Some interesting intake changes!

[Anonymous]

Not to start a war....but, since I also own a MOPAR, I study those hopups, too .... and one of those hopups fit our sixes!

One that's VERY applicable to these sixes is the 30-degree intake valve angles that have become standard on drag racing engines of all kinds, popularized by the MOPAR crowd. This angle is possible on our sixes (at least, as I measured it on the late-model head) because the valve size is right and the intake tract just happens to be at the right angles!

What this is about, for the uninitiated, is this: changing the face of the valve and valve seat to 30 degrees at the sealing face (instead of the standard 44/45 degrees) causes a LARGE flow increase at the beginning of the intake stroke. This results in the same effect as adding (in a MOPAR 360 engine) 12 degrees of intake valve duration, but without losing the compression that a long intake duration would cause.

The tests I saw showed 15% increase in flow at the point where the valve is open .030" to .080" on it's way open (and closed). The flow is only increased about 5% when the valve is fully open (.410" lift on this engine), but the extra from the beginning and end are still there.

The dyno results after reworking the valve seats are undeniable and repeatable on the 318 and 400 engines as well. Now, I want this on MY 200.

To get it, the intake valve must be back-cut, then the seats recut to 45/30/15 degrees instead of the stock 60/45/30. This will require a little blending work in the chamber, which will increase the volume, so it's gotta be milled again.. :roll: :roll:

I gotta find me another head. :idea:

 

[Anonymous]

the Cummins 855 14L iesels use a 30 degree seat and valve face angle. I wonder if they were thinkin when they designed that motor...

 

[MustangSix]

I recall Pontiac V8's using a 30 degree seat on the intake valve as well.

 

[addo]

So did the '68-70 Ford 221 sixes here.

 

[Anonymous]

If I can do it without violating copyrights, I'll try to post the specifics here.

 

[Anonymous]

Hmm...interesting, but would it apply to the big sixes? Methinks it's time for some homework.

Edit: 30+ pages of results from google and no such luck. Is it possible that it's never been looked up?

 

[sefus]

hey mark, im a fellow mopar owner and just finishing up a 360 dart, after its done i get to go crazy on my i6 mustang. so this sounds like quite a bit of work, is it a common change that you could tell your head shop to do and they'd know exactly what you'd need?

 

[Anonymous]

Got the gears a turnin in my head now, why is there only 30 and 45 deg seats? Only proablem I see with 30s is for the same valve and port diameter there is less contact between the two for sealing and heat transfer. Maybe use 30 for the intakes and 45 for the exhausts?
As in build a head up using stainless 30 deg backcut intakes of stock size and oversized 45 deg exhuasts.
I think there might be some advantages to a hot running intake valve for fuel atomization perposes.
Anybody know of another angle used?

 

[82F100]

I remember reading an article in Circle Track magazine awhi8le back on increasing head flow on restricted class engines.I'll try to find the issue and the article,The article stuck in my mind because they talked about back cutting on 1.85 size intakes etc and believe there was some flow #'s aswell.If you haven't looked at the roundy round mags lately it might be a good idea they have some very good tech articles in reguards to engine performance that can be universal to help our sixes.

 

[Anonymous]

Hey sefus;
The article was about mod-ing the 360 engine, exactly. I have one of these in my motorhome, hence the interest.
The geometry in the 200 I6 fits the profile, less the natural shrouding of this engine. However, since the shrouding is there whether we use the 30 degrees or not, it's bound to improve the flow situation. De-shrouding these engines is possible, but at cost of lost compression ratio unless the head is milled to make it back up.
Adding to that the low-RPM nature of these sixes, and this is like the perfect fit for finding power when we need it without losing MPG when we also need it.
Let me go find the magazines: I'll post the dates of the 2 issues in a few minutes.
--Okay, found it - Jan. (intake) and Feb. (exhaust) 2000 issues of Mopar Muscle. They subbed in a 30-degree 2.20" valve where the stock 1.88" 45-degree used to be (cutting the seats to match), then tested at only .250" lift. At this low lift, the 2.02" size should have minimal impact because the cross-sectional change isn't much. BUT - they flowed 20 CFM better, from 142 to 162 cfm at .250" lift. The other porting actions they took were to improve the high-RPM breathing, which we can mostly ignore in this case, as we can't easily reach the 6000 RPM they're talking about.

The drag racers I know swear by the 30-degree cuts because it "gives them better hole shot torque", which usually means lower RPM power.

If the Milodon valves are used (30 degree, 1.88"), they should fit in the 200. The stock 200 is 1.75" now, but I don't know about the valve stem sizes (yet). Also, the Milodon valve can be cut down, if needed, because it is that type of valve. Keep in mind, though, that a 1.88" valve is almost the exact size for a 30-degree face cut over a 1.75" valve at 45 degrees. It may come close to a drop-in, if the cylinder wall has been bored. (Mine is already .040" over stock).

Now, if I can find another head....

 

[Hudson Nut]

I am using 2inch intake valves with a 30 degree seat, and 1.6875 exhaust valves with a 45 degree seat on my Hudson engine. This is part of the factory racing setup from the 50's that dominated nascar at the time. (called 7x) I don't, however have any flow numbers. I must breathe pretty good... I chassis dyno'd it... rear wheel numbers: 186 hp at 4200 rpm, and 275 ft. lbs torque at 2700 rpm

 

[mugsy]

From what I have read "traditional" Pontiacs have the 30 degree face on the intake and 45 degrees on the exhaust. Teh larger contact on the exhaust valve is needed to transfer heat from the valve to the head.

I was wondering, for the small Ford Six if the 1.75" intakes could be cut to 30 degrees and then a hardened valve insert with the same angle be installed in the head? This would make the most sense on a pre-'78 head obviously.

Tanx,
Mugsy

 

[Anonymous]

Mugsy;

I'd check with CZLN6 to be sure, but installing the 1.75" valve into a pre-'77 head should be no problem if you're changing seats. The head didn't change much for the later 1.75" intakes, except I've noticed that the intake runners were better on the later heads (larger).

In any case, adding the 30-degree angle will improve the early-lift flow.

 

[CZLN6]

Howdy All:

I've been looking for an old Hot Rod article on this very thing. Have yet to find it, but IIRC, the advantage on the SBC was increase flow at low and mid lift! Perferct for a street engine. I'll keep looking.

Valve stems for our six is 5/16" which is smaller than most performance valves. SBF valve stems are 3/8". Heartache!

We are looking at the 30 degree seat on the intake side only, on an "M" head that will be upgraded with hard seat inserts and a 1.75" intake valve from SI Industries. The seat will be surrounded by a 15 and 45 degree cut for the three angles. The "M" head casting has even larger log and port volume and has a flat-top log for mounting two Holley/Weber 2 barrels with direct linkage and two chokes and idle systems. Since we have no experience with the H/W carbs we might be biting off a big bit. I do know of a similar system on a 250 Chevy that worked great.

Intake valves larger than the late model 1.75" are shrouded, not only by the combustion chamber, but also by the small bore of our engines. Anything larger would only make matters worse, IMHO. Better to spend time and money to maximize flow.

Is that what you were proposing, Mugsy?

What do you think?

Adios, David

 

[MustangSix]

David,

I think you'll find that the stems on a small block Ford are 11/32".

Actually, I think you could use a stock 1.78" SBF intake if you cut the valve length down, open the seat slightly, and put a new groove in for the keeper. Then you would only have to ream for the 11/32" stem, saving you the cost of new guides. Same for exhaust valves, but the diameter would need to be reduced. That would give you a cheap source of stainless valves.

 

[80broncoman]

Could a person using a oversize valve on a efi 300 head go with 30 degree on the intake side so you wouldn't have to unshroud so much?
Seems like a sound idea to me. maybe take a 1.94 and cut it down to about 1.90 ? I stuck a 1.94 in a extra efi head i have lying around and it nearly touches the shrouding in there. I think it might make things much worse if it is not unschrouded.
Is there a calculation to go by on how much to unschrouding valves?
I have been doing clean up work in the bowls of the head but i have never delt with the schouding issue before and need some guidence.
Jim

 

[CZLN6]

Howdy All:

Thanks for the "Gotcha" Jack. I was going from memory and that's dangerous these days. As usual, the devil is in the details. I guess the correct generality is that all SBF V8 valves after the 221 and early 260s use a larger diameter stem and are longer.

Has anyone ever tried using V8 valves with a larger ID valve guide? V8 valves would still need to be modified to the correct length for use in a Six. SI Industries valves may still be the best deal.

Jack, you've got me waiting with baited breath, from your comment on the "Cross Flow" post about "significantly improving" the flow on a log head. Can you tell us anything at this point? You've certainly got my attentions!

Adios, David

 

[MustangSix]

Don't hold your breath. I have lots of other stuff to do first.

But if you want to, run a head thru a bandsaw lenghtwise and take off the log and the exhaust flanges flush with the 1" freeze plugs, then mill the whole thing flat. You'll be amazed.

 

[addo]

I think that's called an SP head.

 

[Anonymous]

30 degree seat vs. 45 degree seat has the same sealing area (depends on seat width) and heat transfer, but not as much "self-centering" action (wedging) so it doesn't last as long.
30 degree improves the low lift flow, but the entire valve open area (complete duration) is only better if the max lift is in the mid .400" range. Once the max lift reaches .500" the better high lift flow with 45 degree pays off.
Pro motors are going to 55 degree on .800" lift.