I have a rebuilt 430 ,.030 with stage 2 unported ta aluminium heads. I have Hemi killer cam, stage 2 long tube headers. I have the ta hei distributor. 10* timing. Vacuum off the intake for dizzy. Vacuum between 5 and 6.5 at idle. Cam installed top dead center. Ta sp1 intake and q jet carburetor. Runs ok at idle. 1000rpm. I put it in gear and it drops to 600-650 rpm. Transmission is a 200-4r with 2600 convertor. Where would you start looking to see why the rpms drop so much?
Are you running vaccum advance on the ported or full time vaccum port? If you are running advance at idle (full time) is your advance good with the amount of vaccum you cam makes? Your converter may be too tight. That can drag it down.
I thought 2600 rpm stall would not be too tight. Maybe I understand converters wrong. Does rpm factor into a tight convertor,? I have full time vacuum at idle. When I give it has the vacuum drops. Is this what shoukf be happening?
Carb was rebuilt. 800 cfm. That's what I was thinking. I checked all hoses and vacuum ports. All look good.
Unless that Q-jet was modified with the lightest primary power piston spring that can be had then your very low idle vacuum will be keeping the primary metering Rods unseated, which is not good! Speaking of idle vacuum, it should not be that low at 1K rpm. This leads me to think vacuum leak, or the Cam was not degreed in right. In terms of vacuum and a race Cam, the motor will always make more vacuum off idle then at idle, the problem with getting a big Cam to idle is having as much initial advance as you can and still be able to crank the motor over when hot. Is your vacuum advance active at idle?
Better to not run full time vacuum at idle with a big cam. Vacuum drops and you lose timing due to low vacuum when you put it in gear.
You have great advice being given. They hit the nails i was thinking....either a vacuum leak or your timing is wrong......try setting timing without the vacuum advance. I ran a lunati hemi killer cam years ago......it mad more vacuum than yours, but I ran about 15* at idle and all in by 2k. For a total of 34* Check everything simple.....even getting 5 and 7 wires swapped can cause strange idle issues. Spray a flammable brake cleaner to check for leaks......I can't give qjet carb advice, never had good luck myself with them
Strikes me as too much mechanical advance at idle. Easy check is put heaviest springs you can find in the distributor and repeat the process. If it acts differently, have the distributor recurved to full advance at 3000.. people have been told for years they have to have full advance in by 2500 but the springs that allows that often brings in 4-5 degrees of advance at 700-800 rpm., which all of a sudden becomes a component if your initial timing. drop it down to 600 rom in gear and all of a sudden you lose that timing and the car runs like crap or you have a huge rpm drop (or both) I've fixed two cars this year that did the same thing, and thats what it was.
Rhett has the correct answer here.. and your killing yourself with that manifold sourced vacuum advance.. a double whammy.. What we see most often is that at 1000 rpm, the distributor is already in the advance curve, so when you put a load on it, it slows down the engine, which retards the timing, as the distributor weights retract and reduce ignition advance.. this lack of timing advance slows down the engine.. and this cycle keeps happening until you get all the way back to base timing. Add to that the same thing happening with the vacuum advance... Here's the fix: With a big cam, you have to run at least 20-25" of initial timing.. with 34* total.. the distributor will have to be modified ( bushing on the advance limit pin, or welding up the slot). Then, you need springs stiff enough to have the advance curve all out, and it on base timing, at an rpm that is above the desired idle rpm. That cam should be able to idle reasonably at 800-900 rpm. Eliminate the vacuum advance, unless your attempting to get mileage out of it, but with that cam, I am guessing that was not your primary goal in building this car. If you want to run vacuum advance, use a ported source, and most likely an adjustable vacuum can. The success of all of this depends upon the correct orientation of the camshaft to the crankshaft.. The intake centerline of a cam like that, has to be around 106*.. You have to get the intake valve closed before 50* ABDC (.050 tappet lift) if you have any hope of reasonable low speed operation. Big cams leave very little room for errors in setup or tuning. Good luck JW
Lock out your timing and use a crank retard box. It's actually pretty easy, and reversible. Remove the springs and weights. Then move the advance plate to full advance. Make a lock out plate with a straight piece of metal that fits over the weight pins.
Thanks for all the support. Who do you recommend for the distributor recurve? I will redo the cam alignment as well.
A lot of people can do it, but Everyday Performance LLC does a great job.. The owner goes by TechG8 here on the board, and has contact info in the vendor section.
I love locked out timing with cranking retard. Its amazing how much egt will drop when your car idle at 32ish degrees
