first run in 2 years. truly horrific!
Well, i guess my new Demon is further off than i thought. I made 5 runs, and they were extremely consistant--- and over 2 seconds and 20 mph slower than my last trip with the Edelbrock. The car feels strong, but the numbers don't lie. Time for a wideband and a tuning kit.
1983 Mustang G.T. No-option stripper- I like strippers.
5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.
What prompted you to switch carbs?
2 seconds and 20 mph is a huge difference, I'd think you'd feel that immediately in the seat of the pants. That's roughly the difference between whether I'm running my 408 or the stock 351 I have. It's night and day which one is under the hood.
Surely there must be some other factor in play here to change the performance that much? Are the secondaries opening at all?
408/T5/3.73's
We're not fast racers, we're more what's known as half fast racers.
Yeah, that's a huge difference...a 20 mph drop is a ton of missing horsepower. Has to be something else. And it's really odd the car still feels strong to you.
Actually, no! Lol. By the end of the night, i had gotten some of the trap speed back by bringing the secondarys in much sooner, but it is massively lean up top. I have some exploring to do with this thing. Low speed, below 3000 rpm throttle response is great-- i don't wind it up much on the street, so the problem was kind of hidden. Glaringly obvious on the track, though.Originally Posted by mmb617
What prompted you to switch carbs?
Surely there must be some other factor in play here to change the performance that much? Are the secondaries opening at all?
I swapped carbs mostly because the Edelbrock never played well at idle. Very rich, even dialed in fairly well. It ran well at the track, but it did it a bit like a double pumper - mask issues with large quantities of fuel. It was reaching the point where track performance was affecting street driveability more than it should. The street demon has far better separation between primary and secondary fuel metering, i think.
Last edited by brianj; 08-08-2015 at 10:41 AM.
1983 Mustang G.T. No-option stripper- I like strippers.
5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.
Ok, so, i had time to really check things out. The throttle cable bracket was not completely tight.. it rotated, and put slack into the throttle cable. It was giving me between half and 3/4 throttle, right about where the secondaries would be opening. Opening the secondaries earlier bandaided the problem a little so i picked up a little mph, but it was still only a little more than half throttle. Still very lean up top, but way better.The fact that 5/8 throttle felt good on the street should give you a little indication how good the part throttle response is on this little carb, compared to the Edelbrock. Stupid rookie mistake! !
Last edited by brianj; 08-08-2015 at 12:53 PM.
1983 Mustang G.T. No-option stripper- I like strippers.
5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.
Glad you found the likely issue...now get back to the track for some faster times!
Yeah, i wanted to tweak my car into the twelves this year. Dropping back into the fifteens was a little, shall we say, upsetting.
1983 Mustang G.T. No-option stripper- I like strippers.
5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.
I recently installed an air/fuel ratio guage- wow money well spent. Very easy to tune the carb and NOS system.
1980 Cobra http://www.cardomain.com/ride/2364382
11.82@115 mph - 2015 - retired due to cancer
1981 Cobra
reborn with a lot of new go fast parts and time to make it look pretty
11.80 @114 mph - 2016
On my wish list! I did pull a 13.4 @ 104, so I'm back where i was, and i know I'm lean in the secondaries. I just changed from a Performer to a performer rpm since then, but i still have not played with the jetting. I'm going to install an air/fuel meter and tweak it this winter.
1983 Mustang G.T. No-option stripper- I like strippers.
5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.
You have the MPH for a 12 as it is. What are you running for tires?
I am running Sears finest all season tires, to the tune of a truly outstanding 2.4 sec 60 foot time! Lol. Honestly, i am more concerned with trap speed at this point, as a tuning tool. Trap speed with weight gets me a fairly accurate hp estimate. ET gets me a very good driver skill estimate, and the driver sucks!
1983 Mustang G.T. No-option stripper- I like strippers.
5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.
Throw a pair of slicks on it or at least some DR's. My combo isn't much crazier than yours and I'm running 12.5@110
Keith formerly STLPONDS
'79 V8 coupe in the works!
Build thread http://vb.foureyedpride.com/showthread.php?t=89153
Haha, better tires will help the driver skill!
I have an almost brand new pair 26x8.5 MT Drags mounted on 10-holes just sitting in the garage...swing by and you can borrow them!
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