1150cc piston kit, re jetting?

[Jeff Bennetts]

Good stuff, Jeff. Re the carbs: Need to verify what model they are first. This is an '82 engine, so they might be late model. Check the number - VB60 or 61 are early carbs, VB62 are '80 only, and VB63 or 64 are late model. Jeff's recommendations apply only to the early carbs. However, with the stock intake, I think you leave the main jet alone. Work on low and mid-range, but first we need to know what carbs we have.

Dave

I missed the part about the engine being a late model, the accel pump adjustments are the same across the range of CBX carbs so at least that will apply no matter what carbs you have and help with the off-idle, low and mid-range.

But as Dave has pointed out, identify the carbs and go from there.

[EMS]

Good stuff, Jeff. Re the carbs: Need to verify what model they are first. This is an '82 engine, so they might be late model. Check the number - VB60 or 61 are early carbs, VB62 are '80 only, and VB63 or 64 are late model. Jeff's recommendations apply only to the early carbs. However, with the stock intake, I think you leave the main jet alone. Work on low and mid-range, but first we need to know what carbs we have.

Dave

Don't know where the VB63s go into, but they could be VB65

[steve murdoch icoa #5322]

Geert, i am assuming you are using the cruzinimage kit?
I know Fasterspider is very happy with his.
http://www.ebay.com/itm/Honda-CBX1000-B ... 2e&vxp=mtr

Has anyone heard of a review of this Forseti kit from Australia?
http://www.ebay.com/itm/HONDA-CBX1000-D ... 00&vxp=mtr

[Jeff Bennetts]

Geert, i am assuming you are using the cruzinimage kit?
I know Fasterspider is very happy with his.
http://www.ebay.com/itm/Honda-CBX1000-B ... 2e&vxp=mtr

Has anyone heard of a review of this Forseti kit from Australia?
http://www.ebay.com/itm/HONDA-CBX1000-D ... 00&vxp=mtr

I see the Forseti 1147 kit is 9.3 to 1 just like the stock pistons but I don't see any compression rating for the Cruzinimage 1147 kit, does anyone know what it is for sure?

[Rick Pope]

Good advice! darn, I need to find that "relay mod" post. Don't even remember that!

I'm thinking falldownphill started it or joined the thread with the mod or maybe it was Kool Biker, I need Pope to remember this for me.

Aris, "Kool Biker" did the mod, and did a wonderful job documenting it.

And I'm still finding those dam Easter eggs......... One grandson has found all but one of his the past couple of years. When we find it, we move it. We play that game all year long.

But Jeff, just wait until you're a bit older. You'll find your hard drive full, so you remember the older, seemingly useless trivia, much to the dismay of you life partner (aka Bev).

[EMS]

I see the Forseti 1147 kit is 9.3 to 1 just like the stock pistons but I don't see any compression rating for the Cruzinimage 1147 kit, does anyone know what it is for sure?

Jeff: Unless the combustion chamber is changed, the calculation for the compression ratio I posted applies. It gets within a decimal point. The only variable is the head gasket area. If they say that an increase in displacement to 1147 retains the same compression ratio, they are incorrect, unless they increase the volume of the combustion chamber or change the surface of the piston significantly. It is engine design basics. Compression ratio is defined as the volume of the cylinder at bottom dead center vs the volume in the cylinder at top dead center. It is not a magical number that is part of a piston manufacturers technology. The volume of the CBX combustion chamber is around 21cc.

[Jeff Bennetts]

It's looks like the Forseti pistons are domed and the cruzin pistons are dished, I'll have to disagree with you on manufactures offering multiple ratios for the same piston diameter and displacement.

Take a look at what JE Pistons offer for the CB750, they are the same bore size, displacement, use the same gasket kit but are different compression ratios, 10.5 and 12.5 to 1 respectively.

http://www.jepistons.com/Catalogs/Power ... 50-tq.aspx

[EMS]

It's looks like the Forseti pistons are domed and the cruzin pistons are dished, I'll have to disagree with you on manufactures offering multiple ratios for the same piston diameter and displacement.

Take a look at what JE Pistons offer for the CB750, they are the same bore size, displacement, use the same gasket kit but are different compression ratios, 10.5 and 12.5 to 1 respectively.

Jeff: you are just confirming what I said. Dished vs domed (piston surface) have different compression ratios for the same displacement. One of the sellers claims their piston are the same as stock, except the bore. JE Pistons obviously offer two different pistons for two different ratios.
All I said was that unless you change the volume of the combustion chamber or the shape of the piston, the compression ratio for a larger bore can be calculated from the stock compression ratio.

[Jeff Bennetts]

It's looks like the Forseti pistons are domed and the cruzin pistons are dished, I'll have to disagree with you on manufactures offering multiple ratios for the same piston diameter and displacement.

Take a look at what JE Pistons offer for the CB750, they are the same bore size, displacement, use the same gasket kit but are different compression ratios, 10.5 and 12.5 to 1 respectively.

Jeff: you are just confirming what I said. Dished vs domed (piston surface) have different compression ratios for the same displacement. One of the sellers claims their piston are the same as stock, except the bore. JE Pistons obviously offer two different pistons for two different ratios.
All I said was that unless you change the volume of the combustion chamber or the shape of the piston, the compression ratio for a larger bore can be calculated from the stock compression ratio.

Actually this is what you said,
Jeff: Unless the combustion chamber is changed, the calculation for the compression ratio I posted applies. It gets within a decimal point. The only variable is the head gasket area. If they say that an increase in displacement to 1147 retains the same compression ratio, they are incorrect.

The top of the piston design has nothing to do with phisically altering the combustion chamber of the head, the piston design will change the volume of the squish area and thus effect the compression, your calculations pertain to flat top pistons which neither of the two kits offered on EBay that we are discussing in the above post are, they are clearly domed.

Your comment that the only variable is the head gasket to alter compression is incorrect in the discussion that is going on here in this particular thread, for the flat top pistons, yes.

[EMS]

O.K. I give up, Jeff.
The combustion chamber or area is the volume above the piston at TDC and is used to calculate compression ratio. Domed or dished pistons alter that volume, consequently the compression ratio.
One of the CBX kits has domed pistons, just like the stock CBX. The compression ratio for these pistons will be higher, as per the calculation I posted. If the other set has dished pistons, the volume above TDC is enlarged, thus adjusting the compression ratio for the larger displacement, in effect it could keep it the same at 9.3:1
If I can't seem to put this into words that you understand, maybe someon else can.

Squish area is the area between head and piston top that is formed by the flat bottom shape of the combustion area, which is not round. It is hwere the compression of the fuel/air mixture starts. Sqish area can be exactly the same for a domed or a flat top piston. The domed part of the piston reaches further into the combustion area.

The point in this thread here clearly is: If someone offers a big bore kit with pistons that are exactly like stock except for the bore (auction description!) the compression ratio of that kit will increase by the same percentage as the displacement. Engine basics.

[Jeff Bennetts]

That's a very complete and detailed explanation Mike, thanks for posting it.

Don't give up on me just yet," hope springs eternal"

[Rick Pope]

That's a very complete and detailed explanation Mike, thanks for posting it.

Don't give up on me just yet," hope springs eternal"

Same here. I'd always thought that compression ratio was only considering the space above the piston, within the cylinder, excluding the head volume. Thank you for clearing that up.

[EMS]

Same here. I'd always thought that compression ratio was only considering the space above the piston, within the cylinder, excluding the head volume. Thank you for clearing that up.

I am sorry, Rick. It must have something to do with me not speaking English as a native language. What did I say different??
I though I said compression ratio is the volume above the piston at bottom dead center compared to (or divided by) the volume above the piston at top dead center???
If I did not, I apologize to you and Jeff.
In case of the CBX: The displacement in one cylinder is approx.175cc. The compression ratio is 9.3:1

Which means; 175+x/x=9.3 or in numbers: 196 (175 + 21) / 21 = 9.3

With 21cc being the approximate volume above the piston at tdc. In almost all engines, at tdc, there is basically no volume left in the cylinder other than the volume in the head (combustion chamber)

[Jeff Bennetts]

I think the lesson here is to keep it simple and stay on topic, IMHO I think more members will benefit from all the awesome knowledge here on the forum and I'll do my best to follow my own advice.

It's probably a safe bet that the Cruzinimage_co piston kit is at the stock compression 9.3 to1, or it would be stated somewhere on the EBay advert, I'm surprised Geert didn't get a spec sheet with the kit.

I found Aris's relay mod thread but it's for the voltmeter, good news is the same theory applies to powering the coils. This relay mod is making it's rounds on two other vintage forums I belong to, so I'm sure a quick google search will find you what you need to perform it.

Here is Kool Biker's (Aris) thread;
viewtopic.php?f=21&t=8137

[EMS]

It's probably a safe bet that the Cruzinimage_co piston kit is at the stock compression 9.3 to1, or it would be stated somewhere on the EBay advert,

I know, it's like blowing in the wind, but I stand by my earlier statement. I looked at both auctions again and both the Forseti and the Cruizinimage kits have domed pistons which look exactly like the stock pistons. This means the compression ratio can not be like the stock 9.3:1.It has to be higher and I would be willing to take that bet.
In order to maintain the same compression ratio with a larger displacement, you have to enlarge the volume above the piston at tdc. If you only selling the pistons, the pistons have to have a different appearance than stock. In the CBX case, they would have to be flat top or dished or have a lower deck height.
I wish fasterspider would chime in and let us know what he thinks about his kit.