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Old 07-08-2005, 02:36 PM   #1
2RS's4US
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Default What to do about Heads

I'm changing my turbo from a GT28r to a 20G and to take full advantage of the 20G I would probably need to have something done with my stock heads...but what? Anyone have any ideas for me?
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Old 07-08-2005, 03:02 PM   #2
Matt Monson
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I say leave them be...
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Old 07-08-2005, 03:04 PM   #3
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But my TWE short block can handle more, just don't want to float the valves
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Old 07-08-2005, 03:28 PM   #4
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then get the valve spring and retainer kit along w/ the cams

i have both and like them a lot
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Old 07-08-2005, 03:44 PM   #5
Matt Monson
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Since you didn't list your set up, based on your current turbo, I assumed you already had springs, and were talking about porting them. Aside from that, even if you block can handle more, Xephyr puts down 400+ uncorrected whp on stock EJ25 heads (with springs) mated to an Ej257 shortblock. If your turbo is big enough, and your tune and intercooling are right, you can make a ridiculous amount of power on stock heads...
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Old 07-09-2005, 02:58 AM   #6
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i'd recomend porting and polishing, 3 angle valve job along with some valvetrain kit ( Titanium Techworks) and a decent sized cam.
I ported/polished, and gasket matched in my class and flowed it. damn things flowed 361 CFM @ .500 lift. i was amazed. so was my instructor. but yeah, im running the Techworks Titanium Valvetrain and Techworks Stage 2 .430 lift cams. makes the turbo happy! i love em. glad i picked em too!
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Old 07-09-2005, 03:10 PM   #7
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An upgraded valve train (meaning springs and retainers) only help you if:

1-You have a way to run the revs way above stock (and you have to deal with valve float)

2-You are running a REALLY big lift cam (not normal on a FI engine) and need the spring help.

Otherwise, you are just padding the vendors pockets or have the "bling" factor.

A P/P may help some at the extreme, but really helps NA compared to FI.
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Old 07-09-2005, 06:51 PM   #8
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u sure about that charlie?
cause what about boost pressure pushing on the valves?
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Old 07-10-2005, 08:40 AM   #9
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Quote:
Originally Posted by White 2.5rs
u sure about that Charlie?
cause what about boost pressure pushing on the valves?
How much boost are you talking about??

Springs are really an issue relating to valve float, not boost pushing the valves open.
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Old 07-10-2005, 01:13 PM   #10
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you dont think its possible to keep the valves held open longer because of 20 psi pushing down ontop of them?
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Old 07-10-2005, 01:33 PM   #11
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You most certainly have to worry about reduced seat pressure with boost on the backside of the valves. It is important to offset the ~1in/sq of valve surface on the back side of the valve that boost pushes on. Thereby lowering the seat pressure effectively by your boost pressure (20psi = -20lbs from seat pressure). The resulting issue is valve float caused by increased boost pressure on the back side of the valve. Manufacturers design valve spring seat pressure to eliminate valve float at high rpm while keeping the valve from wearing both the valve seat and the valve surface at a rate that would require a valve job throughout the engines "life". If you want to know that means - they don't use an stronger spring than they have to keep the valves from wrecking the seal against the seat at the rated max rpm over the life of the engine. This is why cars with radical cam's designed for high rpm use that require higher seat pressures to deal with the longer durations, don't usually expect a long engine life between rebuilds.
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Old 07-10-2005, 02:27 PM   #12
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Joncas: since I don't know the spring pressure with the valve seated, I won't push the argument.
You are correct that the OEM will run as light a spring as they can to reduce parasitic losses (in the valve train) as well as not pounding the valves/valve seats.

As to higher spring pressures for radical cams, it has more to do with trying to keep the valve train in constant contact during very fast cam movements, not to increase the valve/valve seat contact pressure.

White 2.5rs: I would have to guess the OEM springs have a closed seating pressure of ~100lbs, thus with 20psi behind the valve with turbo pressure, there is still ~80lbs of pressure left over to keep the valve closed.

Is it an issue?, I can't say.
I am just trying to add some info as too many people feel they HAVE to have super dooper springs since they have modded their cars.

Maybe someone else that has done this (like Xephyr) will step in and either say:

OEM springs will allow you to burn your valves with increased boost

or

OEM springs work fine with 25psi boost and 7000RPM redlines.
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Old 07-10-2005, 02:34 PM   #13
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You are correct charlie, my point was with a longer duration they must keep the valve contacting the valve train harder so that when the cam lob moves out of the way the valve will close without floating.

I have both the factory springs and the aftermarket twe titanium springs. I'm actually doing a 3 angle valve job and redoing the valve seats right now on my heads in our shop. Just for fun I'll measure the spring pressure to see the difference between stock and aftermarket and post them here. I can't remember what they were when I measured them - I was just looking to make sure they were a matched set. I'm doing a ej257 sohc hybrid right now and my brother "Joncas2" is doing the ej257 dohc ('98rs) hybrid.

It was my understanding from different sources that the stock 1998 dohc springs were good past 15psi where as the stock sohc springs would start to float above 15psi.

Last edited by Joncas; 07-10-2005 at 02:41 PM.
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Old 07-10-2005, 03:07 PM   #14
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From http://www.cobbtuning.com/tech/sohc/page2.html

Valve Spring Pressure (@ seat) 50 lbs
Valve Spring Pressure (@ max lift in/ex) 125/110 lbs
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Old 07-10-2005, 06:41 PM   #15
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yeah charlie the stock springs when i took them out i could compress like half an inch w/ my fingers
the twes dont move


OEM springs work fine with 25psi boost and 7000RPM redlines.

no way lol
valve float hasnt been happening lately on here, or atleast tha tpoeple talk about

go back a year or 2 on the turbod stock ej25s and see the posts about bent valves
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Old 07-11-2005, 04:42 PM   #16
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Charlie,
You know that I agree with your tech 99+% of the time, but on this one I have to beg to differ. The core DOHC EJ25 heads I recently picked up are cores because they were revved to 7000+ on around 20psi and they floated and the valves hit the cylinders. I think on a turbo application, higher tensions springs are good cheap insurance.

And anyone who wants to read about Xephyr's and HOK's and a number of other folks personal experience and opinions on springs look for a thread about whether to use aftermarket cams or not, that Graham put up when he was doing his EJ257 with Ej251 heads. Good relevant info to this disucssion as well since it has much detail on cam timing and whatnot...
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Old 07-11-2005, 05:03 PM   #17
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This is great info. Thanks alot you guys
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