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Changes don't seem to affect performance

11/05/2018 08:29
RADAR
I have made modification to try to dial in my car at the dragstrip. Over the course of 16, quarter mile runs I have made no significant improvement to mph and I'm wondering what might be holding things back. My mph has varied only a small amount from 94 to 96.5 with very little of that I can tie to the changes I made. I'm wondering now if there are one or two variables that might be holding me back, and the other changes I've made are being throttled by that one variable. I wondered about fuel supply, but it’s not sputtering or otherwise feel like It’s running out of fuel at the top end. I’ve wondered about my exhaust (see attached pics of non-mandrel bends) but the bends don’t seem to be too bad. What could be throttling performance? My changes have included timing (34-40 total), carb spacer, complete tune-up, changing shift points (4800-5300). These aren’t major changes but I would have expected some noticeable change to performance. My setup is 400-bored 40 over, 068 clone cam, long-branch manifold, original 4-speed Muncie, 2 3/4” exhaust (non-mandrel bends), 670 heads, Carter 4-barrel rebuilt by Cliff Ruggles. Thoughts?
11/05/2018 08:52
JOE PENTIUM
40 on the total advance seems a bit much but that's just me, I never took my car to the track as I am still building.
11/05/2018 08:59
JOE PENTIUM
Have you looked at this?http://www.pontiacstreetperformance.com/psp/camselect.html
11/05/2018 09:22
ASHLEY P
What's the car weigh, and what are your 1/8 mile ET/MPH numbers?
11/05/2018 12:42
RADAR
I just noticed the exhaust picture was imported upside down. Joe, the 40 (timing) was actually by mistake, but the funny thing is that between 34 and 40, the MPH numbers didn't seem to change, at least not much. Camshaft is a Summit 2801 – 214 int./224 exh. (if I remember right from 16 years ago). Ashley, the car is a stock 67 Firebird 400 with stock dual plane intake, port-matched heads, updated but stock points ignition, 3.36 rear gears. 1/8 mile ET: 9.775 - 10.386 and MPH: 74.34 - 76.28.
11/05/2018 16:05
ASHLEY P
Well, I'll give you some very general ideas that might help. First, MPH vs ET. MPH gives a rough estimate of peak HP produced, while ET tells you how much of that power is getting to the ground. So, tune the engine for maximum trap MPH.........................................Second, start tuning on the "safe" side. Safe timing is "retarded", safe fuel is "rich". When at the the track, retard the timing a couple degrees per run until the car is a couple MPH slower, then raise timing until it again gets a little slower, keep records and go back to the timing with max MPH. Same thing with fuel, increase fuel (richen) the metering rods until MPH slows, and/or read spark plugs (google that to get a thousand different opinions) ...................Third, try cheap stuff first. Clean air filter, drop exhaust, swap ignition coils (I've seen a weak HEI coil make my car doggy on the top end. Be aware that your car may be near it's potential if your mods don't seen to change much. Especially if your air is thin....what's your elevation/air temp?
11/05/2018 16:09
JOE PENTIUM
OK, here are just some things to think about doing, I think you have gone as far as you can go with what you have to work with. Carb: maybe a Street Demon or a professional built Quadra jet, Exhaust: change from headers if that's is what you are running back to manifolds, a Ram Air Restorations set they are the best set if you hate having to change header gaskets every 2 months and they are a superior casting compared to the ones sold by Ames Performance or Year One, as for the intake manifold: I would go to a Performer RPM as its power band is from 1500 to 5500 I believe, and now for the rear end: Is it a positrac unit? I think you could stretch the gears to 3.73 with the 4-speed, as for the distributor: HEI hands down as I think you said you were running points still, a bone stock unit will give you all you need for what you are doing as of now and they are very affordable and don't forget to re-gap your plugs to 060. Just my 25 cents worth.
11/05/2018 17:15
ASHLEY P
Checking your bio...are you at an elevation of about 4300'? Your combo of heads/cam might be at/near it's HP limit especially if the air was hot during those runs.
11/05/2018 22:04
RADAR
Yes, I'm at about 4300 ft. When the carb was rebuilt, I gave my combination, elevation, and goals to Cliff so I'm assuming it was build and jetted appropriately. Joe, yes it is a positrac rear. The coil and points are new and gaped appropriately. I stayed with points because from what I've read, HEI, while more reliable, may not buy much, if any, performance in a lower RPM application like mine (<5200). I can't remember where I got my RA manifolds but I suspect they were from Ames.
11/05/2018 22:19
ASHLEY P
I'm at only about 450' elevation. A couple decades ago my 69 GTO had a 406, #48 heads, original intake/carb, exhaust manifolds, 2" pipes. 4 speed. Ran 9.05/79.8 in the 1/8 That was about all I could get out of it. Could you be near the limit of your combo? What do similar engines run at your track?
11/06/2018 08:21
JOE PENTIUM
+1 Ashley P, I did not realize you were at that elevation RADAR. Is there some way to cool the air and fuel maybe? Nitrous anyone?
11/06/2018 16:58
ASHLEY P
I'm still curious as to the air temp during the runs, and what comparable engines/cars run on the same days..................................... Regarding your 2.25 exhaust pipes, they are flowing better than the 2" I used to run. What mufflers BTW? Cheapy mufflers can slow one down....
11/06/2018 19:53
RADAR
Air temps were all between 70 and 85. Mufflers are Dynomax (Ultra Flo I think). I also have an x-pipe. So maybe (?) I'm near my limit with my current setup, why haven't my changes have much effect? I have mostly been methodical about the changes, trying to change one thing at a time. Also, my goal isn't to make drastic changes (Nitrous, etc.), but rather to just get the absolute most out of my current setup. Seems like I could get a little more out of it.
11/06/2018 19:59
JOE PENTIUM
Flowmaster 40s on mine. I had to add twin catalytic converters as the CO was terrible. I used the short 4" dia.
11/06/2018 20:29
ASHLEY P
If you only changed timing 6 degrees, that's possibly not going to affect MPH a whole lot. Did you advance it until MPH began to decrease, then put the timing back where MPH was max? And beware: a balancer can slip and give you inaccurate readings, so set the timing to the most MPH. Shift points: Due to the wider jump between 3-4, I liked to turn the engine 200--300 RPM higher in 3rd to help compensate. I never was at the track to check that approach, but it probably would not have changed MPH, maybe ET a smidge.
11/07/2018 12:46
JOE PENTIUM
Hey RADAR, I just saw your car and understand why you don't want to go too crazy on it. With that said I think a Quadrajet would be the only thing to change. Pontiac performance engines were developed and flow tested with this carb. you might want to give these guys a shot. Baldwin Performance Carburetor 7 Hasty Hill Rd. Thomasville, NC 27360 baldwincarbs@gmail.com 336-457-4244
11/07/2018 14:26
ASHLEY P
Joe, doesn't Radar have a Carter Quadrajet by Cliff? Cliff does great work from everything I've ever heard/read.
11/07/2018 15:25
JOE PENTIUM
I was under the impression it was a Carter AFB, my mistake. I will leave this discussion alone in the future.
11/07/2018 15:54
ASHLEY P
By all means, stick around and give suggestions. No one person has all the go fast ideas. Your link to pontiac street performance was an excellent idea.
11/07/2018 15:59
RADAR
Yes, I have a Carter Quadrajet re-built by Cliff
11/08/2018 13:30
JOE PENTIUM
The only thing left is what tires are on the back?
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