Valve size???????

[68stcracing]

2 barrel mercruiser intake, 9:8:1 compression, 360 CID max. 5/16 mile dirt oval or smaller -3,100 lbs car.
Max 6600 rpms. 4412 gauge legal carb---VORTEC 906 HEADS, must run 1.250 valve spring

My question,for a short track, 1.94 or 2.02 intake valve?

[ap72]

What head mods can be done? Cam restrictions?

I'm guessing the 2.02" will be the best bet but I wouldn't rely on my guess. The biggest factor comes down to the valve job.

[wil8115]

post up all the head rules.

[wyrmrider]

cam rules
rocker rules
exhaust rules
etc

[groberts101]

2 barrel mercruiser intake, 9:8:1 compression, 360 CID max. 5/16 mile dirt oval or smaller -3,100 lbs car.
Max 6600 rpms. 4412 gauge legal carb---VORTEC 906 HEADS, must run 1.250 valve spring

My question,for a short track, 1.94 or 2.02 intake valve?

there's obviously a lot of turning to be done on the smaller tracks. In that case, 1.94 all the way.. UNLESS you can grind on the castings to fully benefit from the larger valve. I've seen some guys go to a 2.05 valve on bigger bores, but unless you're willing to spend many hours of work on them?.. I myself haven't personally seen or witnessed others make much gain past a 2" valve in these tiny little MCSA ports. I once puttied the hell out of a set(.150" offset rockers) and made just over 280 CFM with a 2" LS valve.

I've also ground a 2.02" valve down to 1.98" to achieve good balance within as-cast restrictions as well. Seat form is essential to get the most bang for your time spent here though. No tulip shapes.. the flatter the better. 5 angle VJ with a shallower 85-86 degree bottom transitional cut works well to open the short side a bit better and remove all the nastiest transitions. This helps average CFM and picks up the midrange torque.

Keep in mind that the floor speed is extremely narrow and therefore "fast" on these castings in factory form during higher lifts.. and bigger valves don't necessarily help the issue. Also.. don;t go overboard on the exhaust port if you are allowed to grind any metal away. My very first Vortec port job was on an old V6 motor in a turbo S10 deal. Over 240 cfm with 1.54 valve and no pipe. I was just about floored since all I had done was pretty much basic stuff, streamlined and profiled guide, polished it to a mirror(yeah, yeah, I know. lol), made a nicely shaped d-port without increasing area at the sides and floor much beyond the need to polish it, opened the throat to 90% of the valve diameter, and put a nice radius over and under it. Pretty great results for a turbo deal.. but not so much if it had been a street cammed 350 with mild compression. Lesson learned. Good luck with it.

PS. If you can convert over to 8mm LS valves on this deal?.. WELL worth the extra cash outlay and Ferrea has some good light designs. I like the polished Manley Nexteks in the 1.25" size(around 150 - 160 lbs/seat). Cheap and easy to sleeve the guides down to 8mm size too.

[F-BIRD'88]

Just installing a 2.02 valve without porting reduces flow on this head. Without the porting it don't work.

[68stcracing]

906 vortecs
no rules on valve size, or weight.
1.250 valve spring 5 full coils
no titanium
23 degree angle
porting and polishing allowed.
solid cam and lifters, flat tappet(no mushroom type) stamped type rocker arm(no rollers at all)
1 5/8 headers with open exhaust
4.040 x 3.480 bore and stroke
hoping to use the existing valves if possible but if I can gain both hp and tq by going with a larger valve(2.02/1.55-1.60)
Plan to run a Jones cam, and lifters

[wyrmrider]

Beehives or tapered springs legal?
some rules
Big Buck porting allowed, hollow stem valves etc
do they allow 1.6 or 1.65 stamped rockers
how about BBC rockers?
with the rev limit maybe the weight savings of the light valves is not worth it
Work with Mike on this one edm the lifters if he goes with a high acceleration profile

[groberts101]

906 vortecs
no rules on valve size, or weight.
1.250 valve spring 5 full coils
no titanium
23 degree angle
porting and polishing allowed.
solid cam and lifters, flat tappet(no mushroom type) stamped type rocker arm(no rollers at all)
1 5/8 headers with open exhaust
4.040 x 3.480 bore and stroke
hoping to use the existing valves if possible but if I can gain both hp and tq by going with a larger valve(2.02/1.55-1.60)
Plan to run a Jones cam, and lifters

ok, I'll play.

2" valve size WILL require moderate to heavy amounts of floor speed mediation. Once you get the VJ roughed in before the port work start.. use the pitot and you'll see exactly what I mean here. I believe that I still have all my printouts from these heads(V6's and V8's) piled somewhere in the office and I can dig if you need to make use of them. Ton's of hi-res pic's too but they're located on my downed computer. Basically a torque and emissions style head.. with a very fast floor, especially beyond factory valve sizes. So, simply installing the larger valve just causes this little overly constricted MCSA port to stall out quicker than it's typical .520" max lift range. BUT.. even if you didn't touch this casting with a grinder.. you WILL pick up low to mid-lift flow all the way across the board with a nice 5 angle(or greater) valve-job and can run a slightly less aggressively ramped cam/rocker ratio to maximize the deal. Not saying you should do that because 70 cfm at just .100" valve lift is entirely possible if you get it closer to fully optimized. Unfortunately, this creates more back-flow potential and you need to take that into consideration during cam choice if low-lift flow is important to you. And for rpm or lift limited applications like this?.. I'd think it should be relevant. And despite the bigger and slightly heavier valves.. this extra area under the curve potentially allows you to get by with slightly less spring to free up.. or at least not have to consume any more power than necessary by mandating a stiffer spring requirement.

Beehives springs with 8mm valves and their tiny little featherweight retainers will easily allow less spring pressure and free some extra power while still maintaining control well past your max rpm rule. Not sure about the number of coils on those though.. have a set I can look at/count if need be. Online pic's should get you close enough.. or maybe ask others in your race class if they are legal to use? Otherwise.. Manley Nextek's(spec'd for an LS1 1.25" sprung application, IIRC) with a +.100 valve and +.050" keeper will work well too. The Manley thinly profiled tool steel retainers are not very heavy designs for those springs either. Another helpful tip.. pay the few extra bucks to get the polished/stress relieved versions and they will hold pressure/live much longer.

Another word of caution here.. DO NOT install a 1.60 valve in these heads. Of course many do, but as I mentioned earlier.. it's VERY EASY to go overboard with exhaust flow on these heads and 1.54/1.55" is all that little header will ever need anyways. This keeps velocity up better coming off the port to avoid as much lift/duration split. Get this side of the head closer to optimized and you can even run a reverse split cam and/or less rocker ratio. Free's up more power and the motor still runs well past peak.

I won't have much more time to be fooling about and playing "expert columnist" on any forums here shortly(work + projects), but you can PM me for contact info to maybe better lay all this stuff out for you and possibly get you some emailed scans of port dimensions, speeds and flow numbers if I can dig them out of the piles.

[wyrmrider]

won't have much more time to be fooling about and playing "expert columnist" on any forums here shortly(work + projects)
always enjoyed your posts
good luck on your "projects"

[groberts101]

won't have much more time to be fooling about and playing "expert columnist" on any forums here shortly(work + projects)
always enjoyed your posts
good luck on your "projects"

lol.. won't go far and I'll probably be back to bug you guys again next fall. Will probably pop back in to share TQ/HP results for my little RHS headed stock bottom ended SBF too. The car("71 Comet GT) will surely look a bit clapped out(solid looking "20 footer").. but the little motor will buzz right up there with some of the little imports. Really happy to be getting back to my roots with the SBF stuff since that's what I cut my teeth on.

later guys

[68stcracing]

I was looking at the weight difference from 1.94 to 2.02, and is there really any major gain to be had by opening it up. I probably won't run anything beyond .530 lift with possibly a 1.6 rocker on the intake but staying 1.5 on the exhaust per Jones Cams Recommendation. I was only going to smooth out any rough edges in the exhaust port, and a gradual opening of the port. Is it better to keep the exhaust port shape for this type of low rpm application?