Any theories on cylinder compression psi?

[mentallylost]

Any theories on my cylinder compression psi #’s?

 

I rebuilt my motor 500 miles ago and decided to perform a 500 mile check up today. Oil change, spark plugs, cap, rotor, valve adjustment (not done yet), compression check, timing, etc… When I got to the compression check I got 185’s and 190’s across the board. Yeah these are good numbers, but I feel that I should be in the 210’s to 215 range. Especially after the headwork that I had done.

 

Yes, I did the check at normal operating temp. Yes, I pulled all of the plugs before testing. Yes, I disconnected the fuel rail. Yes, I wedged the throttle wide open.

 

All of this was brought on after a trip to the local drag strip this past Friday. The car performed horribly. I had a best pass of 16.283 @ 83.67 mph. I had no top end power and 3rd gear just seemed to last forever.

 

Engine:

83 280zx F54 Block

Bored .040

Flat Top Pistons

L28 Crank

Main Journals .010

Rod Journals .010

 

P79 Head:

Shaved & Shimmed .080

Port Matched

Polished Runners

Semi Polished Combustion Chambers

Hardened Valve Seats

Hardened Valve Guides

Schneider Cams 260/270 Int./Exh. .460 Lift 110* Separation

.080 Longer N42 Valves

 

Intake Manifold:

Polished

Port Matched

Stock Injectors

Stock Fuel Rail

 

Exhaust:

MSA 3-2-1 Header

Cat-less

2 ½ Pipe

[JMortensen]

If you had a stock cam you probably would have been in the 210 range. Your bigger cam lowers the numbers for the compression test. As long as they're all even you should be fine.

 

As for your performance at the drag strip, that does sound pretty bad. I looked it up online, and stock was apparently 16.9 according to this page: http://www.albeedigital.com/supercoupe/articles/0-60times.html so you were almost a second faster. Have you drag raced before? Might be that it just comes down to the 16.9 being done by a pro who drag races all the time vs a first timer. I'm not a drag racer, but in my kind of racing the driver makes all the difference.

 

IIRC the ZXs with the T-tops had 3.90 gears, and the ones without had 3.54's. I'm not positive on that, so double check me, but if that is the case the 3.90 gears would certainly help with the long 3rd gear feeling.

[mentallylost]

The rear end was replaced before I purchased the car. It's now a 4.11 lsd. Fun on the curvy roads, but horrible on the highway. Although it does not spend much time on the highway at speed.

 

I didn't realize that the larger cam would lower the cyl.'s psi. And I am not real happy with this cams performance. I think that I may try and advance my cam sprocket from the #1 hole to the #3 and see if that helps. I have read that advancing these 8* increases the top end perdormance. If that doesn't help I may find a new cam shaft is in my future. I knew what I had wanted when I bought this one and I still let the Schneider tech down-talk me into a smaller cam.

 

But no, this is not my first time on a drag strip. Although it has been over a decade since my last time on a track.

[Thumper]

With my 280zx with just an intake and exhaust I ran a 15.6 @ 85mph with more to go. It sounds like either your lifters are too loose or possibly your cam is off a tooth. But if your cam was off a tooth you would have much lower compression. It could also be ignition miss or lack of fuel at high rpms. You should be able to get into the low 15's atleast with those mods.

[oinojo]

The rear end was replaced before I purchased the car. It's now a 4.11 lsd. Fun on the curvy roads' date=' but horrible on the highway. Although it does not spend much time on the highway at speed.

 

I didn't realize that the larger cam would lower the cyl.'s psi. And I am not real happy with this cams performance. I think that I may try and advance my cam sprocket from the #1 hole to the #3 and see if that helps. I have read that advancing these 8* increases the top end perdormance. If that doesn't help I may find a new cam shaft is in my future. [u']I knew what I had wanted when I bought this one and I still let the Schneider tech down-talk me into a smaller cam.[/u]

 

But no, this is not my first time on a drag strip. Although it has been over a decade since my last time on a track.

 

I had the same thing happen to me when i went down to San Diego to have my cam reground. I told them i wanted a .495/290-290 and they suggested i take the .488/284-284 However i called them the following day and told them to grind it to the .495

[JMortensen]

The rear end was replaced before I purchased the car. It's now a 4.11 lsd. Fun on the curvy roads' date=' but horrible on the highway. Although it does not spend much time on the highway at speed.

 

I didn't realize that the larger cam would lower the cyl.'s psi. And I am not real happy with this cams performance. I think that I may try and advance my cam sprocket from the #1 hole to the #3 and see if that helps. I have read that advancing these 8* increases the top end perdormance. If that doesn't help I may find a new cam shaft is in my future. I knew what I had wanted when I bought this one and I still let the Schneider tech down-talk me into a smaller cam.

 

But no, this is not my first time on a drag strip. Although it has been over a decade since my last time on a track.[/quote']

Advancing the cam will give you more low end power and less top end power. Sounds like you want to retard the cam.

 

The problem with the stock FI is that it can't handle a larger cam than that, WHICH IMO IS WHY SCHNEIDER RECOMMENDS IT. If you get rid of the stock FI then a bigger cam would definitely help out with the top end. I hate that cam, and I have repeatedly tried to warn people that it is too small here, on classiczcars.com, and elsewhere. I think you're right, it really is too small, but I think its sold specifically to people running the FI, and the stock FI is a big limitation. In terms of performance, you'd be much better off with SU's and a larger cam IMO.

[mentallylost]

lack of fuel at high rpms.

 

I have been considering that it could be a lack of fuel at rpm too.

 

The problem with the stock FI is that it can't handle a larger cam than that' date=' WHICH IMO IS WHY SCHNEIDER RECOMMENDS IT. If you get rid of the stock FI then a bigger cam would definitely help out with the top end. I hate that cam, and I have repeatedly tried to warn people that it is too small here, on classiczcars.com, and elsewhere. I think you're right, it really is too small, but I think its sold specifically to people running the FI, and the stock FI is a big limitation. In terms of performance, you'd be much better off with SU's and a larger cam IMO.[/quote']

 

A larger intake system is in my future. I have not decided exactly what yet, but I am leaning towards megasquirt and a custom fabricated intake manifold. Either way, those purchases will have to wait til after the move to Washington this summer.

[zeiss150]

one word... turbo. Thats a heavy Z compaired to the 240 so your gonna need lots of HP to get that Z into 12's on the quarter mile. unless you are in love with the N/A motor (which I wouldn't blame you, the instant throttle response is a blast) you might as well build the motor for the kind of HP you "really" want. Instead of dropping almost $200(closer to $400 if you get the springs for lift over 460 and new nissan rockers) on a custom cam. get that custom ECU and 440 cc injectors,60mm TB, turbo exaust manifold, and a Z31 water cooled T3 turbo, intercooler and 15lbs of boost. That will get you closer to the 300 whp range and 13 sec 1/4 (just a guess). I built a nice N/A L28 and now I'm re-doing it into a turbo. If I was gonna do it again I would go turbo. Just my 2 cents.

[twoeightythreez]

My '78 280z that I bought from the junkyard, as it was, stock exhaust, stock TB, stock injection, stock 4-speed and stock 3.54 R200 non-lsd ran a 16.3@83mph at Carlsbad raceway in Carlsbad,CA.

 

I pulled the stock exhaust off it, advanced the timing, and richened the AFM a bit by reducing the spring tension one tooth.

15.8@86.

 

I went home for the day.

 

Two months later, I had the money and bought the MSA 3-2-1 header, the 60mm throttle body, the centerforce stage two clutch and the Fidanza lightweight flywheel.

 

I installed these parts and put a junkyard '81 280zx 5-speed transmission behind it. I also had a muffler shop put on a 3" exhaust WITH a cat and an ordinary super turbo muffler. (they told me it was too big, that I wouldn't have any torque. I responded that I could just richen up the mix a bit.

Took it to carlsbad, on one of the last days they were open.

Ran a best of 15.2@90mph. I then blew the transmission. I had the trans rebuilt and went to the MSA show, where they had a mustang dyno set up.

Same mods, never so much as opened the engine to adjust valves (and she needs adjustment!) Dyno says: 172hp and 179lb. ft from about 2000rpm to 4800rpm, flat as Kansas. (what torque loss)..which was measured at the wheels. Don't ask me how. Guess Nissan built a good one with that motor. (N42 block, N47head, stock internally!) I was surprised to find out that I had out-horsepowered a similar Z with the cam you describe. I hate to say it, but with stock FI you're better off with the stock cam.

This was back in 2005.

I deployed for the second time to the persian gulf, the car sat.

I came back, found with dismay that Carlsbad is now a housing development.

My drag racing is now limited to the 1/8 mile drag races at Qualcomm, in between underways, etc.

Did I mention I bought this car in 2003, beat the crap out of it every single day, and the only casualties so far are those (weak) Nissan 5-speeds?

 

I now set about making her look nice. She was starting to rust, and I needed to do something. (rust hole in the ROOF)

I ponied up $2500 for a paint job that looks nice but I'm not happy with. It's only a loan, right?

I resealed the whole body, re-did the interior, and got some nice period OZ 16" wheels.

I put about 150lb of sound deadening into her, she's as quiet as a new car now. I also used expanding foam to make her more civil.

I put some EL glo faces in the dash, added an air-fuel ratio gauge and tuned her some more.

She sat some more while I was busy fixing the (supposed) daily-driver Q45 I had just bought, then I just ended up driving the reliable datsun.

I threw a fan belt on the I-5 and kept driving, as I eventually want to go turbo and of course, she overheated.

I replaced the belt and drove her home. #3 cylinder sounds like a dwarf with a hammer, I guess I wiped the cam a bit.

My latest time, for 1/8 mile, with full interior, A/C, and the '76 crash bumpers (over 100lb between them both) and the tapping, oil-burning wonder, with 110psi cranking compression on #3 and the highest cylinder only at 160psi,

is (drumroll)

9.8@66.5mph

And the mph is so low simply because she has no HP anymore, still has so much torque that I think I may be breaking a halfshaft, and the THIRD transmission is making all kinds of noise now.

So, I think you're making SLIGHTLY LESS POWER than you should.

I can provide dyno graphs and timeslips, just need a fax machine.

[twoeightythreez]

Oh yeah, with full interior, bumpers, sound deadening, the 16" wheels, etc. and me, that car is easily over 3000lb. Just a thought.

[twoeightythreez]

Oops...forgot to mention...I installed a non-LSD 4.11 rear into the car, actually made it SLOWER becasue she can't hook up as well at Qualcomm, and the extra shift to 3rd makes it slower.

[twoeightythreez]

Still average 10.0, once in awhile I get a half-decent launch and manage a 9.9 or 9.8 in the eighth, this is with me having to granny shift 2nd gear because the forks are bent, the syncro is shot, and the tranny is about to go.

[mentallylost]

I ended up pulling the cam sprocket and advancing it from the #1 hole to the #3 hole. The psi #'s did bump up to 190 to 195's and I seem to have more top end power now. It pulls quite a bit stronger from 3500 rpm and up. But not as strong on the bottom end now. I won't be able to tell if this helped the track #'s though until Friday though. That's the next test and tune.

 

zeiss150,

 

I know that this car is a heavy car. And I know that some people will be bothered by this, but this shell is only temporary. I have every intention of locating an earlier "z" not "zx" after relocating to Washington to perform a body up restoration. This motor, trans, diff, etc. will be transfered into the new body.

 

I'm not looking for a turbo either. The ultimate goal is about 225 or so ponies with a very flat power curve. I know that I am driving it on a drag strip right now, but this is just a little bit of playing really. It's final evolution will be into a snappy and responsive road hugger for winding mountain roads. Possibly autocross duty and an occasional track day.

 

twoeightythreez,

 

I liked the story of your z. What are your intentions with your motor after flattening the lobes on #3?

 

I see a new cam, intake, and megasquirt in my future.

[twoeightythreez]

Actually I'm planning on swapping in a turbo L28. The old engine I'll probably sell to help recoup the losses. SHe still runs good, considerin.

I have the engine, a rebuilt stock turbo, and an intake with custom fuel rail. (I traded my 68 510 wagon for those pieces) I need a computer, wiring harness, turbo fuel pump, an external wastegate, downpipe, and blow off valve, and I'm set. Anyone on here have stuff laying around?

My email is edgarb@nimitz.navy.mil

[zeiss150]

I commend your desire to keep it N/A. A lot of guys go the LS1 route to get that high torque N/A ride, not that you would want to do that, I'm just say'n. The 225 WHP N/A L28 is a rare animal. It looks like you are on the right track for that though. If I was you I would either switch to tripple carbs or at least do the 240SX 60mm Throttle Body swap. Its a direct bolt on .... sort of... You do have to port out the intake to make it work but once you do that it bolts right on... then you have to hook up the throttle linkage. Also I would get larger injectors and a wide band O2 sensor along with a after market computer to controll it all. I think tripple webbers are about $800 or you could get the other stuff that I mentioned for about the same price or a little less.

 

What is your compression Ratio?

 

That 460/270 cam is barely a performance cam, I have that one in my Z It pulls real hard from 3k to 6K after 6K I loose power, I'm running SU's BTW. I plan on putting my Z (72 240) on A dyno before I make it a turbo to see what kind of WHP I get. I would be thrilled if I get 170-180. but It is most likely 150-160. Once I go turbo I should have close to 300 WHP almost twice what I have now. I would guess that 1/4 mile times with that kind of HP would be in high 12's

 

You can deffinatly get 225 RWHP with a N/A L28 it just depends on how much CA$H you wanna spend. Good luck and keep us posted.

[mentallylost]

What is your compression Ratio?

 

Currently 10:1 cr

 

A lot of guys go the LS1 route to get that high torque N/A ride' date='

[/quote']

 

I often wish that I had chosen that route. I could have been done with the motor by now. Or as done as a motor ever really is.

 

If I was you I would either switch to tripple carbs

 

I am also considering the triples. I kind of like the "idea" of a high performance FI setup though.

[JMortensen]

I ended up pulling the cam sprocket and advancing it from the #1 hole to the #3 hole. The psi #'s did bump up to 190 to 195's and I seem to have more top end power now. It pulls quite a bit stronger from 3500 rpm and up. But not as strong on the bottom end now. I won't be able to tell if this helped the track #'s though until Friday though. That's the next test and tune.

I suggest you get it to a dyno before you do too much else, because what you're saying here is contradictory. Unless your cam was way out of whack when you started, higher cylinder pressures should mean less top end.

 

Did you degree the cam when you got it, or did you just throw it in there? To get the most from any cam it needs to be degreed, BRAAP was nice enough to do a good writeup on how to do that:

http://forums.hybridz.org/showthread.php?t=111523

 

Timing the cam is different than timing the ignition. On the ignition, the earlier the spark happens the more time the engine has to burn the mixture, so you want more advanced spark timing at high rpms (up to a point usually in the mid 30's degrees BTDC). The cam is opposite. I tried to explain why this is, and couldn't. I looked a bit online and couldn't find a succinct explanation.

 

Check the bottom of this page:

http://www.webcamshafts.com/cam_glossary.html

[mentallylost]

I suggest you get it to a dyno before you do too much else' date='

[/quote']

I intend to sometime soon.

 

Did you degree the cam when you got it' date=' or did you just throw it in there? To get the most from any cam it needs to be degreed, BRAAP was nice enough to do a good writeup on how to do that:

http://forums.hybridz.org/showthread.php?t=111523

 

That is a great thread. I've read it a few times. But no, I did not degree my cam. I do not have a micometer or degree wheel yet.

 

Timing the cam is different than timing the ignition. On the ignition' date=' the earlier the spark happens the more time the engine has to burn the mixture, so you want more advanced spark timing at high rpms (up to a point usually in the mid 30's degrees BTDC). The cam is opposite. I tried to explain why this is, and couldn't. I looked a bit online and couldn't find a succinct explanation.

 

Check the bottom of this page:

http://www.webcamshafts.com/cam_glossary.html

I understand ignition timing and the events involved. It's the cam timing that I am having dificulty understanding. I read the descriptions of the causes and effects and beleive them. I just don't quite understand them.

[Mr.INSANE]

This might sound stupid but how was break in did you experience and troubles and did you do what your supposed todo ala go easy first 500 oil change at 100 and 500

[mom'sZ]

...what you're saying here is contradictory.... The cam is opposite

Jon is right, retard the cam for more top end power, advance the cam for more low end grunt. Maybe his seat of the pants butt dyno needs recalibrated (kidding)

Generally speaking, if retarding the cam does give more top end, that is a sign the motor is under cammed.