Thinking of getting a new set of ported stock lt1 heads and I am considering getting 2.05 valves in them but have some questions:

1. is there any benefit to going beyond a certain valve size? Someone once told me that when ideally ported stock lt1 heads wind up at 2.00 intake. I know the le3 use 2.05 valves however, so it would appear there is reason to use a larger intake valve. I am wondering what the trade-offs/ benefits are (at diff rpms etc.)

2. If my goal were more a circle track motor where the rpm's are kept relatively low should I be looking at going bigger on valve size or keeping the stock size?

3. what would the cost be for putting 2.05 valves in the head? (just the intake side not exhaust?) i.e. the cost for allowing a 2.05 valve to be installed in a stock lt1 head?

4. can stock ls1 ls2 ls6 valves be made to work in an lt1 head?

 

To big will kill the HP
4.00 bore=2.100
4.030=2.115
This is on a max effort race engine.
2.050 won't hurt but consider the cost vs another set of head's that already have the bigger valves.

 

then you would have to add the price of porting to achive any good results

 

Yep.
After market heads also have larger runners that help big time,even without porting.

 

flow numbers on "out of the box" aftermarket heads are usually less than ported stock

 

I think really smart head guys have equations. But for a standard type of head, the intake should not be larger than a bit more than ~51% of the bore. The issue is valve shrouding. So, if you have a 4.030" bore up to ~2.05. As to how much that is worth v. a 2.00" valve, it depends on the rest of the head. If the throat area is unchanged, there will be no gain.

Rich

 

Yea ,I agree.
Compare them both unported and the greater potential of the aftermarket heads VS the money spent to out flow them with stock heads.

Rich,
This is the rule of thumb I have gone by.It's a little over 51%
4.00 bore=2.100
4.030=2.115
This is on a max effort race engine.

 

Pretty in line with what I have used. Everyone should keep in mind the following.

Valve Area:
2.00" = 3.14^2"
2.05" = 3.30^2" (5% increase)
2.10" = 3.46^2" (10% increase)

However, if nothing else is changed, especially the throat area above the valve, the increased valve size will do little to nothing. If the rest of the port is enlarged in proportion, there will be more flow on a bench but not necessarily in a running engine and there may be a loss due to a "lazy" port. And as the valve gets bigger relative to the bore, there can be an increase in shrouding that more than negates the larger valve size. I'd go with the head porter recommends.

Rich

 

 

Short Answer: 2.05s will likely increase the flow of any head over 2.00. Don't really know how much power you're leaving on the table as that has a lot to do with head design, bore, and cam specs.

 

I built this car http://1994-ta-gt.blogspot.com/2006/...d-history.html for the original owner ( my cousin) in 2000, with 60k on the clock.. at this point, with over 100k on the stock short block, and stock injectors and fuel pump, it still makes 430rwhp with heavily ported Afrs and 2.080 valves.. If you have the right setup it will run great, This car had about 5k in porting on the heads and intake..

 

5k?

 

Not to sound crazy, but I have a set of heavily ported LT1 castings on my 396ci that has slightly larger than 2.10" valves (yes, the seats were replaced) and the porting (TWICE) and seat replacement was less than 3G's

Why the hell would you put 5G's into porting 23 degree heads?!

 

True for peak flow at high lift, but I think the gains aren't even that much since at low lifts (during opening and closing) you're really comparing curtain areas instead:

1.95"= 6.12" x h (-3%)
2.00"= 6.28" x h
2.05"= 6.44" x h (+3%)
2.10"= 6.60" x h (+5%)

No hard numbers reallyl just speculating... but there does seem to be some gains. If your cam selection in both set ups keeps the ideal hp curve below valve-float/red-line I'd be (and was) tempted to go with the larger valves; typically this happens with larger displacements whice can eat up a some cam and lower the red line (making similar hp, with less revs / breakage).

 

At low lift is where the shrouding is the worst. The real gains, if any, occur at high lift.

Rich