1045 vs 1075

larrycavan wrote:

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.

This statement really sums it up. I've always thought to myself when I rebuilt my engine it would be with 1075 pistons and some mild porting with cams. This seems to be an enjoyable setup. So I think I may go that route. Then on the next built I may go bigger on the cc's.

Yep...I know you were not implying to over cam it to get around the static number...

Hey.....who stold the edit button AND WHY DID THEY STEAL IT:huh:

Edit function is back...

I was kinda wondering myself on why a 1045 when the 1075 is basically the same price for pistons & rings...

Nothing over 10.5:1 most definitely... Especially here in Arizona, that thing would sooooooo over heat.... :laugh:

I know someone local that want to get rid of a 1045 kit pretty cheap. So I was wondering what differences I could expect. If buying used 1045 kit was really worth it when I really want a new or relatively new 1075 kit.

I doubt that you would ever be able to tell the difference in +/- 3% of displacement. The big difference will be in proper breathing. Think of it this way. My old Camaro with a 6.6L engine had around 290HP my jaguar with a 4.2L engine has 310HP. When the blower is engaged it has 400HP put your extra money in proper head work and a good set of street cams. I had the same dilemma on my J motor should I go with the 1140 kit or the 1170 kit. I decided on the 1140 due to a reliability factor and cooling. I doubt that the size difference would be 2-3HP for either of us. In my case the price was exactly the same. In your case you can actually save money. It's a no-brainer in your case.

Look at Larry Cavanaugh's web sight. It will explain everything.
www.flowbenchtech.com/porting/CRH/kz-data.htm

According to Larry, the difference between a 1075 and a 1327 is about 3HP. What do you think it would be in our case?????
1.5??

One thing about Larry C, is that he is not trying to sell you anything. He is just giving you raw #s to work with. I personally trust him implicitly. I have never met Larry in person, but I have talked to him on the phone a # of times and he is always willing to help and there is no BS from him. I would say, take the money you save and send him your head and gain 20+ Hp that way. you will still keep the reliability of the engine and have the honest HP you want.

PLUMMEN wrote:

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

Amen! You said a mouth full. It's all about the intake closing point.

otakar wrote:

Look at Larry Cavanaugh's web sight. It will explain everything.
www.flowbenchtech.com/porting/CRH/kz-data.htm

According to Larry, the difference between a 1075 and a 1327 is about 3HP. What do you think it would be in our case?????
1.5??

And what would that extra 1.5 hp cost?

kzz1p wrote:

PLUMMEN wrote:

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

Amen! You said a mouth full. It's all about the intake closing point.

Consider this: On a street engine, you want maximum cylinder filling (volumetric efficiency) in a usable power band. Say between 3000 and 7000 RPM. Expect 90% - 110% volumetric efficiency on a well tuned KZ in this RPM range. No way that is going to run on pump gas with 13:1 compression. Let me rephrase - 10.5:1 compression is the limit on a well tuned street engine with good volumetric efficiency.

As pointed out earlier, if your engine is in a horrible state of tune or your cam duration is so radical that you don't get decent VE until 8000rpm then maybe you can run 13:1 compression with 93 octane fuel on the street without knocking. The engine will run like s**t and have no power until you wind it up to 8K then it'll knock like crazy.

A 1045 or 1075 with 10.5:1 compression and mild performance cam is the foundation of a good street engine. Once you install the cam and piston kit, the power will come from tuning. In my experience, exhaust tuning is one of the most important and overlooked pieces of the puzzle. A good 4-1 exhaust with the right size baffle will go a long way to making broad streetable power. Also, a well tuned exhaust will "pull" air through the intake during valve overlap (scavenging) which aids in carb tuning.

Yes the dome on a 13:1 piston will hurt VE greatly. I would guess that most people could not tell the differance, between a 10:1, 9:1 or an 8:1 motor. So why stick your neck out and risk it all? I have seen more broken big block motors, then smaller motors.

Please remember the term "street sleepers" Some cam companies suggest very large lift and duration with stock air boxes, carbs and exhaust pipes..........