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Discussion Starter · #1 ·
I have been asking some questions, but maybe in the wrong order...

Building a 347, cam not picked. The posts have convinced me that a 347 is the way to go. Doin it.

New 9 inch needs to go in: 8 inch leaking at the bearings, mini spool is a pain, brakes are shot and new leaf springs screwed up driveshaft length. Ordering this week.

So the new question is, should I pick the gear ratio FIRST (based on the weight of the car + engine size)?

OR

Finish the cam selection and THEN match the gears to the cam??

Seriously, say you buy a new project and building to go fast, what is the first thinig you pick to get the combo going??

Car wont change, trans wont change,tries wont change in size and now just trying to get a decent set up together.

Another funny thiing is that I checked with one guy that posts here because he has a car like mine that really hauled, he said to use a combo different from his becasue his was too high strung.

Thanks!
 

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First, decide what you want out of your engine. Then pick the heads and then the cam and then the gears. If you have an automatic, you'll have to choose a converter that's matched with your cam and gears.
 

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The first thing you need to do is figure out what you want to use the car for today and in the future. And be realistic about it. People say how they're going to drag race it and drive it once a week on the street. Then build it so raditical that it sucks. Usually when people say they're going to drag race it all the time, they end up actually street racing and parked all the time because it isn't any fun to drive. Pick the purpose and then the components. What do you already have that you're matching up too? Tires what kind, etc.
 

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Discussion Starter · #4 ·
Ok dacofa, good point: already have AFR 185's, likley ET Street's or similar 275/60, Air Gap, frame conecters, tko 5 spd, super comps, x pipe, 2.5 exhaust 670 avenger (willing to change it), petronix igntor 2 with coil, new cooling system.

Will drive it to cruise nite that is 25 miles away, or to track that is also 25 miles, maybe the other track thats 80 miles. Street yes, drag sometimes, but i have a stocker 69 camaro for slow cruising, so this is more on the fast side. Fast but still fun. Not going for 10.50's on the motor, more like 12 flat or better if the combo really worked.

The budjet is showing that a roller 347 is doable. I usually over build on the hard parts because i dont like it when cheap stuff breaks.
thanks dacofa!
 

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questions to ask yourself:
What is its use?
How fast do I have to turn it to do that?
How fast can I afford to turn the engine?
Then you select the parts to make the engine stay together when turning it at that RPM.
Questions that don't need to be asked:
How much compression do I need? - all you can get, if you are running on the street somewhere between 9.5:1 and 10:1
when slecting cam, carb, intake, and headers - BIGGER is NOT always better. if you buy a carb and cam that will allow your engine to turn 8500 rpm and you are using stock cast pistons and rods that will break with sustained use at 6000 rpm you are wasting your money.
the cam is designed to give peak HP at a given RPM, most manifolds are designed to work best up to a set RPM, Carbs are designed to flow air up to a given RPM (CFM), and headers are designed to flow best at certain rated RPMs (CFM) so it is important to pick each component to run best when your engine is at that RPM that you have selected. After you have done that you can pick your tire and rear gears so that you cross the traps at the end of a 1/4 mile in high gear at your peak rpm.

If you have a certain hp in mind that you simply must meet then you need to find out how much air and fuel it will take to make that much HP and build your engine to the RPM that will flow that much air and fuel.
The design stage of your engine is crammed full of math - or the advice of a competent engine builder.
 

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Looks like a good set of 4.10 gears for your setup. I'd keep the 8" and have a strong posi 3rd member and forged steel axles from Currie or Moser for it. That'll save weight and ne very strong. Cam, you want a 1500/2000-6000/6500 rpm range cam. I'd go with the roller hyd for ease of maint. Pistons forged, strong rods with ARP bolts. Windage tray and baffled oilpan. Electic cooling fan, oil cooler, alum waterpump and radiator. Beefup the brakes because the faster you go the more stress they have. You might think about a fiberglass hood with and opening to help get cooler air to the engine and reduce weight. Lakewood scatter shield. In the engine use only ARP or Milodon grade 8 studs or bolts. I prefer a manual steering and brake system, even disc, because if the engine fails I still have good brakes and steering. Also use braided steel hoses on your braakes and anywhere else flammable liquids have a hose. Wheel studs replace with good aftermarket grade 8 studs. Safety
 

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Discussion Starter · #7 ·
do you really think a 8" will hold up behind a 5 speed with good tires? I thought it would fall apart after I get the 347 in..

on the 4.10's, if the idea for a more steet type engine is a cam that is between 1500-6000, dont you want a gear that doesnt rev the engine to quickly? This is the exact spot where I dont understand which way to go. I would think that 4.10 would be ok, but am I running out of engine when setting up more of a low end cam?

I hear you on the saftey stuff. I always go through all that before I buy hipo parts.

Thanks for your thoughts...
 

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One thing no one's mentioned here, is that if you pick 302 based parts, that have an advertised rpm range of 7000, you'll never get it by putting that part on a 347. ALWAYS err on the slightly larger side with a strip/street 347, when deciding on the 302 based parts...in particular on the headers/intake/carb side. If you don't, you'll end up with a tow motor that won't rev, then wonder why you bothered with a stroker. The cam can be chosen from 351W offerings (or better, custom) which should match the rpm usage much more closely.

~edit~ This does NOT mean choose 5000-8500rpm parts while hoping for 6500rpm performance. It means a 3500-7000rpm part is going to get you 2500-6000 or so. A 347 needs more air to operate than a 302 =). ~edit~

I have also run as much as 11:1 compression on the street with aluminum heads, on a 347 no less. It's all in how the cam is designed to run with it. You can make a 9:1 motor kill itself with detonation with the wrong cam choice. I also would not build a 347 that couldn't rev to a 6500rpm shift point, with a 7000rpm redline, or you're not really taking advantage of the main advantage these motors have over windsor based strokers. Rpm's.

All in all the above advice is pretty good. A 3.73 to 4.10 gear will keep you happy with a 6000-7000rpm motor. If you limit yourself to 6000, go with the 3.73's, you'll be happy. If you take my advice and build it to do what it wants to naturally...do the 4.11's, and hold on =).

Cris

<font size=-1>[ This Message was edited by: Is1BadFord on 11/17/06 9:30pm ]</font>
 

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Lots of good advice here, I'll throw one last log on the fire -- you might ask the cam grinder if the recommendation would change at all with a step or two in either direction in the final drive ratio. My hunch is not much...

Look carefully at your low gear multiplication with the TKO, too, with 4.11's, make sure your low gear isn't TOO short, a rule of thumb is that anything more than 12:1 ratio (low x final drive, roughly, does not account for tire loaded radius) is probably overkill, and will have you against the limiter almost before you can pull the knob.

BOB
 

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First, start with how quick you want the car to be. 13's? 12's? 11's? etc.....

Then determine the HP that it will take to get there.

After that, decide if you want to run pump gas or race gas.

That decision will drive your compression ratio.

The displacement will determine how much RPM you'll have to turn.

The cam will then be selected to make the HP at the RPM you need it at.

The heads, intake and exhaust will all work to make the engine more or less effecient, depending on what parts are chosen and how much work is done to them.

I am sure I left something out, but the general idea is that the cam selection is somewhere in the middle of the engine design, not at the beginning.

Greg
 

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On 2006-11-17 10:54, GregP wrote:
First, start with how quick you want the car to be. 13's? 12's? 11's? etc.....

Then determine the HP that it will take to get there.

After that, decide if you want to run pump gas or race gas.

That decision will drive your compression ratio.

The displacement will determine how much RPM you'll have to turn.

The cam will then be selected to make the HP at the RPM you need it at.

The heads, intake and exhaust will all work to make the engine more or less effecient, depending on what parts are chosen and how much work is done to them.

I am sure I left something out, but the general idea is that the cam selection is somewhere in the middle of the engine design, not at the beginning.

Greg
Agree with everything, excepting the cam/heads. Imo those need to be reversed. The last thing chosen in a performance engine build should be the cam. A cylinder head should be chosen that supports your rpm/displacement/hp choices, in both cross section, and flow. Not to mention total port cc's (which will be compared with cross section to determine efficiency). After this, the cam can be chosen to work with the cylinder heads to either tame a slightly too large head, or to take better advantage of a slightly too small head.

Other than that you're right on track imo Greg!

Cris
 

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Discussion Starter · #12 ·
all good stuff, thanks everyone. One more question on the gears part of the advice:

with my trans and 4.10's I am shifting really quick. I just saw on line that 1st is 3.27, so 3.27x4.1=13.4.. is that why all those 5.0 mustangs only run 3.55 / 3.73? As maurderman pointed out, I am redlining superquick, but not really going any where.
 

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I have a 5 speed like you do in my 67 mustang. I have a set of 3.80 gears in it and first gear comes and goes pretty damn quick (as does secong for that matter). The one reason why I want 4.11's instead is because at about 55mph (the speed ad which everyone likes to drive here for some reason) the engine is not in its torque band in 5th and revving at about 3000 rpm in 4th. I think with the extra torque of the 347 you shouldnt have as much of a problem. I would go with some 3.80s if I were you and a cam with about 230* of duration at .050.
 
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