Rev limit

Graham.Fountain · Postby **Graham.Fountain** » 30 Dec 2013 07:43

I'm looking for references for the rev limit for the slant four engine, and finding it difficult. Does anyone have anything published that gives this for the TR7?

I don't have a TR7 owners handbook, but the 1977 TR7 Sprint one, AKM 3967, gives 6,000 for the "Maximum recommended engine speed (intermittent)" in the section on Running instructions, though I know the tacho is redlined at 6,500.

TR7 Sprint VVC 697S (some of)
TR7 Sprint A TR7 16V (fake, rusty):
B&Y '73 Doly Sprint (kids!)

Workshop Help · Postby **Workshop Help** » 30 Dec 2013 12:05

The RPM limit is when the connecting rods burst thru the crankcase. For all practical purposes, 5000 RPM is a realistic maximum point to shift to the next higher gear. In my case, I tend to upshift at about 2700 RPM, or lower if going downhill.

People, this is engine is a low RPM torque maker, like a tractor engine.

Over revving is painful to my delicate sensibilities.

Mildred Hargis

DNK · Postby **DNK** » 30 Dec 2013 12:13

Would expect nothin else

Don
Stick a Wedge In It
80 TR7 V8 Kick in the pants

Graham.Fountain · Postby **Graham.Fountain** » 30 Dec 2013 14:32

There aren't that many engine and gearbox combinations where the torque at the back wheels doesn't fall when you change up, even when you delay right to the rev limit. Therefore, to get maximum acceleration, that's where you should change - right at the limit. I think that mightn't be the case for a TR8 changing up from 4th to 5th, but I'm not absolutly sure.

Anyway, you know what they say: "Torque is cheap".

As to the ref., it's okay, I've found a copy of the RTC 9210 handbook for the TR7, and it says the same as the Sprint handbook.

TR7 Sprint VVC 697S (some of)
TR7 Sprint A TR7 16V (fake, rusty):
B&Y '73 Doly Sprint (kids!)

Beans · Postby **Beans** » 30 Dec 2013 17:02

According to some old test info, the cruising "speed" for the slant-4 engine is 5200 rpm.

<center>

1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
[url="http://www.tr7beans.blogspot.com/"]My full Weblog[/url]</center>

kstrutt1 · Postby **kstrutt1** » 30 Dec 2013 18:05

bottom end is basically the same as the sprint so 6000rpm should be safe, on the other hand they are so harsh when revved I never used much more than 5000rpm when I had a 4 pot. I used to work with a guy who preparred tr7 race engines in the 70's the weakest link was apparantly the block which split vertically between cyl 2 and 3, apparantly they had some strengthened ones cast to overcome it.

Workshop Help · Postby **Workshop Help** » 30 Dec 2013 20:50

Beans, my friend, a 5,200 RPM cruising speed? According to my rusty, trusty pocket calculator, the one with the sliding beads, in a four speed car with the 3.63:1 differential this computes to velocity of 93.08 mph in 4th gear. This is 5.08 mph faster than is needed to achieve time travel when equipped with the optional factory flux capacitor.

Other than the Autobahn in Germany, I can't think of a stretch of road to accommodate a 93 mph cruise. Around this neck of the woods, the local law enforcement folks would dearly love to start writing expensive citations for this burst of vehicular hooliganism.

Mildred Hargis

Graham.Fountain · Postby **Graham.Fountain** » 31 Dec 2013 13:14

As said, the handbook says 6000 for intermittent use, but the tacho says 6500. I had one that would rev to at least 7k for better bigend bolts. And I know of one that gave peak power at about 8k on Weber 48s and possibly reved to a fair bit more. But that one didn't even use a standard block!

Those were both 16 valve engines though, which are much more willing, rev-wize.

TR7 Sprint VVC 697S (some of)
TR7 Sprint A TR7 16V (fake, rusty):
B&Y '73 Doly Sprint (kids!)

FI Spyder · Postby **FI Spyder** » 31 Dec 2013 13:18

The 8v engine runs out of breath at over 4,000 rpm (unlike my Integra that just gets happy then). I like to keep it between 2 to 3 thou as I want it to last the expected 180,000 miles it should go between overhauls. Highest extended was 80 mph which was around 3,600 I think but as that's red flashing light in the rear view mirror country, I don't go there often.

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

nick · Postby **nick** » 31 Dec 2013 17:02

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by FI Spyder

The 8v engine runs out of breath at over 4,000 rpm (unlike my Integra that just gets happy then). I like to keep it between 2 to 3 thou as I want it to last the expected 180,000 miles it should go between overhauls. Highest extended was 80 mph which was around 3,600 I think but as that's red flashing light in the rear view mirror country, I don't go there often.

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

<hr height="1" noshade id="quote"></blockquote id="quote">

Until I made modded my DHC it too ran out of breath around 4 or 4.5k. But now it breaths well up to 5.5K. I've been scared to go any higher.

[img][IMG]http://i615.photobucket.com/albums/tt234/nickmi/TR7%201975/Yellow.jpg[/img]
nick
'79 TR7 DHC
'76 TR7 FHC

Stag76 · Postby **Stag76** » 31 Dec 2013 18:49

The factory 6000 rpm was probably using the original bearings. The "cream cheese" type used in a lot of rebuilds today can result in a failure if a gear is missed...refer SydneyWedgehead. The original 1850 bottom end and block was never designed to produce 200 bhp at 8000 rpm, with a fairly long stroke, heavy pistons, jack shaft carrying a fairly heavy load, and, in the 16v case, complicated valve operation.

I have my rev limiter set at 5800 rpm, and things are getting pretty anxious at that stage.

TR7 Convertible
Sprint Motor
MegaSquirt EFI

Hasbeen · Postby **Hasbeen** » 31 Dec 2013 22:27

Every one who had driven my 7, & has some knowledge of them agree, mine goes much harder than most, & harder than you would expect. Granted, in the scheme of things that is not all that hard by todays standard.

The thing I like most about it is how it goes from about 2200RPM in 5Th. It's in gear acceleration in 5Th is way above the usual of todays buzz boxes. Because of this low down torque, it is rare for me to see 5000 on the clock. There is just not much point in revving higher.

Having been driving my 9000 RPM vetch S2000 Honda for 3 years now, I do occasional rev the 7 higher than I used to, overtaking in 3Rd or 4Th, but it really makes little difference in acceleration compared to 5Th.

When I first got this car on the road, my son wanted to do some acceleration tests of all our fleet, at a wide range of speeds. We were so surprised to find the thing accelerated more quickly from 2000 to 3000 RPM in 5TH than it did from 3000 to 4000 RPM, that we went back to our quiet back road, & repeated the test.

Starting at 2000 it took 2 seconds less to add 1000 RPM, [33.3Km/H], than it did starting at 3000 RPM. All our senses told us it was accelerating quicker at the higher engine revs, but the stopwatch doesn't lie, particularly when you can repeat the readings.

It is so easy for to fool yourself, with all the noise & action, many would be surprised to find their long held "feelings" about cars are not substantiated by a stop watch.

Hasbeen

Graham.Fountain · Postby **Graham.Fountain** » 04 Jan 2014 13:17

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Starting at 2000 it took 2 seconds less to add 1000 RPM, [33.3Km/H], than it did starting at 3000 RPM. All our senses told us it was accelerating quicker at the higher engine revs, but the stopwatch doesn't lie, particularly when you can repeat the readings.<hr height="1" noshade id="quote"></blockquote id="quote">

This is because the aerodynamic drag, which dominates rolling resistance above about 50 mph, goes up with the square of speed. So you need the thick end of four times as much torque to give the same acceleration at twice the speed, e.g. between 50 and 100 mph. And because the point of application of that torque is now moving twice as fast, it takes the thick end of eight times as much power. So now you can work out how many horses you need to get a TR7 to do 218 mph. Well, some idea anyway.

This is one of the reasons I like the 16 valve slant four over the Rover V8 - the rpm for peak torque with the 16v slant 4 is so far up the rev range, that most of the time you drive on the upslope of the curve - the faster you go (in the same gear) the more torque there is, and the more willing the engine feels. Conversly, the peak torque on a stock V8 is so low down the range, if you drive with any verve and gusto, you mostly drive on the down slope of the curve, so the faster you go, the less torque the engine gives for a given throttle opening, and the harder it is to get the same acceleration.

TR7 Sprint VVC 697S (some of)
TR7 Sprint A TR7 16V (fake, rusty):
B&Y '73 Doly Sprint (kids!)

Beans · Postby **Beans** » 04 Jan 2014 13:58

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Graham.Fountain

... So now you can work out how many horses you need to get a TR7 to do 218 mph ... <hr height="1" noshade id="quote"></blockquote id="quote">
Dropping it out of an aeroplane is probably the only way to achieve that kind of speed with a wedge [:p]

But agree with your views on the Sprint versus V8 [;)]

<center>

1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
[url="http://www.tr7beans.blogspot.com/"]My full Weblog[/url]</center>

Graham.Fountain · Postby **Graham.Fountain** » 04 Jan 2014 18:50

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Dropping it out of an aeroplane is probably the only way to achieve that kind of speed with a wedge<hr height="1" noshade id="quote"></blockquote id="quote">

Oh, I don't know. With stock aerodynamics, it shouldn't take more than 820 bhp to do 218 mph, if it didn't take off itself first. That Le Mans TR7, http://www.triumphtr7.com/documents/articles/stories/lemans.asp, did 201 on "well in excess of 500bhp". Roughly speaking, were the aerodynamics the same as a stock TR7, which they weren't, it should have required 658.4 bhp to do 201 mph, assuming that rolling losses were alerady negligable at 109 mph. Don't know which way that whale tail would have changed the drag factor though. There's also probably an error because BL probably cherry picked which TR7 they used to get the max speed at, I assume, MIRA. So you might get 109 mph on a bit more or a bit less then 105 hp. Presumably BL weren't alowed to run the test one way, in a Christmas gale though.

TR7 Sprint VVC 697S (some of)
TR7 Sprint A TR7 16V (fake, rusty):
B&Y '73 Doly Sprint (kids!)

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Rev limit

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