Some of the big block Chevy guys are grinding custom cams to accommodate a 1-8-7-3-6-5-4-2 firing order rather than a 1-8-4-3-6-5-7-2. They say there is less crank deflection, a broader torque curve, and they even promise lower operating temperatures. Anyone care to comment on this. Maybe this might be an area of interest since crank wobble means disaster for a Buford. Has anybody done this or know of someone who has in any V8 application? What are the results? Josh
4-7 SWAPS ARE A GOOD THING.As you say crank deflection is decreased therefore taking the load away from the center 3 main webs.The next benifit is the 5-7 lean out that some get due to 2 cylinders firing right next to each other is taken care of.If you were to go with a 4-7-3-2 swap no cylinders will fire next to each other.From every thing I have seen either firing order will pick up hp.When and if we get the Bulldog block I will have 55mm cam cores available in either firing order swaps. I heard a rumor that Mike @ TA was going to look into stock sized core firing order swaps in flat tappet and roller.I'm sure he will do the roller this is no problem to change the machining and switch the order.Now the flat tappet is a whole different deal that requires a new casting $$$ so I don't know if he would be willing to put the money out for this due to the low turn around on this type of deal. But once again firing order swaps are a good thing.
cams What about 4-2? Last I looked these were still side-by-side?? :Brow: I'm not so sure I buy this swap, 7-8 are still firing back-to-back on the same throw on the most highly loaded journal in the engine, and 4-2 become the new 5-7. I have heard both sides talk of small improvements. For all the hassle of changing, I think I'll stick with stock, I have 25 years of personal experience dealing with 5-7 and have never had a problem. Of course I don't run anything on the ragged edge. :TU: My .02 Jim
I think you mean 3-1. Having considered it for my current 383 and future 351 SBC, and doing much research on the concept; its true that you get rid of cylinders 5&7 fighting for the air/fuel mix but at the cost of having 3&1 fighting for the mix. In a stricktly drag setup the 5/7 issue isn't too bad considering the G-forces at launch will force more of the air/fuel mix to the rear of the intake causing #1&2 to run slightly leaner and 5&7 have more air/fuel to draw from. By doing the 4/7 swap you are bassically leaning out #1&3 even more and hurting your power. That why Top Fuel & Alchol Funny cars run more compression & high A/F ratios in the front cyliders than in the back cylinders.
It is 3-1 (as stated above)o No: This type swap has been around for about twenty years, that I know of, so I don't think it is a huge secret. I just believe that for the benefits you have a lot to change in addition to the firing order. I don't really have issues that this would address, but, I only drag race(seriously) so I may be all wet with respect to other forms of racing. I had a friend(passed on now) that always rode me about doing this or that to gain that extra tenth. I always responded: "Am I not going fast enough?" That usually got his attention. It all comes down to how fast to you want to go and how much can you pay. Jim
You got me I forgot about starting the cycle over again.My bad.I agree it's been around for years WJ's been playing with firing orders for at least 20 years.But most people had no clue about this up until 4-5 years ago now it's becoming more mainstreem. On loading the 7-8 crank pin I would rather load this pin than the 5-6 pin which is what you have with the stock firing order.When loading the center of the crank you are more likely to flex the block which is a big issue in a high hp buick.I would rather load the rear of the crank at the rear bulk head/main which is the stongest area of the block.I myself like the 4723 swap because it for the most part spreads the load better on the block aka taking some load out of the center 3 mains.This hasn't been done on a buick yet (I think) but running this firing order may help big hp buicks live longer with a stock block.Just a thought.
Hey guys , The benefits are there . They are more pronounced in an open plenum manifold(tunnel ram). It helps the plenum get "cleared" without cylinders fighting each other. The lean situation with the cylinders next to each other is also a concern. This would be more of the benefit on a single carbed /single plane intake . It is worth it on a max effort deal. One would have to wonder whether the expense would be worth it on a bracket style motor though. Besides the cam the only change is the plug wires by the way. Hope this helps George in DC
George Looks like the ET on the Probe dropped..Congrat's,I'd love to see some video,Mostly for the sound :TU: What'd you decide to do w/ the Skylark?
Gary-- thanks , new clutch program plus more hp. We found a rocker ratio issue on the freshen up and pow! The clutch is rediculous . Its soooo small. 142 tooth flywheel 6 inch 3 disc. Less than 25 lbs total.You can practically put a clutch disc in your pocket! It needs to come out after every pass--period. We are trying some new tighter splits in the tranny and leaving at 65-6800 now versus 6200 max before .Its just stupid. It sounds like a small block. Im gathering pieces to convert the skylark over . I am ready to order the jerico. Just figuring out ratios. Clutch is on order.The bellhousing is going to take a bit of time. I had to special order it. Not many running a slipper clutch behind a buick. I am just going to stick with buick power for now and just have fun . I will up compression a bit and switch to a set of stage 2 te. It will go as fast as it will go. When the new blocks start shipping I will order one and build a stage 3 or 4 motor. I will just stay with the small tire . There is a "bolt on suspension only" class at MIR I can play in for now. If I cant get that combo in the nines with stage 2s and a stick I need to keep it on the trailer. How is your stuff coming ? George in DC
George: I guess that is what I was trying to say, the benefits are small compared to other things the average guy can do. Any order will work, some may work better, with tuning. But, you still have to do the tuning! What most of us run, us average Joes with average mills, :Brow: will be a combination similar to something a hundred other guys have used. There will be no huge unknowns and it should be fairly easy to tune. If you don't have the time and money to wring every last HP out of the combination you have and verify the stresses in the engine somehow, is there really any benefit to a different firing order? My opinion is there is no benefit to a different firing order, for the average guy, unless you already have every last horsepower anybody could possibly get from the combo you have. I am also a guy using a single plane manifold and a single carb, as you say, a "bracket style" motor. There is always room for improvement, but, I like to stay on the conservative side of "maxed-out" because I have a very limited budget. Of course, there is an awful lot more money out there in racing now than when I started 30 years ago and those guys will probably figure something else out. A good thought, too. I guess that I don't make enough HP with a Buick motor to worry about that and I don't worry about it with my Chevy. Jim
Don't forget the Crankshaft!!! What about the crankshaft in all of this??? The crank needs to have the piston in the right position (TDC) to make the changes in firing order you guys are talking about. So now we are talking about a redesigned crank??? Stay with the way it is 18436572. I'm sure the engineers thought of the best way and made it already. As for lean-out, as already mentioned on this thread, 5 & 7 are well compensated for during hard acceleration. Pete
There are 4 firing orders that will work on a v8 with out changing crank pin locations.If you look at the new gm ls series motors they have the 18726543 firing order. The ford 302-351 windsors have 2 different firing orders both work on the same crank.So the crank doesn't become a problem in the switch.
Big block Ford has the same issues. The thing is actually fighting itself if you dont change it . If you ever wanted to race one (someone has to) that is the first thing you change . I actually would be interested to judge benefits on a BBB and block deflection and shift with the firing order change . Sometimes its minor changes that make all of the difference. I know that the benefits in my race stuff are smoother idle (relative to almost an inch of intake lift), a smoother torque curve, and of course it is supposed to make more power. It would take some dyno time but it would be interesting. George in DC
The problem with loading the 7-8 crankpin is the leverage it creates on one end of the end of the crankshaft. By loading one end you stress the other. It's like holding a stick and have someone push in the middle or at the other end...it will be easier the hold stable with the pressure in the middle. If you're worried about stressing the 5-6 pin the T/A block girdle or new Bulldog block takes care of block bottom end "weakness issues". Pete
If you are going to wrap the crank it starts at the front and works it's way back.True a block girdle helps but it's not the end guy's still break blocks even with the girdle.I am trying to get a little more insurance.I have spoken with some pontiac guys that have found the firing order swaps have helped keep the center 3 main webs from moving around in their stock block issues.Now the bulldog block we won't have to worry about block issues but I want every possible hp I can get.But for right now the bulldog is a no show 4500 invested and nothing to show for it :af:
The problem with loading the center is there is no support.ok push on a stick in the middle with little support what does it do? deflect right
You have to look at where the resistance is. It is at the flywheel. Firing 2 cylinders on the same crank pin is best when kept closest to the flywheel where the most resistance is at. Plus the #5 bearing has the largest bearing surface of support. Also, the transmission flange offers more casting support at the back of the block. So if nothing else, I'm all for putting 7-8 together in the firing order on a stock block. :TU:
After more thought on this either firing order still fire 2 cylinders after each other on three crank pins during the cycle. Ok 18436572 first you load #1(2-1 cyl) crank pin then #4(8)then #2 (4-3)pin then #3(6-5) then #4 again for 7 then back to #1 for 2-1cylinders 18726543 first #1 pin (1) the #4 pin (8-7)then#1 for #2cyl then #3 for (6-5) and finally #2 for (4-3) Ok the LS1 18726543 firing order fires the #1 pin twice in the order to take the load off the front of the crank.Rather than firing 2 cyl's in the beginning of the order on # 1 pin (2-1) for the stock order which fires the rear pin twice in the order.So looking at this the crank will not want to rap up as bad.Once the crank starts twist the main webs are not long for the world.Any way you look at it the crank is loaded different either way.To me the LS1 fo is easier on the crank and block.This is most likely this is why GM uses it now.Look at the power the LS makes.Now I am not saying all of the hp came from the cam but it is part of it.Then you need to look at GM NASCARS I highely doubt any of these guys use 18436572 nor do PROSTOCKS.When I look for hp gains this is who I look at.
Grumpy had a revised firing order in his sbc in the 60s. It has been around for a long time its just that everybody didnt talk about it. Both Nascar and ProStock have used it as part of standard proceedure forever.Personally I have used it in my full effort stuff since the eighties but my street stuff has stayed standard firing order. I know that it makes a power difference in my race stuff but I just never thought it was worth the added expense for a custom billet on the street in a non bbc application. I know Comp will pretty much grind anything, so maybe they will do so for the buick. The only thing is the benefits are usually upstairs in rpm . For a big torquer like the buick it would take some side by side comparison to really see the benefits. If I had the new block, I would definitly do it. Whats an extra 300 bucks or so for a custom billet at that point? Just by its nature, you are at max effort when you buy that block so take advantage of ALL of the proven hp methods. Hope this helps George in DC
