I have a mildly built 350 with the original TH350, 3:08 posi and 275/60 X 15 T/A radials. My best 1/4 mile time this last year was 15.679 with a 60' time of 2.148 shifting manually at 5000 rpm because the ignition breaks up at about 5100 to 5200 rpm.
My question is if I replace the plug wires with spiral core to take care of the break up, rebuild the transmission with a good shift kit, install a torque converter and recalibrate the governor with a B&M kit so it shifts automatically for more consistent shifts, how much might I improve my ET's. I'm not looking for anything spectacular but would be more then happy if I could get into the 14s, do you all think this is possible? If I can get close to that, I can tweak the timing, jets and vacuum on the secondaries on my spreadbore to gain alittle more.
I'm not looking to do any other mods as this is my daily driver and I'm not looking for trophies, just good old street legal drags at PIR on friday and saturday nights when they start back up in April.

If your HEI ignition is in good shape it should be able to rev to 7000+ without any trouble. I'd probably look elsewhere for the sputtering problem unless the plugs, wires, and cap are really, really old. Exhaust too small could be one problem or weak valve springs or weak coil (in the cap) or or.....Dan

The cap, module, rotor and coil were all replaced this past spring with an MSD HEI kit, i also changed the plugs but I did not change the wires which were put on new last November, they are Accel super stock resistors not spiral core, that's why I think the breaking up is caused by them not being able to handle the MSD. My cam and lifters are from a Summit kit (SUM-K1104 224/224 duration @ .050) rpm range is 2200 to 5200 rpm. Any ideas on how the other mods will effect my ET?

To be perfectly honest we have seen very little reason for using the MSD on engines that are turning less than 7000rpms unless they are race only engines running dead rich all the time. The chassis dyno just does not show any apprreciable gain over the stock HEI unless the compression and rpms get pretty much out of the streetable range, but since you already have it and if you think the wires may be suspect ?????? From what you describe for your engine there are only a couple reasons for it not to crank well past 5000 wires might be one reason, (carbon core wires are pretty much a one use item as they don't like to be tugged on or moved after they become "seasoned"--it cracks the core). I would also suspect a lean condition---If you have a chassis dyno available in your area with an exhaust gas analyzer it may be money well spent to give it a go. In this area we get about a hundred an hour for dyno time. Usually you can get three or four pulls and jet changes done in an hour.......................Dan

The wires were disturbed after they were on awhile and the MSD is the kit that goes completely into the HEI, no outside box or coil. For the sake of argument let's say new spiral wound wires cure the breakup, what improvement in my ET can I reasonably expect from the other mods I said about ie: rebuilt transmission, torque converter, recalibrated governor? Is a half second reasonable? As far as a lean condition, this is possible but it breaks up when tached up in neutral or under load as when going down the track. Either way it breaks up and the tach goes nuts at about 5200 rpm, load or no load.

I really don't know, but could it have to do with the cam? Some aren't made to spin that high. I don't know :lookround:

The point of my question is not what's causing the breakup at 5200 rpm. At this point I don't care, I'll find it eventually. The point of my qeustion is what kind of improvement can I reasonably expect for the mods I've described in my post.

Oh fine, 1/2 second sounds perfectly reasonable :P

A good shift kit and converter with a higher stall will help out your et's. However, the converter will make any traction problems worse. But if you don't have any, the converter will help quicken up your 60' times. Should get you into the 1.9xx's for sure.

Letting the transmission shift on its own will take a lot of work to calibrate it to get it to shift where you want it to every time. My suggestion would be to get a ratchet shifter and shift manually, JMO.

When you put in that cam did you replace the valve springs? If you didn't you might be floating the valves, causing the break up. Do you have a rev limiter? If so make sure its not the cause of the break up too.

I'd say you could see half a second to maybe a second depending on how high of a stall converter you get and if you can keep traction.

78 Elky, thank you, that's what I'm looking for an intelligent answer 8-) . I know it'll take alot of runs to recalibrate the governor, but that's the way I would prefer to go as I don't want to get too serious on this, as I said I drive this car daily and just run the Friday and Saturday street legal drags for fun so I don't want a floor shift. At this time I don't have a traction problem, takes most of what I have to turn those 275/60X15 T/A radials. As far as the cam and springs are concerned: the engine was put together by the PO last year about 150 miles before I bought the car, he did give me all the receipts from the build and the heads did go to the machine shop, but I don't know if the springs were changed however I would suspect that they were tested if it was a halfway decent shop. I don't have a rev-limiter, so it's not that. From what you know so far any recommendations on a torque converter?

Since you want to keep it a daily driver, I wouldn't go higher than a 2500 stall. You'll get better acceleration and won't absolutely kill your mileage. As far as brand, B&M, TCI, Hughes all make pretty good stuff for off the shelf applications.

How do those drag radials fit? I'm looking at getting the same size for my car next summer but don't want to get into frame notching or fender lip rolling right now.

Since you want an intelligent answer try this------right now your range of acceleration is from about 1500-5000 rpms in each gear. After the tranny rebuild and new torque converter with say a 2500 stall your new acceleration range will be 2500-5000. The car should launch quicker and get on down the track just fine until it hits the limit at which point it will stop accelerating-----my duess is it should even out , maybe a tenth or two either way. Sorry for the earlier mis-understanding I just normally try to get the best possible time out of my cars before I do more to it. To just let my engine run crappy and work on drivetrain and chassis is just foreign to me................Dan

2500 stall is pretty much where I was thinking of, but seeing as I've never had one before I thought I'd get some opinions from some other people with experience before buying. 78Elky the tires I'm running are regular B.F. Goodrich T/A Radials for the street, not the drag radials, as far as clearance they are close at stock rear suspension height, they do rub if I load the bed and don't air up my airlifts. I haven't notched the frame nor rolled the fenders. My front is dropped 2 inches but the rear is stock height.
As far as the engine I do plan on finding the problem there, but that is not a mod just a repair, and I prefer not trying to diagnose problems here as you know from reading the forums people tend to tell you all kinds of stuff ( I garuntee that some one in here thinks my break up is caused by my white letters on my tires being dirty 8O or the left headlight being a bit dimmer than the right ).
Coot, I do appreciate your response also, the intent of my question was only to get an idea of how much better an ET I might get with these few mods, I do want to get the best performance I can with what I got, but like I said earlier the breakup is something I can diagnose and repair. I appreciate your ideas of a lean condition or valve springs, but like I said I'm going to try better plug wires first as I think my old ones can't handle the voltage of the MSD, if that doesn't work then I'll move on to other things. I could be wrong but I don't "think" it's valve springs as I've had cars where I've experienced valve float and this isn't that, but it's not ruled completely out at this time. My method is try the cheaper easier things first, so it's plug wires then carb then valve springs.

PS, as it is now I'm barely into third gear when crossing the finish line, it takes a long time to get wound up with those 3.08s and 275/60s, if I get 7 grand out of this motor I might be crossing the line still in neutral :lol:

A perfectly logical approach---I just went back and read the entire thread and spotted a couple things I may have missed earlier........A 2:14 60 ft is not too bad on street tires so it would seem that those tires work pretty good and so does the engine/3.08 combo. With a little more stall you might get in the 2.0 or even the 1.9s if the tires will hold it---that would be big by the other end....now you say the tach goes crazy when you get the miss---my thinking is that the tach gets its input signal from the low side of the coil not the high side so plug wires may be needed but I'd be surprised if they fix the problem. It is possible that they are feeding back through the coil but I doubt it. More than likely its the module in the distributor or the pick up coil or even the bushings on the shaft letting it wobble. I know the module is new but new doesn't necessarily mean good---thats why they give you a warranty. Next suspect is valve springs and since you said it does it even in neutral I would put a lean carb way down on the list but still on the list..................Dan

You need to be careful using the 2500 rpm converter with 3.08 gears. If your normal cruising rpm is at or below 2500 you may be driving with a converter that is slipping all the time. If you don't want to run a lower axle ratio you may want to consider a milder cam that builds power down low. If your barely in third at the end of the quarter I doubt your using your cam to its potential.

I doubt a shift kit would make much difference unless your trans is slipping. And if it causes you to spin the tires on the 1-2 shift you might actually slow down.

Whatever is causing you to break up at high RPM could be affecting your engine throughout the RPM range reaching its worst at the peak. Timing too far advanced or too much centrifugal advance could cause a breakup and slow you down as RPM increases.

Without knowing all your engines specs it's impossible to determine the weak link. What speed are you reaching at the end? If you are in the 90+ range than look to the drivetrain, but if your not reaching those speeds you may not be making enough power. As was stated before your 60 ft times aren't bad at all. My GP will run 14.5's on a 60 like that and 14.3's if I'm below 2.1.

Your timeslip can really tell you where to look sometime. There is a consistency. A mid 14's car will probably 60 ft at or a little better than yours, 1/8 mile about 9.2 at speeds in the low to mid 70's. Cars that make a lot of power and don't hook well might see higher 60's but lower 1/8. A good 60' but bad 1/8 is a sign that power is down but the driver is adept and the car launches but is not pulling.

I'm no big time racer but I spent a few years dialing in my 69 GP. Race weight about 4400 lb's. With a .30 over 400, stock heads, 10.5:1 compression, 3.36 gears, factory HP cast iron exhaust manifolds, and a 2.25 exhaust it ran a best of 14.305 and will consistently run in the mid 14's. The cam is a 204/214, it's got a B&M 2400 Holeshot converter and a stock TH400.

Come to think of it, with those gears you might want to short shift it out of 1st so you could get into 3rd a litter sooner. So many things to try.

Thats good advice from Bige, using a high stall converter with those 3.08 gears will probably cook the trans. The MSD HEI kit didn't turn your ignition system into a fireburner and those Accel wires should easily handle whatever increased spark energy that was generated. You seem very defensive when people suggest that you might have valve float, I would listen to them beacuse I think they are right. Whatever is causing the engine to misfire at 5000rpms or more when fixed will probably drop you right into the 14s. Good Luck!

The point of my question is not what's causing the breakup at 5200 rpm. At this point I don't care, I'll find it eventually. The point of my qeustion is what kind of improvement can I reasonably expect for the mods I've described in my post.

Your biggest (and probably cheapest) improvement will come from fixing the breakup at 5200. With your cam, your engine should be making it's max power closer to 5600-5800 rpm. In order to achieve max accelleration you need to be able to shift several hundred rpm beyond peak so that you're still in the power when it hits the next gear. If you suspect the wires, by all means replace them (you're talking about spending much more for converters and tranny mods anyway).

As already mentioned, valve springs are a suspect. New stock springs can handle your cam just fine but old valve springs might not. You said that it breaks up regardless of load but at the same rpm, that would be valve springs or a pulled stud.

Ok guys, the reason I included about my engine breaking up in my original post was because that was one of the conditions at the time. The question was what kind of improvement could I reasonably expect from the modifications that I want to make taking into account that my engine was not running perfectly at the time of this time slip ( by the way due to my occassional dislexsia that should have read 2.418 60' time not 2.148, sorry about that, I know that throws off the calculations from y'all but it was unintended :oops: ). As far as diagnosing the problem with the engine you all need more information then what I had already put in here, such as with the stock components still in the distributor before I installed the MSD kit it was breaking up around 4500 to 4600 rpm, whereas now with the MSD it's breaking up around 5200 rpm. Why the 600 to 700 rpm difference? My theory is this: the only thing I did not change was the wires which are Accel Super Stock carbon core resistors, now if the wires were bad to start with and and were causing the problem at 4500 to 4600 and now with the much stronger coil (I know it's no fire burner, but it is much stonger than stock) from the MSD forcing the voltage through the same problem shows up but not until 5100 to 5200 rpm. So first thing to do and easiest is to replace the wires with spiral cores ( which according to every post I've read in here are the ones to run) and recheck centrifigal advance and timing. If that does not take care of the problem next step, which is the next easiest is like Old Coot said check the distributor bushings as I have no idea how old a unit this is and this was not changed when I did the MSD conversion. Then check the valve springs ( no I'm not defensive about this, but it is alot more work than the other options so this is further down the list. Although I would think that the problem would still be at 4500 to 4600 rpm and not change when I installed the MSD).
Now before I buy a convertor I will be calling the experts at TCI, B&M and Hughes to figure out which one will work best with my set up and driving situation, but I was looking for ideas such as that from 78Elky and others. If a 2500 stall won't work then I won't get one of them, I'll get something else.
Now for my time slips that night so y'all can play with them:
1st run; R/T .709 (sleeping) 60' 2.355, 330' 6.684, 1/8 10.191@70.10, 1000' 13.204, 1/4 15.761 @87.99
2nd run; R/T -.097 (red light) 60' 2.389, 330' 6.693, 1/8 10.174 @70.70, 1000' 13.162, 1/4 15.698 @ 88.60
3rd run R/T .380, 60' 2.439, 330' 6.756, 1/8 10.220 @70.97, 1000' 13.203, 1/4 15.735 @ 88.89
4th run; R/T .595, 60' 2.418, 330' 6.708, 1/8 10.168 @ 71.02, 1000' 13.148, 1/4 15.679 @ 88.79
5th & final run; R/T .756, 60' 2.388, 330' 6.705, 1/8 10.176 @71.00, 1000' 13.157, 1/4 15.697 @ 88.09
Now remember this is just for fun, not serious racing. I'm just trying to improve my times a bit, not something wild. If I can get into the lower 15s that would be great, high 14s real cool but not expected.

Just a couple of observations. That MSD HEI kit basically is a tune -up kit for the HEI distributor-new coil, module, cap etc.. It doesn't change the HEI into something akin to an MSD 6 or 7 which are capacitive discharge multi-spark ignition systems. GM designed the HEI for easy starting, smooth idling and miss-fire free low speed operation; it is not designed for high engine speeds and a stock HEI is pretty much all done by 5000rpms. Your modified HEI is probably good for another 1000 or so rpms but for the best performance you need a capacitive discharge ignition box. If the distributor is in good condition keep it as it is a good spark distributor and spark trigger but dump the module and get a MSD 6.

Your 60 ft times suggest your spinning a lot off the line or you need to make more power down low. Your cam should have a higher stall converter, and lower gears. Do you have compression and exhaust to take advantage of the cam? If not, you might get the performance your looking for from a smaller cam like 204/214. Something that will give you pull right off idel. Then you wouldn't have to shift out at 5200 RPM to take advantage of the power band.

Nope ain't spinning the tires, not bogging down off the line either. I'm not changing cams nor gears. In fact I'm not changing anything except for my torque converter and rebuilding the tranny with a shift kit. ALL I WANTED TO KNOW WAS WHAT KIND OF IMPROVEMENT I MIGHT SEE IF ANY FROM JUST DOING THESE TWO THINGS Thank you :roll:

shift kit=NOTHING, torque converter=a couple of tenths which could disappear in spinnig tires with those gears

good luck

A simple fix that in many cases is good for a 1/2 second right out of the box and costs $2.

Replace your fuel filter. Any fuel starvation will show up at higher RPM first and feels alot like ignition miss. ( cause it is missing, just fuel and not spark! ) I have personally done this a bunch of times and usually got a better ET.

Also, consider more fuel in. ie - new Holly Mechanical Fuel Pump and 1/ 2" line from the pump to the carb. Bigger line simply makes more fuel available to the carb and smooths out pulsation of a mechanical pump . Much like a larger plenum in an intake manifold. (or consider a low cost electric fuel pump )

THx,
Diablo :twisted: Doug