the subject: 8ba .30 over stock replacement pistons a little porting stock valves Edmonds heads Fenton intake ( 2 carb) dual holley 94s headers and straight pipes chevy dist full adv. 2000 Isky 400jr cam My questions are what is a good starting point for a tune up? What should the starting jet sizes be? What size ya runnin? Where is the timing supposed to be? is the timing mark top dead center or is the recomended 8 degrees? I am just looking for some baseline ideas. What are you guys running?
Can't help with the 94 jet sizes as I am running a Holley 600 4-barrel. The nub on the crank is actually 2 degrees BTDC. Use a timing light with the adjustable firing feature to adjust your timing.
I can't help much with the jetting either, but what from I've heard, it's easiest to set your carbs up on a single intake. Adjust them for highest vacuum, then when you put them on the dual intake they should be matched. There is also the uni-sync or something like that for muti-carb set ups. As far as the timing, the make blown49 mentioned us "about" 2 degrees. Depending how exact you think you need to be you may need to find the exact top dead center and go from there. My engine sounds very similar to yours except I am running a Holley 390, I have my initial set about 6 degrees BTDC with 18 degrees advance, all in by 2K, also have vacuum advance. I set my timing and adjust my carb with a vacuum gage.
thanks for the info on the timing, I figured it could use more timing. Now I am sure! well crap, I am sitting at like 2 degrees advance. What is the max RPM that a flatty should be turning? Jeff
It'll tell you the RPM. It will run out of breath long before any dangerous R's and you'll clearly know there is no point in revving any further in that gear. Probably 4800--5000 area for typical mild rod, lower if it feels stifled. Ol'Ron on Fordbarn has recently been flogging timing curves on the dyno extensively recently and has good recommendations for a basic curve and how much advance vac unit should start with. Usually static is low, 4 to 6 area, but desired curve comes on fast just off idle. Start off with stock jets, circa 50. Sometimes a bit less is right because there is less need to compensate for distant cylinders with a dual, and lower the tip in point of the power valves from stock. Do your full throttle testing with vac off, then pluggit back in and road test to find out what the engine likes at cruise and low throttle driving.
thanks Bruce. I dont know if it matters, but I dont have vac advance with my chevy dist. That rpm ceiling is what I was hoping for, a about 4000 it is pulling pretty good and I was hoping that I would be able to let it go a little higher. On the jets, I have .40s and couldnt find any smaller (if that is the way I need to go) I am at the stage of tuning this thing and this is really going to help.
40's are pretty damn small...jet size relates directly to the venturi, not number of carbs or anything. Listen for popping on first run...I think you will notice problems as soon as jets take over the metering, maybe 1,000 RPM. By smaller than 50 I meant like 48 or 9! Tune the thing as is (you need the blockoff strap thing to prevent plate from moving around aimlessly with no vac can), then when you are happy get a vac can and start experimenting so you have full power at low throttle use...which is most of the time, actually.
wow, Bruce I do have some popping going on. I was thinking it was something else though. what do you mean about the block off strap thing? I hate to ask , but this is all new to me. When it is hot out it runs really crappy, I mean Realllyyyy bad. sometimes barely idling and alot of popping at speed. Also, do you recomend power valve block offs or what size of valve (would it be half the size that is in there now?)
I just got this thing working. I got some .50 jets ( a little big, but it got me close) I will have to order some 48's and try that.. I also got the ignition working between 3000 and 4000 rpm this thing really runs
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