Strange problem

Camarob859 · 06-26-2011, 11:04 PM

Hi all
I have an issue with my car, runs up to about 5 to 5500 rpm in first gear and kinda quits making power, i shift then runs fine to 6000 in both second and third wondering if any of you have any idea as to where i need to start digging to find the problem ???

Jody Lang · 06-27-2011, 12:20 AM

I would guess valve spring pressure. Springs can't keep up in low gear being it is RPMing quicker in 1st than it is in 2nd or 3rd.

What motor combination do you run?

ss3011 · 06-27-2011, 05:59 PM

What transmission are you running ? I have experienced something similar with three speed trannies. Sometimes at the top of 1st gear, the high gear clutch will start to drag, and the car feels like it's running out of power, but when you shift to 2nd, that drum stops spinning, and the drag goes away. There is an easy fix for this, by drilling a small vent hole in the high gear clutch drum.

X-TECH MAN · 06-27-2011, 07:00 PM

Quote:

Originally Posted by Jody Lang

I would guess valve spring pressure. Springs can't keep up in low gear being it is RPMing quicker in 1st than it is in 2nd or 3rd.

What motor combination do you run?

Not to argue with Jody but I disagree with his solution. Im no expert but I always thought that if it was valve springs the problem would show up more in 2nd and high gear. The RPM come so fast that the engine swings thru the valve float before it becomes a problem at the shift point but the slower RPM swing in the upper gears causes it to show up more in the upper gear ranges. This is just backwards from what Jody said. This showed up in the old Jr. stock days for me with OEM valve spring pressures and the early days after NHRA changed the cam and valve spring rules before the "Shubeck" type lifters came onto the scene allowing the crazy valve spring pressures of today. Anyone who builds engines have a comment? Adger are you out there? Again not to argue about it but just what I have experienced.

Camarob859 · 06-27-2011, 08:05 PM

im running a th350 and its not a stock eliminator combo was just wanting some outside input

goinbroke2 · 06-28-2011, 12:17 PM

Quote:

Originally Posted by X-TECH MAN

Not to argue with Jody but I disagree with his solution. Im no expert but I always thought that if it was valve springs the problem would show up more in 2nd and high gear. The RPM come so fast that the engine swings thru the valve float before it becomes a problem at the shift point but the slower RPM swing in the upper gears causes it to show up more in the upper gear ranges. This is just backwards from what Jody said. This showed up in the old Jr. stock days for me with OEM valve spring pressures and the early days after NHRA changed the cam and valve spring rules before the "Shubeck" type lifters came onto the scene allowing the crazy valve spring pressures of today. Anyone who builds engines have a comment? Adger are you out there? Again not to argue about it but just what I have experienced.

I too experienced valve float in 2/3 but in 1st (or pissed off in neutral) would spin to 6700.
Wrong springs came with cam. Spring pressure was correct for those springs, but the cam called for a bigger spring. The clue (after chasing EVERYTHING but springs because they were "new" and "showing correct") was when I added a .030 shim and picked up 700-900rpm before nosing over. Threw on an OLD set of much bigger springs and the bitch went to 7000 no problem!

So, what is it? Need more info really. One thing I would ask is what size of fuel line and how much pressure does the pump push...actually..the pump is pushing fuel not pulling from the front right?
Here's my thinking; If you have replaced the factory line with a bigger 1/2" fuel line and and you have a smaller/weaker pump, even if you have the "proper psi at idle" when you leave the line the weight of the fuel in the line is going against the fuel trying to be pumped forward basically stopping flow. Once your into 2nd the G's drop off and the pump can overcome the weight of the fuel.
But, not knowing carb/pump/line size/if you wheelstand/etc it's a shot in the dark.
So, one check is watch your fuel pressure when you leave the line and see if it snaps down then slowly creeps up.

Camarob859 · 06-29-2011, 09:18 AM

its a holley 750, magna fuel 275 and ive got half inch line, whatever it is , is very related to heat almost wondering if 7.5 psi of fule pressure isnt enough for a 9 to 10000 adjusted altitude day or maybe the line is too close to the header, i did pull the plugs yesterday and they are fouled, could to much jet cause this?

06-26-2011, 11:04 PM	#1
Camarob859 Junior Member Join Date: Jul 2010 Posts: 52 Likes: 4 Liked 8 Times in 3 Posts	Strange problem Hi all I have an issue with my car, runs up to about 5 to 5500 rpm in first gear and kinda quits making power, i shift then runs fine to 6000 in both second and third wondering if any of you have any idea as to where i need to start digging to find the problem ???

06-27-2011, 12:20 AM	#2
Jody Lang Member Join Date: Mar 2002 Posts: 299 Likes: 28 Liked 81 Times in 25 Posts	Re: Strange problem I would guess valve spring pressure. Springs can't keep up in low gear being it is RPMing quicker in 1st than it is in 2nd or 3rd. What motor combination do you run?

06-27-2011, 05:59 PM	#3
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 885 Likes: 63 Liked 221 Times in 102 Posts	Re: Strange problem What transmission are you running ? I have experienced something similar with three speed trannies. Sometimes at the top of 1st gear, the high gear clutch will start to drag, and the car feels like it's running out of power, but when you shift to 2nd, that drum stops spinning, and the drag goes away. There is an easy fix for this, by drilling a small vent hole in the high gear clutch drum.

06-27-2011, 08:05 PM	#5
Camarob859 Junior Member Join Date: Jul 2010 Posts: 52 Likes: 4 Liked 8 Times in 3 Posts	Re: Strange problem im running a th350 and its not a stock eliminator combo was just wanting some outside input

06-29-2011, 09:18 AM	#7
Camarob859 Junior Member Join Date: Jul 2010 Posts: 52 Likes: 4 Liked 8 Times in 3 Posts	Re: Strange problem its a holley 750, magna fuel 275 and ive got half inch line, whatever it is , is very related to heat almost wondering if 7.5 psi of fule pressure isnt enough for a 9 to 10000 adjusted altitude day or maybe the line is too close to the header, i did pull the plugs yesterday and they are fouled, could to much jet cause this?