This is the first model. It's a bit crude. I couldn't get the reducers from Flowmaster overnight, so we cut the 3' extenders and put a taper on both pieces then expanded the outer piece to slip over the inner, then welded it together. It's about 2 and 3/8s at the constriction. If this gives me any improvement at all I'll order the proper pieces from Headers by Ed. I'll get them painted tomorrow.
close.. but you want the constriction as close to the ends of the primaries as possible for full effect. Not sure how well that will work out. Might not hurt anything.. but might not help very much either. IOW's.. you want the venturi section closer to the ends of the primaries. Crude drawing but you get the idea here.
We'll see Friday night. My muffler guy wanted to put it farther out, and since he was doing it gratis, I went with the flow. I am going to order the pieces to do it right in any case.
So what do you hope to gain with this, I understand the principal but was just wondering how much improvement you will gain and where you will see it the most as far as et, 60'. I know you goals are to be close to 12.00 so you can be the faster car in the sportsman class
If I understand the theory, I'm hoping for increased low end torque and mid range, and maybe quicker 60' times. 1/10th improvement in 60' time will get me pretty close to my goal, assuming I don't lose enough hp to hurt my ET. Right now, I'm just trying to tweek some things with the combo to see if it helps. Over the winter I will make some major changes. We'll see if my crude attempt helps. I may shorten the straight portion before the venturi tomorrow if I have time.
OK, here's a pic of it after we shortened the reducer section. Still crude but closer to what it should be.
First run: 12.354/110 Second run: 12.305/111 Third run: 12.295/104 on a 12.30 dial-in. Broke out and lost. This even though I let off before the lights. Had the other car beat, but he let off too and ran a 12.19 on a 12.05 dial. Temps all three rounds were mid 70s. The car was definitely a bit faster tonight. Fastest it had been before was 12.32/109 with temps in high 60s. 60" times for all three runs were in mid 1.8s. I could tell it was faster because it was on the rev limiter well before the lights. On the second run as soon as it started dropping cylinders I look at the tach and it was holding at 5800 as I went through the lights. For the third run I raised the rev limiter 200 rpm. I couldn't tell if it made any difference because I let out of it to try to keep from breaking out. But it never bumped the rev limiter. Verdict on the venturi header extension? Car was faster and rev'ed faster. 60' times were unaffected. I had only ever gone 110 mph one time and that was a run with a 20 mph tail wind. Both practice runs were 110 or above. I expected that if the venturi header extensions made more power it would be on low end torque. It appears they affected mid-range more than low-range. Engine sounds different as I expected and it seems throttle response is crisper.
To really make sense of what is going on besides the changes you made you need to have a weather station and know how good the air is altitude wise but I imagine you have a friend or somebody that has one,the temps dont tell the complete story. Then it gets really fun changing jets for optimum performance keep a good log book and mark down everything you notice for every run. At any rate it sounds like you are pretty close to your goal and with the changes you will make this winter it should be well with in your grasp hopefully you can go under 12. and learn how to handle it and more seat time
Not trying to be negative but I'd bet better air is why it's picking up. Its good your getting closer to your goal of 12.0 but seems like your going the long way around. But, if your having fun doing it that's the point really.
Better air is certainly good. But, when I compare to earlier in the year when it was in the 60s and 70s the car was running 12.50s, so there is improvement there outside the cooler temps. I'm not trying to go the long way around. Please share a shortcut or two. Running cleaner and faster is fun. Going out in the first round isn't.
That last iteration isn't bad at all for a crudely tossed together design. I bet there is more to be gained with an even smaller choke ID.. say 2 1/8 - 2 1/4" constriction with a true meg style extension transitioning into a 2 3/4"(tougher to find but I have several sources) straight section that is tuned/cut to length. The basic idea is that a smaller constriction makes the engine think the primaries are smaller and/or longer(fatter powerband).. bigger makes it think the primaries are bigger and/or shorter(peakier powerband). More depression at the collector wards off power robbing reversion into the combustion chamber and helps get/keep the induction pulse moving in the right direction. As for ET/throttle response gains.. my guess is this. The stock stroke is just too short to make much torque gain at that too low a stall speed. At least with that still too big a design(remember the spec's from that engine combo in the vid above and you can see your system is still too big for only 302 CID). You're hearing/feeling the throttle response below peak torque but the gains just aren't enough to cause the converter stall to rise enough to really help the 60 foots out. You could also very well likely use a bigger more abrupt accelerator pump shot now too. I'm also betting that the extra depression created by the return wave from the expansion of the exhaust pulse is helping to better evacuate the volume above the piston at TDC after the exhaust stroke. That's the entire premise of this design. This low-pressure wave then passes through the intake valve(s) and gives the intake process a torque-boosting(or in your case enables slightly better throttle response) head start, even though the piston has not yet gathered much speed on its downstroke(even truer with a smaller stroke/long'ish rod/higher rod ratio such as this one). Again.. even though the boosters are staying more active with faster fills.. you still often need even more pump shot(won't load up as quick now that the engine rpm's more quickly). A smaller constriction mentioned above will add even lower levels of depression and will gain more usable torque earlier in the powerband to help bandaid that pitiful converter flash speed. As with everything.. you may end up robbing Peter to pay Paul(more low end for a slight loss up top) but still end up ahead due to greater average power output during the 12 second runs. All about balance and the ET slip never lies like the dyno will. As for the extra rpm capability? The engine is now running richer on the top end due to the greater depression created at the collectors. That cams extra exhaust duration was always there.. now it is being utilized to better carry out the peak power. You're also helping the induction system to become more efficient in an area where it was never really designed to be most efficient. Daul planes are not best suited to well above 6,000 rpm full power blasts(they're an "average power builder" type design). A 1" open spacer will help top end even more as the exhaust constriction gets even tighter and you'll still maintain low speed torque and throttle response like it was still fully divided. And possibly still gaining even more of it while also allowing the induction to breathe even deeper on the top end charge(the upper plenum volume is significantly too small for 4 of those 8 cylinders). Enough random thoughts for now. Oh.. after all that I forgot to ask.. did you mark/cut the length yet? The race would have been the perfect time to check the burn marks.
Looks like I may be done for the year. Possibly might run on the 30th. It depends on how elk season goes. If I fill my tag early I'll race the last day. Best so far this year has been 12.21/111.
You have your priorities right, elk season is only one time a year and you can race several times a year. Elk season does not start here until November after race season. We have a split elk season with a 4 day hunt for branch bulls only and a 7 day season for spikes only. Good luck with your hunt get him early and get in the last race. I have always wanted to come over and watch the Halloween classic, lots of action You have actually done pretty good going from a 12.54 earlier in the season to a 12.21, time and money and you will be there. I am actually just the opposite of you I have to slow down or be the slow guy in pro although the car does not win races the driver does. Our best sportsman driver runs in the mid 12s and has been the champion forever
I have a cow tag this year, so hopefully I can fill in the first few days and get it in the freezer for the winter. Then go back to racing. The Halloween Classic is quite the show and race, but it falls right on opening day of elk (15th) so I will miss it this year. I'm off to chase antelope this afternoon for a couple of days. I'm going to make some changes to the car over the winter. For sure lifters and improved header reducer. Probably go to 4.11 gears also. Or, I may just jump into the deep water with a 347 short block, two-step. etc. and move into Pro. It's all money dependent since I have four other projects plus the second Maverick I bought on Saturday.
