Maximizing flow limited combos?

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Mean416

Mean416

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Hey fellas. This is a different spin on a common theme here, relating to power potential vs. flow capabilities of the cyl head.

My particular challenge, at present is I have an OOTB set of aftermarket heads that are flow limited. These are slated for attachment to a 4" stroker combo. (In my case it's a 340 based, not that it matters much). Combo has flat top pistons with valve reliefs and will be around 11.5:1 compression with my gaskets and deck. I have hedman hussler 1-7/8 headers, and (right now) an M1 single plane. I do plan on a head upgrade at some point but it's not in the cards now.

So I totally understand that this combo is very flow limited and from what I've seen pretty much everywhere it'll do good to make in the range of somewhere between 450-500 crank HP, and will probably top out sub 6000 rpm.

My question is, what "tricks" can someone employ to get the most out of a combo like this? For example, I could consider valve job, valve sizing, cam, rocker arm, intake, carburetor, ignition, some exhaust changes etc. It would be nice if said parts would also play well in the future with an upgraded set of heads but not absolutely necessary.

What would you guys do to max out a set of heads? What would a "stock port" class engine do?
 
Different valves of the same size can flow surprisingly different amounts, maybe one the flow bench guys can tell ya the best ones.
 
PRH said:
-11.5:1 416
-RPM heads
-decent single plane
-1-7/8” headers

With enough cam, it should easily exceed 500 hp.
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What would be enough cam to hit 500 hp ? Like 250° range ?
 
If I wanted to be sure I went over the 500hp mark, I’d be at least in the mid-250’s.
The particular lobe family used would be a factor.
(Although, if it were going in a bracket car, at 11.5 CR it could be noticeably more…….depending on various vehicle related considerations)

All the heads would really need is a once over to correct any potential “issues”, and a spring/retainer/lock upgrade.
 
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@PRH thanks. That's what I'm looking for.

What would you consider noticably more?

Anything different under consideration relating to other valve events?
 
Mean416 said:
Ohh I'll definitely hit it with nitrous shot anyway but I won't stop at 100 HP lol
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I'm limiting my nitrous set up to 100hp, cast crank, hypereutectic pistons. 50 HP under each plate

17276352039097111207352321151843.jpg
 
Mean416 said:
@PRH thanks. That's what I'm looking for.

What would you consider noticably more?

Anything different under consideration relating to other valve events?
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The application would dictate the basic duration numbers.
But, in the right application I don’t think low-270’s would be “too much”, but that would be something like a light weight dedicated race car with plenty of stall and a narrow operating window.

If you’re going to spray it anyway, I wouldn’t get too worked up about maximizing the N/A power.
 
Why not just send out the heads to someone with a CNC program. Which are they? Seems like you have the budget to say change other pieces of the puzzle. Why not port and have the heads checked out. Or is this together already and you don’t want to pull the heads. Just read it is not together. I personally would not consider that VERY flow limited.
 
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furrystump said:
Why not just send out the heads to someone with a CNC program. Which are they? Seems like you have the budget to say change other pieces of the puzzle. Why not port and have the heads checked out. Or is this together already and you don’t want to pull the heads. Just read it is not together. I personally would not consider that VERY flow limited.
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Well, I already have most all of the parts and pieces. So if I can tweak a couple things and get another 50hp or whatever....I'd definitely consider it.

Sending for porting, including necessary valve changes, etc. That's gonna end up costing a couple grand.

I could manage a cam change, maybe some valve job, different valve sizes etc. something along those lines is still gonna be a lot less costly.

When I do end up getting new heads they'll likely be Bloomers.
 
I would use a sol roller cam. After selecting the LSA & duration for your desired power range, I would then select lobes with as much lift as your valve train will operate with. Once lobe lift is known, pick a lobe series that has as much area under the curve to maximise the 'valve open' time of your heads.
Example from Comp lobes. Duration at 050/200/lobe lift.
TC series 252/172/436
TK series 253/179/430.

For a 252 @ 050 cam, the TK has more area under the curve.
 
I rarely see people running cams like we did in the 1980’s to get junk to run good. Today guys thing a .650 lift cam is big but we ran 332 duration ( [email protected] ) and .750 lift with 906 heads on our big blocks. My combo that ran 9.82 in my 74 duster had a lot of Chevy and ford guys losing sleep. Mother Mopar gave us a pretty nice combo to put together with stock blocks, stock cranks, stock rods. Lol. Local dirt track racers thought we were crazy running cams like that.
 
furrystump said:
Why not just send out the heads to someone with a CNC program. Which are they? Seems like you have the budget to say change other pieces of the puzzle. Why not port and have the heads checked out. Or is this together already and you don’t want to pull the heads. Just read it is not together. I personally would not consider that VERY flow limited.
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I was just going topost that very sentiment !
 
Should the focus be more on the intake side of the cam or the exhaust?

Anything elsewhere in the system that would help? I.e. exhaust, carb, intake, etc
 
Jon Kaase won the EMC using a cam that had less exh duration. I have been using these for over 20 yrs. Quite a few EMC entrants have used reverse pattern cams. You would not have seen that decades ago, but you see it now or lower ratio rockers on the exh.

img083.jpg
 
mbaird said:
But would the same be true for an older factory head design with less efficient exhaust ports ?
Modern heads have way more efficient exhaust ports .
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That’s why I sent you a PM. The math I use doesn’t ask for airflow.

It doesn’t use intake flow, exhaust flow or the ratio between the two.

What the equation does use is bore, stroke, compression ratio, rod to stroke ratio, and for the intake lobe it wants rpm where you want peak torque.

Based on that number (intake duration) you calculate the exhaust lobe, the LSA and the ICL.

I’ve been using it for awhile now and if your engine is over square and the rod to stroke ratio is relatively high you end up with a single pattern cam IF the rpm is fairly low. Like 6k and under.

As the rpm goes up then you get a split.

I’ve checked lots of combinations and I’ve yet to see it call out anything with a 4 degree split.

I think the least split was for my W2 engine and it was 9 degrees.

I’ve seen as high as 14 but that was a 632 I ran the numbers for.
 
Newbomb Turk said:
That’s why I sent you a PM. The math I use doesn’t ask for airflow.

It doesn’t use intake flow, exhaust flow or the ratio between the two.

What the equation does use is bore, stroke, compression ratio, rod to stroke ratio, and for the intake lobe it wants rpm where you want peak torque.

Based on that number (intake duration) you calculate the exhaust lobe, the LSA and the ICL.

I’ve been using it for awhile now and if your engine is over square and the rod to stroke ratio is relatively high you end up with a single pattern cam IF the rpm is fairly low. Like 6k and under.

As the rpm goes up then you get a split.

I’ve checked lots of combinations and I’ve yet to see it call out anything with a 4 degree split.

I think the least split was for my W2 engine and it was 9 degrees.

I’ve seen as high as 14 but that was a 632 I ran the numbers for.
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Sorry .. no pm . Might have sent it another member.
 
This is why I like to use a custom cam grinder that has long term experience in cam design .
Although my W2 roller was ground by well revered guy in circle track and he gave me a split pattern of 246/250.
But it may have been Ryan @ Shady Dell that specified the profile and had him grind it ?
 
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