Engine work versus head swap?

Okay here's my question:

I had originally planned to overbore my 1015cc by 2mm to get 1075cc. Get the low comp pistons, and set up a draw through turbo setup.

I did some more reading and apparently a J model head will fit onto my cylinder block with only minor mods and drop compression two points(APE's website).

By cost:

Low comp pistons: $475
bore and hone: $150?
Liska cam chain top idler & blocks from APE: $160
total: $785

Ape adapter: $125
Good used J head: $200?
Total: $325


By cost is seems a no-brainer. Anybody want to guess which would be the more fun to ride? A bored out turbo'd 175cc versus a stockish 1015 with a J head to lower comp and has bigger valves for better breathing?

Sam

put both togeather. :whistle:

Having been down this road many times with turbo and blower bikes, here are a few things to think about. I'm assuming that you are working with a Z900 or KZ1000 model ??

1.Most draw thru turbo kits were designed for stock bikes as far as compression ratio. As long as you don't go crazy with the boost, carburation and ignition, and use top quality gas you should be OK with a stock setup as far as compression ratio goes.

2. Here is the big one though. Before you go turbo, make absolutely sure that the rest of your motor is bullet proof.Really important. I have literally had dozens of friends think they could just throw a turbo kit on in the morning and go out and do burn outs in the afternoon only to see them come whimpering back with blown motors. Really !!!!

3. Depending on what kind of bhp you are shooting for, here are a few things to look at.

a. weld and balance crank - a must
b. undercut tranny gears while you are at it
c. windage tray under crank
d. heavy duty crank main bearing brace and studs
e. heavy duty crank studs
f. deep sump or modified oil pan with gate
g. change timing of exaust cam
h. slotted cam gears
i. maybe update ignition system
j. better valve springs
k. APE cam chain tensioner
l. maybe heavy duty cylinder studs

There are a few others - but you get the idea.

Zippy

zippy wrote:

Having been down this road many times with turbo and blower bikes, here are a few things to think about. I'm assuming that you are working with a Z900 or KZ1000 model ??

1.Most draw thru turbo kits were designed for stock bikes as far as compression ratio. As long as you don't go crazy with the boost, carburation and ignition, and use top quality gas you should be OK with a stock setup as far as compression ratio goes.

2. Here is the big one though. Before you go turbo, make absolutely sure that the rest of your motor is bullet proof.Really important. I have literally had dozens of friends think they could just throw a turbo kit on in the morning and go out and do burn outs in the afternoon only to see them come whimpering back with blown motors. Really !!!!

3. Depending on what kind of bhp you are shooting for, here are a few things to look at.

a. weld and balance crank - a must
b. undercut tranny gears while you are at it
c. windage tray under crank
d. heavy duty crank main bearing brace and studs
e. heavy duty crank studs
f. deep sump or modified oil pan with gate
g. change timing of exaust cam
h. slotted cam gears
i. maybe update ignition system
j. better valve springs
k. APE cam chain tensioner
l. maybe heavy duty cylinder studs

There are a few others - but you get the idea.

Zippy

Thanks for the pointers, but I have most of this thought of already. Its 1978 KZ1000A2
1.APE main bearing studs
2. the crank has been to Falicon and been supercranked
3.had the tranny apart and shift dogs are excellent (15000 miles on this motor)
4.oil pump is within spec
5. have the APE cam chain tensioner
6. liska cam chain bits are on the list, as well as replacing any remaining oem rubber bits
7. stock clutch; i like the feel and if it wears I can always replace them.
8. HD cylinder studs are on the list
9. extra oil pan: make it a deep sump to hold an extra quart and it'll be tapped at the bottom to feed the external oil pump which which supply the oil cooler and turbo. I'm still fishing for a nice place for the turbo oil return.
10. i passed on the main bearing supprt cap, places like ape and falicon that do the machining tell me its usuallt for drag bikes making >200hp. I'm aiming in the 140's so i should be fine.

Good to see ya on the right path - You are gonna have a lot of fun !!

Woo Hoo

Zippy

A "properly built" 1075 turbo will walk all over the J head project...no 2 ways about it.

Why do you think a J head is going to make all kinds of power?

Although I have been tempted to do a turbo bike,
a NOS bike sure seems more affordable and when
not on the spray it will ride like a normal bike.
Either will reguire an oringed head though I think.
And maybe external oiling to the head?

larrycavan wrote:

A "properly built" 1075 turbo will walk all over the J head project...no 2 ways about it.

Why do you think a J head is going to make all kinds of power?

That's not what I was trying to say exactly. Its not that the J head would be all-wonderful. I was looking at it as an economical option to buying new low compression pistons. Because the J head on my engine would lower compression anyway.

Your opinion though is what I've read mostly. Bore it out, make sure its properly built and away you go!

thanks!