The Triumph Dolomite Club - Discussion Forum

The engine in my Sprint just won't rev much over 6000 rpm. According to rolling road readouts it's makes it's max. BHP at 6000. I've had this problem well, ever since I've owned the car really. I am running Weber DCOE 45s with:-

Chokes - 42mm.
Mains - 145
Emul. Tubes - F16
Air Corrector - 155
Acc. Pump Jets - 50
Idle Jets - 60/F9

I have fitted a TT10106 camshaft equivelent from Newman Cams, this cam sits between the STR091 & STR0139. I timed the cam in at either 106 or 108 deg ATDC (I can't remember which or whether it makes that much difference):-

Duration - 292 degs.
Valve Lift - 0.408"

I have a Megajolt system fitted & I have been advised that some of my ignition advance settings are too high:-




The exhaust system is a stainless steel sports system from Rimmers with the s/s downpipe. Another suggestion was that the exhaust bore may need to be enlarged.

I'm pretty sure that this setup should let the engine rev to 7000rpm quite easily.

Any thoughts from the gurus would be much appreciated.

_________________
Sprintless for the first time in 35+ years. ... Still Sprintless.

Engines, Gearboxes, Overdrives etc. rebuilt. PM me.


1997 TVR Chimaera 450

Mart - is the head gas/air-flowed? It may be that you need to go to 48's. What type of inlet manifold are you using as they can make a big difference? The exhaust manifold is meant to be bigger in an ST set-up (not just the downpipe, but the actually manifold too), but this alone should not account for the restriction. What pistons and compression ratio do you have? i.e. do you have any above block petrusion? DO you run a filter - have you tried running without it? By way of comparison, we only have an STR091 in SOE, but with 48's and a flowed head and protruding JE's it is producing about 197 bhp and would rev to well over 8,000 (I had it up to well over 7,500 most of the time at Race Retro). We know we can get a further 10bhp by using the original short sweep inlet manifolds as well. I suspect it will be a combination of factors leading to the rev limit restriction. An easy test if you have a second manifold and 48's, would be to take off your 45's as a complete unit and swap them for a complete jetted 48 set up and see what difference it makes. When SOE was last rolling roaded, we noticed a bow or pressure wave in the carb throat at certain revs, where the cam was not allowing the fuel in quite as smoothly, but this was at lower revs, so we did not care much. Anyway, don't know if these ramblings help or not?

I have standard Mahle pistons (no protrusions) so standard CR. The head was ported by the PO & hopefully he made a good job of it. One thing I've just realised is that I don't think I matched the ports to the manifolds when I changed to the Weber carbs, as it was P&Pd when it was running the standard SUs. Food for thought anyway, thank you.

_________________
Sprintless for the first time in 35+ years. ... Still Sprintless.

Engines, Gearboxes, Overdrives etc. rebuilt. PM me.


1997 TVR Chimaera 450

Hello, max 32 degrees advance. The sprint head has a well shaped modern type of combustion chamber and doesn't have to have so much advance. High advance is working against. Are the valvesprings doing their job?

Jeroen

_________________
Classic Kabelboom Company. For all your wiring needs. http://www.classickabelboomcompany.com

I took the Webers off today and the ports have been enlarged.



I did quite a bit of cleaning/tidying under the bonnet. I also retorqued the head down whilst I was in the mood.



As I was reassembling the throttle linkage I suddenly had a thought, what if the butterfly valves aren't opening fully? So I got Mary to put her foot on the pedal & when I looked down the barrels I could see the valves were not fully horizontal. By pulling on the linkage I could open them at least another 10 degs. before being fully open. That might have something to do with not being able to reach 7000 rpm. do you think?

Edit: I also measured the camshaft, the base circle is 30mm. & the dim across the lobe is 40mm. this is only giving me a lift of 10mm. (0.394"). I was expecting to see a lift of 10.36mm. (0.408"). I think someone sold me the wrong cam?

_________________
Sprintless for the first time in 35+ years. ... Still Sprintless.

Engines, Gearboxes, Overdrives etc. rebuilt. PM me.


1997 TVR Chimaera 450

See a lot of guessing here.
Put it on a proper roiling road what can tell you accurate figures and AF readings.
This could tell you more.
BTW 42 chokes in 45s ??

Just an example, look to the fine details, that is all information.
I don't trust the often seen by far to smooth curves made up by some program after probable less than 15 measuring points.

Hans



Power, torque and AF readings 4' gear.
It is clear this standard bike is to rich in the lower revs. The torque curve show 2 massive dips, but remember NOT only the mixture is responsible.

If you've got everything else sorted and it's an abrupt drop off in power at 6000rpm then I'd say valve springs are worth a check?

If you get it on a rolling road you'll be able to see if the drop off in power is very abrupt (valve springs) or if it's a shallowing off of power (general flow restriction. ie, cam).

You'll also see your AFR reading and it will tell you if fueling supply is a problem.



Not a bad way to spend £30 eh?

OK, the first read out is from 2005 just after I'd installed the cam & 45s...




THe second read out is from 2010 after I'd installed the Megajolt system. The red lines on the graph are the first run before any adjustments, the black lines are the final settings...

_________________
Sprintless for the first time in 35+ years. ... Still Sprintless.

Engines, Gearboxes, Overdrives etc. rebuilt. PM me.


1997 TVR Chimaera 450

Somethings not right for sure. First things first. Have you done a compression test to check for broken rings etc. next I would check the ING timing. Unplug the megajolt ecu so the edis unit goes into limp home mode. This will give you a fixed 10 deg btdc. Check this with a fixed timing light, if your light has a dial back function on the advance set it to zero ( you can't use this function with some timing lights when using wasted spark ING. It will give you false reading at differant engine speeds). Check the timing at differant speeds it should always be 10 deg btdc.
After that it's check the exhaust system is ok. Ie none of the boxes have collapsed internally. If all that's fine I would be changing the valve springs for uprated ones. A wild cam will require harder springs to follow the more aggressive ramps of the cam.

Std new valvesprings do fine with all sorts of cams at high revs. If the rings are broken i do not think you have a output figure like that.

The max advance is about 32 degrees and set this at max from 3500-4000 revs and more. I hope you have the vacuum disconnected with webers. Above the 32 the engine does not want because the pistons are pushed back because of too much advance.

It's alway's very funny to read the test figures of engine power output measured at the wheels.

Jeroen

_________________
Classic Kabelboom Company. For all your wiring needs. http://www.classickabelboomcompany.com

No vacuum advance on the Webers. I used to have uprated valve springs fitted (still have them in the garage) but was told that these can affect power output & std springs should be fine. I have a new set of standard springs so could fit those.

So on my advance curve configuration table, all the boxes from say 4000 rpm onwards should contain 32? The loading doesn't matter at this point onwards?


Edit: I've just noticed that the red lines on the second graph are from a different Sprint.

_________________
Sprintless for the first time in 35+ years. ... Still Sprintless.

Engines, Gearboxes, Overdrives etc. rebuilt. PM me.


1997 TVR Chimaera 450

It is always a bit tricky to comment on dyno figures you did not measure yourself, but I trow in a few things.

If the ignition timing is by far to late the engine will give a very aretick power curve higher up in the RPM curve.
I don't see this on these figures, but as sead before very smooth curves like this make me always suspicious about how the data has been smootned

A quick comparison with a good build standard Sprint engine shows that the torque curve of this engine start to drop far to early, it almost impossible that even the baddest valve springs start to play up that early.
I have not hear this, but did test this operator a few times in a row your engine to see if the results are the same every time within very small margins, just a single run is not telling the whole story.
I know people sell runs instead of testing an engine, we get these questions also, what cost a run, I don't sell a run, we test your engine and if we need 5 or 10 or 15 runs so be it, you must be sure that you can trust the outcomes.

The extreme drop in power looks more like a bad 2 valve head, not like a Sprint head.

I'm also surprised about the big difference between the curves, can't understand that the ignition is responsible for that, what happened?

And to be honest, beside the steep drop of power, with a proper cam and these carbs (supposing that the mixture is more or les ok) the output is not even close to what I would expect.

Still don't see AF figures though.

Hans

Both of these Dyno graphs were the result of 4 hours on the rollers with 6-10 runs & jets being changed in between. I don't have any AFR readings Hans. But bear in mind that the throttle may not have been opening fully at these times. I think this is something basic that should have been checked by the technicians but I'm not sure it was in either case. So maybe the graphs are misleading and of no use?

The rollers at the second venue I beleive were way out of calibration. But that apart, there was a big improvement in power between the first & last test.

_________________
Sprintless for the first time in 35+ years. ... Still Sprintless.

Engines, Gearboxes, Overdrives etc. rebuilt. PM me.


1997 TVR Chimaera 450

Quote ; But bear in mind that the throttle may not have been opening fully at these times. Quote
You are kidding me are you??
Quote ; The rollers at the second venue I beleive were way out of calibration. Quote ;
Your kidding me again ??

This last one proves again that an inertia roller is the most accurate, you simply put the power against the mass of the roller, no outside influence at all, no slip also, the roller is about 6 feet in diameter 1600Kg.
But we stop this dino discusion here, it's about your engine problem in the first place.
If the mixture is about ok it's not even necessary perfect in this stage, I suppose 36 till 38 chokes, you run about 31' comp. ratio 10.5 and up, the cam is timed at 106' or whatever what is listed.
Than you can expect at least close to180Din hp 200Nm torque and at least always over 170 between 5.5 and 6.5K revs.
This engine is far below so I would try immediately a new (not a regrind) cam to compare.

Good luck,

Hans

What fuel pump do you have, what fuel pressure are you running. I would expect to see at least 170 BHP @ the wheels with your set up. When I first built 33 in 1988 I used Mahle pistons with a 10:1 CR,139 cam & 48's & got 190 Bhp @ 7,200 @ the wheels, I am now getting 195 @the same revs with the JE pistons. I have just built another Spint engine using a Group 1 thick wall block & have developed a new cam for it & am now getting over 200bhp @ 8,000 @ the wheels using 11.8:1cr. with no power drop off. I am trying to build upthe couragfe to take it to 8,500!!

31 deg advance is all you need. Obviously the lower the CR the more advance you can put in. I just use the Lumenition system in most of my cars from Rimmers or elsewere. It all fits neatly inside the distributor with no extra wiring needed.