Efi single plane intake manifold.

[scott woodward]

Question on manifold runner sizing.
Engine is 365 Ci HOLDEN.
12.3 comp running on pump fuel.
Soild roller cam 260/268 .670 lift 108 lsa.
Heads 2.07in, 1.6ex. 90.5% intake throat.
Pinch is 2.78.
Port entry is 2.88.
Manifold runner lenghts are 7.8 long and 6.150 short.
Long runner entry size is 2.9 and short is 3.0.
The injectors are in the end of the manifold runner shooting on the back of intake valve.
I'm after some opinions on the intake manifold runner sizes?
The engine being efi. How much difference between manifold design using a carburettor to using efi?
Engine rpm I'm looking for is around 7500.

[MadBill]

If you can supply airflow numbers or good estimates, I'll run your engine through PipeMax and see what it says for x-section areas. Might as well throw in exhaust specs and we'll get some power estimates too. (Is that 7500 for peak HP or for red line?)

I'd say unless designed from the start (e.g. LS Chev) for FI, there's not a lot of difference between them. EFI should be less or in-sensitive to plenum size (including spacers) and a big TB has no downside beyond possible low throttle sensitivity.

[scott woodward]

I have run this engine through pipe max.
I'm on size with the ports and manifold recommendations.
What I'm curious about is how much difference in the manifold runner size should there be because I'm using efi with the injectors at the port entry. The manifold should have to deal with fuel and air mix like if there was a carbi on top.
You have not put much taper in the manifold runners.
Heads flow
.200-143
.300-216
.400-270
.500-305
.600-318
.700-328
.800-334

[MadBill]

There is probably more variability in how much fuel vaporizes in the intake system due to carb design diiferences (e.g. annular vs. straight boosters), ambient and engine temperatures, the many dozens of different fuel distillation curves, etc. than between a typical carb and ditto injector. I'd say it's not worth worrying about.

Impressive specs. With that flow, I assume you're expecting 700-ish HP?

[scott woodward]

I'd be happy with early 600hp on pump fuel.
The dyno I use is a stuska, and it dose not have any gst.

Don't have a lot of cam shaft in it. 260/268.

[pamotorman]

the location of the injectors must be important as NASCAR has a spec for the location of the injectors on the manifold

[MadBill]

A number of high-end engines use two per port, one down near the valve for low speed and one spraying into the mouth of the runner at high RPM. The NASCAR rule should save a ton of money by eliminating the need for $$$ development work.

[scott woodward]

The manifold I have with this engine has the injector bosses at the exit. I had to change the angle by 6 degrees to
Line the injectors up to shoot over the back off the intake valve.

[pamotorman]

The manifold I have with this engine has the injector bosses at the exit. I had to change the angle by 6 degrees to
Line the injectors up to shoot over the back off the intake valve.

looks like the NASCAR deal has the spray hit the bottom wall of the intake runner maybe to get better atomization.

[Newold1]

Obviously you guys down under have some great pump gas as my calculators say it's got to be in the 105-108 range to stay out of detonation.
Those must be some heads to flow those kind of numbers out of a 2.07 intake? Wow , impressive. I assume also they are aluminum? Got any pics of those bad boys!
Based on calculations with most of the specs. you will be making about 700HP+ at 7200rpms. if we've got good data here.
The math shows with a single plane manifold the total runner length needs to be about 9.85" for best HP and about 12.5 " for best torque, so I would suspect you will have to average that number due to the difference between the inboard versus outboard runners you would have on a single plane intake manifold. I am assuming this is a spider type high rise intake?
You would make the best power most likely keeping the injector up higher in the runner, but aiming them at the valve should not be as important in your use as the actual injector spray atomization characteristics. What size, type and cfm of a throttle body will you be using?

[scott woodward]

The injectors are low in the manifold runners. That's were the boss is. Is wish I had time to experiment with the injector placement.
Throttle body is 1000cfm edelbrock. I'm using the Holley HP computer.
I have extended the centre runners and shortens the long runners.
I've tried to make them close to Larry's recommendations.
When sizing intake ports and the manifold runners, I used 106.5% Ve in pipe max.
It's saying around 650hp and 509ft.

[Cutlassefi]

Injector timing will play a role here as well.
And NASCAR spec'd the location of the inj due to the different head characteristics of each engine and combination so they put them in the middle to even the paying field. However most teams would actually put them closer to the valve. There's a good time lapse photo in RET mag from a few years ago showing the fuel coming out of the inj going back up the runner away from the valve. Interesting.......