I really did try to search this before asking, but my search-fu must be low.

Is there a generally accepted max RPM for each stock displacement assuming a stock or nearly so engine? Seems like this crank/bearing design might impose some limit short of "just before when the valves float". Any threads on this topic that I might refer to?

Specifically I am dealing with a 170 that was reportedly rebuilt by the PO before the member here that I bought it from. As to the quality etc. of that rebuild I know nothing.

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Thom

Cross-threaded is tighter than Lock-tite

When you say "stock" we will assume that you have a 1bbl carb.
A SL6 1BBL carb flows about 185 cfm so that will limit rpm on a 170 to appx. 4500 RPMs
DD

185 CFM is at a measured constant vacuum level. The 170 can pull alot harder than 4500. 185CFM is 5000 RPM on a 170 at .75 VE. Thats about right for durability. 5000 RPM on a 225 using the same 1920 needs 244CFM on the same spreadsheet. NASCAR 390 CFM carbs pull like 800 CFM to make 600 HP but look at the RPM pulling the air through those! Plus they weep fuel out of every controlled orifice allowable. $4500 gets you a real NASCAR 390. Just sayin a carbs CFM is only a rating at a specific level, not the level a certain motor can pull.

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I didn' t buy it, I built it.....

Thank you all.

I tend to think only of internal parts when I think "is it stock?" and failed to consider the external mods. Sorry about that.

To address all of the externals, this particular engine has the OE electronic ignition system conversion, Clifford intake, Holley 2300 series 2 bbl (unkwn CFM from an unkwn OE application) w/ a Percy's needle jet plate, and a 2.25" exhaust system on the unmodified stock exhaust manifold. As far as I know all of the internals are stock or stock replacements. I need to update my gallery thread with pics of the new stuff.

What brings up the question is that with the V6 F-car T5's pitiful OD ratio (.86) and the Ranger axle's 3.73's I'm wondering if 100 mph is sustainable or only safe (for the engine) for brief moments. This has become a goal for the car, to be able to go 100 mph for at least a couple minutes. (Of course this would only happen on a closed course, etc.) With the current tire my spreadsheet predicts 4350 rpm at 100 mph. I've been looking for a V (ideally) or a P or R code T5 for their much taller OD (.72), mostly to make commuting easier on the car.

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Thom

Cross-threaded is tighter than Lock-tite

.86x3.73=3.2078

I can tell you that you won't want much less torque multiplication than that with a 170 unless you live in a very flat area and don't mind frequent down shifting. Keep in mind that 3.23 and 3.55 were the stock axle ratios used with the 170. The 170 will live a long and happy life with a 3.21 overall high-gear.

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Joshua

76 Dart hardtop slant six rated at 100hp had a top estimated speed of 99 mph with a 2.76 rear. weighed in at about 3030 lbs. This looks to be a super six as another 76 model was rated at 91hp. Both 4sp and TF models were at 99. the 91hp model was at 94 mph max. Estimates only from a car performance web site. With better breathing of the clifford (debateable) and the 2.25 exhaust, I would imagine 100 is not out of the realm of possibility.

67 dart rated at 145hp had identical specs but they measured HP at the flywheel, not at the wheels back then. Uncork the exhaust or better, run Dutra duals or headers. I bet that will put you over the top.

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I didn' t buy it, I built it.....

BTW, build thread with a recent update here: http://www.slantsix.org/forum/viewtopic ... sc&start=0

I'll make whatever mods are needed to get to 100 mph, I just don't want to hold it up there if the engine is going to tear itself apart in the process of going that fast.

The curious thing is that audibly there is no difference in highway rpm between 4th (direct) and 5th (OD). I've been meaning to hook up a tach just to see what the difference is, but based on sound it can't be much - maybe 100-150 rpm. It is pretty much pointless to use 5th except on longer stretches of Interstate. Even then it doesn't seem to do much, I just feel like I should use it since it's there. I can't find a shorter (closer to 1:1) listing for the T5's OD ratio than .86 or I would accuse it of being that.

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Thom

Cross-threaded is tighter than Lock-tite

So it looks like you are asking the mechanical rpm limit of a stock 170.

I figure there are a couple of limitations:
- points bounce (do you have EI?)
- valve bounce
- max piston speed
- max speed that the oil pump drive can handle


Not sure about #1, #2, or #4, but #3 could be fairly easily guessed at... Assuming a 3500 foot per second max piston speed and a 3.125 inch stroke, looks like you could rev to almost 7000 rpm without the pistons coming apart!

I can tell you that a 1976 Stock Feather Duster with 80K on the clock 2.94 and A-833 OD runs out of road before you see the limit...I had my dad's car pegged at 110 mph and still slowly accelerating before having to go back to the speed limit (and catching up to traffic fairly fast....)...

The 1967 HP listing is also 'engine without accessories' during the test (no A/C, no alternator, etc...), so it's not even a comparison once you put all the goodies back on the engine (unless this is just a drag race for 1/4 mile time with no belts...)

-D.Idiot

...which bugged the crap out of my buddy who topped out at that speed too with his 1968 Fury 2 with 383-2v and 727....LOL...I told him he gets there faster, but I pass him at the pump....

I got same pointless .86 od on my mazda p/u. Should drop 4th 1:1 14% going into 5th. Id love to have a T5 .68- .75 OD.

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I didn' t buy it, I built it.....