Cruising RPM's

I haven't been able to find an answer by searching this site or google, so here goes...

What is a safe RPM range on a stock motor (1600)? I don't mean redline, I mean cruising RPM. I am getting married in August, and I have a 2-hour drive between home and the wedding site when we're doing planning. Driving the Speedster is a lot more fun than the Subaru, but it takes a lot longer b/c I'm afraid of over-revving the engine. I have only been doing 3000-3200 RPM's -- can I go higher? I guess it's good that I'm only doing about 55mph, so I stay out of trouble with the police, but a little more speed wouldn't hurt.

My plan is to replace the oil pressure gauge with an oil temperature guage, which will give me a much better idea of where it's safe to run, but in the mean time, I need you guys... (Also, if you have any good suggestions for the oil temperature gauge and sender, I'm open to them).

THANKS!
Adam

if your rpms are at 3000-3200, even with a 4.12 (or 4.11, i cant remember) ring and pinion, your speedo must be out a little. What tires are you rinning? (size?). With a early r/p you should be doing about 65-68mph at 3200 rpms, and stock tires. You can safely run (at cruise) anywhere between 2900rpm - 3400rpm. Actually lowering the rpm by changing the gear ratio in a stock setup can actually effect cooling negetavily. For the oil temp guage, you can use a VDO guage and sending unit that installs in the oil relif plug location (typically the front, front being the front of the car) if you case is a dual relif case. They are cheap, and work well to give you an idea of oil temps, good oil temps are 175*deg F - 190*deg F on the highway. Anything over 200* and i'd start to worry slightly.

You can get the guage and sender from CIP:
guage: http://www2.cip1.com/ProductDetails.asp?ProductCode=VDO%2D310%2D012

sender: http://www2.cip1.com/ProductDetails.asp?ProductCode=VDO%2D323%2D064

good luck.

martin

I use my speedster as a commuter to and from work. I run around 3500 at 75Mph. I'm only driving for 30 min though. I have no cooling problems.

It's a 4-speed Porsche tranny that came with the car -- I have no other information about it. Maybe a 901 out of an earlier 911, I think?

My speedo is way off (about 8 mph at highway speeds), but I've used GPS, and those signs on the side of the road that say how fast you're going to see my actual speed. Plus other cars go flying past me...

I think my tires are 165/15, but that's a guess since I'm at work.

As far as the gauge, I'm trying to find one that matches... but that's pretty close to what I'm looking for, Martin.

I've read about hooking up the temperature sender in the same place where the pressure sender is hooked up. I would think that's a pretty accurate location. Is the oil relief plug different from the drain plug?

3,500 rpm is fine. For a long trip you ought to vary the speed from time to time. Almost everyone agrees that a consistent/constant rpm will cause overheating, but a varied rpm helps with a cooler and better running engine for the long hauls.

A handful of quick (just 3 minutes even) stops makes a big difference for the better as well.

We all caravan to the Connecticut shows (3 hours drive) during the Summer and have it down pat!


Oh, are you SURE that you wanna get married . . . ? I'd think twice about it.

OK, sure, it DOES mean that you'll probably never have another un-squeezed blackhead in your ear or un-popped pimple on you your back again. But is it worth it . . . wait until the fall, give it a little more serious thought.

i agree with TC, even about the marriage parts!!! I still have to pop my own pimples cause my wife thinks it's gross, hard to do in the mirror, everything's backwards!!!! You must have a older model than mine, and be at least a few more cows lighter than me for the purchase!!!!

adam, the oil pressure location i guess could work, but i hav'nt seen a sender that goes there for temp, the one i have is for the oil pressure (for the guage) and the idiot light, those work well, although some people complain that the light comes on at 10psi, where the stock idiot light pressure sender comes on at <5psi, but i'd rather know what the actual pressure is. TC mentions alot of really good points, like taking breaks, varrying speeds, ect...all excellent advice and it really works. The oil pressure relif valves are under the car, drivers side, if you have a dual relif case look for 2 big plugs, with a large flat head slot on them, one in the front, and one closer to the rear, the one in the front is the 2'nd one that indicates that it's a dual relif case, don't confuse this with a dual port case, 2 different things. Those valves control oil pressure, and bypass excessive oil pressure from the oil cooler and main oiling system in a over pressure situation such as cold start-up to prevent blowing seals, and oil coolers. It is a very good location to take oil temps. ALso you can use any 0-300 deg F guage with the sender, so you can match the style of guage, stock porsche guages work as well with that vdo sender. Also your tranny is most likely a beetle tranny, the 901 tranny (porsche) is a 5-spd, used in early 911's and 914's, i think.......


martin

1. Marriage - It was her idea to take the Speedster this weekend when it was 55 degrees (no heat in the car). She's a keeper. Plus, she's a CPA, and is gainfully employed while I finish my last year and a half of grad school.

2. Gauge - It's good to know that any temp gauge will work. I just need to find one that matches. I'll have to get under the car today when I get home and check things out for the sender.

3. It's a 4-speed 901. I had to order a reverse light switch. It was $75 instead of the $12 for a VW version.

A long time ago I heard someone quote the fan as at optimal efficiency at 3200 RPM with stock pulleys. I don't know why, but it stuck.

During the Summer I typically do shows and cruises with the TYP356 club out of the Boston area. They're all running original (steel) 356's from early 50's through 1965 or so.

On Interstate Highways we all typically do 3500 - 4000 rpm, sometimes for a couple of hours or more at a stretch. We've also been known to do shows in Vermont that are four+ hours ONE WAY! They all have calibrated temp gauges and they all try to stay under 230 degrees (and most easily do). I have a dip stick thermometer with which I've "calibrated" my repro 356 temp gauge (with magic marker lines on the gauge glass) and I stay at 195 - 205 if I'm running hard, but I also have an external, full flow, fan assisted oil cooler.

For highway revs on a stock 1600 (with all proper cooling stuff in place), anything from 3250 to 4000 is fine, and cruising forever at 3,500 - 3,750 is a nice range (and nicely keeps you up with traffic).

I got my dipstick thermometer from Mainely Custom by design, so look here: http://www.mainelycustombydesign.com/engine_components.html#dipstick

Hard to say what your car should be doing. We know it's a stock 1600 engine, but we don't know what you've got installed for cooling accessories or whether your engine heat shields are installed and so forth. All that makes a BIG difference. Also, with a 901 with popular gearing (gear ratios could be selected by the customer when the car was ordered) you should probably be running a shade under 3500 rpm at 70 - 72 mph.

gn

Gordon,
Thanks a lot. That looks like a meat thermometer! How do you check it while you're driving? (just kidding). That would be an easy way to figure out the temp without installing a whole new gauge and sender.

I have the tins on the engine, but I don't actually have the barrier between the upper and lower half of the engine installed. I know that's a bad idea... but you know how it is.

What would "redline" be on an engine like this? When I drive it like a rental, I just shift when the engine runs out of power, which is maybe around 4500 rpm.

I don't know how I would survive without this forum.

Adam:

Those horizontal heat shields are as important as the rest of the cooling tins. Without them, hot air from around the exhaust is sucked up past the engine and goes into the cooling fan and the overall engine temp rises, often more than 20+ degrees. Not good. Those make the difference between running 220 - 230 on a highway, and 200 - 210 under the same circumstances, and the engine will last a lot longer. There are several alternative heat shield designs, depending on what make your car is (CMC, Vintage, etc.) and you should seek out the design for your car, fab up a set and install them. Shouldn't take more than an evening or afternoon.

RPM "Redline" on a stock 1600 would be, in my opinion, about 5,200 (it'll probably run out of power around there anyway).

If you're bringing it smoothly up to 4K - 4,500 and shifting there, that should be OK - that would keep you above 3,000 at the bottom of the next gear and keep the engine nicely in its' stock power band.

BTW: as rule, I never let my engine go below 2,000 rpm under load. In other words, if it's getting close to 2K, I'll shift to the next lower gear to bring it back up closer to 3K, and then shift up around 3500 - 4K if it's a lower speed area or if I'm in traffic. These engines rely on spinning the cooling fan to keep them cool, and the fan is more efficient above 3K. If you're just doggin along at 2K then it's not being cooled as well.

My engine hates being under load and under 2000rpm. She starts to buck on me a little. Fun to use to scare the girl tho. Ka-thunk, Ka Thunk.....uh oh I think we are breaking down hun.