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 Post subject: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 9:30 am 
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Hi everyone. I bought a 66 mustang for my kid to work on and race. Its a kick to drive on the street. The motor has a std bore and a 3.4 stroke putting it at 347 cubic inches, Has a 750 carb, cam lift is .536in .560ex duration 248in 258ex. Compression is 12 to 1. I took it to the track and my plan was to shift at 6500rpm but it felt like it was never going to get there, so I shifted at 5500rpm. It pulls really hard out of the hole and keeps pulling like everything I would ever hope for and then just runs out of steam just past 5000rpm. It doesn't feel like its running out of gas. I am going to the track this Sat and am going to try pulling off the air cleaner this time. Any other ideas? Could this cam actually be running out of steam this early? Thanks in advance for your help.

Ty


Last edited by fasthappy on Tue Dec 13, 2011 1:25 pm, edited 1 time in total.

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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 10:35 am 
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Valve springs or fuel......Is my guess =;

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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 11:15 am 
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Fuel. It's running out of gas. What is in the fuel system? :-k

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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 11:21 am 
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Beretta wrote:
Valve springs or fuel......Is my guess =;


thanks barry. can valves float hurting performance without engine damage and noise? Interrresting. I'm going to ck the fuel pressure and volume too.


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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 11:31 am 
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Ken0069 wrote:
Fuel. It's running out of gas. What is in the fuel system? :-k


its a holley blue pump and regulator set at 11psi (yikes, I'll get that turned down) could that have hurt anything? Im going to pull the hose off the carb and see if its pumping freely with no obstructions.


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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 11:35 am 
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Ty you need to check fuel pressure when it lays over down track! Pressure at idle or in your shop doing whatever isn't going to give you the info you need as there's no G forces involved. The highest fuel consumption rate in a run occurs in low gear where the engine is turning it's fastest RPM increase per second. If it's not getting enough delivery there, then it's likely not going to recover down track either until you're off the throttle.

Not saying it couldn't be valve float mind you but usually you get some noise with that.

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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 11:38 am 
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I expect you have a defective fuel gauge, that or it's reading pressure BEFORE the regulator in which case those blue pumps are usually up around 20psig. If you're reading that fuel pressure AFTER the regulator then I suspect you got a gauge that's no good. Holley needle seats won't seal with much over 8psig on'em and certainly not with 11psig.

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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 11:54 am 
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What heads and rocker arms are you running?

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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 12:08 pm 
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Ken0069 wrote:
I expect you have a defective fuel gauge, that or it's reading pressure BEFORE the regulator in which case those blue pumps are usually up around 20psig. If you're reading that fuel pressure AFTER the regulator then I suspect you got a gauge that's no good. Holley needle seats won't seal with much over 8psig on'em and certainly not with 11psig.

The gauge is after the regulator before the carb. I turned the regulator down and the pressure creeps up while Im watching it with the pump on but the car not running. Maybe thats why the thing runs so rich.

There is something I didnt tell you, when I shift into 3rd a little past 5000rpm the car pulls fantastic again. I see a reciept for "performance " springs purchased in 03. The guy I bought it from never raced it, he was into car shows and it didnt get driven much because of the horrible milage. (maybe due to the fuel pressure?) but it's a fairly mild build and it seems to me that even tired springs will rev to 6500rpm. no?


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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 12:15 pm 
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Ken0069 wrote:
Ty you need to check fuel pressure when it lays over down track! Pressure at idle or in your shop doing whatever isn't going to give you the info you need as there's no G forces involved. The highest fuel consumption rate in a run occurs in low gear where the engine is turning it's fastest RPM increase per second. If it's not getting enough delivery there, then it's likely not going to recover down track either until you're off the throttle.

Not saying it couldn't be valve float mind you but usually you get some noise with that.


I guess that means running a gauge into the car for a test?


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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 12:25 pm 
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WR169 wrote:
What heads and rocker arms are you running?


the heads are Canfield (sp?) and the rockers are blue roller rockers but I dont see a reciept for them so I dont know what they are.

this puzzles me- the engine build sheet says "valve lash:Hyd (Intake), Roller Flat (exaust)", but I see reciepts for solid lifters, and a flat tappet cam. Does this make sence to anybody? This probably isnt related to my problem but I thought flat tappet cams were used with solid lifters. Is "valve lash:Hyd" just a misprint?


Last edited by fasthappy on Tue Dec 13, 2011 1:27 pm, edited 1 time in total.

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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 2:17 pm 
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fasthappy wrote:
I guess that means running a gauge into the car for a test?


Well, yeah but most ppl mount them on the cowl outside of the drivers area since it's not NHRA/IHRA legal to have one inside the car unless it's got one of those fuel separator diaphrams in that line.

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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 6:17 pm 
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You really need to sort out the problems with either fuel supply or valve springs or whatever before you go to the track as engine damage is likely to occur.
I suggest you check the valve springs with the correct tool, it can be done on the engine.
Just because you have receipts doesnt always mean thats whats in there. Checking is essential.


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 Post subject: Re: lays over at 5000rpm
 Post Posted: Thu Oct 27, 2011 11:00 pm 
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So you have a cam spec, what is it? Are you sure that's what's in it?


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 Post subject: Re: lays over at 5000rpm
 Post Posted: Fri Oct 28, 2011 12:06 pm 
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Yea, When you buy somebodies car you don't really know whats in it.
I may have bumped into the problem though. Bad fuel regulator, and ignition timing that would first advance and then retard as the rpm increased. I don't like timing advance in a distributor anyway so I drilled a hole and made the timing fixed with a screw. Sure sounds better. I'll try it tomorrow. I should take the time to check everything out but that car has got all the effort it is going to get out of me for awhile.


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