Tuning Port and Hat Nozzles

OK, long story short.
I have my RPM data logger all set up and running. I had my port nozzles/ egt temps real darn close. Now, over the winter I bought a new Blower shop 10-71. HH rotors. Mostly open bottom (at my request)(long story too) So, now there is some more work to do.
My question is.. how much do you worry about idle temps (before launch). This is a drag boat application. We need to make 900 ish hp to run our number, so mild tuneup. But with the hat nozzles being spread egt wise, it takes almost 3 seconds into the run before port nozzles balance out temps.
I hope that makes sense.
Wags

 

What psi does the port check pop at ? The port check on our's was 15 on the Roots. May need to bring the ports in at a lower psi/rpm. Whats the psi at idle at the port block ??

 

Port nozzles open at 15psi. I think idle is 6ish or something like that.
Wags

 

Wow! Must be a record. Over 300 views and the only response was from a buddy I have on speed dial.
Amazing.
Wags

 

That 3 seconds may just be the time it takes for the probe temps to react.

 

I hope that it does not take 3 seconds for propes to react to show correct temp. that being said you may have to reconfigurate your fuel system to get a good launch. how much got changed will affected your performance. too cool a piston temp and you will have to work motor harder to get the same effect on a launch that somebody else has to do with a fuel setup that is correct. that is the main purpose of a data recorded is it not to assist us to get setup right and help prevent damage . I trust the data given to me on a racepak data recorder

 

I also have a RPM Data logger in my PE boat with a 14-71 and my egts go up steadily all the way to the line. Don't worry about it as long as the highest temps are not going over 1200. I try to keep mine down around 1125 with 30* timing. If the plugs have less than 90% cadmium on them keep them in for a couple of more passes to make sure they all look close to each other. I don't push it to the two thread limit like some. Joe

 

The probes on my RPM system are very quick to report changes. I had an ignition fault last weekend that lasted .4 seconds then recovered. The EGT dropped 100 degrees in that time.

Another comparison. My temps at idle, in gear (powerglide), just before the hit are spread 46 degrees hi-to-low, with #1 being hot and #4 being cold. 1 second into the run my average temps go up 30 degrees and have a 45 degree spread with #7 being high and #4 being low. Just before I lift I have a 79 degree spread with #7 high and #4 low. (Kinda looks like I need to fatten 7 and lean 4 next time out).

The only reason I'm posting this is so you can compare your RPM box behavior with mine to see if it looks like your box is responding in a similar way.

You didn't mention what your idle spread was, and what it changes to when you get 3 seconds in.

What is your leakdown %? In my case I had the leakdown too rich when I first got the car and it was drowning the front cylinders and causing the rears to show hot. I had something like a 400 degree spread from front to back. When I leaned out the idle the temps came back together. I just kept leaning it out little by little until the fronts warmed up and the backs cooled off. When they bunched together I left it there. I think I ended up at around 78%. I would imagine if I had launched it rich it would have taken some time to "clean out" and start to balance. Also, at that time I was very worried about my idle temps being too high. I kept trying to get them to come down (which is how I ended up with the high % to start with). I think it was Bruce Mullins that finally set me straight. He told me set it at 80% and quit jacking with it. Turns out he was just about dead on. At his suggestion I really don't worry about idle temps anymore. Good advice.

I hope something I've posted might help you.

-Brian

 

Hmm. OK, this gives me something to work with.
1) I am fat at an idle. In boat world, it helps to slow down idle so clutch engagement is not an issue.
2) I think the highest to lowest was 150 ish... have to look, though. On another computer.
3) Since blower change my spread during the run has opened up. No surprise.
I was just wondering if I should worry about idle temps at all, or just go for tuning after ports open up.
Wags

 

Scouder, I think you solved our problem thanks. I now believe my BV is set too rich also and that's why it takes a couple of seconds to clean up. I'm going to set mine around 90% and see what the idle temps look like. Thanks, Joe

 

I worked on hat nozzles this weekend. I have them closing up temp wise. I want to get them faily close, then keep going with port nozzles.
We only got 3 runs this weekend. Mother nature did not cooperate for boat stuff.
I'll keep flogging it.
Wags

 

Basically we launch from idle. The engine is idling for x seconds. When it is time to leave the holding rope, we go to full throttle. The clutch engages at 3000 rpm (on mine), and off we go.
Wags

 

Mike et al, jet boats are in gear at the starting rope with the motor off and the jet exit closed. Once we pair up, the starter asked us if we are ready; if both of us give him a thumbs up he activates the starting lights. The sequence is a blinking yellow light which gives us permission to start our engines. The blinking yellow light is followed by a count down from 1 to 10, in 1/2 sec increments. You can leave the starting rope, which I think is 120 feet behind the starting line, at any time as long as you don't get to the starting line before the end of the count. The trick is to get to the starting line at the fastest speed possible right at the end of the count when the lights go green.

A jet boat has to hit the throttle (at idle) and open the jet at the same time at the start. I believe this is the reason for the egt response time delay. With my current tune, and by no means am I claiming is correct, the egts dip and steadily rise to ~1100 at the end of 1/4.

From the previous posts are they implying that the egts should start and finish near the same temp?

Thanks, Joe

 

In my case, for whatever reason, my idle EGT is always high, I idle at around 750-800. There is nothing I can do to bring it down. I assume that it has something to do with the altitude here. I just don't have enough cylinder pressure at idle to burn the mixture, so it burns in the pipe. As such, since I run a little rich, I don't see alot of temp change during the run. I believe most guys, however, will have a much lower idle temp, and shoot for a much higher top end temp.

-Brian

 

what are you using for the ignition system mag or dist.

 

MSD 7al for me. Remember, we are not burning a lot of fuel. I have a 600 enderle pump. 10gpm roughly. I ran an 80a-1 for years. It was just a little small for 1 race we ran a year.
I was just wondering if I could influence idle temps enough with hat nozzles. Then go to port nozzles. I am headed the right way. Port nozzles are pretty close.
I will have to open up the rpm computer to see what idle temps are. I leaned on barrel valve also this weekend. (we were set up fat to help slow down idle)(I know, bandaid on setup)
I guess my point is there is "right" and there is "i've done it that way for years and never had a problem" I'm a "right way" guy. Not a "done it that way and never had problems".
I've had relations with bar tramps and no condom and never had a problem, that don't make it right. LOL
Wags

 

OK, lets back up to go.
I had a 10-71 mooneyham gas blower. I stepped up to a 10-71 blower shop alcohol hh piece. Mostly open bottom (my request).
When I bolted this piece on, my egt's changed (were pretty close during run with old blower).
So, since I have to retune cyls... my original question was does idle egt cyl to cyl balance matter?
I have the coldest cyl at 250 and the warmest at 436! So, I figured I should balance idle temps somewhat (using hat nozzles) then fine tune cyls with port nozzles???
When I had all the same hat nozzles my port nozzles were spread from .029 to .042. (I had no logger then, so no idea what idle temps were, just going off spark plugs)
So, am I on the right track (hat nozzles to get cyls close then port nozzles {obviously after the check valve opens and ports become active}) Or am I just making more work for myself and idle cyl to cyl egt does not matter?
Wags