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Old 09-21-2003, 04:53 PM   #1
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making my own intake.. need help with runner length math.

mmk, this EFI intake will have the runners going mostly straight out from the head into a plenum.. kinda like a lt1 intake with slightly longer runners.

prob im having is doing the runner length math. i think this is right, but im making alot of assumpsons that i would like some feedback with..

to keep from retyping everything, im going to be swiping some info from here: http://www.grapeaperacing.com/GrapeA...ntaketuned.cfm


mmk.
Quote:
We must take into account the intake duration, but you want the pressure waves to arrive before the valve closes and after it opens (air wont pass though a closed valve). To do this you must subtract some duration, typically you take off 20-30 from the advertised duration. 30 works well for most higher rpm solid cammed drag motors. So the Formula to figure effective cam duration (ECD) will be:

ECD = 720 - (Adv. duration - 30)
mmk i will be using comp cams 286HR.. specs can be found here:
http://www.compcams.com/Technical/Ca...03/142-171.pdf

For a this cam with 286 of intake duration it will look like this:

ECD = 720 - (286 - 30)

The ECD of that cam would be 464
Quote:
The formula for optimum intake runner length (L) is:

L = ((ECD 0.25 V 2) (rpm RV)) - D

Where:
ECD = Effective Cam Duration
RV = Reflective Value
D = Runner Diameter
If our engine with the 286 race cam needed to be tuned to 5500 rpm using the second set of pressure waves (RV = 2)

L = ((464 0.25 1300 2) (5500 2)) - .5D

heres my prob... i dont know what to put for the runner dia. since i was going to make my runners the same size as the heads intake port, i used the head measurements of 1.340 x 2.210 and averaged them to get my runner size of 1.480. is that correct??

anyhoo i then solved it.

L = ((464 0.25 1300 2) (5500 2)) - .5*1.480

and i got a runner length of 26.6 inches. waay too long.

so then i said, mmk, instead of the 2nd pressure wave, lets use the 4th.

L = ((464 0.25 1300 2) (5500 4)) - .5*1.480

that got me a runner length of 12.9 inches still a little longer then i could stuff under the hood.

the 5th wave gave me 10.2
the 6th 8.3

its not until the 8th pressure wave that i get 6.11... and the max runner length i can fit with my design is roughly 6.5"

other then totally redesign it to fit a longer runner, what can i do? should i forget about tuning the runner length altogether or what?

this intake needs to flow agood amount of air... it will be going on a 400 or 383 with that roller cam and 220cc heads... i dont want to choke it with a diffrent runner design, and i dont have the abilitys to make any kind of a curved runner... ideas? is my math even right? did i do the conversion for the runner dia correctly?

while i can look at my design and know it will work, i kinda want it to work as good as i can make it...

Last edited by MrDude_1; 09-21-2003 at 04:55 PM.
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Old 09-21-2003, 08:13 PM   #2
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anyone? i see a bunch of views, but no replys...

any other sheetmetal intake tips?
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Old 09-21-2003, 08:34 PM   #3
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The runner diameter needed is relative to the cross sectional area
not the average of length and width of the port.

You realy want to know the cross sectional area

area of a circle is pi x radius x radius

3.14159 x radius x radius =

Area if a rectangle is length x width

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Old 09-21-2003, 09:38 PM   #4
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mmk. so my 1.340 x 2.210 tube is 2.9614


therefore:
with dia being 2.9614

2nd pulse -> 25.9" runner length
4th pulse -> 12.2" runner length
6th pulse -> 7.6" runner length
8th pulse -> 5.3" runner length


so that helped a lil athough i donno if i can fit a 7.6" runner.... and 5.3 seems kinda short.
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Old 09-21-2003, 09:39 PM   #5
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i donno, that doesnt seem right....

it wanted the runner dia, not the area.......
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Old 09-21-2003, 09:40 PM   #6
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That's why nobody that really goes fast uses "tuned" runners.... it only works for low-RPM motors (viz. TPI)
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Old 09-21-2003, 09:49 PM   #7
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Quote:
Originally posted by RB83L69
That's why nobody that really goes fast uses "tuned" runners.... it only works for low-RPM motors (viz. TPI)
i just got off the phone with a friend of mine that works at a race fab shop in texas...


apparently the only people that do that are the all out dragster guys with their sheetmetal tunnel rams..


he said to just make it as long as i can and still have it fit under the hood with some plenum volume and id be fine...

(well he said that in alot more words, but you get the idea)
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Old 09-21-2003, 09:52 PM   #8
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ahhh big math problems nooooo sorry couldnt help
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Old 09-21-2003, 11:28 PM   #9
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Quote:
Originally posted by MrDude_1
i donno, that doesnt seem right....

it wanted the runner dia, not the area.......
No, you need to calculate the area.

then use the equivilent diameter that ='s that area
for your formula.

Heres a hint, a Edelbrock Victor JR is about 5in from the port enty to the plenum.
Works very well at making power from 2700 to 7000rpm.
on a 350ci motor.
A edelbrock Performer RPM's runners are also about 5" long.
But because of it's dual plane design it favours the lower end
better than the top end of this rpm range.
5" runners are not nessessarily too short.

You actually want the runner to be a little larger at the plenum
and neck down in cross sectional area as it gets to the port.
So the air speeds up as it runs to the valve.
Look at a modern tunnel rams' runners and you'll see.

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Old 09-21-2003, 11:39 PM   #10
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Quote:
Originally posted by MrDude_1
mmk. so my 1.340 x 2.210 tube is 2.9614


therefore:
with dia being 2.9614

2nd pulse -> 25.9" runner length
4th pulse -> 12.2" runner length
6th pulse -> 7.6" runner length
8th pulse -> 5.3" runner length


so that helped a lil athough i donno if i can fit a 7.6" runner.... and 5.3 seems kinda short.
I get a figure of 1.941" for equivelent runner diameter.

the biggest problem is you'll need a box o' camshafts
and tons of dyno time to make it work ( right)
The volume and shape of the plenum is very imprtant to the success of any tuned runner manifold design. Plan of spending some time and experimentation here.
All the math will only get you so far. It leaves out may unaccounted factors.

Last edited by F-BIRD'88; 09-21-2003 at 11:43 PM.
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Old 09-22-2003, 12:00 AM   #11
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Quote:
Originally posted by F-BIRD'88

You actually want the runner to be a little larger at the plenum
and neck down in cross sectional area as it gets to the port.
So the air speeds up as it runs to the valve.
Look at a modern tunnel rams' runners and you'll see.
yea i know about the length on other intakes, but i wanted to try to be "better" heh....

anyhoo, about the tapering as you get closer to the port to speed up the air... i want to do that eventually, bu i think i will wait until my 2nd intake to do that.

the only goals of this first intake is to:
1. flow better at mid to high RPM then the TPI
2. flow enough air not to choke my 400
4. build it the best way i can afford to.

unfortunatly, i dont have a way to cheaply make the runners anything but rectangles right now... so im just going to wait... im sure this isnt my only intake. just the first of several

from another site:
Quote:
To further help fill the cylinder, it helps to have a high velocity at the back of the valve. To do this the intake port can be tapered. To be effective, there should be between 1.7 and 2.5% increase in intake runner area per inch of runner, which represents a 1-1.5 degree taper. For an example, lets say you're looking for a 2% increase per inch taper on the 2.02" valve we discussed earlier. We already came up with a port area of 2.56 square inches at just before the valve. Now lets say the total runner is 10 inches from the valve to the plenum and we're looking for a 2% per inch taper. This turns out to be a total of 3.12 square inches where the port meets the plenum. As you get near the 2.5% per inch taper point, you are pretty much at the limit of helping air flow. A larger taper will only hurt signal strength at the carb.
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Old 09-22-2003, 12:07 AM   #12
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Quote:
Originally posted by F-BIRD'88
I get a figure of 1.941" for equivelent runner diameter.

the biggest problem is you'll need a box o' camshafts
and tons of dyno time to make it work ( right)
The volume and shape of the plenum is very imprtant to the success of any tuned runner manifold design. Plan of spending some time and experimentation here.
All the math will only get you so far. It leaves out may unaccounted factors.


well im poor and dont have cheap access to the dyno, or a bucket of cams, so im just going to have to try my best with what i have...


honestly, i have my doubts if this cam will run with the TPI... some say yes, some say no, but everyone agrees it wont be easy.... im just going to try my best with what i have... :lala:


worse comes to worse, i can stick a victor jr and a carb on it and i know i will hit over 400 hp
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Old 09-22-2003, 12:10 AM   #13
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The more i look at this thread the more problems i see.
You're starting off at the wrong point.

You're trying to build a manifold to match a certain camshaft.

Some basic goals are missing.

What size motor ( cubic inch) are you building? Pick 1.
The tuning and cam timing will be quite different to reach a certain horsepower level on two different sized motors.
the total airflow needed will be about the same.
How much horsepower do you want to have when you're done?
A runner of a certain diameter will only flow so much air.
If the runner is short on basic airflow you wan't make the hp you're after, reguardless of all your design and tuning efforts.
ram tuning effect will only get you so far.

Therefore make sure your runner diameter flows enough air (cfm) before you commit to it.
Rule of thumb..... You'll need about 2cfm of total intake port flow at 28" on a flow bench per horsepower. this is for a naturely aspairated motor with good ram tuning design.

Design the motors' induction and exhaust system to work together as a whole. Then cam it.
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Old 09-22-2003, 05:45 AM   #14
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There is a engine simulation program called "Engine Pro"
that will help a lot.
Another good but complicated one is "Dynomation"
I think you can still download a demo..
Do a search and see if you can find it.

" worse comes to worse, i can stick a victor jr and a carb on it and i know i will hit over 400 hp "

This is why I used a Vic Jr as an example.

Send me an email I have a page of runner specs and flow figures for various TPI manifolds and the Vic Jr and RPM manifold.
I think you'd find it interesting.

russ_q@hotmail.com

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Old 09-22-2003, 05:53 AM   #15
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Air Volume of Various Intake-Component Parts
(All flow testing done at 28-inches H2O with the approximate temperature at 68 F)

Runners (measured individually)
Stock....................203.17 cfm
ACCEL................242.02 cfm
Extrude/ACCEL...275.83 cfm
Super Ram............289.18 cfm
Intake manifold with 3/8 inch radiused intlet
.............................222.45 cfm

Stock intake manifold with runner
Stock....................198.72 cfm
ACCEL................213.52 cfm
Extrude/ACCEL....217.11 cfm
Super Ram............220.67 cfm

ACCEL Hi-Flow intake manifold with 3/8 inch
radiused inlet.........251.51 cfm

ACCEL Hi-Flow intake manifold with runner
Stock....................215.83 cfm
ACCEL................232.53 cfm
Extrude/ACCEL....243.21 cfm
Super Ram............240.24 cfm

Extrude-Honed ACCEL Hi-Flow intake
manifold with 3/8 inch radiused inlet
............................275.83 cfm

Extrude-Honed ACCEL Hi-Flow intake
manifold with ACCEL runner
............................266.94 cfm

Edelbrock Performer RPM manifold
(Stock)..................286.51 cfm

Edelbrock Victor Jr.
.............................275.24 cfm
1989 Corvette head cfm
(Stock head with 3/8 inch radiused inlet,
6 inch extension, 1 3/4 inch diameter exhaust)
Intake cfm at inches of lift
60.68 @ 0.100
117.28 @ 0.200
156.81 @ 0.300
176.47 @ 0.410 (stock 89 Corvette cam lift)
177.97 @ 0.437 (1.6:1 rockers)
183.89 @ 0.499 (1.5:1 rockers, 211/219 split
duration ACCEL cam)
185.37 @ 0.533 (1.6:1 rockers, 211/219 split
duration ACCEL cam)
186.85 @ 0.550 (port stall point)

Exhaust cfm @ inches of lift
38.53 @ 0.100
99.84 @ 0.200
137.28 @ 0.300
156.32 @ 0.423 (stock 89 Corvette cam lift)
157.90 @ 0.451 (1.6:1 rockers)
161.05 @ 0.525 (1.5:1 rockers, 211/219 split
duration ACCEL cam)
162.63 @ 0.56 (1.6:1 rockers, 211/219 split
duration ACCEL cam)

Intake/Exhaust ratio @ maximum lift
Stock............1.5.........88.5%
....................1.6.........88.7%
211/219........1.5.........87.5%
....................1.6.........87.0%


This chart has been directly pirated from the December 98 issue of Hot Rod. Anybody interested in fuel injection NEEDS this issue, so go buy it now and maybe this shameless plug will cut me some slack when they sue me for pirating this info



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

Lengths To Various Points In Cyllinder Head and Intake System

Length from intake port in head to valve seat = 6.125 in.

Manifolds
Stock TPI manifold passage length = 8.000 in.
ACCEL TPI manifold passage length = 8.000 in.
Edelbrock Performer RPM passage length = 6.000 in.
Edelbrock Victor Jr. passage length = 5.500 in.

Runners
Stock TPI runner length = 11.250 in.
ACCEL Hi-Flow runner length = 11.250 in.
ACCEL Super Ram runner length = 7.000 in.

Total Lengths from Plenum to Valve Seat
Stock TPI = 25.375 in.
ACCEL Hi-Flow components = 25.375 in.
ACCEL Super Ram components = 21.125 in.
Edelbrock Performer RPM = 12.125 in.
Edelbrock Victor Jr. = 11.625 in.
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Old 09-22-2003, 01:04 PM   #16
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Quote:
Originally posted by F-BIRD'88
The more i look at this thread the more problems i see.
You're starting off at the wrong point.

You're trying to build a manifold to match a certain camshaft.

Some basic goals are missing.

What size motor ( cubic inch) are you building? Pick 1.
The tuning and cam timing will be quite different to reach a certain horsepower level on two different sized motors.
the total airflow needed will be about the same.
How much horsepower do you want to have when you're done?
A runner of a certain diameter will only flow so much air.
If the runner is short on basic airflow you wan't make the hp you're after, reguardless of all your design and tuning efforts.
ram tuning effect will only get you so far.

Therefore make sure your runner diameter flows enough air (cfm) before you commit to it.
Rule of thumb..... You'll need about 2cfm of total intake port flow at 28" on a flow bench per horsepower. this is for a naturely aspairated motor with good ram tuning design.

Design the motors' induction and exhaust system to work together as a whole. Then cam it.

i confirmed it this morning with my uncle, i got his old 400 block, so i will be building a 400 and putting roller conversion lifters in it.

the exhaust will be hooker coated long tubes, with a custom Y pipe going into a catback. not right away, but eventually i'll have a elec cutout.

so i know my exhaust, my displacement, my final cam, my final head selection is between the motown 220 heads and the 220cc intake runner pro topline iron lightning heads.

the compression should be around 9.7:1
the spark will be the computer controled divorced coil HEI with a MSD blaster coil
i usually run Accel header sparkplugs and Accel wires


this motor is being built in short stages over the next year, but i dont mind it not being perfect until i get all my final parts together.

im just wondering if i can get a decient jump in power by making the intake better....


a thought i had lastnight...going to sleep



look at the pic below... the top is the manifold as i have it now.

the bottom has a triangle added in the center..

heres the idea.. look at the blue line, its in the rough center of the port/runner... the wave coming out hits the triangle, bounces flat off the bottom of the intake, and back up to the triangle and into the port...

that SHOULD give the effect of longer runners right?
the red line shows how it works for the top half of the port, and the green shows the only problem area... it just misses the triangle and only part way reflects.... the rest of it goes by the triangle like normal.



so what do you think? think i can do that to lengthen my runners, or is it not worth it?
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Old 09-22-2003, 01:06 PM   #17
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i realize im trying to use my plenum area as runner space too.... but even though the wave will widen alot outside the port, think i will still get some effect?
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Old 09-22-2003, 02:08 PM   #18
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Just thinking, but it you wanted longer runners, cuoldn't run them to the opposite side of your plenum, not sure what it would do to flow, but if the plenum were wide enough...kinda "T-ram" style, abd have the runners come in before the sides of the plenum.

I dunno, that's why I buy things these days, don't have enough time to play with ideas.
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Old 09-22-2003, 02:26 PM   #19
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I thought that the 2nd wave was the strongest and thats why GM used that one with thier 21"? TPI length. But most of the fastest motors I know use a super short "untuned" runner that has a good flat power curve. Thats what an LT1 intake is anyway.

And thats what you wanted to mimic right?
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Old 09-22-2003, 03:02 PM   #20
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Quote:
Originally posted by Blown WS6
I thought that the 2nd wave was the strongest and thats why GM used that one with thier 21"? TPI length. But most of the fastest motors I know use a super short "untuned" runner that has a good flat power curve. Thats what an LT1 intake is anyway.

And thats what you wanted to mimic right?
orignally, i was just going to mimmic the LT1, but after talking to a few people, i decided i would atleast try to be better...


athough i may just end up building it like i orignally planned... a good LT1 knockoff. *shrug*


theres alot of general info on the web, but noone seems to go into the detail im looking for.
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Old 09-22-2003, 03:35 PM   #21
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I doubt the pressure wave will see the triangle as a reflective point.

Much better to have the positive pressure spike that occurs when the valve closes arrive at the next valve in the sequence as it opens. This will happen at whatever tuned lenght rpm equals the total of the two runner lenghts with a effect of the plenum.

the plenum basicly acts like a capacitor or like a header's collector.

You can have multiple rpms where one or another tuned ram effect comes into play.
This what happens on the short runner manifolds like the Mini ram and LT1 intake.
Thats one reason why they have such flat torque curves.
Where is the longer runners like a TPI intake have one or two
in tune ram effects over the usable rpm range. With one being the most prominate. the rest of the rpm range it is out of tune.
this is why these motors usually have a peaky torque curve.

The "anti tuned" systems can tolerate a higher static compression ratio because of the flatter torque curve.
thats why the TPI motos are built at less than 10:1 and Lt-1, lt4
and MINI ram motors like a little more cr.

The trouble with picking a cam just cause you have it, is it probabily won't be anywhere near the right one for the combo.

But cams are relitively cheap ( once you have the valve train for it.
You can always sell it off and get a better one ( for your combination)
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Old 09-22-2003, 03:45 PM   #22
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Quote:
Originally posted by F-BIRD'88
I
The trouble with picking a cam just cause you have it, is it probabily won't be anywhere near the right one for the combo.

But cams are relitively cheap ( once you have the valve train for it.
You can always sell it off and get a better one ( for your combination)

im not picking it because i just have it... im picking it because its the cam i want... and aftermarket roller cams arnt cheap



now hyd flat tappet cams are.
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Old 09-22-2003, 05:52 PM   #23
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Quote:
Originally posted by MrDude_1
im not picking it because i just have it... im picking it because its the cam i want... and aftermarket roller cams arnt cheap



now hyd flat tappet cams are.
If you want to design and build a "Better intake" best to get a cam the the motor wants, not what you want cause it looks good on paper or in the catalog.

A "better" successfull combination depends on taking full advantage of the laws of Physics.

There will be many built in limitiations that you'll have to work around but the camshaft is one area where you have a lot of freedom to match it to the induction and exhaust system
and make it work well.

Way too important.... but..... it's your project.

You may eventually end up with a intake that matches your favourite cam but it will be one of many and may not make your car go.

Like I said cams are relitively inexpensive resellable and easy to change. There are many computer programs and experts that can really help you nail down the best one (a custom grind),, Each intake you build will cost alot more. Once you've gotten a matching cam in the motor that works well with the intake you can give it whatever feel good numbers you like.... The motor or the laws of physics won't mind a bit.

Have to ask yourself, do I really want to go fast(er) or do I want
make a feel good motor.
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Old 09-22-2003, 06:18 PM   #24
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lets put it this way.

with the motor and the cam that i am putting in it, it will be exactly the way i fuggin want the motor to be. just streetable enough to drive in the rain. it would be perfect with the victor Jr,

the only reason im not using the victor jr is that i would like this motor to have MPEFI, and since the rest of the motor will remain constent, having this intake made to work as good as it can WITH THE REST OF THE MOTOR would be fine..


but i could go the "regular" route of taking a off the shelf intake (thats easier to swap then a cam) and then tailor grinding a custom cam (like anyone needs a custom cam for the street)



this is a street car that sees occasional (3 times a month during summer) track use.... the car isnt full drag, its going to see autoX too, i just want to make the best intake i can for the motor. i dont need anyone fighting over the rest of my combo. tell me one thing thats wrong with that cam for my combo.
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Old 09-22-2003, 07:22 PM   #25
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Whats wrong with it?

Never mind that it's just a cam out of a book,
it does not even suite your aplication as discribed by the manufacturer When you consider the parameters you want out of it.

Its not even recommended for EFI or a daily driven car with
infreaklent track use.

Phone or email Comp cams and get their recomendation.
They are the experts on their stuff. they even recomend you don't pick a cam out of the book.

Don't tell them the cam you want, tell them what you want it to do in the motor.
I beat it'll not even be close. It will cost the same. they do not charge extra for custom grinds.

Three words sum it all up, right out of the catalog. "Marginal brake effectivness".
Hope ya never get behind me in traffic "in the rain".

Seems I've hit and emotional hot spot for ya so I leave ya with it.

Good Luck to ya....
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Old 09-22-2003, 08:35 PM   #26
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Quote:
Originally posted by F-BIRD'88
Whats wrong with it?

Never mind that it's just a cam out of a book,
it does not even suite your aplication as discribed by the manufacturer When you consider the parameters you want out of it.

Its not even recommended for EFI or a daily driven car with
infreaklent track use.

Phone or email Comp cams and get their recomendation.
They are the experts on their stuff. they even recomend you don't pick a cam out of the book.

Don't tell them the cam you want, tell them what you want it to do in the motor.
I beat it'll not even be close. It will cost the same. they do not charge extra for custom grinds.

Three words sum it all up, right out of the catalog. "Marginal brake effectivness".
Hope ya never get behind me in traffic "in the rain".

Seems I've hit and emotional hot spot for ya so I leave ya with it.

Good Luck to ya....
actually, thats the cam they gave me.

i like it rough on the street, and im running a elec vac pump for power brakes and the AC air doors.... he said its edgy if it would work with efi, but he thinks its can be done... and yes it says
Quote:
HYDRAULIC ROLLER-Great for Street Machines. Best with headers and aluminum intake. 2000+ stall. Rough idle.
Marginal power brake effectiveness.
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Old 09-22-2003, 09:47 PM   #27
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" he said its edgy if it would work with efi, but he thinks its can be done."

He's right about the edgy bit.


Did you sell him on the cam or did he sell you?
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Old 09-22-2003, 09:47 PM
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