Tuning question?

I just changed cylinder heads from out of the box big duke 18deg #1802 to the new big vic edelbrock 18deg heads with full port and chamber work. New heads flow 510 cfm intake and 370 exhaust vs old heads flowing appox. 430 intake and 300 exhaust. Fuel pump is an enderle 1100 flows appox 17 gal per min. at 8000 engine rpm's. Cam is roughly .828\.800. 509 cube motor with a psi 14\71 low runs. Cam is set 6 deg retarded to kill some of the power on the line, I run a powerglide with a 10in convertor. Seems that after the head swap the car now runs really lean at idle, haven't made a pass yet, but I will tommorow at the rock (Top Dragster). Is it possible that the heads flow so much more air that a total change needs to be made to my jet and nozzle setup? Port check is 9 lbs, high speed is 40lbs with a .90 jet (it sets on top of the shutoff valve). Been running a .115 main. Hat nozzles are .52 and ports are staggered large at front to smaller at rear. High 60's and low 70's in the front cylinders to 50's in the rear cylinders. Sorry for the long post but I tried to provide all the info about my combo the first go-round. Any thoughts from the guy's that run BBC combos or anyone else for that matter? Also if it helps I run an MSD 10 pus ing. Thanks in advance for the help.

 

fatten the barrel a bit..

 

I don't know much about blown motors,

but I would think that in addition to the barrel valve adjustment (to address the idle temps) you would need to change the main jet (due to increased airflow throughout the rpm band) and also maybe wait a little longer to bring in the high speed lean out since the heads should help the motor make power higher into the rpm band.

I am also curious why you are not running more fuel into the blower and just using the ports to balance the cylinders?

I am posting all these questions hoping for a free education, not to be critical.

R/G

 

Gorr did the set up on the original combo, since the head change it seems really lean at idle. Already turned the bv a complete turn... it helped at lide, no more fire out of the pipes May try to run a .45 pill in the high speed insted of a .90, at least for the first pass. Thanks Jody

 

Jody, isn't 40 lbs on the H/S a little low?

 

tune

if your system is right, you may want to make sure you don't have a vacumn leak especially at the intake to head. or a cracked burst panel, I've had weird things happen over the years lol..

 

fuel shutoff

It reminds me of a time...
We had the 3 way shut-off valve spool in wrong. We checked it to make sure the passage was open to the BV and it was, but it was also open to return. What I noticed was a lean idle, what quickly happened on the track was a blown head gasket.

 

Just a thought..... Why not call Ralph or Spike and ask them

 

tune up

Ralph or spike

 

You said you were thinking of changing the high speed !! It has nothing to do with your idle because it opens with more pressure when at idle pressure..

 

Idle fire out the pipes

Hi Jody,
just to throw a spanner in the works I have also had fire from the pipes when it has been real rich at idle. Seems like with these engines you cant take anything at face value.
Jim

 

Sorry for the non-responce, I was runnng at the IHRA Spring Nat's. So here goes.... to keep the fire down in the pipes I had to richen the b-valve one whole turn, seemed ok at idle so I made an 1/8 mile check-out pass. It was a turd, ran 3th's slower than with my old heads, but I had a small main jet in it to play it safe. Next pass I cherried out and left my three step switch on but it was still a turd down low with a leaner main pill. Last qualifier I leaned it a little more and it ran a 6.66 at 213mph but it was way off till the gear change. 1st round on Sat. I had a .009 light but the car picked up and ran a litttle better and I broke out with a 6.636 on a 6.65 dial killing around 35 mph in the process. On every other run the rpm's rose eratically(spelling?) and slowly to the gear change but on this run they just rose slowly. A friend of mine found the coil wires pinched together and I closed the crank trigger pickup to .035. Now here's something I may have to forgot to mention, I have the cam 6 deg. RETARDED, to try and calm it down off the line. Is it possible that the heads flowing 100 cfms better need the cam to be run straight up? Gorr had me set at appox. 76% leakage and now it's at over 85%. Any new thoughts?

 

I don't like the idea of a retarded cam... as long as you don't have clearance issues, straighten it up!

EDB

 

Jody,

You have not mentioned the cross sectional difference in the port size. If the port flows that much more air, then I would assume it is a much larger port cross sectional and overall cc, which would indeed slow down the port velocity and lower the engine response at lower RPM. Going back to basics and bringing the camshaft back into a more normal relationship will surely help the signal and acceleration response.

I would not have thought you would have had to raise the BV leakage that much, but the bottom line is the BV needs to be rich enough for engine response. Other than that you will have to work out the tune on the engine to see how much fuel it wants. With the increase in airflow one would think there would need to be an increase in fuel flow to attain the same A/F ratio as these are constant flow injection systems and not air flow signal and draw calibrating like a carburetor. As mentioned, a call to Gorr would not hurt.

Good Luck!

 

Jody,

I just got to thinking a little more about the head change. It would be interesting to know the difference in flow of the cylinder heads during the overlap cycle. The new heads may be passing a lot more air and with the cam so retarded, it may be passing the air right through the engine, which would make it lean acting.

The intake to exhaust percentage from the peak numbers you provided is 72.5% exhaust to intake on the new heads where the previous heads were at 69.8%. This means the exhaust port is stronger in relationship to the intake and could be more so at low lifts depending on the valve/seat angles.

Correspondingly, the intake flow increased 19% (if measured at the same lift) on the intake and 23% increase on the exhaust. Advancing the cam may help this relationship or consideration of a wider lobe separation cam if the engine does not respond to your changes.

Gear

 

Mike the rpms were acting crazy so I just threw something at it to see what it did. I'll move the pickup back to appox. .050 out. Thanks for all the advice, no kidding on the bv though. It had good responce at 76% like Gorr had me set it for the big duke heads but there was fire jumping out of the pipes on the way back down to idle after a run-up to appox. 3000 rpm's, thats why I fattened the bv so much..to put out the pipes. But I feel like it loaded the motor with fuel. Yes, I'll run the cam straight up and see what happens, I know it flows alot more on the exhaust side than the old heads did. I'll call Gorr after I check a few more things, I hate to be a bother, not to you guys but to Gorr.

 

I think Mike is right on. I think .050 is too close for the pickup. Closer is not better if the spec is .100. Just don't want to see you create a problem trying to fix another. Too rich is just lazy. Moving the cam back just effects everything else. Can't you help the bottom end by moving the tire pressure up or changing the gear to kill power. Maybe a little mag retard or two step. At least the motor will run. Gorr always wants to know cranking pressure. 185 lbs at least. Just some ideas.

 

fuel system

There is a good chance I am wrong, I would be leave fire in the pipes is to fat to start with. That fire is unburnt fuel in the pipes. Call Gore and ask him for the changes. I am sure you paid good money to flow that system. His leak down and yours may well be different. I am sure his leak down tester is different than yours. Did you leak it with something like a 80 jet? Put everything back and start looking at things one by one. Was the mag set and working good? Don't mess with the the cam timing. There is to many ways to change the car with fuel/ mag/ tires /weight/ etc. There are many times you can't fall out of a tree in the beginning, and be running really good at the end of the season. It's called FUN and learning. Think it through on your own and GOOD LUCK you will figure it out. Don