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#21
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In the early 90's, my cousin had a '78 T/A, daily driver, 400, lots of mods, ran mid/low 13's on his daily driver tires (drag radials didn't exist, and we couldn't afford slicks). I had a '79 T/A daily driver, mild 455, and about the same performance. We both had the same headers and exhaust systems.
One day my cousin decided to open his headers at the track - he ran 12.9's! Several tenths faster than the car had ever ran. Encouraged by his success, I opened my headers a few weeks later. My car stumbled off the line and ran a couple tenths slower. We later realized his carb was too rich with the exhaust connected, but AFR was about perfect for open exhaust. Mine was about perfect for full exhaust, but leaned way out too much when I opened it. To make any test fair, you have to correct the AFR.
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'73 T/A (clone). Low budget stock headed 8.3:1 455, 222/242 116lsa .443/.435 cam. FAST Sportsman EFI, 315rwhp/385rwtq on 87 octane. 13.12 @103.2, 1.91 60'. '67 Firebird [sold], ; 11.27 @ 119.61, 7.167 @ 96.07, with UD 280/280 (108LSA/ 109 ICL)solid cam. [1.537, 7.233 @93.61, 11.46 @ 115.4 w/ old UD 288/296 108 hydraulic cam] Feb '05 HPP, home-ported "16" D-ports, dished pistons (pump gas only), 3.42 gears, 275/60 DR's, 750DP, T2, full exhaust My webpage http://lnlpd.com/home |
#22
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Thanks, will monitor the AFR.
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#23
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Engine Masters has had some good episodes on this subject and determined that a 3" diameter extension from the collector. 18" long is the ideal setup for maximizing torque. They also tested a 3" single pipe system against 2-1/2" duals and found the single to be as good as long as the y-pipe was far enough back from the engine.
In another episode, they evaluated cut-outs, especially how the dump pipe was spliced into the main and got some very surprising results. Low rpm performance can be impacted very negatively because of pulse reflection back towards the engine from the dump pipe. In all cases though, A/F ratio needed to be adjusted with rejetting. |
#24
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Quote:
3 single pipe vs 2.5 duals is fine for smaller hp builds I'm sure..but either is grossly small for higher hp. I did take interest in the cut out video, it for sure showed there is an ideal spot for cut outs...many street guys will just do it for sound not realizing it is a hp loss but sounds "cool" The test I'm interested in and have never seen is the X pipe vs the collector extensions
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#25
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Many times, cutouts are installed where it's feasible under the car. Each car being different with floor clearance and other obstacles.
What I've always done is make sure the cutouts are at least 18 inches from the header collectors, as in the picture I showed above. Sometimes that varies a few inches, again because of other obstacles. This mimics what has been shown time and again that open headers with some sort of extension is more beneficial than just having headers open at the collector. The only issue I see with cutouts after an X, as I have on one car here, is the cutout ends up being even further back. That one, by the time it exits the cutout and makes the turn, ends up being at the front of the mufflers, which is basically at the rear end housing of the car. X placement also varies per car. Is that too far back? Don't know. Haven't tested this one yet, but it does at least remove the rest of the system from the equation when the cutouts are open, meaning no more mufflers and no more over the axle tail pipes, and tailpipes on this car are super long too. I can say cutouts as I pictured above, which end up being about 20" from the header collectors and are a straight shot before they hit any bends in the system, work exceptionally well at the track vs the full system, and that's not a restrictive system by most standards with 3" pipe, Dr. Gas X and Dynomax mufflers with torque tech 3" tail pipes. |
#26
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I ran my car with the Y type cutouts between the headers and exhaust. 3" Torq Tech pipes and Walker dynomax mufflers. Car was 12.0 @ 110. Open vs exhaust was less than 1 mph and a tenth. I did run 18" extensions with the old paint stripe to try to find length. Wasn't any faster. When my 1 3/4 headers shot craps I put on Heddman Hustler 2" primary 3 1/2" collector I had sitting for years with 18" extensions. Ran the 1/8 and hit 91 mph forget et but first time over 90 in 1/8th. Have to get to !/4 to see what happens. Also have an X pipe to try but it's tight going 3 1/2, reducer to 3, X pipe, mufflers etc.
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#27
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An additional comment about track time. When racing through the mufflers vs someone with open headers I don't like not being able to hear my engine and having to rely on the tach/shift light. I like it better if both cars are quiet or both loud.
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#28
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Yes, also the first burnout with no exhaust is pretty intense!
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#29
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Not identical but on my 70 gto back in the day I had 1.75 hooker headers, 3" x pipe,3" to 2.5" reducer cones,2.5" ultraflows and 2.5" tailpipes. Unhooking the headers with no collector made no difference really in ET.. Ran 11.7 at 115mph at 3950 race weight.
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72 lemans,455 e-head, UD 255/263 solid flat,3.73 gears,,,10" 4400 converter,, 6.68 at 101.8 mph,,1.44 60 ft.2007 (cam 271/278 roller)9"CC.4.11gear 6.41 at 106.32 mph 1.42 60 ft.(2009) SOLD,SOLD 1970 GTO 455 4 speed #matching,, 3.31 posi.Stock manifolds. # 64 heads.A factory mint tuquoise ,69' judge stripe car. 8.64 @ 87.3 mph on slippery street tires.Bad 2.25 60ft.Owned since 86' |
#30
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When I race the cars muffled I can't hear much anyway with the helmet on so doesn't matter much to me.
Racing the auto cars is of no consequence, I let the trans do the shifting, all I have to do is stab and steer. |
#31
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Staging isn’t to bad for me with the noise I don’t like starting it in the lanes surrounded by open exhaust cars.
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#32
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Quote:
That's how dad's GTO is configured, with the electric cutouts in the 3 1/2" section. Fits nice on any A-body without issue. F-body would be a little tighter, depends on what you're working on. |
#33
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In high school we used to have "Open header Fridays" If a cop was around shut it off and coast-most were stick cars back then! At night letting off the gas and the flash/pop back in the collector was quite a show!
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#34
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Quote:
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Darby 74 Grandville 2Dr 455 c.i 4550# 2011 1.60 60 ft,7.33@94.55-11.502@117.74 2017, 74 firebird -3600 lbs (all bests) 1.33 60 ft, 6.314@108.39 9.950@134.32 M/T 275/60 ET SS Drag Radial 2023,(Pontiac 505) 1.27 60 ft, 5.97@112.86, 9.48@139.31.... 275/60 Radial Pro's |
#35
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That's been tested a bunch. Most recently on the engine masters show.
They did in fact find that about 18 inches from the end of the collector to be about optimum. Any shorter hurt power and longer didn't seem to matter at all. |
#36
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What intrigues me is the "longer doesn't seem to matter theory"..and will an x added on create power.
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#37
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Quote:
We only have one car at the moment with cutouts that are actually behind the "X" cross over. I'd like to test that one out sometime. |
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