single plane intake and firing order

Moderator: Moderators

single plane intake and firing order

Postby NixVegaGT » Mon Jan 07, 2008 3:03 pm

Anybody know if there are some advantages to firing order and single plane intakes for intake efficiency? I've heard some stuff out of context in regard to this issue…
- Nic '73 Vega GT "DogBoxx" Batwing LS1
http://www.cardomain.com/ride/2357894
User avatar
NixVegaGT
 
Posts: 2196
Joined: Sat Nov 11, 2006 2:24 am
Location: Minnesota

1973 Chevrolet Vega GT


Postby Sirshredalot » Mon Jan 07, 2008 4:57 pm

Hey nick,

Could you be more specific please. Because as i read it now, You cant change the fring order of an intake manifold...cause it doesnt fire.....you could change the camshaft sequence and therefore change the intake pulses...is that what you mean?

Anywho...I always think that a single plane is more efficient than a dual plane. Especially ones that are designed well....like the Super victors and the Motown intakes....also the Darts.

The difference is in runner length IMHO.
Look at the heavy hitter drag racers turning 10,000rpms with 572-632CI.

All of their intakes have very large plenum volumes with very short (3-5 inches) runners. The larger the plenum volume and the shorter the runner, than the weaker the intake pulse or carb signal is at lower rpms.

Have you read "How to build horsepower Vol.II"?
I would recomend it to you...covers alot of this stuff.

But there are simple modifications that can be done to most intake to help out this situation.
a long and slight tapered at the cyl head intake runner will provide great low end torque as well as excellent top end....The straighter runner provides less restriction for the incoming column of air and the length keeps air.fuel velocity up...so long as the runner is adequetly sized for the application...especially for small cube motors like ours.

God bless
-Shred
User avatar
Sirshredalot
 
Posts: 1384
Joined: Wed Aug 23, 2006 3:12 pm
Location: Muncie, Indiana

1980 Chevrolet Monza Spyder

Postby cjbiagi » Mon Jan 07, 2008 5:07 pm

If you are building a street engine with a rpm peak of 5000 or so I think you will be better off with a dual plane. If you are building a high rpm engine then a single plane is better. It's like any other part of an engine, it needs to be matched with other components which are designed to operate within a certain rpm band.
Clyde.........75 Monza 2+2
User avatar
cjbiagi
 
Posts: 8608
Joined: Sun Jun 25, 2006 2:37 pm
Location: Glenwood, Illinois

1975 Chevrolet Monza

Postby spyder_xlch » Mon Jan 07, 2008 6:10 pm

Single planes are good at high RPM. Like Clyde says, a street engine will be better with a dual plane. I think if you have a carb that is too small on a single plan it may work better than a dual plan with too big of a carb. I'm not sure what Nic is asking either.
User avatar
spyder_xlch
 
Posts: 4693
Joined: Sat Apr 14, 2007 4:14 pm
Location: Northeast PA

1979 Chevrolet Monza 2+2

Postby NixVegaGT » Mon Jan 07, 2008 7:18 pm

LOL! Can't I just scratch off the numbers and reorder them on the intake and change it's "Firing order"? LOL! Yeah sorry guys.

Here's what I mean: Some engines have been proven to do well at low to midrange with a single plane because of the firing order of adjacent cylinders. This is based on a loose reference in my Q-jet book. I remembered some past articles in CarCraft that showed numbers better for some engines with single plane manifolds…

I was hoping someone had some hard data at hand to head off extensive research on my end. I'm still planning on running dyno numbers with the single plane I got from Australia and my Edelbrock dual plane. The problem is the Edelbrock intake isn't spread bore so I can't use the same carb… I guess I could run a square bore carb on both for a test. I'm kinda fixated on using a Qjet though.

Thanks for the quick response guys!
- Nic '73 Vega GT "DogBoxx" Batwing LS1
http://www.cardomain.com/ride/2357894
User avatar
NixVegaGT
 
Posts: 2196
Joined: Sat Nov 11, 2006 2:24 am
Location: Minnesota

1973 Chevrolet Vega GT

Postby spyder_xlch » Mon Jan 07, 2008 7:34 pm

I understand now. You want to know if a certain engine with a certian firing order would work better with a single plane than another engine with another firing order. Or perhaps would a SBC with the 4/7 cam swap work better than a stock SBC firing order.

As far as scratching the numbers off the intake, sure, you can do that and rename the cylinder numbers and come up with your own firing order. Just keep the wires from the dist to the plug in the same order the factory had them before you changed the numbers. :lol:
User avatar
spyder_xlch
 
Posts: 4693
Joined: Sat Apr 14, 2007 4:14 pm
Location: Northeast PA

1979 Chevrolet Monza 2+2

Postby Sirshredalot » Mon Jan 07, 2008 7:58 pm

Its been my personal experience that single planes DO perform well at low rpms. My truck weighs dang near 4000 lbs....especially with everything that i haul in the bed.

I had a 355 with about 8.5:1 compression and a very mild cam with a wide LSA...114*.
I went from a perfromer Q-jet manifold to a Weiand IMCA single plane with an edelbrock 1406 600cfm carb....vacuum advance stock distributor and not only did I not lose any low RPM torque....I gained ALOT of midrange and fuel mileage.
The truck had a 28" tall tire, 2.67 gears, and an overdrive transmission.
First gear was a 3.09, manual transmission.
I knocked down 22-23 MPG cruising at 1800rpms in a heavy truck with at least an average of 500lbs in the bed.

The SBC has a very efficient firing order IMHO, as do most vehicles with a 18436572 firing order....Ford engines have trouble with low RPM torque when used with mild cams and single planes because they have a different intake pulse pattern....Im not sure if that is the sole reason for it for im sure it contributes.
Also the SBC style intake pattern with the grouped runners provides a more consistant runner length than a staggered intake pattern like a ford or mopar.

I noticed that your intake shares the middle two runners with the outer two isolated....uneven runner lengths.
You can extend those runners by welding small aluminum squares to the runner walls and extend them into the plenum to lengthen them.
Also doing the same thing on the wall where the outer two runner joint at the tight angle will further extend the runner length.
The longer the runner....I feel....the lower the rpm that peak torque will occur.
also the cam has alot to do with it....a cam with a wider LSA like 112-116 with have more signal and more low end than a peakier cam with a narrower LSA like 106-110.

Regardless I think that even without mods to your intake, you will be happy with that intake. The car is light with more than enouh rear gear and tranny gear to make it happy.

God bless
-Shred
User avatar
Sirshredalot
 
Posts: 1384
Joined: Wed Aug 23, 2006 3:12 pm
Location: Muncie, Indiana

1980 Chevrolet Monza Spyder

Postby mldeolde » Mon Jan 07, 2008 8:42 pm

it escapes me at the moment who but i think some of the NASCAR SB-2s were useing a modified fireing order and i believe Comp cams was making a special cam for them...
User avatar
mldeolde
 
Posts: 1718
Joined: Mon Jun 26, 2006 4:21 pm
Location: Riverside,California

1975 Chevrolet Monza IMSA

Postby spyder_xlch » Mon Jan 07, 2008 8:46 pm

You can get a cam that will swap 4 and 7 in the firing order. I also heard of a 2/3 swap cam but haven't seen any yet.
User avatar
spyder_xlch
 
Posts: 4693
Joined: Sat Apr 14, 2007 4:14 pm
Location: Northeast PA

1979 Chevrolet Monza 2+2

Postby NixVegaGT » Tue Jan 08, 2008 11:13 am

That's a good point about the port location. It's a bit easier to make equal length with the SBC I'm thinking. I did notice that the web between the middle two ports is quite a bit longer than the transition between the middle and outer two ports. I guess that's what they were thinking.

I set the Qjet base on the manifold last night to get a look at it. The primaries are a lot farther away from the rear cylinders. I wonder if that matters…

The firing order is: 1.8.4.3.6.5.7.2
Layout is like this:

2.4.6.8
1.3.5.7

So you can see that 8 is going to have to slosh the charge from 1 to 8 after taking from 2 to 1. The primaries pretty much sit right over 1/2. I think 5/7 will be fine because they pulse together. So it seems 2 and 8 take the worst slosh… So maybe I put a ridge on the floor over all but those two ports? Do you think there would be any benefits from splitting the floor down the middle?
- Nic '73 Vega GT "DogBoxx" Batwing LS1
http://www.cardomain.com/ride/2357894
User avatar
NixVegaGT
 
Posts: 2196
Joined: Sat Nov 11, 2006 2:24 am
Location: Minnesota

1973 Chevrolet Vega GT

Postby Sirshredalot » Tue Jan 08, 2008 3:35 pm

well....the intake charge is already suspended in a moving column of air.
The trouble is playing with physics....what is in motion will stay at motion until acted upon by an opposing force.

The intake charge in the plenum will be flowing towards the number 1 port when the number 8 ports starts to draw it.

A larger plenum would ease this problem but also stiffle mixture velocity.

I dont believe on that design of a manifold that dividing it is the best route.
With extensions into the plenum from the shorter runners you would help build "resistance" on opposing banks during an induction stroke.

So the number 1 cyl will draw the air and then the number 8 cyl will draw air but with the extension in the manifold it will retain more of the charge in the plenum to equalize what each cylinder draws. Helps with mixture distribution....because as it sit now your center two cylinders on both banks will run slighty richer than the outer most cylinders on both banks...
Also mixture velocity will be lazier for the center ports as opposed to the outer 4 ports which can create more velocity....therefore more torque.

i wish i had a scanner so I could post what Iam trying to explain.
Compare a Victor Jr. plenum to a Super victor plenum and you will see it.

As for primary vs seconday positioning over the plenum...Im not sure what i think about that yet....I have really never put nuch thought into it because i am running two carbs....lemme chew on that one.

God bless
-Shred
User avatar
Sirshredalot
 
Posts: 1384
Joined: Wed Aug 23, 2006 3:12 pm
Location: Muncie, Indiana

1980 Chevrolet Monza Spyder

porting single plane intakes

Postby chevyart » Sat Jan 12, 2008 12:55 am

Sirshredalot.there is a good article in Hot Rod Magazine(I thikk either Dec or Jan Issue. There is a guy out there that specializes in intake manifold porting. He did a dual plane. Victor Junior single plane. and the next one up above the victor jr. He got the most power increase from the biggest single plane and guess whal; he got that added power dowm in the lower and mid range. Im a believer (now) in the single plane manifolds. I have one on my new 408 cu in SBC for the street and im not even concerned about loosing low end power Chevy Art
chevyart
 
Posts: 1964
Joined: Fri Oct 27, 2006 10:00 pm


Return to Carb/Intake/EFI Induction Tech

Who is online

Users browsing this forum: No registered users and 7 guests

cron