1045 vs 1075

How would a 13:1 1045cc compare to a 1075cc 10.5:1? Would the 1045 be a good streetable engine? Meaning run well on pump gas and no overheating issues. Would it be as reliable as the 1075 engine. I need to beef up my engine and not sure which way to go. I mainly plan to use this as a street bike with some get-up and go maybe a track day or street racing here and there.

Pros and cons please...

Unless you want to run race fuel, you might want to consider sticking with the 10.5:1 compression (or even a bit lower). Specially on an air cooled engine.

My 2 cents....

X 2 However, I really doubt there is a real 13.5:1 1045 made.

you'll be running at least cam 2 in a 13.5-1 engine..

13:1 is not streetable on an air cooled engine. Water cooling is a different story. Even a 10.5:1 KZ is a challenge to keep cool enough to run 93 octane without knocking. I've been able to manage well with a good oil cooler and fan setup on my 1075. But 10.5:1 is the limit with an air cooled head.

davel wrote:

13:1 is not streetable on an air cooled engine. Water cooling is a different story. Even a 10.5:1 KZ is a challenge to keep cool enough to run 93 octane without knocking. I've been able to manage well with a good oil cooler and fan setup on my 1075. But 10.5:1 is the limit with an air cooled head.

depends more on youre actual cylinder pressure than a number on the side of a box.with a set of long duration cams youre cylinder pressure will drop quite a bit

Yeah, some big ol' thumper cams with a boat load of overlap would for sure reduce the cylinder pressure. But then you end up with a "peaky" motor. That kinda' defeats the request of a "good streetable engine.... run(nig) well on pump gas and no overheating issues.

If it was my money, I'd go for a 1197 at 10.25:1 (with an oil cooler), 29mm smmoothbore carbs, and .375" to .400ish lift cams with around 280 degrees duration.

But I'll admit that I have no "big block" experience. I'm a "small block" guy (i.e. KZ650). But I do have RC400 cams with Venolia race pistons. So I have an idea about too much compression & cam in a bike that spends 99% of it time on the street.

My suggestion to TW, go for the torque in that big block man!!

You don't really have to go big block to get a big torquey motor. We can do 1260s in stock KZ1000 blocks that are not leakers.

Jay

Jay, when you say 1260 kit that is a non leaker, what exactly do you mean by non leaker? Would this size engine be a good reliable street engine without overheating issues? One of the main reasons I have not tore appart my stock engine in that it is solid and reliable with no problems at all. I think I may have one of my spare stock engines rebuilt.

From a cc perspective, there's not a hell of a lot of performance difference between the 1045 vs 1075. What's going to bite you is the 13:1 compression.

As for cams and cylinder pressure....that's related to two areas, IVC and TDC Overlap lift / duration.

If for example you had a motor with too high static compression for the street. You could band-aid the situation with cams. But that's total foolishness when you're starting with a clean slate.

If you want to understand how this all plays into an engine combo, do some research on dynamic compression vs static compression.

IMO, just get the street compression pistons and select carb size and camshafts that suit the way you really ride the motorcycle. Be honest with yourself. Be wise in your selection & you'll have an enjoyable motorcycle.

i realize big cams arent the answer im just saying that depending on how the rest of the engine is put together you cant just go by the numbers on the side of a box. :laugh: i wish somebody would start making 9:1 pistons to deal with the reality that pump gas aint what it used to be

tw.. wrote:

Jay, when you say 1260 kit that is a non leaker, what exactly do you mean by non leaker? Would this size engine be a good reliable street engine without overheating issues? One of the main reasons I have not tore appart my stock engine in that it is solid and reliable with no problems at all. I think I may have one of my spare stock engines rebuilt.

1260 Kaws and GS Suzukis used to use the same sleeves. On the Kaw KZs, you would bore thru into the air passages to install those sleeves. Oil only had to come up the sleeve anout an inch then it could excape. Used to be that 1200 was as large as you could go in a KZ without boring into the air passage.

We have now done a sleeve for 1260 KZs that doesn't bore into the air passage, so it no longer leaks there.

Jay