Chasing Torque

New year so a new challenge.
3 years ago I managed to get hold of a late PRV engine as I wanted to build an engine with loads of low down instant torque rather than top end HP, I got as far as porting the heads and doing the valves and seat’s, and then I got involved in building my short WB Citroen Ds which put the PRV job on hold.

Now the Citroen is completely finished and we are in lockdown I have dugout the engine project, things have also got more interesting as I then bought an A610 engine in need of work and also some 24v heads that came along, so my engine choices to fit into my lamans are difficult, for the most flexible engine.
I might do the odd track day but mainly road use so top speed is not the aim, but immediate flexibly is so I am thinking a low pressure turbo engine with a higher compression ratio to get a lovely long torque curve.

So I have taken one head of the 610 engine so you can see the difference between the normal head and the one I worked on. The ports are of the exhaust and the valves are inlets standard and re shaped, the valve seats are 4 angle cut to get a smooth radius, weeks of work looking back.

Well I managed to find my flow figures when I did the Headwork, I am fortunate that a chap not far from me has a flow bench.
I was amazed that I got about an extra 7% on the inlet as the 3lt inlet port is not that bad as standard this is with a 9mm lift, but the best result was on the Exhaust port about 14% uplift on flow.

So now I have to decide what I am going to build, one of my main issues is the Wt of the engine the beauty of the Atmo is it it’s light on the back which I love, just lifting the extra components of the 610 engine it’s a lot of extra Wt hanging over the back, also the 24v is a lot heavier.
The next issue is complexity of the engine to work on and repair, I’ve always lived by keep it simple.
I think the 24v is out as even with the duel length inlet 4v per pot have always been poor at low down performance, they love to rev high so for track stuff a top end speed good choice.
So I think I will cut out as much stuff of the 610 engine as modern management means things can be removed plus ancillary stuff.
Or it’s normally aspirated with good engine management, if I could get near 300 on the torque and 200/215hp with a light Wt engine that would be a pretty smooth immediately delivered energy package, with no heat issues and easy to work on.

Decisions, decisions...

Rupert's 24v Le Mans was very light overall, plus I'm not sure about the whole low down torque question with 4v per cylinder as I've always thought a lot of that is just masked by better breathing at the top end that makes the lower end seem more subdued.

Can you lose much from the 610 engine? Hellas on Facebook has done huge amounts in carbon, inc the cam covers, really amazing work. I've always though the heat-shields and induction could be fabricated in carbon if someone had the time and experience to do so.

Anyway I'm sure it'll be good whatever route you take.

The Gta is a light car it’s where the Wt is distributed, the 610 in its day was was pretty impressive 5 odd seconds to 60 in something that’s about 1450kg.
I had a weigh in of all the bits this is all the ancillaries probably half could be removed but all this is hanging out the back. The turbo block is just under 11Kg but it is the right side of the rear wheels, the 2 boxes one is 23kg the other one 24kg - 4kg for the boxes that’s 54kg this excused the exhaust manifolds and inlet manifold as they are on all engines, so what ever engine stuff you do in a rear engine car Wt is a vary important issue, you may have a lot more power but in a Gta you will get more under steer when pushing hard
So it’s no wonder they had to put more Wt up front on the 610 but they also had crash stuff to comply with.
I have had a 610 and it is a nice car and fast very and stable at higher speeds compared to a Gta,

Up until 2hr ago I was going to do higher compression smaller turbo, as I have got a good % increase in exhaust flow so I would get a fast spool up and then it would run out of puff at 230/40hp.
However I just don’t have the energy to start doing a lot of car modifications after doing that for nearly 3 years on the Citroen, if I do normally aspirated I have all the cams which were done 3 years ago and it should just go straight in, all I will have to make will be the throttle body stuff and a new ecu so I think this is the way I will go, and there is no Wt increase no heat issues and it’s simple to work on, boring I no but I am done with doing big mods.

Well a change of plan after a week of clearing up the work shop and painting the floor to keep all the dust down, and after going through all the stuff I forgot I had I have enough to build both plus the 610 engine is a pretty rear engine, so it’s at the balancers it will be Interesting to see how far out they are and how well things were done in the early 90s.
The 70s stuff was pretty bad seeing how far out the Citroen engine was.

Well i now have the bits back from the balancers and the 610 engine was pretty poor evidently apart from the flywheel every thing was out, the pistons where bad and the crank has a new drill hole in it and surface grinding as well as metal of most of the rods so the blocks are pretty strong to hold all that in at 5000rpm.
I finished prepping the heads and they are now at my head specialist for the 3 angle cut on the inlet but as it’s a turbo I am leaving the exhaust seat as standard to aid valve cooling but I have opened up the port to Mach the exhaust manifold and removed the restriction behind the valve that’s as far as I’m going.

Well I thought I was now at the end of modifications and repair but I just thought I would check the exhaust manifolds and I think they where welded up on Friday afternoon after a nice French lunch break.
So much extra metal sticking up it’s even cracked with the heat good for flow and turbo spool up, so more work to clean it all up.

So everything is slowly coming together but as I was cleaning parts I put the other identical crankshaft from the other 3lt engine along side the balanced crank and it was not just one extra hole drilled.
Mass production is one thing but if you want to lose energy fast an out of balance engine is the way to do it. This other crank will be off to the balancers soon so it’s going to be interesting to see if it comes back the same.
Just lapped in the valves on the big ported heads for the normally aspirated engine.
I have spent about 4hrs getting the cylinder liner heights and orientation in the block right as the factory cannot machine a flat to the top and bottom of a liner, it’s even put in the engine build manual .

So everything is slowly coming together but as I was cleaning parts I put the other identical crankshaft from the other 3lt engine along side the balanced crank and it was not just one extra hole drilled.
Mass production is one thing but if you want to lose energy fast an out of balance engine is the way to do it. This other crank will be off to the balancers soon so it’s going to be interesting to see if it comes back the same.
Just lapped in the valves on the big ported heads for the normally aspirated engine.
I have spent about 4hrs getting the cylinder liner heights and orientation in the block right as the factory cannot machine a flat to the top and bottom of a liner, it’s even put in the engine build manual .

Enjoying reading up on your progress

Sent from my SM-G935F using Tapatalk

Really enjoying your write up.
As I am about to start cleaning up and ordering new parts for my engine this has really got me thinking..
I had not even considered having crank balanced until I read your piece.....

I'll certainly look into it now...

Great stuff!
Peter

Thanks I no not many people look at this sight much now but it gives you a historical record that people can refer to.
These are the last engines I will probably build as I am getting to old and have other things to see and do before my body gives up grovelling around cars.
You have to put your self back in time and what was around in the 80s engine wise and an all aluminium light Wt v6 mass produced engine was on the money, but like all manufactured stuff then quality control was lacking.
Spending time on simple improvements can make the engine release its potential, the 610 engine is a one off as they aren’t around and I have kept it standard apart from the exhaust port small improvements.
but the other engine 3lt normally aspirated engine I have pushed the limits on the head and the cams have been done for torque rather than power which I am more interested in to be honest as you never no what all your work will achieve until it’s on the rollers it could be sh it or outstanding or just the same as standard, that’s the addiction to me have your ideas worked or not.
If you are just building a standard engine it’s just spending time setting it out like the liners the machined suffice on the top and bottom off the liner has a wide tolerance as per the manual which you have to spend time.
If you want to hopefully get a good improvement for not spending much money the exhaust ports are a must and if it’s an early engine a cam re profile to get the bigger lift is the way to go, no point in putting a big exhaust system on if the gas can’t get past the valve.
Engine balance is always a must how to lose energy in a big way plus I never worry about reving the nuts off a balanced engine, well they just rev without trying.
Just putting the heads back together and then cam timeing I am probably guessing it will be 1980s.

So the heads are back on and as suspected the timing was interesting. I started setting out as per the book with the one timing mark on the timing chain gear.
I then put the gage on the rocker and checked against the timing disc surprised that the right bank was spot on but the left bank was out in the end by one link compared to the official timing mark so always check, you will need to have a camshaft timing disc.

So more work this weekend to try and seal this engine up, one of the down falls of the PRV engine is the oil pump as there is no oil filter before the oil pump there is a coarse wire filter but what happens is anything damaging can get through and scores the oil pump body, so cleaning everything is a must that’s why re my liner post on my other engine any type of media grit around this engine you should be very careful, as grit or glass is not attractive to a magnet which you should have in your sump plug.

Hopefully then things should speed up soon as it’s ancillary components, but as I am then trying to get the Wt off this engine probably not.