Shaun @ Tru6

ABSOLUTELY STUNNING!

SwayBar

Wow...!

Catorce

Yep, and while we don't actually have the manifold in our hands the fabricator has redeemed himself by putting out a work of art. Can't wait to see what this thing will do; should handily beat the carbon manifold that's floating around out there without any of carbon's bad behavior.

The goal is to ultimately manufacture this design for the 928 crowd.

Oh, and it fits under a stock hood....

FredR

That is some piece of kit. It will be interesting to see how it performs relative to a stock manifold on the same motor and specifically so on a 5 litre motor.

Catorce

That comparo won't happen; this manifold was designed with my 6.57 liter stroker in mind; I am not sure that it would materially enhance a 5 liter motor.

SwayBar

What are the runner lengths, and their inside diameter?

Rob Edwards

Here's a representative pair of dyno results from Anderson's old 6.5 with that carbon intake on it from 10 years ago, should be a reasonable target to aim at. The warbling above 6500 rpm is ignorable, shoot for an even 500 SAE rwhp.

GregBBRD

Beautiful fabrication!

Looks like a short runner American Tunnel Ram, except for the 90 degree and 180 degree air flow direction changes required for the air to get to the intake valves.

What is your target power range?

ptuomov

Looks nice. On your 6.5L motor, I would expect this manifold to start pulling ahead of the ported stock intake after 4500 rpm. But that guess and $2 will get you a cup of coffee at Starbucks.

The bottom feeder design is pretty much guaranteed to distribute air evenly, so this is going to work with high likelihood by my guess. Plenum volume is very close to irrelevant when all right cylinders feed from the same plenum, there just has to be enough volume such that all runner inlets are unshrouded.

What size throttle body is this designed for?

Here's how I think about the throttle body size for a single-plane EFI intake manifold on a V8:

For k percent power loss from throttle body restriction (relative to an infinitely large throttle body), the throttle body CFM should be 1.6*HP/sqrt((k/100)*(14.7-0.7)).

For example, Porsche seems to size their street-car plenum manifold throttle bodies for 2.5% or lower power low due to restriction. That is, for a 320 hp motor, they pick a 75 mm throttle body that flows about 896 CFM. The formula says that 2.5% power loss is achieved using a throttle body that flows 865 CFM, and the observed 896 CFM is a little better than that.

For road race engine that requires some operation of the throttle, maybe I'd size it for maximum 1% power loss? A 320 hp road race engine would need 1.6*320/sqrt(0.01*(14.7-0.7)) = 1368 CFM throttle body. For a 550 hp engine, 1.6*550/sqrt(0.01*(14.7-0.7)) = 2351 by the formula?

How to go from CFM @28" to throttle diameter? I pulled the data on Accufab's web site and regressed their reported CFM number of the throttle body diameter in mm squared. The coefficient on that is about 0.1567 from my regression, and the 95% confidence intervale is 0.1471-0.1662. Taking the point estimate says that TBCFM = 0.1567*(diameter in mm)^2. Alternatively, if you know the required TBCFM, you can convert it to throttle bore diameter using the formula diameter in mm = sqrt(TBCFM/0.1567).

So in the case of 320 hp road race motor where you don't want to lose more than 1% power due to the throttle plate restriction, the formula would suggest sizing the throttle body at sqrt(1368/0.156659) = 93 mm. For the 550hp engine, you'd size the 1%-loss throttle plate at about sqrt(2351/0.156659) = 122 mm.

In other words, I'd stick the largest throttle body into this manifold that fits. The same for feed pipes, as large as fits.

Carl Fausett

In an earlier post in this thread I mentioned that the TB bolt pattern I designed for is that of the Chevy LS motors. That way the customer has their choice of many TB's from 90 to 104 mm easily. I am fitting this one with a 90mm MSD Atomic Throttle Body with a parabolic opening for better tip-in responsiveness. I put one on my race car and it made a big improvement in drive-ability compared to the Holly TB that I took out.

ptuomov

I’d go big in this case, 104mm. And I’d feed it with the biggest pipes that fit and the lowest restriction filter you can find.

By my computation, if the "unrestricted" engine would make 550hp, then the 90mm throttle body is going to cost you 19hp: ((((550*1.6)/(0.1567*(90)^2))^2)/14)*550 = 18.9hp. If you go to 104mm throttle body, it'll only cost you 10.6hp. The net gain from 90mm -> 104mm throttle body swap should be about 8.3hp. That's not nothing, in my opinion. (The obvious caveats about the formula apply.)

We’re feeding the turbo car now with 2x 3.5” pipes on the low pressure side and the turbos are working a lot less hard with the unrestricted inlet.

Carl Fausett

There is a difference between building for a big show-off number on a dyno; and building for good throttle-response and drive-ability. A desire for good throttle control in the mid-range.

Yes, ptuomov, your math is all about max HP output and its not wrong.
But on race day (or for the street), you can benefit from the better throttle control a slightly smaller TB will provide. BT, DT.

ptuomov

Do you agree with the rules of thumb that a street car should have a throttle sized to produce a 2.5% power loss and a race car should have a throttle sized to produce a 1% power loss? Those aren't gospel, they're just what I've observed in competent high-budget efforts.

By my math, the 2.5% power loss street car throttle would be sized at 97mm for this engine, assuming that the motor would make 550hp with a very large throttle body. The equation for @28" CFM is 1.6*550/sqrt((2.5/100)*(14.7-0.7)) = 1487 and the equation for the throttle plate diameter in mm is sqrt(1.6*550/sqrt((2.5/100)*(14.7-0.7))/0.1567) = 97mm.

I believe (but of course don't know) that had Porsche built this kind of 550hp motor for the street with a single throttle blade, they would have put in something like 97mm throttle body.

Personally, I think that 90mm throttle body is too small for this engine even for a street car, let alone for a race car.

Catorce

Thanks Greg,

I know nothing about this manifold specifically; it was Carl's brainchild - I'll let him answer.

As to power, I believe we did 510 HP on the engine dyno with the stock manifold plus spacers. There is no set goal other than to exceed that number; i would be happy with an additional 50hp from this manifold but in the end that might be asking too much; we are all going to find out one way or the other if this thing works as good as it looks......

Carl Fausett

As a point of reference: the stock throttle body on the 5.0L S4 motor is 75mm. The throttle body I ran on the extrude-honed intake was 90mm throttle body.