Max bore on stock SR sleeves, compression ratio for track usage

[Def]

I know I know, an old topic that's been gone over a thousand times... usually by people who think a 13 second WOT is as rough as it gets... so I thought I'd throw it out there.

Thoughts on bore size for stock SR sleeves? 86.5, 87, 87.5mm? General consensus is that 87mm is fine, but what about a little larger if you're sticking to less than ~400 rwhp?

Compression ratio? 8.5:1 or 9:1 for 93 octane usage on track? I'd be inclined to think the 8.5:1 setup can safely make more power, since you're talking about a couple of percent thermal efficiency (max) vs. being able to run a bit more boost.

[Epstein]

I've seen a sectioned block. There's not a lot of meat in the sleeve towards the bottom. "how much is enough" is more of a materials / ME question. Unless you want to rely on user experiences, which have a margin of error probably 200%.

Does anyone even make 87.5mm pistons? Or are you talking about putting in VG oversized slugs?

My personal feeling on 8.5 vs 9.0 is "whatever". My thermo book says 6% per point of compression, which makes this 9hp on a 300hp setup. "Running a bit more boost" doesn't mean much until a turbo is listed and a displacement as well. I always wanted a 10:1 motor and run lower boost levels. More off-boost power, and less boost means less lag (perception) and less power transient when the turbo comes on.

[Epstein]

addendum. Apparently I was thinking of a sleeved sectioned block. Here's a pic courtesy of MotoIQ via JWT.
http://photos.motoiq.com/MotoIQ/Tech/JWTs-killer-QR25DE/7-Block-Sections/768400936_pvreR-L.jpg

[Def]

Supertech makes some 87.5mm SR pistons, but yes the size is not common.

http://www.frsport.com/Supertech-P4-NSR20-87-5CR9-Forged-4032-Aluminum-Pistons-SR20DET-87-5mm_p_15923.html


As for materials calculations, it starts to get hard towards a low safety factor with assumptions you have to make. Better to just use emperical testing (which can be a crapshoot of course, but better than some hand waiving guesses at that point IMO).

[PerilousActs]

I have a buddy running 87mm with no issues. Car has been going for about a year now with no major issues. Not much track use though.

[Matt93SE]

One of the things explained to me by JWT the other day is simply cylinder pressures.. you can only run so much cylinder pressure before things start coming apart. you can do that with low compression and more boost, or higher compression and less boost.

After you reach max cylinder pressure, the only way to go faster is to increase power pulses per mile. i.e. higher RPM, shorter gearing.

That's all pretty much a given consdering how much everyone posting here knows about engines, so what does it mean in empirical numbers? I dunno. Torque it till it breaks. then build another one and stop just before that point. ;)

[silverbullet]

One of the things explained to me by JWT the other day is simply cylinder pressures.. you can only run so much cylinder pressure before things start coming apart. you can do that with low compression and more boost, or higher compression and less boost...


... so what does it mean in empirical numbers? I dunno.


I'm guessing Wolfy didn't give any real world cylinder MEP figures, but what about bhp figures? It is directly related.

[Matt93SE]

Of course not.. that might be giving away trade secrets. :rolleyes:

[Def]

So any other thoughts? I'm heavily leaning towards 87mm 8.5:1 pistons since last weekend has forced me to speed up my build schedule.

I figure a hair more displacement will easily make up the torque difference of 8.5 to 9.0 at low rpm like 3k, and with 8.5 I can run a bit more boost. I currently have a .64 GT2871R, running only 12-13the psi on track according to my mechanical Stack gauge.

Im also thinking springs and stock retainers will let 7800-7900 would be possible with HLA. I will shift before 7.5k normally, but the occasional zing will be needed to hold a gear for a little longer.

[leetfade]

CP makes 90mm (+4.0MM) SC7329 :-P

Here's the specs for them:

Comp Ratio: 9.0:1
Size: +4.0mm
Comp Ratio: 9.0:1
Bore: 3.543(90.0mm)
Comp Height: 1.260
Comp Height: 1.260
Size: +4.0mm
Bore: 3.543(90.0mm)

And I'm disappointed, Def. All links should point to www.endurancemotorsports.net!! HAHA j/k


Sub 8k RPMs are fine on the HLAs. Between 7.5k and 8k gets into the gray zone but I would make sure you at least have RAS on there because the rocker arm float may be the bigger issue.

Are you trying to run more boost, get more torque, both? With that .64 the spool is so early I don't see why the 8.5:1 wouldn't do what you need. As mentioned, less material = greater damage potential. If you want more torque, I would probably look at 86.5 with 9:1 (example SC7325 CP). That is if you're sticking in that sub 1 bar range.

They make a 10.5:1 86.5mm but wtf? That is a TON of money to make a 10.5:1 compression work boosted... Hell I can't even see it.. LoL

[Def]

Duly noted on the endurancemotorsports. :D

I do have RAS, or will. I don't know if they really help, but figure springs + those will be fine for the occasional zing over redline.

The .64 does spool early, and I'm going back to the stock intake mani to get a little more midrange (where I usually feel like I need more oomph, although I'll probably want the top end the FReddy gives). I just feel like I get pulled a good bit coming out of anything that's not a higher speed corner on exit, even though I'll have superior exit speed. Mainly talking stupid high HP Vettes and whatnot, but still, it's where I feel the most time is to be gained with this car.

I'd like to bump the octane a bit and run more like 16-17 psi on track, which is where I'm getting a tad bit nervous on the 87mm bore. But then again, that's "free" displacement. Not much, but a tiny bump to up the torque and increase the midrange. That's also why I'm leaning with 8.5:1 vs. 9.0:1.

I'll have 264/264 HKS Step1 cams. Nothing too fancy, but they'll give me a reasonable powerband.

Don't want to sleeve the motor, so it's between 87 and 86.5mm.

[leetfade]

I have a set of RAS I will sell you cheap.. BNIB Circuit Motorsports. I bought them and never installed them and now the car is gone. :-/

Did you already buy the HKS? I had some nice mid-range with my JWT S3s. With my stock T28 turbo weakening, no fuel upgrades (other than Walbro 255), and stock valvetrain, I had a solid power curve at 258.8 HP / 253.1 TQ on a PFC tune @ 9 PSI. (Keep in mind I sell HKS and not JWT LoL. I just like the JWT cams even though the HKS are still really good)

I would be REALLY surprised if the 87mm made it as weak as you think. I've known people with 87mm 8.5:1 running 18-21 psi on their SR20.

[Def]

I already have all the stuff in my old motor. Although I wouldn't mind trying the JET S3s if you've got a set for sale. New prices are no bueno from JWT for my budget.

[leetfade]

LoL Yeah, sorry bud. They went with the car. I only have a set of stockers left.. I got a great deal on them used or I wouldn't have swung it either.

[CodyAce]

Im also thinking springs and stock retainers will let 7800-7900 would be possible with HLA. I will shift before 7.5k normally, but the occasional zing will be needed to hold a gear for a little longer.

Why couldn't you do that before?

[Def]

Why couldn't you do that before?

I could have. I just knew I was going to build another engine so I was saving that for when I had a head off since its so much easier.

Btw, ordered 87mm 8.5cr CP pistons, Manley rods, and Manley valvesprings. Planning on stock retainers since I don't think Ti will buy me anything with HLA and I want long term reliability and low maintenance.


Now I just have to decide if I want to build my old Redtop or the blacktop S13 that really spun a rod bearing. I have a good condition crank for the blacktop if I go that route.

[leetfade]

I hope you had a connection on those, big guy! We have HUGE discounts on Manley and CP :-P I know Manley has a pretty significant mark-up.

[Def]

I hope you had a connection on those, big guy! We have HUGE discounts on Manley and CP :-P I know Manley has a pretty significant mark-up.

Yes, I had some pity taken on me due to recent events (which I will detail whenever I get some more time and stop being so pissed about it).

I will give you a shout for some more parts though. :D

[leetfade]

Hey we just want to make sure you get the best deal possible. ;-) Hell I've turned people away because they could get parts below what I could offer before.. I should probably quit doing that though! LoL

[CodyAce]

I think you're headed in the right direction. The only thing I really don't like to do is mix and match springs with other valvetrain components. Not to say the Manley springs are wrong, I just don't believe they were designed with much beyond seat pressure in mind (even if they did research at all)

In regard to intake manifold, stay with the Greddy/Freddy football. To me the minimal gains you'll get in the midrange (which honestly I've never seen a good dyno that would ever make me want to ever go back to stock) are totally negated in the top end falling off the cliff and not keeping power to redline.

Where you drive the car, what are you RPM's? I'll agree even with my car there are times that I'm still forced to 'lug' a gear because dropping a gear creates tire spin city when it rips up into boost.

Other than that, just be sure the bottom end work is done with a torque plate, and the rest is wavy gravy.



PS: You saying you're looking for some JWT S3's huh...how soon? I'm going with HL's after october...

[Def]

October would work as I imagine that's the soonest I get the rest of the other stuff done.

IMO, valvetrain harmonics is an overhyped thing by JWT. Anything changing the mass of the valvetrain is going to change the vibration characteristics. I understand JWT stuff is proven, but I don't think all of their reasoning is sound...

As for the football vs stock, I probably spend an even amount of time between 3.5-5.5k as 5.5-7.5k. Maybe even more often down low. The Freddy gives great gains above 6.5k , but it definitely loses like 5-10 ft lbs below that. I remember a back to back comparison on FA way back in the day. It probably isn't hosted anymore. If I drag raced more I'd keep it, but I think it will be a step i'm the right direction. Maybe I'll try to shorten the runners on the stocker. As the engine really needs something tuned yo 5-5.5k rpm, while I think the stocker is just over 3.5k IIRC.

[Def]

Found a little info on the GReddy style intake manis and the powerband:

http://www.nissansilvia.com/forums/index.php?showtopic=93684&st=0&fcat=

Seems to basically mirror my experience, but I think they backed off the timing on the GReddy mani so the graphs would actually cross about 500 RPM sooner. On track there are plenty of straights where I'm just pulling up to about 7k RPM before braking. So there was a lot of time pulling where the GReddy powerband just kind of sucks compared to a stock mani.


I do think cleaning up the stock mani will help a lot. Most have a horrible TB mismatch and I'm betting the two halves don't match up perfectly either. The general finish isn't bad, but I think a little casting flash clean up will gain a few CFM on them in addition to paying attention to details. The GReddy will kick its ass over 6.5-7k RPM, but I think midrange is where I stand to gain the most with this motor. A hair more displacement, a little more boost, and more midrange due to the intake mani should rip pretty well.

The stock exh mani is as ported as it can be, and might even rival an extrude hone since I really increased the radii on a few "problem points" of it. I'd need to cut open #1 and reweld it to really clean that up though, but there's probably not a huge amount there since I've got it about 60-70% ported/cleaned up.

[kognition]

My motor should be back next week from my builder (Mark Brett) here in San Diego. Seems like forever i have waited to get this thing rebuilt from basically stock. S14 SR, i opted to go .5mm over on the bore of the stock sleeves, and a 9:1 CR. They are thin sleeves when you look at them, not alot of meat as someone put it. So i opted to improve the metal to metal contact by treating both the pistons AND the sleeves with WPC surface treatment. In addition to damn near every other component that has a bearing surface. I am still up in the air on an intake, but likely to go with a MazWorx intake. Also am going from the stock T28 to the Borg Warner EFR 7064 and .92 trim. I am travelling out of state to events next year, so my goal is to reduce the friction as much as possible, fast spool and about 450-500 hp pulling 2,000 lbs of car. Going larger on the sleeves or new sleeves seemed more than what i need for this car. And with the cost associated with travelling to out of state events, i am really just wanting to keep the motor together as long as possible for a season at least.

[Def]

I'm not too worried on the 87mm bore killing things. A quick search will show a couple of 450-500+ rwhp drag motors that hold together just fine with 87mm bores. The extra heat of track usage won't really affect whether it holds together vs. cramming another 100+ rwhp through the engine and revving it higher.

If I were trying ot max out a 7064 I might keep the bore as small as possible to really zing it though, but I just have a little ole' GT2871R so the engine can take way more than the turbo can put out.

[kognition]

It didn't feel right when i pulled the perfectly good T28 off of my car, its a great turbo. But i want to push the car hard with my aero on it.
I'm not too worried on the 87mm bore killing things. A quick search will show a couple of 450-500+ rwhp drag motors that hold together just fine with 87mm bores. The extra heat of track usage won't really affect whether it holds together vs. cramming another 100+ rwhp through the engine and revving it higher.

If I were trying ot max out a 7064 I might keep the bore as small as possible to really zing it though, but I just have a little ole' GT2871R so the engine can take way more than the turbo can put out.

[CodyAce]

October would work as I imagine that's the soonest I get the rest of the other stuff done.

Cool. I'll let you know then, and obviously take a bunch of high-res photos for you as well.

IMO, valvetrain harmonics is an overhyped thing by JWT. Anything changing the mass of the valvetrain is going to change the vibration characteristics. I understand JWT stuff is proven, but I don't think all of their reasoning is sound...

It's actually more scrutinized in the LSX/LSA world (more so on the newer stuff) as well as the Porsche world than the Wolf stuff would ever really get into. It's really something to look into (theory of it aside) as the companies that stress keeping the valvetrain koesher in the harmonic sense are the same companies with successful and reliable engines. Not to say you can couldn't throw some heavier seat pressures at them, and mix/match springs...but on the other side of the debate, those who keep things 'the same' often have no valvetrain related issues.


Maybe I'll try to shorten the runners on the stocker. As the engine really needs something tuned yo 5-5.5k rpm, while I think the stocker is just over 3.5k IIRC.

I'm actually very interested to see your personal results, as our modifications are similar and engines are close. The 87mm is going to increase torque without a doubt, but marginally at best.

but I just have a little ole' GT2871R so the engine can take way more than the turbo can put out.

And that's why I really love the turbo, even on overboost it's not going to chuck a rod out :D

[Def]

The thing with "harmonics" is it takes large differences in mass and/or spring stiffness to affect the natural frequency/harmonic peak frequencies. IMO, there isn't going to be a huge difference in spring rate/seat pressure between springs that work. Yes, you can get some crazy dual springs that really ramp up the pressure, but most single springs are more than fine for the RPM range I'm talking about and I'm betting their stiffness doesn't vary by more than 10-20%. Mass is the same, so you're not looking at a huge change in harmonic frequency.


There can be some power lost to excess valve train excitation, and in extreme cases increased valvetrain wear, but IMO it's not a major deal.


Does JWT advocate changing the retainers to Ti? Or do they calculate assembly frequency response with all stock components, valves etc.? I'm assuming they have an SR20DE and SR20DET spring set as well?

[Tower240sx]

lol now you're being pragmatic DEF


I have wondered if there is an off the shelf beehive spring that could do the job...I like what i've seen of them in the SBC's and LS's

[cutter]

I made 423 whp with 9-1 comp 87mm bore. I had a precision sc60 with t04s compressor housing. I had 01 g20 lifters and 99 se-l rocker arms setup reving to 9,000 rpm. the car was drag raced for a year then it saw the road course twice. never had a problem. i daily drove it for 8 months aswell. watts shop in lavon texas did the machine work. he is a wizard. i traded it off and the new owner tried to run a gt28rs at 18lbs with stock injectors and melted the pistons. I abused it for 2 years. 87mm is fine.

http://i244.photobucket.com/albums/gg4/sloth240sx/chris1.jpg
http://i244.photobucket.com/albums/gg4/sloth240sx/chris0.jpg

[cutter]

if i could go back i would do 10-1 compression for more low end power.