dereknkathy

so i got this L29 i am gonna try to turn from lopo to medpo. apparently they can barely handle .500 lift. i remove spring and valve seal and see .700 valve travel. so what are we lookinjg at? .1 for the seal and .1 for clearance? so if i wanna go with 550 or so guides need to be shortened about .50 so mebbe .100 tops? also they say to remove rotators and replace with .300 shim same thickness as rotator. i would think a very thin spring seat and longer springs would make more sense. .25 to .3 extra space to reduce coil bind and compressing the spring less percentage of it's overall length. if this was a good idea, it would be in common practice. what is the flaw in my thinking? i am thinking 500 efi cam. what are those orig heads.? iron rectangle ports?

MILD THUNDER

iTrader: (3)

I'm somewhat confused Derek. What do you mean by cutting down the guides

sutphen 30

its common practice when going to a seal of .531" id to cut the guide down .300".gives you a better seal and room for higher lift cams.

Quick2500

+0.100 stems is a very easy way... Make sure you get new springs to correct the seat and # @ x lift pressure. You'll also need to get pushrods made to the correct length.

dereknkathy

aren't valve guides machined shorter for higher lift? or is longer valve stems which means new valves the only way to increase valve travel?

TooLateVTEC

iTrader: (1)

The valve guides can be machined down for clearance, correct.

How much before its a problem IDK, but its possible and a helluva lot cheaper than buying new valves.

tpabayflyer

I have some data from a Chevelle website that shows flow data from the vortec heads.... Before porting and after porting with removal of the ski jump in the intake ports...... End result is don't waste your time building the vortec heads as they just don't flow well for any kind of performance usage. About a 4% gain in flow and I don't think the intakes even went above about 250cfm. A larger cam will give you no extra power with these heads as I think the flow did not increase hardly at all with valve lift above .530........ I have them on my 7.4 wellcraft cruiser and I estimate 400 HP. I installed larger valves and removed the valve rotators and used the 502 Mag hyd roller cam .510/.540 lift cam. No extra machining needed as this cam came as original eq on factory motors. My stock motor was 310HP and I have some excellent mid range torque and it planes very easy. Great torque motor and these heads excel for that. I never really exceed 3,700 rpm and 4,400 rpm is all I get with a 24P B3 drive...... I would look at the Dart iron eagles as they are reasonably priced and work well. My Donzi with ported rect port heads and matching cam and decent exhaust makes so much more power than the vortec heads it's ridiculous!

dereknkathy

i figured you would weigh in eventually. i think you lost a little flow shoehorning those big valves in these little chambers. i am leaving the gen 6 bottom end alone. with flat pistons the head choices are few. i have a set of 366 truck heads, 1 7/8ths intake valves. yes, the size of real exhaust valves. 100 cc chambers though. old 396 bathtub heads-just as flow restrictive as these heads till you unshroud the intakes by about another 15 cc's of metal. back to 8 to 1. edelbrock alum rpm 100 cc chamber heads. if i am gonna spend 2k on heads i will rethink my pistons...next engine. i have seen dyno results aroiund 440 to 450 hp with L29 heads. all i am hoping for, not really expecting. this Pantera i just got came with a decent set of long riser gil exhausts. so i am rethinking the LSA i can maybe get away with. so unless somebody talks me out of it, i am considering the ZZ502 cam. that 502 mag cam is 480 lift 115.5 LSA. not a lot hotter than the truck cam that is coming out. i am pretty sure GM designed that cam to run with their stock lifters. so just trying to get info on valve to guide clearance and appropriate springs.

tpabayflyer

OK... I would think you should meet your goal but I would not spend much time at all on the heads as the gains will be very little....... I used the 502 HO cam bought from here:

http://paceperformance.com/search.html#!sq%3D24502611

No machining required to the heads and will use all your stock valvetrain parts. I don't think you will get any more gins in power by going with any more lift or duration. The cam actually sounds pretty good! When I flush my wellcraft n the lift and the prop is out of the water it has a bit of a bark! You can even use your old roller lifters if they are in good shape. Here are the cam specs........

454HO/502HO cam
GM PART # 24502611
dur @ 0.050 - 211/230
Lift .510/.540

Lots of good reading right here:

http://www.chevelles.com/forums/arch.../t-246505.html

Overall I am happy with my Vortec heads and upgraded cam..... I was able to use all my stock valvetrain and pushrods etc, to keep costs down. Keep us posted on the build........ TBF

dereknkathy

oh, the 502 HO. actually decent specs. 112 LCA is the limit for stock exhausts. your prev post said 502 mag cam. that is a lot milder. 115.5 LCA 480ish lift. you removed the ski jump? i thought if you remove it all you hit water. positive seals or umbrella? did you do without on the exhausts? just got back from new york with my pantera, but that is for another thread...we may be moving down your way in the next year or 3.