L20 cam timing / power band questions

[Lozer]

So im going to slap some r1 carbs on my l20b and I assume I can adjust the current power band of the stock u67 head/ Cam  to give me a tad more top end to match up better with the carbs. 

 

My question is do I adjust it to the #1 hole or a couple teeth and which way?????  

 

Current power band falls flat @ 5500.

 

Im running a 4.44 rear end with a 4 speed torque is not an issue. 

[Cheetahking]

What hole is currently on?  Each hole change is about 4 degrees.  Each tooth change is about 9 degrees.   

[datzenmike]

What hole is currently on?  Each hole change is about 4 degrees.  Each tooth change is about 9 degrees.   

 

This is correct. Of all the cam events, later closing of the intake valve makes the most difference at high RPMs. By moving one hole position lower you add an extra 4 degrees to the closing of the intake valve. On an L20B the intake closes at 128 degrees before TDC. This would change to 124 degrees. L20Bs come from the factory set on the #2 hole, L16s are on the #1 hole.

 

At very high RPM the fast moving intake air flow has slightly more time to cram into the cylinder before the door closes. Take note that this later closing is the opposite at lower RPMs and the fast rising piston will actually push some of the intake air back out of the cylinder. The effect is very subtle so don't expect much on a stock engine.

 

Try one tooth counter clockwise for 9 degrees cam retard

Try one tooth CCW and one hole lower for 9+4=13 degrees advance.

Try one tooth CCW and one hole sdvance for 9-4=5 advance

 

Lots of combinations. See what your engine likes. Hole #2 is the best all round running.

[Stoffregen Motorsports]

5500 rpms for a L20B is kind of a lot to begin with, and you want more? How built is the motor?

 

To answer your question about how to adjust the cam timing, there were a few different cam sprockets over the years so using just the hole number is not very accurate. You really should learn how to do it with a dial indicator.

[banzai510(hainz)]

444 gear ratio? is to low in my opinion. 390 is better for general street use.

How about a cam?????? stock ?Your stuck then get a longer duration cam since you got a 4.44 gear ratio.

[Dolomite]

Damn, 4.44 and a 4spd! Is it even freeway capable? I feel like I'm lacking top end speed at times with 3.90 and 5spd.

[G-Duax]

On an old L16/521 I had, with no other mods, adding 4 degrees retard allowed the old girl to actually hit 100 mph.

stock timing kept it about 70-75 max.

 

Although after several years of abuse, it did shower the freeway with bits of pistons, rods, and block........

Don't recomend you going there, unless you build the lower end to take it.

[Lozer]

lol at 70 im hitting 5350 rpms. and yea its a bit much. Ive got an 83 5 speed i gotta jam in there. 

[datzenmike]

lol at 70 im hitting 5350 rpms.

 

This can only be, if your tire is 19.5" in diameter or the tach and/or speedometer are way wrong. Likely your speedometer is way out from adding the 4.44 gears.

 

For example, a 24" diameter tire with 4.44 differential and forth gear is only 4,351 RPMs at 70.

[Lozer]

your correct i am a little off.  4.44 gear final drive of 1 and tires diameter of 23.08 = 4600 rpm give or take a hundred @ 70 mph and yes my speedo is so far off its silly. 

[datzenmike]

I get just over 4,500 RPMs at 70. So at 6K your speed would be 93MPH

 

Installing an '83 zx 5 speed with the taller of the two over drives would give 3,500 at 70 MPH and a 'top speed' of 120 at 6,000.

[Lozer]

@ 120 in a 510 you get a hearse and a free bodybag.

[datzenmike]

Had my 710 to 110 once but the 510 is a brick.

[scooter]

It will pull harder on top by putting the carbs on it, i wouldnt fuck with the cam timing as the marginal top end gains will co-incide with loss of bottom end below 3000. Even with a race cam i ended up with best overall horsepower with the cam advanced

[scooter]

And i have all you guys beat 220 kph or 135 mph in the 200sx.. And theres more left in it. I bet i can hit 150mph.. About 1000 left in 5th..

 

Gps certified.