Tuning 428 for throttle response

[saltshaker]

I'd like to tune my 428 for more low end throttle response and could use some help! It is in a 2500 lb cobra replica and seems to lag a little on the bottom end....up to 3000 rpm. If I launch the car leaving at 1500 or more there is no problem but if I let the clutch out and put the petal to the floor it will break the tires loose but just feels sluggish .
Engine: 428 .40 over,10.5 comp, C4 heads w/cj valves ported (280 cfm @ .600 lift) Isky 8005a springs, MR 2x4 w/600 vac holleys, Ford dist with Petronix 18 int and 38 total and Comp 282S cam....WR top loader and 3.50 gears.....any suggestions?

[jerry clayton]

take off the 2x4s and use ONE 850-950 dp

[HOSS429]

i dont think any of us will nail your problem on the first stab .. ( although jerry most likely did ) you simply need to play with things .. i`d start by increasing the size of you carb squirters .. you probably have 28`s there now .. go up to 30`s and see what gives . then play with the pump cam .. it should have several settings .. you mite play with the advance springs in your distrubitor .. go with a lighter set ..

[saltshaker]

I looked and the squirters are #25's....so I can start there. I also noticed that the mufflers in my side pipes are 1 7/8's ID,seams kinda small?
As for 1 carb....yah it would run better just not that wow factor!
Jon

[John Palmer]

I would agree with Jerry that a single four barrel will give you better low end respone. But, I like vacuum secondary over the double pumper for a street engine.

One "easy thing" that you should look at is the advance curve on the distributor. Pull the distributor and take it to someone with a old SUN distributor machine and have it checked, and maybe recurved.

Basically the curve you want is for the distributor to retard enough to allow the engine to crank easily (start) when hot, but advance quickly from idle to give a good low end throttle response. You can file out the mechanical advance stops to get 12 degrees (24 at the crank) and use soft enough advance springs to get it all advanced by 1000-1200 RPM (2000 to 2400 RPM at the crank). Then set the initial timing at 12 to 14 for a total of 36 to 38 degrees.

It will respond well to some advance.

[saltshaker]

Thanks, the dist had been recurved when rebuilt with 20 deg in it and all in by 2700 rpm...so it is set at 16 int and 36 total ...will recheck it. As I mentioned earlier I'm wondering if the sm ID of the mufflers could be causing a problem.
Jon

[34_40]

As I mentioned earlier I'm wondering if the sm ID of the mufflers could be causing a problem.
Jon

Maybe at W.O.T., not off idle. My 390 mustang had 2" duals, never an issue for what I was doing with it. Not racing it daily...

[jerry clayton]

your carbs are mounted backwards with the linkage properly installed down the right side?????the carbs seconary diaphrams have a vacume hose running between them? and the dist is a mech advance only one or if dual advance the vacume hose is to the correct port on the primary carb??????

[jerry clayton]

Typing at the same time Louey-----did you have hot dogs for lunch??

[jerry clayton]

I had 2 packages of Banana Bread instant oatmeal-----lot of karma around here plus brown sugar

[saltshaker]

Vacumn tops are not connected yet and dist is mech advance...linkage is set that second carb starts to open when first one is 1/3 open.
Jon

[techinspector1]

Use this chart from Barry Grant to determine the initial timing at the crank based on the 0.050" duration of your cam....
http://www.barrygrant.com/demon/default.aspx?page=5