Automotive Catch 22 - wtf

-
OK, now we're getting somewhere. Yes, you can keep changing things but that costs money too (and you'll never get anywhere near what you paid for the old stuff). Try and hit your target the first time...

Tell us more about your planned engine. A stock 360 rebuild? Not going to run 10's with that. Do you already have the block or any parts at all? Look at stroker kits if you're going to be buying a rotating assembly anyway. "No replacement for displacement" ;)

Finish line RPM for a modestly priced smallblock will likely be no more than 6500. Yes, you can build a smallblock that turns 8000+ but you aren't going to like the price of the valvetrain, heads, rods, etc. necessary to do that. Now plug 6500 and 28", optimistically 120 mph trap speed, into an online calculator and you get something around 4.30 gears. Definitely driveable 10 miles to the track since you'll be turning half that RPM (3250) at 60 mph.

Remember that a 5000 stall converter can be driven on the street depending on its internal design (and oil cooling, and weight of the car)... it does NOT mean you have to rev to 5000 before the car will move! It only takes about 20 hp to cruise at 60 mph. There are lots of different options from the manufacturers, and (as initially pointed out) that's why they need to know your combo before they can build you one.

I really recommend you start with a realistic budget for the entire project. That will to a great extent dictate how fast you can go, as the ancient quote summarizes. Do you have any idea what you can invest in the engine and the car?
 
You can't just pick a ratio and go racing.

You have to have a budget before anything
For a 360;
A 4.30 gear is good for 120mph with big power and costs big money.
A 4.30 is good to 112 with a much more modest cam the kind you put in a weekend warrior. And your still spending a lotta money to go there
And 4.30s are good to 104 with a small cam, the kind that you put in a streeter.

So the 4.30s may ultimately be the right gear, but........ That's not the place to start. The budget is.
Say you spend $6000 on the engine and find out the trans won't take it, the gears are wrong and the TC is useless. Can you cough up another 4 or 5 Gs to get the combo right? And another 2Gs to make it hook? And don't forget that when you get to the traps you gotta start thinking about slowing down.So now you need brakes. And what if the front suspension needs a G? Or you need upgrades to the cooling system,fuel system, and ignition system?,maybe up to another 2G? Wheres all that money coming from?
You gotta start with the budget.
Then a solid car, as in the suspension steering and brakes are gonna be there when you need 'em.And the chassis welds are still holding things together. And the suspension pick-up points are solid. Etc.
Then you're gonna need to figure out how fast you can afford to go. Speed costs money. The faster you want to go; the more it will cost, and the cost of speed progression is not linear.
Then you will need to figure out how quick you can afford to go. Low ET costs money; lots and lots of money.
Once you have those targets decided, then we get to the how-to-do-it part.
With no stated budget No one can help you.
If you have $6000, it's one build. $11,000 another, and $15,000 now 'yer talkin'.
With $6000 you can't do much. The chassis will suck up the biggest part of that, the chassis being; suspension steering and brakes, a narrowed rear for the slicks, An LSD,a traction aider,upgrades to the cooling,fuel, and ignition systems, New HD U-joints,new tires all 'round, and modifications to fit your car into whatever class you have decided to attack. So there might be enough leftover for a trans rebuild with HD parts. But no engine yet.
With another $5000, you get a dressed 12 second engine, and a matching TC, and maybe some gears.
The last $3000 you get to spend on goodies; Like;a helmet, an 8000rpm 270* sweep tach, a gauge pack, a rear-bumper shut-off, A little graphics,a new seat, you know things to make everybody happy.
But less than $6000 well that's a tuff chew. I think you need to re-examine your priorities. If you spend it all on the engine, and nothing else, that would be a waste. Lots of tire spin, no low-ET and crappy mph to-boot. Plus without the chassis upgrades, she's an accident waiting to happen.
Remember when 340 cars were new? Yeah like; those cars were way overpowered for their chassis.Handled like a barge, pendulummed when changing lanes,drifted on every corner, but I can't complain about the brakes, I'll give then that. But one thing I can tell you; they do not work unless the tires are on the ground!
So back to page #1, what's the budget? And have you spent any money on the chassis yet?
By the way, getting that Duster into the 13s is not that pricey, And low-13s are pretty impressive, on a budget.
Mid 12s ain't too bad either.
But mid 11s are expensive, but just getting into the
10s, NA, is rent-your-wife-out crazy money.....

But if you just want to have some fun, that's a whole 'nuther story.......
 
Dr. Charles said the 904 may not/will not hold up. Properly build, it is the weapon of choice. NOT the 727. But ether will do when built right. The 727 eats up approx. 50 or so HP easy.

You say you want to go as fast as you can. At what displacement? Are aluminum heads in the budget?
Are $700 roller rockers to much?
We gotta have some idea of what you have, willing to change out or upgrade to.

An excellent all around tire/gear would be 4.10's and a 28 inch tire.
It figure you will want a pump gas engine. What you could do is build a 360 with KB-107 HyperU slugs at zero deck. Combined with Edelbrock aluminum heads the ratio will be under 11-1 by a hair and good for pump gas with a big-ish cam required to run quick. Or with iron (AKA Stock) heads it will be approximately 9.8-1. Again, excellent for pump gas with a big-ish cam.
Speaking of cams, a street strip suggestion here would be a Lunati solid cam. Part number 30200743 (old number - 60443)
288/296 @.050, 259/267-.586/.606 lift, 110/106 - .016 lash
Suggested 3500 stall
Serious shift kit installed, deep trans pan & cooler infront of the radiator.
Hughesengines roller Rockers
Headers @ 1-3/4, 3 inch exhaust pipes.
RPM intake, 850 Holley.


When money allows, fully port the heads and intake and move up 2 steps on the cam.

Is this what you want?
 
AJ/FormS said:
You can't just pick a ratio and go racing.

You have to have a budget before anything
For a 360;
A 4.30 gear is good for 120mph with big power and costs big money.
A 4.30 is good to 112 with a much more modest cam the kind you put in a weekend warrior. And your still spending a lotta money to go there
And 4.30s are good to 104 with a small cam, the kind that you put in a streeter.

So the 4.30s may ultimately be the right gear, but........ That's not the place to start. The budget is.
Say you spend $6000 on the engine and find out the trans won't take it, the gears are wrong and the TC is useless. Can you cough up another 4 or 5 Gs to get the combo right? And another 2Gs to make it hook? And don't forget that when you get to the traps you gotta start thinking about slowing down.So now you need brakes. And what if the front suspension needs a G? Or you need upgrades to the cooling system,fuel system, and ignition system?,maybe up to another 2G? Wheres all that money coming from?
You gotta start with the budget.
Then a solid car, as in the suspension steering and brakes are gonna be there when you need 'em.And the chassis welds are still holding things together. And the suspension pick-up points are solid. Etc.
Then you're gonna need to figure out how fast you can afford to go. Speed costs money. The faster you want to go; the more it will cost, and the cost of speed progression is not linear.
Then you will need to figure out how quick you can afford to go. Low ET costs money; lots and lots of money.
Once you have those targets decided, then we get to the how-to-do-it part.
With no stated budget No one can help you.
If you have $6000, it's one build. $11,000 another, and $15,000 now 'yer talkin'.
With $6000 you can't do much. The chassis will suck up the biggest part of that, the chassis being; suspension steering and brakes, a narrowed rear for the slicks, An LSD,a traction aider,upgrades to the cooling,fuel, and ignition systems, New HD U-joints,new tires all 'round, and modifications to fit your car into whatever class you have decided to attack. So there might be enough leftover for a trans rebuild with HD parts. But no engine yet.
With another $5000, you get a dressed 12 second engine, and a matching TC, and maybe some gears.
The last $3000 you get to spend on goodies; Like;a helmet, an 8000rpm 270* sweep tach, a gauge pack, a rear-bumper shut-off, A little graphics,a new seat, you know things to make everybody happy.
But less than $6000 well that's a tuff chew. I think you need to re-examine your priorities. If you spend it all on the engine, and nothing else, that would be a waste. Lots of tire spin, no low-ET and crappy mph to-boot. Plus without the chassis upgrades, she's an accident waiting to happen.
Remember when 340 cars were new? Yeah like; those cars were way overpowered for their chassis.Handled like a barge, pendulummed when changing lanes,drifted on every corner, but I can't complain about the brakes, I'll give then that. But one thing I can tell you; they do not work unless the tires are on the ground!
So back to page #1, what's the budget? And have you spent any money on the chassis yet?
By the way, getting that Duster into the 13s is not that pricey, And low-13s are pretty impressive, on a budget.
Mid 12s ain't too bad either.
But mid 11s are expensive, but just getting into the
10s, NA, is rent-your-wife-out crazy money.....

But if you just want to have some fun, that's a whole 'nuther story.......
Click to expand...
Budget, well that's probably the most limiting factor in this whole deal. My initial budget is pretty low so anything big money wise will have to be saved up for. I finally got around to checking out the rear end and I'm going to have to get another one. That can get expensive.

Here's what I've got - I've got a '74 Duster with no engine, tranny, or driveshaft with an 8.25 open rearend. I've got a deal worked out for an '89 360 and tranny but don't have them in my possession yet. The 360 is stock and the PO was going to "freshen" it up. The heads have already been gone through. The trans is an OD unit and at first I thought it would be a good idea to use it. But after reading an article on getting it to fit an A body I'm not interested in using it. Just going to stay with a regular 'ol 904. If the engine checks out I plan to drop it in with a freshened 904, deal with the rearend, fix whatever...and go racing. I will be installing sub-frame connectors as one of the first chassis mods I do. I plan on more serious modifications in the future, but not till I get the car squared away. Right now I want to have some fun and as I make modifications it will be fun to see what effect they will have.

Here's a question - what is the safe max rpm for a stock 360? I've read 5500, others have said 6500, or more.
 
Think of a 5 year plan.....get the engine/trans in the car...get rear end work done...go racing..
next year...upgrade the suspension....new springs new shocks..new gears ...
keep racing...
next year bolt on performance parts....better intake..better carb...keep racing..

Have a final goal of a master plan...buy parts new or used that fit the master plan so you are not buying stuff twice..
 
Maximum safe rpm varies with the build sorta
But think shift rpm first.
And powerband requirement
With no stated budget nobody can help you.
You can rev that 360 to 7500. But to make use of it will require a very expensive build.
You can rev it to 6500, like a typical hot-street and if you go there regularly, it could still be pretty expensive.
You can set the limiter to around 6000 and get away with it for years, until one day you wind it out a little low on oil and whoops, there goes a rod, and maybe it takes the crank with it.
You can build it pretty cheap to shift at 5500, tho, and it could last over 100,000 miles.
Each of these builds is an engineered build with all kinds of different stipulations. Like the cam and compression ratio are practically married.And the heads set the stage for everything.
The higher revs require oiling mods to survive. The carb and intake need to be matched to the operational rpm. And of course the support systems have to keep pace.
Then there is the small matter of the required powerband.
The A904 has ratios of 2.45-1.45-1.00. The splits are 1.45/2.45=.592; and 1/1.45=.69... This means whatever you rev it to, when you outshift, the revs will fall to these percents. So say you rev it to 6500, then the shifts will fall to 3848 and 4485. So your powerband requirements are 6500less the above two inshifts,or 2652 and 2015. So if you want your engine power to peak somewhere in the middle of the requirements. And you want the powerband to be wide enough to cover both ends of the rpm band with a generous amount of power. So generally a guy might sacrifice the 1-2 , cuz you'll be whamming thru there pretty quick. But the 2-3 has to be spot on to trap well.
Ok so where do you want the peak power to be? Again generally, depending on the shape of the power curve, you might want the peak to be at 60% of the requirement. So 60% of 2015 is 1209 added to the bottom of the powerband 4485,is say 5700. So then you select a cam to put the powerpeak about there. This is a pretty big cam, and will normally need a lot of compression to keep the bottom-end from getting soggy. But you are a racer so don't care aboutbottom end, cuz you can put a convertor in there to cover that situation.
So you put this monster cam in there and of course the stock heads become an instant choke. So bigger heads have to go on, or at least some serious porting needs to be done. Either way it's gonna get expensive.
But say you get the heads up to speed and now you are making some serious power, over the rpm range that you need it to be, to use that transmission.
Now you have three more choices to make; the rear suspension and tires,the rear gear, and the TC.
Well TC first. This cam, is gonna want a big TC. The power peak comes at 5700 remember, and the torque peak will be at about 75% of that or say;4300. So you might think a 4300TC is the place to start
But at 4300 this 360 is making a lot of power; so you are gonna have to spend a lot of time and money to make it stick. Lot's and lot's of money.
Cuz if you don't, the tires go up in smoke and the guy in the next lane is laughing. So what do you do? Two choices; spend more money, or reduce the power delivery.
Reducing the power delivery can be one of several ways, but probably the cheapest is to swap out that 4300TC.

So now you see that your question about; what is the safe max rpm for a stock 360,IMO, is not the right question to ask.
Cuz if you build the engine to take advantage of such a number, the rest of the combo is gonna cost a lot of money to make use of it.
IMO the right question is something like this; I have xxxx dollars to spend on this project, how should I divide it up.
 
Last edited:
OMG! My eyes bleed again!

OP, do what 70aar said.
Stock rpm limit of a 360 is beyond where it makes power. In other words, it will stop making HP around 4500 for the 2bbl. Version and 5000 for the 4bbl. But both will rev past 6500 in neutral while in gear it'll be about 6K. At that level, it's not making any power. You'll go faster only due to rpm
 
Here's a question - what is the safe max rpm for a stock 360? I've read 5500, others have said 6500, or more.
Click to expand...
What?
He said maximum safe rpm
:)
IDK; maybe those factory pistons are the weak link,good to 6800. That means at 6801 they self destruct and everything comes to a screeching halt.
Maybe the crank is. No that can't be it, mines been to over 8000
Maybe the rods, yeah.... no, mine have followed the crank wherever it leads for over 100,000 miles.
Maybe the valve train, yeahno even if the valves do float, and the lifters pump up, those deep-dish buried in the hole pistons will never get close to the valves, so that can't be it.
So .........
Oh I know, it's the fan belt. Just rev it up until the belt flies off, then dial back 100 rpm.OK no my belt has never flown off.
Oh man, maximum safe rpm? hmmmmmmmm
Nope, it's not coming to me......lol
The 4speed cam was a 268/276/114 IIRC. That cam peaks at maybe 5000/5200 right? The 727 has a powerband so wide, it requires a 1-2 shift at about 6200, and a 2-3 at about 6000. Since Chrysler sold Stick-cars without rev-limiters, I reckon they were Ok with that.So throw in a fudge factor of 10% and I still see 6800 as safe.
6801? I can't say..................
Anybody ever blow up a 360 related to overspeed? What did the tach say?
 
Last edited:
Idk! But I've taken mine higher. Not saying it made power there.
 
You must log in or register to reply here.
-

Back
Top