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Stag engine TR250 rebuild


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Thanks, seems that some revision on this item is necessary.

i always liked the idea only to put energy into the pump when needed

and not let it work heavily against a half closed thermostat.

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And that Toledo sounds like it's a Fun Motor,any Pics?

Here are a few taken a couple of years ago. It has a twin plenum 3.5 with megasquirt, but still had the flapper system when these pictures were taken.

 

It may also be appearing in Practical Performance Car magazine next month, the one later this month should have my pair of Stags in it.

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Edited by Stag powered
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Here are a few taken a couple of years ago. It has a twin plenum 3.5 with megasquirt, but still had the flapper system when these pictures were taken.

 

It may also be appearing in Practical Performance Car magazine next month, the one later this month should have my pair of Stags in it.

Thanks Neil,as I said sounds like Fun and also looks like lots of Fun,Enjoy and Thanks for the Pics.
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Thanks, seems that some revision on this item is necessary.

i always liked the idea only to put energy into the pump when needed

and not let it work heavily against a half closed thermostat.

 

It seemed like the best idea to me as well until I tried it on the Toledo.

Biggest problem is lack of heater output. The first one I did on the TR retains its thermostat and uses the resistor to drop the voltage, this works absolutely fine.

 

The Toledo was the next one I used with the controller, heater output was dreadful so I refitted the thermostat. Somewhat better but still **** in cold weather.

 

The fundamental problem is that the pump works in bursts at full power. When at its rated temp it works for 10 seconds in every 30. if the water temp rises by about 5 degrees it goes to 20 seconds in every 30 and finally switches to continuous at about 10 degrees over its set point.

 

When driving on a frosty night there is never any possibility of the pump running for more than one third of the time hence the **** heater output.

 

You can buy a heater circuit pump to cure this problem, but at significant extra cost.

 

When I built my 246bhp stag engine I went for the resistor option, saved a lot of money and got a working heater!

 

Having used the Toledo a few times in frosty weather this Winter, I think I might well remove the controller before next winter.

 

Neil

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Had same problem with my Rover V8 with the anti clockwise pump.

I bought a little electrical pump for the heater circuit and switched

it on with the second stage of the heater fan.

 

I agree this switching on with full power and than switchimg off is

not the best idea, it might shock the engine.

 

MegaSquirt has a provision for the fast idle solenoid with only

a on-off function. I keys in several times in a second and

forms fron that an input of lower voltage to give a defined lift

and bypass.

 

I would prefer to optimize that instead heating a resistor.

 

At present it can switch up to 1 amp but maybe the

transistor can be changed to a high power unit that

is in use for the multispark coils.

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  • 2 weeks later...

Getting a lot closer to finishing now, got the hood back on and the interior refitted, needs a damn good clean as everything vinyl is covered in mildew due to the damp garage.

Took a couple of photos of the front end, engine bay as it can't normally be seen from this angle, and the TR6 front spoiler I fitted when I first fitted the Stag engine.

The idea behind fitting the 6 front spoiler was to help with the cooling when I fitted the Stag engine, but I didn't expect the huge difference in high speed handling it caused.

When I had my TR6 before this 250, it had a front spoiler fitted and was rock steady up to maximum speed, the TR250 on the other hand was horrible over 80mph and I spent a lot of time checking the suspension geometry without finding anything amiss.

 

The Stag engine is virtually the same weight as the straight six, so that is not a significant factor, but after fitting the Stag engine and front spoiler the high speed handling was transformed.

Some years ago during a track day at Mallory Park I noticed that TR6s without front spoilers lifted significantly at the front end on the faster parts of the circuit, you could actually see the gap between the tyre and the wheel arch increase with speed, the car adopting a front end up "speedboat" posture. The ones with the front spoiler tended to sit level throughout the speed range.

 

The spoiler wasn't particularly noticeable when I still had the bumpers fitted, but when rust set in some years ago I couldn't be bothered with the cost of rechroming yet again, but the spoiler is there to stay!

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At last it lives again!

 

Much to my amazement no leaks of fluids occurred as I ran it up to temperature. It certainly sounds better without a dozen or so pin holes in the old exhaust system.

 

Tomorrow I can take it for a bit of a run and see if the fueling needs a bit of re mapping, I am not expecting much difference except at wider throttle openings.

 

Hopefully I can get it on the rolling road at the International Weekend and see how much difference the new exhaust system has made. The TR now has the same design system as the Stag, the remaining differences in output will be down to the porting work and slightly better designed inlet manifold. The Stag also has a slightly higher compression ratio at 10.5 : 1 rather than 10.1: 1 but both still run on regular unleaded.

 

Next Winters project is to build another engine for the TR, I am probably going to aim for 11 :1 compression and use super unleaded, I am hoping to crack the 250bhp level but at a slightly lower rpm than on the stag, hopefully peaking at 6500rpm rather than the 6800rpm on the Stag. I have nearly all the parts I need.

I had the rotating assembly of the Stags engine balanced, expensive, but it is so much smoother than the TRs engine. I will definitely have that done again.

 

Below is the dyno sheet comparing the power and torque of the Stag and the TR last year. The green line is the torque output of a factory spec Stag engine.

 

Neil

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Nice performance!

Many Rover V8 would be happy to have that.

 

How did you do the balancing?

Did you manufacture the bob weights or weight the pistons and rods?

I had a lot of problems to find somebody to balance and at last took

a "normal" balancer who requiered the crank fully equipped with the bob weights.

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I balanced the pistons and rods myself using a set of digital scales.

 

The rods are pretty good from the factory, they must have selected sets that matched as I have several sets from scrap engines that are all within 3 grams for a set, but different sets may be 15 -20 grams different.

 

It was more difficult for the end to end balance of the rods, so I made sure all the small ends were similar thickness by swapping a couple of rods from different sets, then balanced the big end.

I could only find 2 companies who could balance V8s, and went with Oselli engineering on recommendation from Tony Hart (who founded the Stag owners club and used to race a Modsports Stag).

Oselli just wanted 1 piston, 1 con rod and the flywheel, front pulley, crank and clutch cover. They do the crank weighting themselves.

 

I should have lightened the rods a bit as the crank actually needed weight adding to balance it, and the special heavy alloy they use (heavier than lead) added and extra £100 approx. to the cost of the balancing!

 

Neil

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