high compression with stock cam?....

[FEnatic]

just put my N47 on my F54 flattop motor but still have the stock cam in there. I am using 70 SU's also, will the stock L28 cam be fine in there, I heard but could not find in the search that the stock cam is close to it's limits with more compression. Thanks

[z-ya]

I built the same motor and got 165WHP with fuel injection. You can only run a max of 26deg timing to prevent pinging. Maybe a different cam and some head work will alow you to run more max advance.

 

Pete

[FEnatic]

Would the SM or Rebello needles take care of the richer mixture better than adjusting the carb? I was looking at these anyway.

[JMortensen]

Adjusting the carb on an SU means doing an idle mixture adjustment. Once you start opening the throttle and the needle starts rising out of the nozzle, your idle adjustment doesn't mean squat anymore.

 

The cam is a serious limiting factor for power anyway. I'd suggest you get a bigger cam regardless of the pinging issue. They aren't expensive, and setting the lash pads isn't very hard, just time consuming.

[FEnatic]

I read on that SU page about the springs too, Do these allow the piston to move up quicker? I thought the oil controlled the rate of rise? Also, the springs are color coded right?

What you are saying is snap the throttle open with the needle in, right? Just use the straw as a mark for 2mm increments.

[b__sosick]

I built the same motor and got 165WHP with fuel injection. You can only run a max of 26deg timing to prevent pinging. Maybe a different cam and some head work will alow you to run more max advance.

 

Pete

 

I've heard the term "pinging" many times amongst mechanic friends and otherwise. I' too afraid to ask friends what it means. Help?

[JMortensen]

Pinging and detonation: http://www.hastingsmfg.com/Service%20Tips/detonation_and_preignition.htm

[Guest bastaad525]

I ran the stock L28 Cam in an N42 head and F54/flattop piston combo, bored out .060 over, compression was estimated at 10.3:1 9 (didnt know if the head had ever been shaved).

 

On stock EFI it pinged BAD above 4000rpm.

 

for me the fix was simple, just dropped in an adjustable fuel pressure regulator and upped fuel pressure about 10psi.

 

no more ping.

 

Otherwise the stock cam worked fine on that motor though it lost power bad after 5000rpm.

[JMortensen]

Didn't you also run like 5º of timing at idle Bastaad? That would be about 22º timing with all the mechanical advance in on a ZX dizzy, so if that is right, then you also had to cut down the total timing to keep it from pinging. There's a lot of power in that last 10-13º

[Guest bastaad525]

With the N/A motor I had my timing set to 8 degrees BTDC at idle. Stock setting was supposed to be 10*.

 

 

It would ping even at 8* before I upped the fuel pressure. I tried lowering timing until the pinging stopped... I got down to 3* BTDC before it did, and of course, the driveability of the car went right down the tube at that setting.

[FEnatic]

So with more fuel from the SU's, it should hold down the pinging? That is till I get a decent cam in her anyway.

[JMortensen]

With the N/A motor I had my timing set to 8 degrees BTDC at idle. Stock setting was supposed to be 10*.

 

 

It would ping even at 8* before I upped the fuel pressure. I tried lowering timing until the pinging stopped... I got down to 3* BTDC before it did' date=' and of course, the driveability of the car went right down the tube at that setting.[/quote']

OK, so at 8º at idle you were running 25º total if you were using the ZX distributor. That's pretty similar to Pete's experience of 26 degrees total. Just my opinion, but I would sooner run 9.5:1 and 35º advance than 10.5:1 and 25º. What would be really interesting to me would be to see what kind of hp increase Pete would get just by throwing in some 95 octane gas and cranking up the timing.

 

FEnatic, everyone says the SU's run richer than the FI, so your statement may be true that you can run similar timing to what these guys ran with a fattened FI setup. I think ultimately you'll have to experiment with it to find out exactly what your combo running the gas in your area needs.

[FEnatic]

Sounds good, I'll just get her running and tune in from there. Thanks for the responses!

[Guest bastaad525]

OK, so at 8º at idle you were running 25º total if you were using the ZX distributor. That's pretty similar to Pete's experience of 26 degrees total. Just my opinion, but I would sooner run 9.5:1 and 35º advance than 10.5:1 and 25º.

 

 

interesting you mentioned that. You know, once when I dynoed that setup, my friend was along with his Z, and he had a VERY similiar motor setup. We dynoed back to back. Our power outputs were within like 5hp.

 

The big difference, is that he was running dished pistons, and I THINK a different head as well, not 100% sure that was like 4 years ago. But at any rate, I remember that his motor was much lower compression than mine, about 9:1 if I remember right. But otherwise our mods were almost identical, including almost identical cam specs, identical header, very similiar exhaust... almost everything.

 

BUT, he was running like 13 or 14 degrees BTDC at idle vs. my 8 degrees.

 

We were both VERY surprised when his dyno came out so close to mine, as we both expected mine to be significantly higher with my much higher compression. That was one of the first times it really hit me just how much power is really hidden away in timing advance. Sure there may have been other things contributing there, but it sure seems to me the timing advance was the most significant difference in our setups other than his being much lower comp.

[JMortensen]

interesting you mentioned that. You know' date=' once when I dynoed that setup, my friend was along with his Z, and he had a VERY similiar motor setup. We dynoed back to back. Our power outputs were within like 5hp.

 

The big difference, is that he was running dished pistons, and I THINK a different head as well, not 100% sure that was like 4 years ago. But at any rate, I remember that his motor was much lower compression than mine, about 9:1 if I remember right. But otherwise our mods were almost identical, including almost identical cam specs, identical header, very similiar exhaust... almost everything.

 

BUT, he was running like 13 or 14 degrees BTDC at idle vs. my 8 degrees.

 

We were both VERY surprised when his dyno came out so close to mine, as we both expected mine to be significantly higher with my much higher compression. That was one of the first times it really hit me just how much power is really hidden away in timing advance. Sure there may have been other things contributing there, but it sure seems to me the timing advance was the most significant difference in our setups other than his being much lower comp.[/quote']

Not surprising. Plus he could probably run 87 or 89 in his, where you were probably constantly listening for pinging on 92. And his would probably have been snappier at low rpms because his timing wasn't so retarded.

 

IMO you only get the disadvantages of the increased compression when you don't have enough octane at the pump to run the correct amount of timing.

[z-ya]

Even though it is a track only car, I run 93 octane most all of the time in it. Last week I was at Watkins Glenn and 100 ocatane was alost $6 a gallon. I ran out durring a session, and limped it back to the pump. I put close to 5 gallons in, $30 (ouch!).

 

Anyway, all of the dyno tuning I've done with 93 octane, because that is what I run, and I don't want any detonation during a track session. So 26 deg is the max advance I've been able to run. About 165WHP, and 175ft-lbs. I'm sure with a better cam I coud run more timing. I am using a stock ZX distributor BTW. Use one of those adjustable timing lights to set your max advance.

 

It's a hoot to drive though. Yes more power would be better, but it's fun to see how much speed you can carry in the corners, knowing that you just don't have a lot in the straights. You've got to work more on your speed in the corners. It's also bullet proof. I did 7 - 1/2 hour sessions at Watkins Glenn, and it didn't miss a beat. Didn't use any oil, and the temp never went over 180 in 90 deg heat (still got the two core 240Z radiator in there too).

 

Anyway, it's a great setup(N series and flat tops), and a bargain to build one.

 

Hear is what the beast looks like at NHIS:

 

[FEnatic]

Z-ya, I also have a E12-80 ZX dist. to hook up to her, it has the 8.5 arms on it. If this set up has 17deg of mech. advance total, then I could only run about 8-10 deg at the crank? I don't mind running 93 oct. it's not a daily driver, just some fun.

[JMortensen]

The 8.5 is the number on the mechanical advance arm. It is only for the mech advance, and not for the vacuum advance. 2 x distributor rotation = crank rotation, so 8.5 x 2 = 17 degrees mechanical advance. I wouldn't run the vacuum advance in a hipo application.

[FEnatic]

I thought the mech advance on those dist. was only 17deg. I'll try running it without the vacuum advance hooked up and see how she runs. Back to my question about total, if this dist. only has 17 total mech advance, then about 10 at the crank should keep me to about 27 total right?

[JMortensen]

Yes.