049 oval port on 396

[TLK396]

Putting together a 396 with 049 0val ports and was wondering if I should keep the 2.075/1.725 valves, because of the cylinder bore shrouding on the small bore 396. Street/strip 10.5to1, hyd flt tap, 236/246 @.050 .580 lift, single plane, stick shift, 3.73 gear, 3500lb car? Any input would be appreciated. Thanks.

[prairiehotrodder]

whats your compression ratio gonna be with the 049 heads ?

Sorry i see you posted 10.5 -1 . Must be a good sized dome.

[TLK396]

Yes 10.5 to 1. What do you think about the bore shrouding the valves and if there would be any gain in 2.19/1.88 on this combo?

[prairiehotrodder]

I'm not an expert on that combo at all. I know in DV's big block book he talks about notching the tops of the cylinders is worth power. I've never done it though. I bet shrouding has alot to do with the amount of lift you have but i could be wrong.
Brian

[F-BIRD'88]

There is a 2.14" valve for this.

[mag2555]

The question then is will the use of a bigger valve and its reduction for this discussion of let's say 1.5 CCs chamber volume allow the use of that 1.5 CCs of unshrouding work to produce a flow gain somewhere in the lift range of your Cam, but also with no loss of flow you have now in that lift range.

I currently do not have a 049 head to try things out on for you , otherwise I would.

One thing you can count on even now is that with your 2.07" valve if any part of the chamber wall on the plug side comes closer then .414" to the valves perimeter within your Cams lift range then things are shrouded already,especially above .300" lift!

A easy flow gain of 10 cfm over the .100" to .200" lift range can be had by just adding a 29 to 32 degree back cut to your current size 2.07" valves.
Just that 10 additional cfm across 8 cylinders is good for a added 14 hp.

One thing that's certain is that your Exh valve should go up to 1.88" just for the means of far better low lift flow since it will allow a nice fat 3 angle valve job.
This mod also can by you back 1/2 a CC in chamber volume that could then be put to use in unshrouding the Intake valve.

[F-BIRD'88]

There is a 1.84" ex valve for that too.

Probably much better off with a dual plane RPM hi rise vs the single plane Intake on this one.

[TLK396]

Mag2555

Thanks for your insights. I agree with what you are saying on head flow with the larger valve size. What I'm wondering, is the 4.094 bore size going to negate any gains from the larger valves? Even on a 4.25 bore big block there is a pretty good bore shrouding effect on the intake side. On a 396 it's even more significant.

[TLK396]

F-BIRD'88

I agree that a air-gap style dual plane will probably work better on this combo. That will probably happen later. I already have the single plane, so that's what I'm going with for now.

[F-BIRD'88]

Was thinking more along the lines of the rpm intake with full plenum divider VS the air gap for your purpose weight and gears.

[gmrocket]

Mag2555

Thanks for your insights. I agree with what you are saying on head flow with the larger valve size. What I'm wondering, is the 4.094 bore size going to negate any gains from the larger valves? Even on a 4.25 bore big block there is a pretty good bore shrouding effect on the intake side. On a 396 it's even more significant.

you can get away with that valve size. dont worry about the valve shrouding on the cyl wall...very little flow goes that away,,its majority biased to the center of the cyl along the common wall of the port.

you do not need a bigger eg valve than you have..its big enough

[jeff swisher]

I built a .030 over 396 for a buddy with 11:1 compression open chamber oval port heads from his 1969 truck 396.
I stuck 2.19-1.88 valves into it and the comp magnum 280H 230@ .050 it will rev to 7000 rpm very quick.

I kind of wish I had tried the small stock valve size with porting.
I did port the heads with large valves.
I was thinking back old school of my dads buddies 1965 396 that came with 2.19-1.88 valves.

On the other hand i ran 305 2 barrel 1978 heads with 1.74-1.50 valves with the 280H cam and it went 12.51 @ 111 MPH in a 3300 lob nova naturally aspirated in a 355" engine.
Yes those small valves were used and heads were ported.

I do not think you need larger valves if you port them properly unless you are looking for the last tenth or so.

In the sbc engines i do notice a trend with the 280H and intake valve size Used the 1.74-1.50 and 6700rpm was it.
1.84-1.50 and 7000 rpm does well 1.94-1.50 and 7200 rpm is the norm.
Last 2 heads were casting 601.
Pretty small valve though compared to a BBC 2.19"

Do not discount valve weight when making decisions either.

[Tuner]

It's been a lot of years ago, but I liked to put the 2.19 x 1.88 valves in the small port heads because the smaller valve port throat was smaller so when the seats were moved out to the larger radius it left plenty of iron to do a concentric "bowl job" with a generous radius from the seat into the port throat. In the exhaust port particularly, when you start with the small valve head you can more easily make the bowl radius conform to the drawing in the old GM Power Manual.

[tenxal]

Dont worry about the valve shrouding on the cyl wall...very little flow goes that away,,its majority biased to the center of the cyl along the common wall of the port. You do not need a bigger exh valve than you have..its big enough.

Agree 100%.

[econo racer]

I would try the smaller valves 1st don;t be surprised if its faster. Yrs, ago my friend ran the smaller valves on his 396 and that car was fast on 2 nitrous kits. Hardly ever lost Forgot my buddy ran the 305 magnum hyd cam. Ran about 11.1 compression. That motor would not die for many cars and yrs