Help in Tuning

john · Post by **john** » Sat Sep 30, 2006 4:14 pm

hi folks, I'm looking for some help tunning my son's 260 z. This is what we have done to it so far, we have taken 1.75 mm of an n42 head, opened up the ports a bit and matched a 260 manifold to it, the other end has two hif SU carbs with 44.5 mm throat that came off a range rover. The exhaust has 3 into 1 extracters , cam was reground with a lift of .465" lift and a duration of 284 inlet, 280 exhaust. This on a standard 280 block, the car is running ok but we were expecting more. Any help would be appreciated . thanks John

geordieggg · Post by **geordieggg** » Sun Oct 01, 2006 3:40 pm

When you machined the head, did you shim the cam towers up and install new lash pads & rockers etc? Machining the head affects the cam timing by shortening the distance between the crank and cam pulleys, thus putitng the cam timing out.

Just a thought, someone else will probably correct me!!

john · Post by **john** » Sun Oct 01, 2006 9:02 pm

Yea shimed the towers 1.6 mm and 208" lash pads , not sure on the size of the lash pad but the wipe pattern seamed good. How far advanced should the timing go to as the revs rise?

geordieggg · Post by **geordieggg** » Sun Oct 01, 2006 10:58 pm

Whereabouts are you located John? One of the members here may be local and may be able and willing to have a good look at it for you.

As for the timing, I'm not 100% sure, still finding out as much as I can before modifying mine. Is it stock ignition? Points? Electronic? What pistons are you running? Dished or flat tops? What compression ratio? What fuel do you use in it? Who built the motor? Who set up the cam timing?

Most important (and not trying to be rude when I ask this) what exactly do you expect from the motor, what do you mostly use it for? And do you know roughly what it's putting out now?

john · Post by **john** » Thu Oct 05, 2006 8:57 pm

The car is in west Auckland, stock eletronic ignition, dished pistons compresion 9.4:1. We are running the car on pump gas. My son and I put the engine together. We plan on puting the car on a dyno and expect to get more out of it than a stock engine. the car will mainly run on the road with occasionl blast around Pukekoe.

bruce · Post by **bruce** » Sun Jan 07, 2007 12:04 pm

you have a lot of factors to sort, and a dyno is the only place to sort them:

SUs - needles, springs, oil weights all interact - you can assume the Rover setup is only a starting point, possibly not even a good one. The dyno and gas analyser will quickly tell you.
cam timing - check with dial gauge
ignition - curve needs to match the SU mixture curve

unfortunately you wont be able to get the mixture right if the ignition curve is out, and vice versa, so you are in for a few iterations.

finally, dont take anyones word for gospel (including mine!) - experiment as much as you can afford, and believe what you see on the dyno!

john · Post by **john** » Wed Jan 24, 2007 9:30 pm

thanks Bruce, we have made some gains by shifting cam timeing and dyno is our next step.
One thing we are learning is how interrelated the the whole thing is .
Trial and hopefully not to much error from here.
Thanks. John