date: Jun 2013 Location: Dexter, NM Posts: 37 Trader Rating: (0) Feedback Score: 0 reviews	Hmm now that you mention that no I haven't. It is the same compression tester I used on the Honda D17 build recently (1st check was : 90-65-30-30 with a bad head gasket, rings, and 2 bent exhaust valves / after rebuild was : 155-155-150-155), but I will get a second one from my grandfather's shop and double check it before I start pulling it apart.

07-16-2014, 02:45 PM	#6
Diehardsr20 Join Date: Jun 2013 Location: Dexter, NM Posts: 37 Trader Rating: (0) Feedback Score: 0 reviews	Pulled everything apart. Exhaust valves needed a reseat job so I reseated all valves and checked them with a micrometer. Cleaned up the head until it was spotless. Cams, lifters, rocker arms all look great. Got to the shortblock and found bad blow-by on the pistons. Checked them with a micrometer and they varied 85.0mm thru 85.5mm and piston 4 had a cracked ringland on the compression ring. All bearings were oil starved at one point but not horrible looking. Cylinders are still round. Head isnt warped. Block deck isnt warped either. Im going to do a quick hone and replace the rings and pistons. Fresh gaskets, then put it all back in. Clevitte 77 main and rod bearings, arp headstuds, new clutch and it will be perfect. Isn't std piston bore size 86mm? Now I have this question : If I were to run sr20de pistons as replacements would that bump my compression ratio to 9.5:1? AND If I went that route would I need a tune from the change in CR?

07-17-2014, 01:56 AM	#8
Diehardsr20 Join Date: Jun 2013 Location: Dexter, NM Posts: 37 Trader Rating: (0) Feedback Score: 0 reviews	Ok I went ahead and bought the je forged set 86mm bore 8.5cr. Quick hone job and ill be happy with it.

07-26-2014, 03:43 PM	#10
Diehardsr20 Join Date: Jun 2013 Location: Dexter, NM Posts: 37 Trader Rating: (0) Feedback Score: 0 reviews	Well thanks for the help everyone... engine is in and running. JE FSR Asymmetrical pistons 86mm bore 8.5 cr with rings. Arp main studs did not work. Crank began binding after 20ft lbs. The head bolts for arp are a 11mmx1.50mm thread pitch not compatible with fwd sr20. No clearance issues and a vr1 oil for the break in. Thank you everyone