| Author |  Topic  | |
Iain G
V4 Fan
United Kingdom
159 Posts |  Posted - 19 Feb 2020 : 18:30:49  
| A bit quiet in the forum so I’ll contribute a question to stimulate some comment......no controversial though......
In what way are the low compression pistons in 1.7LC engines different to high compression pistons in HC engines?
Are they shorter?
How much?
Cheers
Iain G |
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melle
V4 Guru
United Kingdom
3833 Posts | Posted - 19 Feb 2020 : 18:42:25
| quote:
Originally posted by Iain G
Are they shorter?
Yes
quote:
Originally posted by Iain G
How much?
1.5mm
www.saabv4.com |
Edited by - melle on 19 Feb 2020 18:45:22 |  |
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Iain G
V4 Fan
United Kingdom
159 Posts | Posted - 19 Feb 2020 : 19:12:39
| Thanks Melle
I knew you would be first off the mark!
Iain G | |
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ratty
V4 Fanatic
United Kingdom
340 Posts | Posted - 19 Feb 2020 : 20:00:53
| | So which of the 1.7's has the best performance? Which one has the most torque? | |
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melle
V4 Guru
United Kingdom
3833 Posts | |
ratty
V4 Fanatic
United Kingdom
340 Posts | Posted - 19 Feb 2020 : 23:31:14
| | Interesting Melle I thought there was a larger increase in torque between the 1.5 and the 1.7 mainly because of the longer stroke of the 1.7. I wonder if the torque increases proportionally as the revs rise? I am hoping to build a high torque 1.7 engine sometime. Have just had the 1.5 rebuilt going back to standard cam, new 32/36 weber, new valves and guides but standard heads and ports, Saab rally type exhaust, standard ignition. Used to have Kent autocross high torque cam, 28/36 weber, worn valve guides and valves, otherwise as before. This trials car never pulled or performed as well as my other car which is also 1.5, has a standard cam and fomoco carb otherwise the same, is 25 years since it was rebuilt and has done approx. 150.000 miles. Bit rattly but still going! The rebuilt engine will hopefully well outperform the other engine now. | |
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melle
V4 Guru
United Kingdom
3833 Posts | Posted - 19 Feb 2020 : 23:56:47
| Above figures are (theoretical) torque peaks for industrial engines with a single 28PDSIT Solex carb, the car engines in standard guise won't be too far off I suppose. There is a torque graph for the 1.5HC engine in the factory workshop manual, I'll see if I can find them for the 1.7 engines as well.
The difference in torque between a 1.5HC and a 1.7HC is very noticeable. I currently have a 1.5 in my 96 (ported intake and exhaust, heavily modified Jetex exhaust, Weber 28/36DCD, VAG Hall ignition etc.) that goes very well, but I'm looking forward to fitting a 1.7 again because I prefer low end power over revs. I've never driven a car with a 1.7LC.
www.saabv4.com | |
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Doive
V4 Fan
United Kingdom
160 Posts | Posted - 20 Feb 2020 : 09:50:41
| We have just converted our 1500 to a 1700 (with thanks to Melle for the crank), and fitted larger 91.835mm pistons as the block was deeply ridged. The resultant engine is torquey as hell compared with the 1500, running a Weber 34ICH and Jetex exhaust. Find myself pottering around town now in 4th as it will pull it comfortably from ~20mph, with no pinking or spluttering. Still running the engine in so keeping the revs low. LC spec gives the option of turbocharging...
1970 95 V4 van
1972 Sonett 3
1973 95 V4 estate | |
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Derek
V4 Guru
United Kingdom
2191 Posts | Posted - 20 Feb 2020 : 14:26:06
| | Pottering around at 20mph in 4th isn't a good idea while you are running in. Revs should be kept quite high but without much heavy loading. Rings have to work a bit hard to bed in and if that's not done you can suffer from glazed bores and very poor oil consumption as well as reduced compression. | |
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TTruckie
V4 Fanatic
United Kingdom
320 Posts | Posted - 20 Feb 2020 : 21:58:44
| the 1.7 pistons have to have a shorter skirt due to the wider movement of the con-rod as a result of the longer through.
Pinto pistons are high compression and will fit if boring the block. 90,91,92,93mm if i remember. Burton engineering were very helpful. | |
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ratty
V4 Fanatic
United Kingdom
340 Posts | Posted - 22 Feb 2020 : 13:09:55
| Yes pottering or loading is not good for the gearbox either. I was told by a Saab trained mechanic many years ago who worked at Chenhalls garage in Paignton to always keep the revs. up rather than down to ease the load on the gr/box bearings. He said use 10,20,30,40 mph as the change speed when under load. He ought to know as he had rebuilt a lot of 96 gr/boxes.
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Doive
V4 Fan
United Kingdom
160 Posts | Posted - 02 Mar 2020 : 22:12:30
| New engine is being run in properly, haven't been allowing it to labour in high gears, was just interested to observe that it seems happy to do so. Gear change points do indeed seem to naturally fall at 10/20/30/40.
1970 95 V4 van
1972 Sonett 3
1973 95 V4 estate | |
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| | Topic | |
Low compression / High compression
