I wrote to Edelbrock and asked them and this is what they said.

"We do not recommend porting, just smoothing of the port exits in the intake should be fine. You don't want to open it up as you will lose torque and you will have uneven distribution. Just leave it as it is or smooth the transition."

Now I know that the GM engineers did not do the best job on the MPFI plenum. It is ok, but not great.

Edelbrock, on the other hand, is a performance company.

I am kind of inclined to believe their engineers.

I really don't understand the reason for restricting the flow on the right bank of cylinders, but, hey, what do I know?

Does anybody know exactly the air flow specs and to what degree porting out changes the torque curve?

Generalities are ok, but somebody must have the torque curves charted.

------------------
Arn Brown, 1985 Fiero GT, 15.474 ET stock
Mods underway.

I can speculate, but remember that's all it is.

Restricting the flow on the right bank?
Hmmm...

On TPI or similar type setups, I've heard that short/big runners help the top end, while long/narrow runners help the bottom end. Each at the expense of the other.
On a carb intake, the small runners will tend to increase intake velocity and help fuel atomization, at the expense of top end flow, while the larger runners will flow much slower on the bottom end, possibly not mixing the fuel droplets or filling the cylinder as well, but will flow more air/fuel mix at the top end.
(I have also heard of header manufacturers staggering the pipe size/length on every other cylinder in order to make the torque curve flatter.)

The manifold may be a compromise to make the torque curve flatter. Since the firing order is 1-2-3-4-5-6 (right-left-right-left-right-left), it could make sense to do it that way.
It would help to smooth out the power pulses.

Again, remember this is all speculation. I've never even seen one of those manifolds in person.

------------------
Raydar
88 3.4 coupe.

Coming soon...
88 Formula, presently under the knife.

quote Originally posted by Arns85GT: Does anybody know exactly the air flow specs and to what degree porting out changes the torque curve?

From my discussion with Edelbrock on the phone, The torque curve is designed to stay flatter across the RPM range. In other words, the torque at the low end is higher and the torque has less roll off at the high end. This provides a higher average torque across the RPM range. As you port out the intake, The torque at the low end drops and the high end rolls off earlier. As I stated in the other post, I just gasket matched the ports which by your Email is exactly what Edelbrock recommends.

Here is a graph from Edelbrocks website showing the torque curve difference from a stock 2.8L carbed engine from an S-10 and how the Edelbrock intake and matched cam raise the torque and how the torque has less roll off at the higher RPM's..

------------------

Happiness isn't around the corner...
Happiness IS the corner.

This intake is designed for use in a 2.8 liter truck. The torque curve that Edelbrock sought will allow this to be used in an air conditioned 4X4 S-10 truck with an automatic transmission.

Edelbrock's cam is a "torque cam", Edelbrock’s headers are small tube headers. The manifold was intended to be part of a PACKAGE aimed at 4X4 truck users.

I am running a Fiero 5spd with no AC and no PWR accessories. My 272H cam is a little “wilder than the cam that Edelbrock offers.

My intake is opened up because I seek the HP/torque at a higher RPM. I would not open the manifold up for a Fiero with an AC and an automatic.

[This message has been edited by DanielKJenkins (edited 12-10-2003).]

Thanks guys,

I tried to get thru on the phone too with no luck.

I checked the Edelbrock site and found the chart. Interesting they make no HP claim on that.

I have the 4-gear transmission and no air.

I take it this rig will somewhat improve my hole-shots and make shifting a bit stronger.

Anybody have any idea what the HP improvement is? I haven't found that chart yet. I've been estimating 10HP for porting the exhaust manifolds and opening up going from 1.5" straight into 2.5" to the tips, and an extra 30HP for the Holley/Edelbrock setup without the cam installed.

Any better estimates?

Arn

quote Originally posted by DanielKJenkins: This intake is designed for use in a 2.8 liter truck. The torque curve that Edelbrock sought will allow this to be used in an air conditioned 4X4 S-10 truck with an automatic transmission. Edelbrock's cam is a "torque cam", Edelbrock’s headers are small tube headers. The manifold was intended to be part of a PACKAGE aimed at 4X4 truck users. I am running a Fiero 5spd with no AC and no PWR accessories. My 272H cam is a little “wilder than the cam that Edelbrock offers. My intake is opened up because I seek the HP/torque at a higher RPM. I would not open the manifold up for a Fiero with an AC and an automatic.

Edelbrock designed the custom cam in my 3.4L which is slightly different than the 272H Crane cam, I have a slightly higher lift and a slightly different duration. (No it is not the off-the-shelf cam they offer with the Performer kit) I called them and discussed how I was using the engine, where I wanted my power and usable RPM range. Then they designed the cam.

The problem with opening up the intake as much as you did (saw pics in the other thread) will hurt torque and fuel distribution. Odds are you will have a problem getting the car to idle correctly, very low vacuum at idle, It probably won't even idle if the outside air temp drops below 50*F, and have low rpm drivability problems. The 60* OHV engines are not really high reving engines. If you were using solid lift and running up to 8000-9000rpm, Then I could see an advantage to your extreme porting on a strictly drag race car.

Sorry to say but I think your going to be disappointed with how that intake acts once the engine is running.

My torque peaks at 4000rpm and my HP peaks at 5500rpm. The engine redlines at 6500rpm.

[This message has been edited by Oreif (edited 12-10-2003).]

My target RPM range is from 2500-6500 RPM.

The design hurts LOW END torque. Mid to upper range torque should be improved.

I only posted those photos after a really big disclaimer because I know that some people might not understand the inherent trade offs involved in opening up the ports to that degree (I do understand). My head porting is also extreme (I won't post those photos until after the car is on the road).

The car will have a narrow powerband and at 70MPH I will have to downshift to pass. Cold weather starting will be a little difficult (get it right the first time or go in the house and come back out later). Stop and go traffic will be an aggravation.

I will post numbers when I get them. In the meantime I will not post any more pictures to save those who don't understand from ruining good parts.

Your posts have been most helpful
Dan

quote Originally posted by DanielKJenkins: My target RPM range is from 2500-6500 RPM.

Most single plane intakes, (which is basically what you made by your porting) Usually don't start making power until 3000-3500 rpm.

The other thing is the cam is only good to 5000rpm Which means HP will peak out around 4500-4800rpm. You would need your peak to be closer to 6000rpm to take full advantage of the single plane set-up.

PowerMax H-272-2
"Good idle, daily usage and off road, towing, performance and fuel efficiency, increased compression ratio and gearing advised, 2600-3000 cruise RPM, 8.75 to 10.5 compression ratio advised. Basic RPM 2000-5000"

This would be a better cam if you plan on spending a lot of time at the higher rpm's:
PowerMax F-228/3067-2-12
"Fair idle, daily performance usage, good low and mid-range torque and HP, 3200-3600 cruise RPM, 9.5 to 10.75 compression ratio advised. Basic RPM 2500-6000"
NOTE: This is a solid lift cam. Which is good in a way because you could move your redline up to about 7500 RPM, Bad side is it's solid lift so it will require periodic adjustments and have a somewhat lump idle.

For more info on the Crane cams:
http://www.cranecams.com/master/apps/chevy1.htm

Update:
Did a selection search and found you might be better off with a Crower they appear to be a better match to your intake:

03066 COMPU-PRO / PERFORMANCE LEVEL 4 -
Hot street/strip profile.
Strong mid to top end torque and horsepower.
RPM Power Range: 2500 to 6500 / Redline: 7500 plus
It is still a hydralic cam and is better suited for your application.
Here is the cam card for it:
http://www.crower.com/misc/cam_spec/cam_finder.php?part_num=03066&x=46&y=8

They do have one size larger that is still a hydralic cam, It is the 03067 cam:
03067 COMPU-PRO / PERFORMANCE LEVEL 5 -
Fantastic top end profile
with plenty of horsepower.
RPM Power Range: 3000 to 7000 / Redline: 8000 plus

Cam Card:
http://www.crower.com/misc/cam_spec/cam_finder.php?part_num=03067&x=38&y=11

I think the Crower's are more suited to what your planning on building then the Crane cams.

[This message has been edited by Oreif (edited 12-10-2003).]

I have looked at the hotter Crower cam, I got a deal on a closeout for the 272H that I could not pass up.

Of course a cam is not the sole factor in RPM range. The crane cam that is sold with the 3.4 crate engine is advertised as:

"The basic RPM range is 1500-4500 with 6500 RPM attainable using proper valve springs. Cruise RPM is designed for 2200-2600 RPM, and a compression ratio of 8.0-9.5 to 1 is recommended"

That is quite optimistic for a cam that has 204º/216º duration @.5!

I notice that your torque peak is at 4200 and your HP peak is at 5200 (I have followed your posts, good stuff). It seems to me that with a torque peak of say 4800 and a hp peak of 6000 that a 5 speed would still be quite drivable. Comparable to say a 1964 chevelle 327/375 horse motor.

It may be that my intake design might have overshot my RPM range.

BTW if I have to eat the intake I will post that fact.

Dan

quote Originally posted by DanielKJenkins: I have looked at the hotter Crower cam, I got a deal on a closeout for the 272H that I could not pass up. Of course a cam is not the sole factor in RPM range. The crane cam that is sold with the 3.4 crate engine is advertised as: "The basic RPM range is 1500-4500 with 6500 RPM attainable using proper valve springs. Cruise RPM is designed for 2200-2600 RPM, and a compression ratio of 8.0-9.5 to 1 is recommended" That is quite optimistic for a cam that has 204º/216º duration @.5! I notice that your torque peak is at 4200 and your HP peak is at 5200 (I have followed your posts, good stuff). It seems to me that with a torque peak of say 4800 and a hp peak of 6000 that a 5 speed would still be quite drivable. Comparable to say a 1964 chevelle 327/375 horse motor. It may be that my intake design might have overshot my RPM range. BTW if I have to eat the intake I will post that fact. Dan

If I remember correctly the Crane 260H cam is what comes in the 3.4L crate engine.
The advantage of the Crower's is the lift differences between intake and exhaust. The larger the difference, the lower your peak torque will be. This is how they increase low-end torque. If you look at the cam listings, as the difference between intake and exhaust decreases the power range for both torque and HP moves up the RPM range. The cam your running now is .454/.480 But the Crower #5 is .470/.479.

As you say with the intake you may have overshot the range you are looking for, But you may be able to correct that by changing the cam. Did you ever think about having the ported intake checked on a flow bench? It might be worth it to check it out and see exactly how it will flow. Rather then building the engine and finding out you need to change something like the cam.

worst case scenario.

I change the intake.

I ain't married to it

Dan

quote Originally posted by Oreif: The advantage of the Crower's is the lift differences between intake and exhaust. The larger the difference, the lower your peak torque will be. This is how they increase low-end torque.

Actually... The shorter duration and lower overlap time is going to be the major factor in determining low end torque.

quote As you say with the intake you may have overshot the range you are looking for, But you may be able to correct that by changing the cam.

I never suggested changing the cam. My intention was to show that the power band of an engine is not solely affected by the cam. I.E. that although the 272H is listed as a 2000-5000 rpm cam this range can be varied greatly by factors such as port volume, carb size, compression ratio, shrouding of valves etc.

I stick with my original statement the the intake was designed for a 2.8 liter truck with accessories and an automatic transmission. The 3 low flowing ports create basically 2 engines in order to flatten the power band of the 2.8.

I have an additional 600cc displacement, unshrouded valves, opened ports, larger cam and my exhaust design will be aimed at higher RPM (1.5" X 27" primaries to 2.5" exhaust). All of these will increased the flow requirements of the intake.

The intake will not hurt low end power as much as you may think. The gain in power from ~3500-~`6200 rpm in combination with my 5 speed will more than make up for the higher torque and HP peaks. The driveability from 2500 up should be acceptable. Idle is easy if you don't have to worry about PS, AC and a torque convertor.

I am new to the 60 degree v6 but I am not new to engine design. I did a carb (Weber 32/36) conversion on a Mitsubishi 2.0 (SOHC), I opened the plenum in that as well. A friend said it would be undriveable for much teh same reasons as you suggest. It idled fine, it drove fine in the winter AND it would stomp the 2.4 liter Toyota trucks (impressive if you have ever driven an 86 Mitsubishi truck with the 2.0)

My first car was a 67 Camaro 327, My second a Triumph TR-6, throw in various motorcycles and a baja bug, and a collection of daily drivers and I have owne quite a few. Trust me

[This message has been edited by DanielKJenkins (edited 12-11-2003).]

I got this explanation from Edelbrock.

"It's because some runners are longer than others and in order to get a even distribution to each cylinder, the size of the runner has been altered to promote even flow. I wouldn't recommend porting it as our engineers have flow tested the intake to determine the correct sizing of the runners. If you port it, the flow will no longer be balanced and one side of the engine may be richer than the other.

Unfortunately, we do not have any printed materials that state this -but I was informed by Engineering as to why they choose to size the runners differently in our Torker manifolds and I have summarized their comments above."

This appears to be consistent with our discussion so far.

------------------
Arn Brown, 1985 Fiero GT, 15.474 ET stock
Mods underway.

This is a very old design. I personally believe that Edelbrock continues to sell this design only because the market will not support a redesigned higher RPM manifold.

Look at the factory TBI manifold, The factory carb manifold, The 3.4 MPFI manifold etc. All of these manifolds have equally sized runners.

I am more inclined to believe that this is a method of flattening out the torque curve. It is designed to work in concert with the headers that edelbrock sells.

But... I have been wrong before.

The lowest risk path is to install the manifold as delivered with a gasket match. Obviously Orief has achieved good results with the manifold.

It is easier to take metal out than it is to put metal in!

quote Originally posted by DanielKJenkins: This is a very old design. I personally believe that Edelbrock continues to sell this design only because the market will not support a redesigned higher RPM manifold. Look at the factory TBI manifold, The factory carb manifold, The 3.4 MPFI manifold etc. All of these manifolds have equally sized runners. I am more inclined to believe that this is a method of flattening out the torque curve. It is designed to work in concert with the headers that edelbrock sells. But... I have been wrong before. The lowest risk path is to install the manifold as delivered with a gasket match. Obviously Orief has achieved good results with the manifold. It is easier to take metal out than it is to put metal in!

First the cast headed 60* V-6's are not high RPM friendly. Once you get over 6500 rpm your at the limit of the engine's valve train capability. This is why the aluminum headed 60* V-6's are better. The splayed valve train is better for the higher RPM's but nobody makes a carb'd intake for them. The over head cam engine's doesn't have the OHV float problems, that is why they are such high reving engines and can be designed for much greater flow. Edelbrock designed the manifold for the cast headed engines and in terms of design vs. function, they optimized the intake for it's intended use on a particular style of a 60* V-6 engine.

Second, If you look at the TBI and carb'd manifolds they are dual plane with equal length runners and a small riser (if any) height. The Edelbrock torker has a 3.5" riser to aid in getting a better air/fuel mixture to create a better A/F charge. This create's a better mix of atomized fuel. The higher riser is why they use the unequal size runners/ports to maintain even delivery and flow without pooling but increase the mixture's charge. On the fuel injected intakes, they just need to move air not air/fuel mixture. Equal length runners increase the flow and since there is no fuel mix in the intake, no pooling happens or concern of messing up the A/F mixture. The injectors spray fuel into the heads based on the readings from the MAP, TPS, O2 sensor, and ECM to maintaing the proper mix. Designing a manifold to move just air allows you to open up the flow a lot. That is why the designs are different.

Thanks Orief,

That was the best explanation I've heard.

Arn

6500 rpms is on the high side of the limitations of a streetable OHV engine.

The OHV aluminum head revs higher because it flows more air! This is a function of unshrouding the valves via the splayed design and of the larger ports. The ports on the cast iron head are small, and the valves are shrouded at low lifts. If these problems are corrected the cast iron head can flow more air.

More airflow with the same camshaft moves the usable power band upwards!

All of the factory manifolds are required to maintain a good idle, good low RPM driveability, cold weather starting AND to limit power/RPM to keep from blowing engines during the warranty! Of course thay use a dual plane design. My point is that none of them have unequally sized ports.

This manifold is designed as part of a package to be used from idle to 5000rpm. I am not suggesting that anyone open up the intake in the manner that I have.

The DOHC motor is a different story.

quote Originally posted by DanielKJenkins: 6500 rpms is on the high side of the limitations of a streetable OHV engine. The OHV aluminum head revs higher because it flows more air! This is a function of unshrouding the valves via the splayed design and of the larger ports. The ports on the cast iron head are small, and the valves are shrouded at low lifts. If these problems are corrected the cast iron head can flow more air.

Yes and no. Splaying the valves allows more flow, but it also reduces the amount of valve float at a given RPM by design. Correct 6500 is about the max RPM for a hydralic lifter. Actually most hydralic lifters start floating about 5500rpm. The difference between a basic stock lifter and a performance lifter is the percentage of float at a given RPM. Basically, as an example, a stock lifter could start floating at 5500 rpm and by 6000rpm have about 40% float, where a performance lifter under the same conditions may only have 25% float.
You can port the intake, heads and exhaust on a stock 2.8L which increases flow, But you will still have valve float limiting the RPM. If you changed the springs and lifters to a good performance set, then you will have less float and be able to utilize the increased flow at a higher RPM.

quote Originally posted by DanielKJenkins: All of the factory manifolds are required to maintain a good idle, good low RPM driveability, cold weather starting AND to limit power/RPM to keep from blowing engines during the warranty! Of course thay use a dual plane design. My point is that none of them have unequally sized ports.

The unequal sized ports are because the manifold was designed for performance not driveability. Hence the factory intakes are generally designed for overall usage. Even most of the performance V-8 intakes use unequal port sizes which have different length runners as well. The port/runner sizes are determined by design of what the manifold needs to accomplish. Ever notice how one side of a dual plane intake on a V-8 has a smaller chamber then the other? Come to think of it some factory intakes like the Pontiac ram air intakes do the same thing. They reduce the carb side of the runners to do accomplish the same thing Edelbrock did on the manifold.

Right on with the springs and lifters and the relationsip of the basic OHV design to valve float. I am still in disagreement on the intake.

The target market for this intake is the S-10 truck market. This is NOT a performance designed intake.

The reason that Edelbrock only publishes torque numbers is that the target audience is concerned with towing.

I have seen intake manifolds dating back to the early 60s. The closest thing I have seen to this design is the old Offy dual port manifold. Granted each cylinder had 2 ports but the design goals are similar.

Show me a picture of another "performance" manifold with this kind of cylinder to cylinder inequality.

I am betting that you can't find one.

[This message has been edited by DanielKJenkins (edited 12-11-2003).]

My last post on this subject.

Orief are you running an Auto? Do you have AC? PW? PL?

quote Originally posted by DanielKJenkins: Show me a picture of another "performance" manifold with this kind of cylinder to cylinder inequality. I am betting that you can't find one.

Well here's one:
http://www.users.pipeline.com.au/tpm/

Look at the top and bottom pics of the carb'd intake. Notice that the 2 center top ports are shorter length then the upper center ports. There is probably a port size difference but you would need the manifold to actually measure it. Also notice how the bottom runners have more plenum volume than the upper runners section.

Actually after looking around MOST dual plane intakes use unequal size runners. The V-8 intakes (both factory and aftermarket) alternate cylinders. 4 of them use the longer top runners, While the bottom runners are actually shorter length (and some have a larger plenum volume just under the carb for half of the carb) for the other 4 cylinders. Since the Edelbrock for the 60* V-6 has 2 different risers (2-bbl or 4-bbl) They changed the runner length and the port size to accomplish the same thing as decreasing the plenum volume for half the riser and changing the length of the runners like the V-8 intakes. This is the basic design of all dual plane intakes. Look at any in-line engine, The do the same thing where the 2 middle cylinders have short runners and the outside cylinders have longer runners. The only intakes to use equal runners/ports (carb'd) are the single plane, tunnel ram and individual runner intakes.

Yes I am running an auto trans (with a shift kit, heavy duty clutch pack's and a street/strip converter), No A/C, and yes on the power windows and locks.

[This message has been edited by Oreif (edited 12-11-2003).]

You had to go all the way to Austrailia to find it though.

OK. I still insist that the variance cylinder to cylinder on the Edelbrock is extreme. This is particularly helpful to automatics with the broad power band that is developed.

The standard trans gives me the option of a narrow power band.

Only time (and money) will tell If I have gone too high and too narrow.

I will probably consult you when I am ready to install.

Dan

quote Originally posted by DanielKJenkins: You had to go all the way to Austrailia to find it though.

Actually that was the only site that shows the bottom and top of the manifold.
Holley and Edelbrock do the same thing but pics on-line of the bottom are not availible.