Need some opinions here to help make up my mind...I'll be building a 496, starting as soon as the block is back from the shop. I'll be using a set of 781 heads, they are now completely stock. Im taking them to the machine shop for routine valve job, check them out, and have the guides machined for good seals, and so I can use double springs. My indecision is in the valve size...do I go the extra money and get them machined for 2.19/1.88's, or just leave the stock size valves?? Keep in mind, this is a weekend cruizer, not race but only street, and maybe to the track a couple times just to see what it will do. I have had a couple people tell me that on the street, I will never see the full potential of even the stock valves, so why go bigger. On the other hand, Im upping the cubes and it will need to breath better. But is it necessary? It's probably a couple hundred bucks more for machining, plus I have to buy the intake valves (I have exhaust)Im also going to do a little bowl blending with either choice. What do you guys think? Now is the time to do it if Im going to. Combo is 454 + .060, stroker crank, 6.385 rods, 9.5 or 10.5 pistons (havnt decided yet) with 118cc chambers (mine cc'd at 117 and 118) Howard's Cams solid roller, 250/256 @ .050,655/663, 108LSA, Performer Air Gap w/ Holley 750 for now.

Well, if you consider what a 502 comes with stock, it's a good idea. 502's come stock with the 2.19/1.88's. It's a mater of flowing enough fuel and air to supply what the motor needs, and I would imagine a large cubic inch motor such as yours would need as much fuel and air as a street 502 would. I'm no expert, but am just compairing yours to a similar cubic inch (different stroke) GMPP motor.

I know my teeny weeny little 414 loves those larger valves! :D

Bump.

With the cam your running and 10.5 compression, I would go with at least the 2.19/1.88 valves. That motor is going to need to breath and the stock valve size is pretty small considering the performance sbc heads are running just a slightly smaller valve set up. The smaller valves would keep the velosity high and give more lowend grunt but with a stroker crank, you can afford a little loss of down low torque. Your cam really isn`t a low end cam anyway so may as well get as much hp as you can from your set up. This is just my opinion and I`m sure others will chime in and give you other opinions.

I have the same set-up, running 496 with the 781's. I went with a 2.10 valve in the head because I thought the 2.19 would be shrouded greatly by the 781's combustion chamber. I built my car for low end torque and i think the smaller valve or stock valve size better suited this purpose.

run the bigger valves thats a fairly big cam you will need the extra air and fuel ..

I'd go with a better QUALITY valve (Manley, Milodon, etc.) before I'd go to a larger diameter valve. The flow you can gain from a better design should be sufficient to feed this engine. A good multi-angle valve job and some pro-flow valves would be my call.

Scotch~!

Go with the bigger valves. I didn't and I wish I had. graemlins/clonk.gif

Just make sure the shop that does the work is known for this type of work. I let a small machine shop with little performance experience modify a set of corvette LT1 heads for me and they ruined them. Live and learn.

Troy.

Bigger valves for sure, you'll be glad you did because when you see your first time slip, you will always want more and you will already have this modification taken care of... ;)

You want to know whether to use the larger valves in this car ???? :eek:
LET HER BREATHE DUDE

http://www.chevelles.com/showroom/Johnny_O/johnnyosride1.jpg

Go with the bigger valves, you won't be sorry. If your worried about not reaching the potential of the bigger valves, why would you put a .655 roller in it? The lift of the cam will be wasted without some decent port work, and bigger valves.

Originally posted by jbird:
If your worried about not reaching the potential of the bigger valves, why would you put a .655 roller in it? The lift of the cam will be wasted without some decent port work, and bigger valves. EDIT-There is fellow TCer Chad (can't remember his user name) that runs a 67 SS 396 in the 1/8 mile with a similar spec solid roller and 2.06/1.72 valves.I believe he runs in the low 7's at 94 MPH with his 396

Originally posted by mr 4 speed:
There is fellow TCer Chad (can't remember his user name) that runs a 67 SS 396 in the 1/8 mile with a similar spec solid roller and 2.06/1.72 valves.I believe he runs in the mid 7's at 88 MPH+ with his 396 I wonder what he'd be running if he had the larger valves ??? :D

For what it's worth, I installed the 2.19 intakes but kept the stock 1.72 exhausts on my 290 heads and just concentrated my efforts on working the roof of the exhaust ports as well as providing a smooth transition from the intake port, through the bowls and across the seats. Although I am only running a 408CI bbc now, these same heads are destined for install on the big rat later this year - as they sit. When you look at the big picture, a lot of heads run a 2.30int with a 1.88 exh. That's an 81.7% int/exh ratio which is basically the same as the 2.19/1.72 ratio of 78.5%. When you consider that you can expel virtually all of the cylinder volume through the 5/8" sparkplug hole, it kinda makes you wonder why you would need much larger exhaust valves. One of the keys to making these work well is plenty of exhaust duration on a wider lobe sep but still have the intake installed plenty advanced (ie 112 - 113 LSA w/ 106-108ICL). Doing so places the exhaust opening a little earlier in the power stroke. The exhaust gas gets moving when at a much higher pressure (especially with a roller) and along with this is increased velocity. I am experimenting with this concept now. So far, at least judging by exhaust sound and the fact that I need to do some carb recalibration I think this is accurate. If it ever stops snowing here and finally warms up, we may actually get to find out if it works or not.

274R comp extreme solid roller with small 2.06/1.72 valves and 390 closed chamber heads. Best run to date is in my sig. The heads just went back on after I bent a valve a couple weeks back. #1 exhaust valve siezed in the guide and tagged the piston. The heads have now been completely bowl blended, undercut manley valves, and a much better looking 3 angle valve job. I am hoping for some better numbers this week at Rockigham. I don't think the larger valves would be worth much more than 20-30 HP at best and that may only be .1 in the 1/8th. I am working with 10:1 now and the larger valves would require some valve unshrouding that would drop my compression even more, so I have just opted to keep the small valves for now.

"There is fellow TCer Chad (can't remember his user name) that runs a 67 SS 396 in the 1/8 mile with a similar spec solid roller and 2.06/1.72 valves.I believe he runs in the mid 7's at 88 MPH+ with his 396"

Mid sevens at 88 aren't too impressive to me for a roller cam engine. I would bet he could run about the same numbers with a good solid or even hyd. cam. That being said, my original point is 781's with small valves probably flow as good at .550 lift as they do at .650. So he could probably save money on the roller cam and lifters and spend it somewhere else, like bigger valves. After all, it is a street engine. Just my 2 cents.

Chad,

I made the same mistake about a year ago and went to a local 1/8" mile strip for the first time. It just happened to be a major pro-mod championship weekend. I was literally blown away. I'm building my car now and plan to enjoy it as you enjoy yours now. Your 7.24 works out to approx. 11.36 in the quarter. Very nice graemlins/waving.gif

Originally posted by jbird:
"There is fellow TCer Chad (can't remember his user name) that runs a 67 SS 396 in the 1/8 mile with a similar spec solid roller and 2.06/1.72 valves.I believe he runs in the mid 7's at 88 MPH+ with his 396"

Mid sevens at 88 aren't too impressive to me for a roller cam engine. I would bet he could run about the same numbers with a good solid or even hyd. cam. That being said, my original point is 781's with small valves probably flow as good at .550 lift as they do at .650. So he could probably save money on the roller cam and lifters and spend it somewhere else, like bigger valves. After all, it is a street engine. Just my 2 cents. ...my mistake..he runs 94 MPH with small valves/roller cam..which is impressive smile.gif

...my mistake..he runs 94 MPH with small valves/roller cam..which is impressive

No problem Chris.

Johnny O- If it were me and you could afford the extra cost I would go ahead and put the larger valves in. With those heads you won't have to worry about the valve shrouding issue. On the street you will never feel the difference. At the track the larger valves as I said before may be worth .1-.15. It's all in what you want and how much you can afford.

I obviously have reasons as to why I opted not to go with the larger valves. Compression, piston to valve (unless I had the valves sunk back into where they are now, or the pistons fly cut which is the correct way to fix the problme), and the cost associated with putting the larger valves in and to fix the above problems swayed me away from doing so.

A buddy of mine spent quite some time trying to get his 396 to ET. The quickest he got was 7.25 with 11:1, comp 294 magnum solid flat tappet, and semi open oval ports with the large valves and bowl blending. Car ET'd the same with World square port heads as well. He has a recipe for a killer 396 from a guy in Texas that builds stock and SS engines, but it would require spinning a 396 upwards of 7500 rpm's :eek: . Not for me. He opted to go with a 509 Shafiroff and sees 6.30's now in his 69 Chevelle.

Trying to get a little 396 to ET in a 3700 lb car and keep the rpm's under 6500 is no easy feet, while keeping consistency in mind for bracket racing.

For comparison, again going way back, we ran SSJA (bascially a stock 396/325, auto '67 Chevelle) in the low 11's. Stock 2.06/1.72 valve sizes, solid roller, 5.13's w/ 13/31 slick. Complete interior plus rollcage - this was no lite weight. The smaller valves are not as bad as you would think.

The advantage of the higher lift cams is mainly to create more time for the valve to be open at the point of max flow. You will see guys all the time that will bolt on heads that have great flow at .600 - .650 lift, then cam them with a .650 lift cam. Doesn't do any justice. A head like this needs a .700 lift cam to create the most time for the valve to be open in the range of max flow. A decent 2.19/1.72 head will flow real good at .550. Need a cam with .600 lift to make this work right. Even worse, you will see guys run heads that flow great at .600+ with a .550 lift cam. That absolutely makes no sense. Not that you can't get away with it, but it just doesn't make any sense.

Thanks for the replys so far....I have much to think about. I can see pro's and con's on both sides. Jbird, thanks for the thought on saving me some money, god knows I need it...but I already have the cam and lifters from last year, so the only added expense this season will be whatever valves I buy, and the machine work on the heads. If I do decide to keep the smaller ones, I was going to upgrade to a good brand anyway, as someone mentioned. Texas70, thanks! The hood is going this year too, Im going with a 4" cowl hood. It's a pain to see over. Last year I pulled up in front of my house and parked, and when I left I dragged a garbage bag full of leaves about 200 yards down the street cause I couldnt see it when I left!