Motor won't rev over 5200-5300rpm... WTF???

[bison]

You know... I have a theory about this...

With all the good parts and technology hitting the streets these days... guys are pushing aftermarket parts to the extreme. Better turbos, alky systems, nitrous, etc... all mean more boost. Also, cam profiles are getting innovative and more agressive.

Something I often think about...
When running 30psi boost, this means there is 30psi of pressure PUSHING on the backside of the intake valve... trying to force it open, much like the air pressure you put in the cylinder to keep the valves closed during a spring change.
I think that 30psi of boost pressure, somewhat subtracts from the advertised/installed seat pressures we see on valvesprings.
This means... a spring with 160lbs on the seat... will have 160lbs of seat pressure at an idle or zero boost... but when we are on the throttle and have 30psi in the intake... you may only see 130lbs worth of pressure on the seat. This won't affect the open pressures, but it may cause the valves to bounce when they close.

I'd love to see some testing done with a pressurized intake port... just to see the effects on a springs actual seat pressure. With enough pressure, you can eventually overcome the spring entirely... and blow the valve right off the seat.

Just something to think about.

Look like 853 in the pic. Id be more concerned about the exhaust side with a small 3 bolt and high hp as far as springs go. The backpressure will hit 70+psi at 800+hp if running a GTQ/3 bolt. Then you really need some strong springs.

 

[wbrophy]

I have both lifters and they look like 853's. That is the type of snap ring that is used in my 853's.

 

[QUIP'6']

You know... I have a theory about this...

With all the good parts and technology hitting the streets these days... guys are pushing aftermarket parts to the extreme. Better turbos, alky systems, nitrous, etc... all mean more boost. Also, cam profiles are getting innovative and more agressive.

Something I often think about...
When running 30psi boost, this means there is 30psi of pressure PUSHING on the backside of the intake valve... trying to force it open, much like the air pressure you put in the cylinder to keep the valves closed during a spring change.
I think that 30psi of boost pressure, somewhat subtracts from the advertised/installed seat pressures we see on valvesprings.
This means... a spring with 160lbs on the seat... will have 160lbs of seat pressure at an idle or zero boost... but when we are on the throttle and have 30psi in the intake... you may only see 130lbs worth of pressure on the seat. This won't affect the open pressures, but it may cause the valves to bounce when they close.

I'd love to see some testing done with a pressurized intake port... just to see the effects on a springs actual seat pressure. With enough pressure, you can eventually overcome the spring entirely... and blow the valve right off the seat.

Just something to think about.

thats funny you bring this up. i was just talking about that same thing this morning because yesterday i turned my boost to 15 and the timing to 20/18 and shut off alky and the car screams it does have a tiny bit of sputter at the top of each gear but can hardly tell. i put on regular tires and it blazes them at 60 mph. when i put the timing to 23/21 and the boost to 24 it sputters bad and lays over. the numbers get rich like 850 to 870 when it sputters. i guess it is fuel building up in the cylinders. so maybe the increase in boost and timing is lowering my already weak spring pressure forcing the valve open from the backside. i am down to this conclusion since i went over every possible scenario. i hope you got your issue fixed. i am going roller in the winter

 

[jasjamz]

I'm finising up my motor as we speak. It's going in the car tonight. It will be running tomorrow. I have the exact same set up minus the aluiminum heads. Everything has been switched over from my old motor. I will let you know how it runs real soon.

Hope all goes well. Hey that turbo is worng for you application, pass it over to me so you can get a billet wheel to go with the rest of your "Bling"

As far as the 30psi of boost being pressure on the back of the valve...You bring up good question. I hope the weather gets better there so you can test your car out.

 

[quickt]

Maybe I missed it somewhere in the 7 pages. Did you try unplugging the knock sensor?

 

[yullose]

Maybe I missed it somewhere in the 7 pages. Did you try unplugging the knock sensor?

Yep, several times and it made no difference.

I have the valvesprings all on now... so it's just a matter of taking it for a test drive...

I 'gotta run out and pick up a couple trannys I found cheap... (BOP TH400's $75 for both) so when I get back I'll take the GN for a ride and report back with results.

 

[mjdwyer23]

hitting the track on the way home?

 

[Jerryl]

.......... Something I often think about...
When running 30psi boost, this means there is 30psi of pressure PUSHING on the backside of the intake valve... trying to force it open, much like the air pressure you put in the cylinder to keep the valves closed during a spring change.
I think that 30psi of boost pressure, somewhat subtracts from the advertised/installed seat pressures we see on valvesprings.
This means... a spring with 160lbs on the seat... will have 160lbs of seat pressure at an idle or zero boost... but when we are on the throttle and have 30psi in the intake... you may only see 130lbs worth of pressure on the seat. This won't affect the open pressures, but it may cause the valves to bounce when they close. ............

Your theory is correct.
A 1.77 valve has approximate area that boost pressure is pushing on of 2.1-2.2 SqIn. At 20psi boost, that is about 40 lbs force. (What's a few lbs between friends? :tongue
On the exh side it is about 66 lbs. Ass-U-Ming 2:1 BP ratio.

 

[davinci50]

Must be running good, He's not back yet. let us know Art.

 

[yullose]

Sorry it took so long to update... I had to pick up a couple TH400's this afternoon, then got roped in to a plumbing project here at home.

I just got back from a nice long ride in the GN.

IT'S FIXED and it runs like a banshee...

I still have a little false KR that makes it chchch at the gear change, but it smooths out as the KR dissipates, allowing the timing to ramp back in and the RPM's go up.

I purposely held it in low gear on the first run and it spun clean as a whistle right to 6000.

I don't have the WB sensor hooked up yet... but that will be next. I'll grab a new one from Autozone tomorrow and get everything calibrated for another couple abusive runs tomorrow night.


I don't even bother trying to build boost to launch it... I have enough trouble with tirespin leaving from a dead idle now. It will walk out about 100ft and start hazing the tires.
The difference in power now is like night and day.

I think I will need to get one of these TH400's put together sooner, than later... I thought I felt my trans slipping at the gear change now...
I made a couple hard runs, but didn't get them all recorded. It's hard as hell to see the laptop on a dark country road with no domelight.

Here's the Powerlogger run I just made, holding it in 1st to 6000.

 

[DailyDrifter]

Thats great man, good to hear.

 

[vacuum 6]

Great its fixed!!!!!!!! So without reading thru 7 pages...the issue was the trans?

 

[DCVING 6]

Great its fixed!!!!!!!! So without reading thru 7 pages...the issue was the trans?

valve springs

 

[turbolou]

Reply

Glad to hear its fixed but I think that is an extreem lift to be useing hyd lifters & have its limitations I would convert to solids useing the correct springs & get the most out of the combination.

 

[yullose]

Glad to hear its fixed but I think that is an extreem lift to be useing hyd lifters & have its limitations I would convert to solids useing the correct springs & get the most out of the combination.

I pulled the 1.65 rockers out and replaced them with 1.55's to try and help slow the valves down a little.

I think a solid roller upgrade will happen over the Winter though...

I've never had a problem running solid rollers... just don't like the short valvespring life when running them on the street.

 

[pajo]

cam

Good job - little persistance pays off in a long run - now how do you like the 214 cam .?

 

[yullose]

Good job - little persistance pays off in a long run - now how do you like the 214 cam .?

It idles like a stock motor... I could probably do without all the lift though...
With the short duration/high-lift combination, it needs alot of valvespring to keep the wheels on the lobes.

In hindsight, I probably should have gone with more duration and less lift... maybe 224/224 with .480-.520 lift.

I still think I may be pushing my luck with these springs and heavy retainers.

I will probably go to a solid roller or at least a set of beehives and Ti retainers in the coming months.
A little research also found that the Crower retainers I have are +.150 installed heights... so at least I have an idea what to look for when shopping for new springs and retainers.

 

[Alky V6]

Solid rollers. Now your talking.

 

[pajo]

how

how does the car feel like above 5000 grand ..

 

[yullose]

how does the car feel like above 5000 grand ..

It want's to rev up there, no question about it... it felt like it was still pulling hard at 6000...