1.7l big bore kit? 1972? Options

[jdlmodelt]

what is the biggest bore I can take my 1.7l to without major remods to the crankcase? recommendations?
thanks,
j

[Cap'n Krusty]

I'm thinking 96mm slip-ins. Gonna make a ton of heat though, and it's unlikely to run very well with D-jet EFI, even if you fiddle with it. You'll have to calculate the compression ratio and shim the barrels to compensate for the big increase, and open up the cylinder heads to accept the new diameter. You DO NOT want to run over 8.2:1. 93s make for a hundred more CCs and your FI will be fine.

The Cap'n

[euro911]

How about 94mm slip-ins, John? ... 1911cc?

[ThePaintedMan]

How about 94mm slip-ins, John? ... 1911cc?

Do the 94s require flycutting the heads on a 1.7? I know you still need to find deck height, CC the chambers, etc, but wasn't sure if it meant machine work to the heads.

[euro911]

My goof. 94mm would be 1832cc with the stock 66mm crank. 96mm would be 1911cc.

Even increasing from 90mm to 93mm (1793cc using stock 1.8L barrels and pistons) you would need to fly-cut the 1.7L heads.

[ThePaintedMan]

My goof. 94mm would be 1832cc with the stock 66mm crank. 96mm would be 1911cc.

Even increasing from 90mm to 93mm (1793cc using stock 1.8L barrels and pistons) you would need to fly-cut the 1.7L heads.

Thats what I thought. Sorry to hijack the OP's thread (IMG:style_emoticons/default/smile.gif)

[Cap'n Krusty]

If you use 94 mm pistons, you CANNOT use the OE spec units without replacing the crank and rods with 2 liter parts. I suppose there may be 94mm aftermarket pistons made for the 1.7/1.8 crank and rods, but I've never seen them. And, yes, any increase in bore will require opening up the heads.

The Cap'n

[Al Meredith]

I have a set of NPR (Nippon Piston Ring) 96MM pistons and cylinders for a 1.7 L making 1911 CC. The cylinders are sized for a 1.7 head and they don't require flycutting. The cylinders are therefore thin on top. I do not have a set of rings but they are still available from Performance as rings for big bore kits. 2MM / 2MM / 5MM. If anyone is interested get in touch. Al

[Cupomeat]

If it were me, I'd bite the bullet and go for the 2056 size engine.

You'll NEVER regret it once it is done.

I know, not the question asked.

As for the answer, you can go the 96mm slip-ins but the sealing surface at the head is VERY small, So I'd either get the one for the 1,8l and have the heads opened or (BETTER) get some 1.8l heads (they have bigger valves).

[jdlmodelt]

OK. So what can I do to the stock 1.7l to improve HP without all the bore upgrades? Can I put in the same displacement but slightly bump up the compression? I'm putting a 2.0l out of my 76 for now but I'm planning ahead when the 2.0l in the 76 and the 1.7l back in the 72

[brant]

OK. So what can I do to the stock 1.7l to improve HP without all the bore upgrades? Can I put in the same displacement but slightly bump up the compression? I'm putting a 2.0l out of my 76 for now but I'm planning ahead when the 2.0l in the 76 and the 1.7l back in the 72

nice to see a colorado guy on here...
the problem with the 1.7 is that is costs just as much to rebuild it with 70hp (correctly) as it does to rebuild a 2.0 motor with 105hp.

your best economical bet would be SSI exhausts
if you really want to open the engine, then a cam and carbs
but at that point, its only 200$ more to put in the 2ltr crank and rods...
your 1.7 heads and valves are really the limiting factor
and rebuilding those with bigger heads are about the same price as rebuilding a set of 2.0 heads with bigger valves....

so stock 2.0 heads are cheaper than big valves on your cores.

for the money.. finding a running $1000 2.0 motor gives you 90 - 95 hp and costs about 1/5th the cost of rebuilding...

if you do open it up to rebuild, most people decide its worth adding the displaceemnt hp at that point for relatively the same costs...

living with a running 1.7 gives up 15-20hp but costs $5-6K less.......

[jdlmodelt]

OK. So what can I do to the stock 1.7l to improve HP without all the bore upgrades? Can I put in the same displacement but slightly bump up the compression? I'm putting a 2.0l out of my 76 for now but I'm planning ahead when the 2.0l in the 76 and the 1.7l back in the 72

nice to see a colorado guy on here...
the problem with the 1.7 is that is costs just as much to rebuild it with 70hp (correctly) as it does to rebuild a 2.0 motor with 105hp.

your best economical bet would be SSI exhausts
if you really want to open the engine, then a cam and carbs
but at that point, its only 200$ more to put in the 2ltr crank and rods...
your 1.7 heads and valves are really the limiting factor
and rebuilding those with bigger heads are about the same price as rebuilding a set of 2.0 heads with bigger valves....

so stock 2.0 heads are cheaper than big valves on your cores.

for the money.. finding a running $1000 2.0 motor gives you 90 - 95 hp and costs about 1/5th the cost of rebuilding...

if you do open it up to rebuild, most people decide its worth adding the displaceemnt hp at that point for relatively the same costs...

living with a running 1.7 gives up 15-20hp but costs $5-6K less.......

Thanks fellow Coloradan!

[brant]

we have a local colorado yahoo group too
you ought to join
we get together for drives and sometimes wrenching too

here is the site:
colorado


where in the state are you?

[sean_v8_914]

have had success with the 1911 at no more than 8.5 on L Jet. requires FI tuning to get AFR correct.
the 1.7 responds well to increase in compression to 8.5 when combined with the SSI or 2.0 HEs and a Bursch type 4-2-2-1 tuned collector
the 1.7 HE has small ID pipe
if you are bold you can match port the exhaust a little. 1.7 heads have small ports and valves, thats why they run forever

[thelogo]

[quote name='sean_v8_914' date='Dec 28 2012, 07:10 AM' post='1791776']
have had success with the 1911 at no more than 8.5 on L Jet. requires FI tuning to get AFR correct. P
the 1.7 responds well to increase in compression to 8.5 when combined with the SSI or 2.0 HEs and a Bursch ty
the 1.7 HE has small ID pipe
if you are bold you can match port the exhaust a little1.7 heads have small ports and valves, thats why they run forever
[/
Hell. Yeh I'd rather have 15/30 less horshpower
An last forever the have a failure rate of over 90% w.2.0 heads
Lack of bore spacing and aircooled do not go together

I always use 91octane if I need more pep

Shout out to the CHEAp S O B

[Dave_Darling]

There have been 96mm P&C sets made for the 1.7s, which give you a 1911cc displacement. They are very thin to fit into the 1.7 heads.

The same kits made for the 1.8 give the same displacement, but are thicker. The 1.7 heads need to be cut to fit them. If you're going up in displacement, that's not a bad way to go.

Except for the 73 CA-only version, all of the 1.7s had relatively high compression (I think either 8.2:1 or 8.6:1) and were rated at 80 HP DIN. They require premium-grade fuel already; going up further in compression is probably not a great idea unless you can figure out how to make sure you don't get detonation.

The Tangerine Racing headers are good for something like a 10% HP bump. Make sure you're sitting down when you look at their price--but it's the biggest "bolt on" HP adder you can find, and they are absolute works of art. Chris also has an option for heat (probably just enough to de-fog the windshield) but most headers lose all semblance of heat. Which is an issue for some of us.

The 2056cc motor (a 2.0 crank and rods, plus the 96mm P&C kit that is made for the 2.0 motor) will bolt together with the 1.7 case, but again the heads will need to be cut to fit the cylinders. Everyone I know who has one of those motors is happy with it... For a while, at least, until the urge for more power hits. (IMG:style_emoticons/default/wink.gif)

--DD