[lust4speed]

Don't want to muck up the current thread on seat blending angles so starting a new thread. Say we have a 670 head and it's ported to flow 265 CFM with 30° intake valves. What happens to flow (and therefore horsepower) when the intake is changed to a 45° seat with appropriate blends?

Heads will be part of a stroked 492ci block with a forged Scat 4.50" crank. The proposed cam will be in the range of 246/250 HR with .608/.618 lift on a 112 LSA. Will be in a Catalina Safari wagon with some strip time every month. Converter will be 2,800 stall.

Was just going to stay with the 30° seat on this set but wanted to go with the Ferrea 6000 series valve and couldn't find a 30° valve listed for the 5.213" valve length. The heads on my blue 67 GTO have had 45° since the mid 80's with lifts over .620" but never knew whether the change helped or hindered performance.

[77 TRASHCAN]

Me, a non expert, going to a 45 degree seat in a big modified engine like yours, I thought was the “norm”. The 30 degree seats being the preferred way to go in a street engine, up to 474 cubes (thinking Jim Hand, here). The bath tub Pontiac chamber, one of few, performed greatly with the 30 degree seats. Of course Pontiac engineers were essentially “only” building engines to go up and down the highway....did a Fine job of that!

Was your 525 Alum engine in your (now sold)race car?

[Cliff R]

30 degree seats work well with the factory machined flat chamber floors. They also work well with longer duration "slow" ramp camshafts not sporting a lot of lift.

With that said I've seen some very good dyno numbers from engines using iron heads and "aggressive" lobe profiles when they were outfitted with 45 degree seats.

Personally I wouldn't mix one with the other. If you are going to a modern shorter seat timing cam with aggressive opening/closing ramps a change to 45 degrees seats would be a good way to go.....IMHO........

[mgarblik]

Originally Posted by Cliff R

30 degree seats work well with the factory machined flat chamber floors. They also work well with longer duration "slow" ramp camshafts not sporting a lot of lift.

With that said I've seen some very good dyno numbers from engines using iron heads and "aggressive" lobe profiles when they were outfitted with 45 degree seats.

Personally I wouldn't mix one with the other. If you are going to a modern shorter seat timing cam with aggressive opening/closing ramps a change to 45 degrees seats would be a good way to go.....IMHO........

X2! The .100-.200 numbers will suffer slightly with the 45 degree seats. But the idea of the much more aggressive cam is the valve will spend little time, (duration) at that lift and will quickly be in the superior flow range of the 45 degree seats.

[steve25]

The question needs to asked as to at what valve lift do your heads attain that 265 cfm flow level?

The intake flow .@ 200” lift point is super important to the so called 5th engine cycle once the 245 duration point @ .050” or above is in the works along with a good scavenging header .

This is a big part of attaining VE numbers above 100%!

Typical a max ported iron High comp D port head with an 2.11” valve , a 30 degree seat will flow 76 cfm@.100” and 148 cfm @ .200” both @ 28”

When the seat Is changed over to a 45 these numbers drop to 63 cfm and 127 respectively.

Adding a 30 degree back cut to the 45 degree seat valve will bring these numbers back up to 69 and 137 cfm respectively.

I am firmly of the opinion that if your build uses a Cam that uses at least. .550” lift at the valve and your power band will start above 3800 rpm along with running a open collector tuned exh system and using a single plane intake, then the 45 degree seat will be the way to set the heads up, other wise it’s the 30 degree seat with a valve mod to reduce reversion at low lifts and low velocity’s.

[PAUL K]

From my past experience, if you are flowing 265 with a 30° seat leave it! All you'll gain is a loss of cfm below .300 and very little gain if any at the higher lifts changing to a 45. Now if you do a good 45° seat with the right bottom cut and reshape bowl you might make a little more power and should gain a little more cfm above .400 lift.... But I've never seen a big gain either way.

[mgarblik]

Originally Posted by PAUL K

From my past experience, if you are flowing 265 with a 30° seat leave it! All you'll gain is a loss of cfm below .300 and very little gain if any at the higher lifts changing to a 45. Now if you do a good 45° seat with the right bottom cut and reshape bowl you might make a little more power and should gain a little more cfm above .400 lift.... But I've never seen a big gain either way.

That's a good point and I agree. I guess I didn't pay enough attention to the OP post. 265 CFM peak with a 30 degree seat is a nicely ported head. Might gain 7-8 CFM at the top with a 45. Allot of work without much to gain there. Low lift numbers will suffer for sure.

[Jay S]

Unless it is pretty low on compression for the proposed cam. I would want 45* with a 4.5” crank. I think the better low lift flows hinder the big crank with all its piston speed and limited air flow. I don’t think it needs help on the scavenging side. I think I would swap scavenging for cylinder fill and use 45’s.

[PAUL K]

Originally Posted by Jay S

Unless it is pretty low on compression for the proposed cam. I would want 45* with a 4.5” crank. I think the better low lift flows hinder the big crank with all its piston speed and limited air flow. I don’t think it needs help on the scavenging side. I think I would swap scavenging for cylinder fill and use 45’s.

I'm not disagreeing with your thoughts, but I would design the cam around the flow of the heads and the stroke.... It sounds like the heads are done and flow pretty good. I'm envisioning everything going South when a well meaning machinest goes in there to change the "good working" 30° seat to a 45°..... I've seen a great head become a mediocre head far too many times from the same procedure.

[PAUL K]

Originally Posted by lust4speed

Was just going to stay with the 30° seat on this set but wanted to go with the Ferrea 6000 series valve and couldn't find a 30° valve listed for the 5.213" valve length. The heads on my blue 67 GTO have had 45° since the mid 80's with lifts over .620" but never knew whether the change helped or hindered performance.

Manley would be my choice for the 30° valve with that length. Part number 11352-8 SI also offered a nice valve that length which was a bit lighter than the Manley.

[steve25]

I don’t understand your train of thought on this either!

The greatly increase stroke ( as if a stock 455s is not enough to try and supply air to! )only serves to increase the demand for air even sooner on the intake stroke, so why would one not want to access greater levels of air flow sooner to at least try to keep up with the demand, especially with a head such his 670’s which can’t go a extra 20 cfm like the later heads due to the low port angle and in turn its lower floor,

[lust4speed]

Some quick clarification. Our club members have had a few heads done by Juan Martinez at Flow Technology in Garden Grove, CA at the 265 CFM flow level, but these 670 heads are untouched and sitting on my workbench while I decide what valves to use. So at the moment only Flow Technology's past results are being used to list eventual flow numbers. We did talk about going with more flow and I think the cubes would support that, but figured I'd list the more conservative flow target. I might add here that SD Performance has always been my personal choice but with Dave's decision to not do iron heads, I've shifted to Juan for cast iron head work.

Two sets of 670's will be taken to Flow Technology; my friend's heads will remain at 30° because of less cubes and gearing and the need for more streetable manners while my personal set will be for an engine a step above being really street friendly.

77 Trashcan. Yes The drag car has the 525 aluminum engine. The engine now in my blue GTO with the 670 heads was the engine I drag raced in the blue GTO for over 20 years and then transferred it to the drag car after I got it put together. Then I built the aluminum engine for the drag car and the old iron block engine went back in the blue car after changing to a hydraulic roller cam and dished pistons. Long process of musical chairs and hand-me-downs with the cars.

[PAUL K]

Oh, then I take back everything I said.... Ask Juan.

Btw.... Are you talking about Juan Mendoza by chance?

[Jay S]

I would move up a size to a Manley 11778 valve if you were switching to 45* from30*s. 2.125 dia, 5.25” long, .3415”.

[lust4speed]

Originally Posted by PAUL K

Oh, then I take back everything I said.... Ask Juan.

Btw.... Are you talking about Juan Mendoza by chance?

Oh crap, yes - Juan Mendoza. Was making sure I didn't call him the coffee guy from the old TV commercials (Juan Valdez) and then still blew it.

[PAUL K]

Originally Posted by lust4speed

Oh crap, yes - Juan Mendoza. Was making sure I didn't call him the coffee guy from the old TV commercials (Juan Valdez) and then still blew it.

Lol.... He does good work. I would run the build past him and go with his advice.... Whatever he does it will be good!

[Schurkey]

Originally Posted by lust4speed

Heads will be part of a stroked 492ci block with a forged Scat 4.50" crank.

I'd be using whatever valve angles came in the aftermarket heads I purchased.

Why are you using OEM heads?

[lust4speed]

Originally Posted by Schurkey

I'd be using whatever valve angles came in the aftermarket heads I purchased. Why are you using OEM heads?

My original plan was to order out a set of Butler's Edelbrock stealth 325cfm D-ports, and I could still end up setting the finished iron heads on the shelf and going that route. I don't know how much longer Juan will be doing heads and I don't want to kick myself for not having the 670's done if he closes up shop and retires. Besides, there is a perverse satisfaction in making good horsepower with iron heads.

I am going to take the above advice of letting Juan choose the intake valve specs. I always hate it when someone brings me a cam and other engine parts in for their build that could easily be improved upon, and no use in doing the same to the head specialist.

[Mister Pontiac]

Originally Posted by lust4speed

Besides, there is a perverse satisfaction in making good horsepower with iron heads.

Heh Heh... This!

[steve25]

Just wondering here, how many folks commenting on this string have a flow bench at there disposal full timel , raise your hands!