Valve float on a datalog

Kevin Panzino · 10-04-2013, 05:31 PM

100 lbs on the seat is not even remotely enough!!!!!!!
And your 12.5 lbs of boost is taking off 39 lbs, so you are left with 61 lbs of seat pressure only!!! Float city!!!!!!!

Mike Taylor 3601 · 10-04-2013, 09:39 PM

We typically run 140 seat 400/425 open on street N/A hyd roller and you need to raise that,coming up with spring probably won't be big deal,the problem is when you start going over that whether the lifters will handle it. When start going over 140/400-425 a lot of lifters will start compressing,there are lifters that will take more pressure,but don't think stock ones will take it.

You'll probably need 180 ish seat 450-475 open.
Don't know all info that need to know,these are just ballpark recommendations

Mike Taylor 3601

Adger Smith · 10-05-2013, 12:38 AM

With a low lift like you have and the low spring installed ht. you need a spring that has a lot more seat, like 200+ and a rate that is very tough ending up with at least 550 to 600 open. That may be hard to find. Then when you get enough spring you need a real stiff pushrod. Those engines have a nice short pushrod with good angles. I would use at least a .125 wall and if it will fit a 3/8 to 1/2 double taper .150 wall pushrod. You need to remember that a boosted engine has trouble opening the valves. The pushrods in an A/fuel engine that I've helped with look like drillpipe.
BTW those are just a good starting point for spring pressure. You could need more because of cam profile and valve/valve gear weight.

Chris Hill · 10-07-2013, 03:52 PM

Could you share more info on your car and engine combo?

I have an 05 Magnum with 5.7 hemi and have thought about forced induction of some kind. But the computer controls intimidate me some.

Are you using a factory or aftermarket computer?

Also, how reliable is the transmission and rear end when more power is made?

dart440 · 10-07-2013, 08:18 PM

Chris:
It's a '73 Dart Swinger 5.7 with a 76 mm turbo. Powerglide with 8 3/4 Mopar diff. I use a MegaSquirt ver. 3x. The set-up and tuning has been difficult, but hopefully will pay off. The Megasquirt worked great with my old motor, and for thousands of other folks too (www.msefi.com) I assume you mean the factory trans and diff behind your Magnum. If so, the trans can be beefed up considerably. The diff., however has its limits. the heavy hitters swap in a 8.8 ford center section ($$$). Check out www.lxforums.com for more info.

Dave

10-04-2013, 05:31 PM	#1
Kevin Panzino Senior Member Join Date: Oct 2002 Location: Pittsburgh Posts: 583 Likes: 304 Liked 776 Times in 142 Posts	Re: Valve float on a datalog 100 lbs on the seat is not even remotely enough!!!!!!! And your 12.5 lbs of boost is taking off 39 lbs, so you are left with 61 lbs of seat pressure only!!! Float city!!!!!!!

10-04-2013, 09:39 PM	#2
Mike Taylor 3601 VIP Member Join Date: Oct 2008 Location: Somerset,Ky Posts: 1,374 Likes: 359 Liked 308 Times in 103 Posts	Re: Valve float on a datalog We typically run 140 seat 400/425 open on street N/A hyd roller and you need to raise that,coming up with spring probably won't be big deal,the problem is when you start going over that whether the lifters will handle it. When start going over 140/400-425 a lot of lifters will start compressing,there are lifters that will take more pressure,but don't think stock ones will take it. You'll probably need 180 ish seat 450-475 open. Don't know all info that need to know,these are just ballpark recommendations Mike Taylor 3601

10-05-2013, 12:38 AM	#3
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: Valve float on a datalog With a low lift like you have and the low spring installed ht. you need a spring that has a lot more seat, like 200+ and a rate that is very tough ending up with at least 550 to 600 open. That may be hard to find. Then when you get enough spring you need a real stiff pushrod. Those engines have a nice short pushrod with good angles. I would use at least a .125 wall and if it will fit a 3/8 to 1/2 double taper .150 wall pushrod. You need to remember that a boosted engine has trouble opening the valves. The pushrods in an A/fuel engine that I've helped with look like drillpipe. BTW those are just a good starting point for spring pressure. You could need more because of cam profile and valve/valve gear weight. __________________ Adger Smith (Former SS) Last edited by Adger Smith; 10-05-2013 at 12:40 AM. Reason: sp

10-07-2013, 03:52 PM	#4
Chris Hill Senior Member Join Date: Jan 2002 Posts: 655 Likes: 8 Liked 244 Times in 26 Posts	Re: Valve float on a datalog Could you share more info on your car and engine combo? I have an 05 Magnum with 5.7 hemi and have thought about forced induction of some kind. But the computer controls intimidate me some. Are you using a factory or aftermarket computer? Also, how reliable is the transmission and rear end when more power is made? __________________ Chris Hill https://ihmusedparts.com

10-07-2013, 08:18 PM	#5
dart440 Junior Member Join Date: Sep 2012 Posts: 7 Likes: 0 Liked 0 Times in 0 Posts	Re: Valve float on a datalog Chris: It's a '73 Dart Swinger 5.7 with a 76 mm turbo. Powerglide with 8 3/4 Mopar diff. I use a MegaSquirt ver. 3x. The set-up and tuning has been difficult, but hopefully will pay off. The Megasquirt worked great with my old motor, and for thousands of other folks too (www.msefi.com) I assume you mean the factory trans and diff behind your Magnum. If so, the trans can be beefed up considerably. The diff., however has its limits. the heavy hitters swap in a 8.8 ford center section ($$$). Check out www.lxforums.com for more info. Dave