Looking for Dyno evaluation/SU carbs-

[madkaw]

Maybe our butt dyno's are decieving. I had no idea what to expect for #'s since haven't driven a Z forever. I was happy to see that the #'s were bigger then yours-sorry-but not happy to see that I ran out fuel robbing me of HP. With you running way rich it shows that it takes the right tune to get the most HP.

Can't wait to use my triples though!

[madkaw]

I took my car to ORP here in indy. 20$ to run all night on the quarter mile is a great deal. Well anyway, I was a bit disappointed at my 15.5 second quarter mile. I will say that I suck at launching and I am very inexperienced at the drag strip. The car felt strong off the line, but getting into 3rd gear it seemed to rev in slow motion. It seemed to take forever to run up to 6500, like it was running out of gas or power to power thru the gear. It never missed or anything like that, but no power. My timing was 20 degrees initial with no vacuum advance, and about 36 total. The weather was really cool.

I still haven't afforded a wideband so I am just guessing to what my afr's are doing.

[doradox]

I took my car to ORP here in indy. 20$ to run all night on the quarter mile is a great deal. Well anyway, I was a bit disappointed at my 15.5 second quarter mile. I will say that I suck at launching and I am very inexperienced at the drag strip. The car felt strong off the line, but getting into 3rd gear it seemed to rev in slow motion. It seemed to take forever to run up to 6500, like it was running out of gas or power to power thru the gear. It never missed or anything like that, but no power. My timing was 20 degrees initial with no vacuum advance, and about 36 total. The weather was really cool.

I still haven't afforded a wideband so I am just guessing to what my afr's are doing.

It sounds like you could improve quite a bit with some tuning. I ran my 73, stock with headers and round tops, at SIR in Tucson and pulled 16.0s consistently. And SIR is at 3000 feet elevation. It pissed me off that I just couldn't quite break into the 15s.

One thing to remember when is that your et doesn't start counting down until you break the lights. So relax a little and concentrate on launching and not on cutting a good reaction time. It's a fun time and can tell you a lot about how your car performs.

Steve

[GreenZZZ]

Some other ideas. Check the barrel mesh filters that are installed before each float bowl. Also check the fuel filter and clogged fuel lines. I had a clogged mesh filter that caused the car to top out RPM wise once. I didn't know those filters were even there before it happened. Another thing to check is the restriction orifice in the fuel return line. If someone opened it up, that can cause a drop in fuel pressure.

If I had to guess though, fuel pump.

[madkaw]

Thanks for some ideas guys. The pump is new, but not a nissan and I guess I can go back to the previous post by Walter regarding the pump-time for a fp guage also. I will check out the filters-thanks.

[GreenZZZ]

Here is my dyno pull from 5 years ago for comparison... Bone stock L24, cam, SUs, exhaust, with E31 head with aftermarket Mallory Unilite ignition. I did this just for giggles. In order by horse power lowest to most, there was my 105 horse chart and the next CZOT club member up pulled a 185 (I think) with a stroker motor in a 240 all the way up to a >600HP pull from a 300ZX. You have a monster setup in the works!

http://www.classiczcars.com/photopost/showphoto.php?photo=24994&ppuser=14083

Edited October 6, 2010 by GreenZZZ
grammer

[madkaw]

Okay, checked out a few things today. The barrel mesh filters weren't bad at all, but sprayed them down and reinstalled them. Purchased a new fuel filter, though I would be suprised there is any issue with it. I do have a new tank in this car. I need to install a fuel pressure guage and I guess in line with either fuel bowl would work??

I was also reading the tech stuff in the SU forums here and found it interesting when they talked about different springs for the chamber. My thinking was backwards on the effect of heavy springs or a slower moving piston. Also I was suprised to read about the heavier weight oil in the dashpots and the effect of to light of oil in the dashpots. It seems to be a tricky compromise to slow the piston down in it's upward movement, but to have it fall quickly also. I was using marvel mystery oil, but that seems to light according to the tech article.

What type of oil should be used?

Too often people use light duty (sewing machine or general purpose) oil in the dash pot assembly. This type of oil does little if anything to impede the upward movement of the piston as the throttle opens.

Engine oil can be too viscous (depending on climate). After 2 hours of driving it ends up in the bottom of the piston, the majority of it sucked into the engine. This happens because it is too thick to pass through the damper as the piston falls causing the oil to flow out of the top of the dashpot.

I use a mix of 20W-30 to 20W-50 and sewing machine oil. The ratio is three parts engine oil to one part sewing machine oil.

When you use the aforementioned oil mix if you attempt to raise the piston when the engine is cold you will find that a lot of force is required to move the piston to its uppermost position. When you release the piston, it will drop to the bridge quickly (less than half a second).

Still lot's to learn about these carbs. --------------------------------------------------------------------------------

[tlorber]

I've been going with 50% ATF and 50% 3 in 1 oil.