Combustion chamber orientation is not the only thing that contributes to flame front travel. Turbulence of the air/fuel charge also plays a major roll, with buick 350 heads having well designed swirl type intake ports. The combustion chambers, while open are shaped well for efficient combustion and have angled spark plugs for good reason too. The chambers are only around 58cc if i recall, maybe less on early models, so not very large. All 350s came with dished pistons as well which is complementary to the design of the combustion chamber. Still end up with 10.25:1 comp. I wonder how flat tops would be? This is probably why they dont like so much ignition lead. Mine is set at 30 right now, but that is a conservative tune. Buick had a very good design team in my opinion, Here are a few cool facts that really show they were in search of a very efficient package back when in the day. Lightest small block, but very strong design where its important. aluminum rocker arms, light valve springs, etc. Small dual pattern camshafts promote torque and efficiency at low RPMs. Seemingly low oil psi and tight bearing clearances eliminate parasitic hp loss. intake/heads are iron. note that buick chose aluminum for EVERYTHING else (block/recip ass. not included). Iron retains more heat energy where it counts. Efficient swirl type head design. I get 20mpg no matter what these days with overdrive. Efficient package indeed.
To: Gs70350 I have full flat top pistons in mine and it works great. The motor seems to like 32 degrees timing with the set up that I have. The split duration cam I believe is the secret to the combo, with plenty of carb and 2 1/2 mandrel exhaust, I tried regular bend exhaust couldn't get enough flow. Went to mandrel and had to do much work on carb, ( jets- flow work). :3gears:
I agree, I get 18-20 mpg on the highway with my 350/350 combo in a heavy car. City is around 15. Can't wait to get a overdrive....
I know fuel economy is a prime thought now days but I don't drive this car much,only to have fun or make money. Have 4.10 gears in the rear. I know some will sat too much gear but for me and my set up and usage it's perfect.I am just growing old not up. :3gears: :beer
When I first had the motor dynoed we tried to use 36 on the timing and we had to keep bringing it down till we got to 32. The balancer was a new one that I got at TA. When I got the new Timing Cover fromTA it did not have a degree mark on it so the engine builder had to put a pointer on it for me. I have confermed the position of the balancer and the pointer with the piston stop that you mentioned. if I try to go higher than 32 on timing the engine starts to miss and seems to be very sensitive to these increases so I just leave it at 32. I run a MSD Distributor with the large advance stop bushing so the timing stops quick and I can run higher initial timing and in at 2500 rpm. I have also read that running Nitrous you have to pull 1-1 1/2 degrees of timing out for every 50 hp of Nitrous so I figured with almost a 150 shot,(I used a125) you need to pull 3-4 1/2 of timing out for this so I stayed on the safe side and went with 5 degrees out on the timing. With the timing at 27 degrees on this day I went 11.87 on spray and went 13.31 on the motor. At Quaker city at the nationals I went 12.13 on spray and went 13.79 on motor with the same set up.
Don't know if anyone has mentioned this or not. And if so, excuse me for being redundant. Before you install another driveshaft, you might want to paint a straight red 1/4 in. wide stripe along the driveshaft. Check it periodically to make sure it's still straight. I was told to do this before I did any racing with my car. And......it was good insurance as it saved me. After my first season of using slicks, my driveshaft had a bit of a twist. Had I not put a line on it and checked it regularly, I would of never known there was a problem a brewin!!! Good luck. John. :TU:
Good idea about the paint stripe. A couple of years ago we had a vibration and could not figure it out till I pulled the drive shaft out and put it in a vice. I put a level on each yoke and found it to be about 1/8" twist, then checked tube for straightness and found about 3/16" belly, ready for disaster, no drive shaft loop then. New shaft and loop fixed the problem.
plugs... Does the motor miss all the time when timing is above 32? What do your plugs tell you?? Set you timing to the electrode and your fuel to the pocelein. If it is missing, it could be cylinder pressure blowing out the spark. If the motor needs only 23 degrees on nitrous, so be it. Just as long as your reading the plugs and et for adjustments. Have you messed with the jetting on the carb since it has been dyno'd? Can you adjust your carb air-bleeds at all? http://www.dragstuff.com/techarticles/how-to-read-plugs.html
I had a timing problem once and found that the early balancers were diffent from the late balancers. Not sure when the change was. Also the front covers are differnt. I guess this means that the cover and the balancer have to match and cant be mixed. Has any one else had this issue? Can we find out what year the change was made? Dan o No:
I had an issue with the balancer and cover marks being different. It drove me crazy (didn't have far to go) trying to figure out what was wrong. Then I decided to go back to basics and make sure of TDC. Thats when I found the problem, Made a new indicator and solved a major headache. My motor is very sensitive about timing, even 2 degrees will make it act crazy, But thats a Buick , not a Chevy, anywhere close and they will be ok.
The motor will only miss when I am in the upper rpm range. The balancer and the mark on the timing cover do line up when checking top dead center. The carb is a 750 dbl pump jetting is 72-80. On the dyno it worked out to be 70-78. But I do have a different cam in since then so this jetting may change a little. I cannot adjust the air bleeds. If I put the timing at 34 degrees the miss gets worse. The plugs I have in there now are AC R42T. The Plug I was using before the nitrous is a R43TS which has the tip extended a little and I have also used NGK UR5 which is equivalant to the R43TS. Again with all of these plugs I can't go over 32 on the timing. I also use about 5 gal of 114 race gas with each tank of 94 sunnoco. I just did a leakdown test and a compression test. The leakdown is about 6-8 percent and the compression test was about 190-195 lbs. My leak from the leakdown was coming from the rings. Da Torquester: Thanks for the tip on drawing a line on the driveshaft. I will try that on my new one. :3gears:
Another thing to check along with the drive shaft is the axles especially in the splines. I had a set one time that twisted a complete spline( line to line), found that during routine check, got lucky. But thats what you get running stock axles, slicks and good horsepower.
mixture, ignition... It should not be missing from a little too much timing. A slowing down/mph drop and/or detonation is a sign of too much timing as is too much heat showing on you electrode strap which is the main indicator. If it is missing, it is either blowing out the spark or dropping the spark. Is it popping out the exhaust at all? The plugs you are using will work fine. What do you have the gap set at? Have you tried different gap settings? How did you go about getting your 30 degree mark on the balancer? If it keeps going faster with less timing then keep pulling it out until it slows down. 190-195 sounds good for cylinder pressure. Should run fine on pump gas on motor. The race gas mix sounds plenty good enough for running nitrous.
I am probably wrong by calling this a miss It is just that the motor sounds like it is missing but I do think the sound is coming thru the exhaust. Even when we were on the dyno you could see and hear when the timing was up too high you would hear that miss sound and you could acually see the motor shake a little and at that point the operator new to shut it down. He was surprised himself that the motor did not need that much timing and was very sensitive to it. I have also played with the gaps on the plugs. When I use the R43TS or the NGK UR5s I ran the gap at .045. With the nitrous and the R42T I used a .035 gap. I use a dial back timing light that is a Sears Craftsman maybe the numbers are not correct on the light but I have to go by what the engine is telling me. I did go to the web site that has the plug chart and that was very informative. Thanks for the info.
Tuning... Just tune it to the plugs and it will be fine what ever the timing may say it is. If it made its best motor pass with 27 degrees timning, then try 24-25 with nitrous at 6psi fuel pressure. It wouldn't surprise me if dropping the fuel pressure isn't what broke your drive shaft. Fuel pressure makes a big difference with nitrous. Too much fuel will kill the mid range power. You will definitely feel the difference of a 1 psi adjustment if it was too rich. Remeber if you are tuning to the plugs, you will only get a few passes to read them correctly before you need to change the plug. Find you leanest plug to tune it by just changing and reading that one plug. No sense in changing the whole set. :TU:
Buicks4Speed: Thanks a lot for your input on my nitrous set up. I am sure your extra tips will help me get the car to the 11.40s. I knew I was close on my set up I just wish the driveshaft hadn't broke as I was trying to lower the fuel pressure for my next pass but that didn't happen. Just think if I could get a singleplane intake on it and then maybe a 150 shot a 10.99 could be possible with a little 350. I can't see why TA Performance would not want to build a Singleplane Intake, at least that. Wouldn't it just be the HOT TICKET if he would build some ALUM. Heads to go with this. Why would he let some other bonehead build those and not cash in on it himself. I see a lot of people asking for these parts. At least do the Intake and see what happens. :beer :TU: :TU:
Try to borrow a timing light that doesn't use a dial. Mark the ballancer at 30 with a stripe and use the covet degree marks. I had trouble with those dial units and just stop using them. At least verify your light is OK. At the track I loand my light to somebody and when it came back It was off. Could not time with it any more and of course they said it was ok when thet brought it back. So I baught a new snap-on and now when someone wants to barrow my light I give them the bad one to use. They never barrow my light after the use the bad one. Dan
I need a single plane intake anybody build one yet. I could use it. Have I just reached the limit of this motor?
