Doing some math tonight, because I did all my finance work last night. All the following flow numbers come from this page here on bangshift: https://www.bangshift.com/forum/forum/bangshift/tech-section/3202-some-muffler-test-info This is to help demonstrate the inadequacy of stock/certain exhaust systems/mufflers and why it should never be forgotten when altering any classic ride (Sorry California) 2" straight pipe flows 239 cfm 2 1/4" straight pipe flows 365 cfm 2" Cherry bombs (what is on the Riv) flows X 2 1/4" Cherry bombs flow 239 cfm Straight pipe calculation 239/365= .77 Cherry bomb calculation 239 *.77= 184 x2 mufflers per car= total exhaust cfm capability of 368 cfm Buick Riviera calculation: Assuming .92 volumetric efficiency* 430(Displacement) * 5500 (Peak RPM) / 3456(constant) = X * .92 (VE) = 630 cfm My exhaust system is woefully inadequate. In fact, here's a bit more food for thought for when back pressure begins to overcome the flow rate.... 430 * 3215 rpm/3456= X * .92= 368 cfm My exhaust is only a restriction above 3,215 rpm, which is where 75% of my powerband lies. Use the above system to determine where your exhaust peaks out and how efficient it is. The only information you will need to provide is accurate flow rates for the mufflers and pipe diameters you are using and an understanding of volumetric efficiency. You must pick your smallest flow number within the system and use it, because that is your restriction. You will need to read up a little on VE to understand, but it is actually interesting, so give it a shot. Hope this helps anyone thinking about exhaust for their car. Keep in mind that louder doesn't mean it flows better, and quieter doesn't necessarily mean it flows poorly.
John, You could install "Cutouts" for when you go racing or those electric cutouts that open with the flick of a finger. Enlarge the exhaust manifold openings from the ( I think) 2 1/8" to 2 1/2". Then you wouldn't have to change the whole exhaust system & may actually work out to cost less $$$$. Tom T.
Thank you Tom, I had considered cutouts, but I had already purchased 2.5" Dynomax ultra flows that flow over 1000cfm each, so all cutouts would serve to do is increase noise levels, and I don't really want a lot of noise on this car as it is. I will be installing the full exhaust system, no question about it, cause I've danced around it for too long. I also have shorty headers now, to complete the form and function, so no need to enlarge anything.
Sometime ago JW posted a worksheet on a 430 engine. If i recall correctly the engineers took a 430 off the production line, put it on a dyno and then took it apart to check the build. I think their purpose was to check a production engine vs. what buick advertised they were selling. Sort of a pop quiz for the engine plant. Anyway what i remember from it was the engine barely ran at 80% volumetric efficiency and had way less than the 10.25:1 compression.
I've eliminated (or intend to finish the job) several of its weaknesses, namely an overheated intake manifold, restrictive manifolds and exhaust, and gave it a cam that loves to breath. As I tune the carb more and more, I should be much closer to an ideal running engine. Maybe not 95% VE, but maybe 90%. Either way, too much restriction
John, Can't you plug or restrict the amount of exhaust going to the intake??? 1st. thing I would do is eliminate the heat riser valve IF you haven't done so already. Tom T.
Quote from JW : "Don't get me wrong, I love manifolds for some builds.. I just pulled a 375HP 437 for a 67 Riv off the dyno last week.. all iron, all stock, with a 212 cam. No reason in the world to put headers on that motor. Love the nice quiet manifolds.." Gives me a little hope for my own engine, the track won't lie, but headers can't hurt on a street/strip Riv, power > quiet for me, but to a degree
John, How about blocking some of the exhaust going to the intake??? You DON'T want to bock it off completely just restrict the amount of exhaust going to the intake. IF you block it off completely more than likely the engine will hesitate when cold, but should improve as the car warms up. I KNOW that on a "Nail" if you block off the exhaust completely from the intake, since it's an 'Air Gap" manifold it will ALWAYS hesitate even after warm & during the summer, but your intake is NOT an "Air Gap" intake & will warm up with the engine as it heats up. In your case warm air is better than cold air as the choke needs it to operate properly. OR, you could just change over to an electric/electronic choke. So you DO have options that aren't overly costly. Just some more thoughts on something you may have done already. Tom T.
Thank you Tom, and that's good insight for the Nail guys as well. I have blocked off the exhaust crossover on both sides, but drilled one 5/64th hole into each plug on the passenger side to work the choke. It has worked very well so far and I can now let wires touch the intake manifold without burning (tach and battery leads to distributor). It opens in good time and I now can touch the carb without burning myself to give the throttle a hand-flick if I desire. With Everyday Performance's block off gasket, the deal is sealed and no more leaking either.
