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Your torque is peaking at 3750 and rapidly declining because there is a significant restriction with the stock cam and heads. A properly spec cam should flatten out you torque curve and heads will allow you to make more power in the mid to upper range. You can probably upgrade the lower pulley to a 8.66 or 9.06 while doing the cam upgrade as well.
Also, the higher the boost ratio, the quicker / faster the cylinder will fill.
Once the cylinder fill reaches about 87%, Roots Blowers become very inefficient.

Roughly a 100% cylinder fill on these engines generates about 755 - 775hp.

Let's say is is 765 fwHP.

87% cylinder fill then will produce about 665 fwHP.
That number will vary some on a chassis dyno.

This is where some move over to E85, as it moves oxygen into the
cylinder, around the induction system.

Then many drivable street strip cars, begin to see around 730 rwHP
to 100% cylinder fill, or about 750 - 775 rwHP. This can be done
with good heads and a moderate duration camshaft.

This 87% induction system efficiency issue, is not just with our cars.
A highly refined NA car will see the losses reduced to ~92%.

NHRA 500 CID Pro Stock heads flow around 630 cfm on the bench
at 'Peak Lift'. That would produce about 1688 fwHP.

But on a Dyno, they only flow about 577 cfm, making around 1500 fwHP.
That amounts to 92%. . .
***Anyone that thinks their induction system will flow much at 'Peak Lift'
needs to reconsider that notion. The time spent pulling air into the engine
at peak lift, is not much. Next time, use 87% of the peak valve lift number.
***Total time to fill the cylinder at only 6200 rom, is only 0.0005 seconds.


It comes down to piston speed (Demand) versus induction system (Supply).

And while the engine can be setup to flow a Max 157% VE, an NA IC Engine
has difficulty pulling in more than 135% - 137%, or roughly 87%.

Cheers
 
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Yeah, I'm a little confused why he let out so early.
Stock cylinder heads flow about 290 cfm on the bench.

That flow is capable of producing about 676 NA fwHP.
A bit more with a Roots Blower. . Depending.:eek:

And since HP is directly connected to engine rpm / piston speed,
that could be why the HP Number was low.
 

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H/C are next on the list (after putting a tire on it). The tuner (big LS/Vette shop) said my next move should be cam, valve springs and ported SC/Snout. I asked about porting the stock heads and he said it isn't necessary at that level which seems contrary to most.
So he is happy that the torque peaked so low then..;)

And one should first target a HP,
then flow the heads,
then determine engine shift point,
then choose the 'appropriate' camshaft. . . .

As cylinder head goes up, the appropriate camshaft requirements becomes smaller.

With too small a head, generally you can't increase the valve lift much,
so one tends to add unnecessary duration.
 
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We first must generate a HP Goal.
That tells you how much air / cfm your engine will require.

You then port the cylinder head.
Once you have that cfm number, you multiply it by the value of four (4).

Why four..lol

A V8 inhales, fires, and expels (Suck, Squish, Bang and Farts) 4-Cylinders per RPM.

-not considering induction system loses-
So if you want to make 800 fwHP, then you divide that by four (4) and get 200 HP / Cylinder.
Now you multiply that value by 1.5. So you need cylinder heads that flow ~ 350 cfm, on the bench.

Now you will need to fit your engine with a camshaft surrounding the flow of those cylinder heads.

The above does not take into consideration the parasitic losses of the induction system, nor the increase in density ratio, provided for by your blower and mass flow recovery system.

That's a much more complicated issue. . .

That's the basics of it..:)

Cheers
 
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It's one of those might as well things. What's killing me is they're having a Black Friday special- Free head porting with cam package.

Unfortunately, I'm getting married this weekend and that whole thing snowballed price wise. She's lucky she's a good woman.
Find out what the heads flow. . . .
 
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