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 1500 vs 1700 engine
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Betsy67
V4 Fanatic

United Kingdom
312 Posts

Posted - 25 Jul 2018 :  19:49:08 Show Profile Reply with Quote
Early this year I acquired a 1.7 crank. I have spare block which is almost stripped bare, just the balance shaft to remove.
Opinions required regarding is it worth going down the 1700 or more route ? More ccs must be better ? Any recommendations for a good spec road engine ?

Edited by - Betsy67 on 25 Jul 2018 19:52:23

melle
V4 Guru

United Kingdom
2592 Posts

Posted - 25 Jul 2018 :  23:03:19 Show Profile Visit melle's Homepage Reply with Quote
I think it very much boils down to what sort of power band you expect and prefer; a 1700 is not necessarily "better" than a 1500 and performance is not defined by cc alone. I've built a few engines, all bar one with used parts (new gaskets and seals of course) and without "trick" bits such as big valves or "hot" cams. They're by no means high performance engines, but most went/ go quite nicely. I find the best upgrades to any V4 (assuming it has decent compression to start with) are 1) Hall ignition (http://www.saabv4.com/index.php/project/hall-ignition/), 2) a 2bbl manifold and carburettor and 3) a better exhaust (e.g. Jetex). I would get this sorted before spending money on an engine, building an engine including heads will easily set you back 1500-2000 depending on what parts you need to buy (and where you buy them...) and how much machine work you need to farm out.

To get a good a good understanding of engine performance, I can highly recommend reading a few tuning theory books, e.g. by David Vizard (he has great book on air flow and porting) or Des Hammill (his ignition book is very good and his camshaft book gives a good explanation of engine timing).

There are many forum threads on this topic as well, sure you can find them with the search function.

Removing the balance shaft is just one hit with a mallet! Best to use a plastic or hide one.

www.saabv4.com
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Betsy67
V4 Fanatic

United Kingdom
312 Posts

Posted - 26 Jul 2018 :  12:46:15 Show Profile Reply with Quote
Already have all those goodies plus Ive worked the heads quite a bit. Throats smoothed, exhaust port opened to gasket size and inlets opened up a wee bit. I didnt have them skimmed as I always intended to go down the 1700 or bigger route at some point. I thought opening the chambers to get the required CR (1700) would be cheaper than having them skimmed. My options for the 1500 are cam swap and upping the CR.
Yes its a nice engine, pulls and revs well, but want more. As with most things when costs are involved it becomes a balancing act ! I would be creating the new 1700+ to a similar spec to the 1500, but is it worth it ?? I would be doing most of it myself apart from any machining work, but it still adds up.
Spent a lot of time in Mr Vizzards A series book[:-)]
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melle
V4 Guru

United Kingdom
2592 Posts

Posted - 26 Jul 2018 :  14:17:37 Show Profile Visit melle's Homepage Reply with Quote
If you open the combustion chambers (which only makes sense if you fit bigger valves I think) and you don't skim the heads, you lower the CR. If you prefer a high revving engine I would stay with the 1500 crank. Combustion chamber templates on my website if you need them: http://www.saabv4.com/index.php/engine-gaskets/sportrally-templates/

www.saabv4.com
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Betsy67
V4 Fanatic

United Kingdom
312 Posts

Posted - 26 Jul 2018 :  18:13:53 Show Profile Reply with Quote
Im thinking that if you use the same chamber volume of the 1500 on the 1700 the CR will increase hence the need to open the chamber up and put more volume in. Ive not sat down and worked it out properly as yet with the CR formula. Seem to remember messing about one dinner time at work and using the same chamber on the 1700 knocks the CR up to over 12:1.
Im still interested if you have some 1.7 pistons upon your return to Holland.
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melle
V4 Guru

United Kingdom
2592 Posts

Posted - 26 Jul 2018 :  19:52:47 Show Profile Visit melle's Homepage Reply with Quote
The heads for 1700 and 1500 engines are identical and piston TDC for both is just under deck with OE HC pistons. If you use Pinto pistons that are too high (TDC above deck), you need to have the pistons machined as they will interfere with the heads, whether you enlarge the combustion chambers or not because all Cologne V4/ V6 pistons have flat crowns. The only reason I see for milling out the combustion chambers is to eliminate valve shrouding if larger diameter valves are used. I think for standard valves they're pretty much the optimal design (see Vizard's flow book).

www.saabv4.com
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Betsy67
V4 Fanatic

United Kingdom
312 Posts

Posted - 30 Jul 2018 :  12:57:10 Show Profile Reply with Quote
Does the 1500 and 1700 run a different CR ?
The stroke is a variable in th CR formula, so the chamber volume should be different?
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melle
V4 Guru

United Kingdom
2592 Posts

Posted - 30 Jul 2018 :  15:35:11 Show Profile Visit melle's Homepage Reply with Quote
Yes, that's correct. Standard 1500 HC 9.0:1, standard 1700 HC around 10.0:1 iirc. Details in the factory workshop manual I think.

www.saabv4.com
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