1.7L Rebuild, Larger Cyls/Pistons Worth It?

jjs3rd914 · 06-25-2006, 04:49 PM

We are rebuilding a 1.7L which AC will be reinstalled? It is a low mileage car and the as found pistons/cylinders are well within tolerance. They really are in excellent condition. We are evaluating reinstalling after honing the walls and installing new rings. A Sanden 508 compressor will be used that supposedly has little HP drain.

Question? If we upgrade to larger cylinders/pistons what is the real HP gain for the expense? We understand drop-in 96mm walls are too thin. We also understand 94mm are a good bet but the heads have to be machined. So what is the real gain? It is that noticeable?

Thanks
Jeff

ptravnic · 06-26-2006, 10:07 AM

Check out shoptalkforums type 4 forum. There's lots of experts o'er there on this topic...

-pt

Bleyseng · Bleyseng's Garage

Depends on which1.7L you have. 80hp with 8.2 to 1 compression (70-73) or the Calif version with 73 hp?

You can install 93mm or 94mm with no problems but you need to keep the compression ratio the same. The 93's or 94mm also need bigger valves to get it to breath right. So off go the heads to have larger valves installed (Adrian at Headflow Masters or Len at HAM) plus have the heads cut for the larger register. I think Jake has some 96's that work without being too thin so ask him or check his site Type 4 store.com
I don't mind keeping the nice 90mm domed pistons running as its a nice combo set up by the domes and small head chambers.
A cam change is nice too as the stock cam is pretty weak and hot.

jjs3rd914 · 06-26-2006, 12:57 PM

Thanks for the replies thus far. The car is a 1972 (not Calif) so I assume it is the 80HP version. The heads were replaced by a former owner less than 10k miles ago and are also in great shape so we are not going to modify the valves. About the only machining being considered is for the larger cylinders if we decide to go that way. I will checkout the type IV forum to see what real gains are available.

Thanks
Jeff

Eat-um-up · Eat-um-up's Garage

I allways like the engines from FAT preformance. http://www.fatperformance.com/type4.htm
With the 911 cooling tin on there the car should scream with power without getting too warm

Bleyseng · Bleyseng's Garage

Going to larger P&C's seems to kill the engine combo if you don't enlarge the valves. The 90mm domed 1.7l is a pretty good engine. The 1911cc is a good engine too but if you just install the 96mm flat top P&C's the combo just don't scream like it should as the chambers are set up for the smaller domed pistons.

If the 90's are good, run em.

hardflex · 07-04-2006, 08:07 AM

years ago, I had a 1.7 that I put 93mm jugs on during a rebuild, I remember it as being more "torquey" than before, but that might have been cuz the engine was fresh. I did notice a big difference when I installed some a 1.8 exhaust system, which is larger diameter. The engine revved really nice and seemed to have power throught the band. I'm sorry I sold that engine.