Shift point

Injected,

The head is basically stock, valves were changed to SS but stock size. Head has been port matched and runners smoothed out, but nothing i would consider actual porting. I know im leaving alot of compression on the table cause i have alot of piston to valve clearance. I know how to rebuild an engine but im learning how to build a race engine one step at a time. so this winter i want to dive into the head/cams area and learn more about that

wrote:

Injected,

The head is basically stock, valves were changed to SS but stock size. Head has been port matched and runners smoothed out, but nothing i would consider actual porting. I know im leaving alot of compression on the table cause i have alot of piston to valve clearance. I know how to rebuild an engine but im learning how to build a race engine one step at a time. so this winter i want to dive into the head/cams area and learn more about that

 

OK, that explains some of your power issues.

A stock Z1 head only flows about 70 CFM (intake side) with a .500" lift cam, but a pro ported big valve Z1 head will flow +110 CFM depending on how big you push the runners. Since all engines are air pumps the more air you can push thru the more potential HP it will produce.

You want the head flow to at least match what the carbs can draw thru. Your RS34 carbs flow about 114 CFM (per Larry Cavanaugh) so you can open up the ports on that head a lot more.

Once you big valve the head you deck it to bring the compression back up lost by sinking and de-shrouding the valves. This is where you can also boost the cranking compression to over 200 PSI. You also want to run higher lift cams (+.435") to take advantage of the increased air flow. All of this requires mocking up with clay to make sure everything works together and has proper clearance.
 

Injected wrote:

A stock Z1 head only flows about 70 CFM (intake side) with a .500" lift cam, but a pro ported big valve Z1 head will flow +110 CFM depending on how big you push the runners. Since all engines are air pumps the more air you can push thru the more potential HP it will produce.

You want the head flow to at least match what the carbs can draw thru. Your RS34 carbs flow about 114 CFM (per Larry Cavanaugh) so you can open up the ports on that head a lot more.

Once you big valve the head you deck it to bring the compression back up lost by sinking and de-shrouding the valves. This is where you can also boost the cranking compression to over 200 PSI. You also want to run higher lift cams (+.435") to take advantage of the increased air flow. All of this requires mocking up with clay to make sure everything works together and has proper clearance.


 

Injected is spot on here.  Although, as the old saying goes, "speed is money, how fast do you want to go?".   I'd say that if you're going to go all in on a cylinder head/piston combo, please make sure that the bottom end of the motor and trans are up to the task.  If you're tempted to take a shortcut anywhere in the process, ultimately it will come back to bite you in the a$$.
And, to address Southpaw's original question, I'd say that a shift light is a whole lot easier to see after launching and while making your way down track.  Although, without a datalogger of some sort, you'd still need a tach to see RPMs when going through the traps.  If you can integrate a shift light into your setup, life will be a bit easier and your runs will be more consistent, IMHO.

I don't know anybody who runs shim over on a drag setup. 

Me neither.  Shim over buckets are a whole lot more convenient for valve adjustment without question, but with high lift cams at high RPMs you're asking for trouble.  Only once did I see a shim get spit out of a head.  Not pretty....

This thread morphed into engine building after I posted that 1075 drag bike example, which in all fairness was not a good example to post. Drag bikes are like snowflakes, no two are alike.

Injected wrote:

This thread morphed into engine building after I posted that 1075 drag bike example, which in all fairness was not a good example to post. Drag bikes are like snowflakes, no two are alike.

Thats ok all this info has my wheels turning, as i said im learning so all the info everyone is sharing is greatly appreciated.
So let me pose a question, would it be better/easier to put a J head on this motor vs. having port and valve work done to the Z1 head?
Would also love to hear everyone's thoughts on this: I have been told I should go up to a 1325 CC engine as it will be more consistent throughout the day with weather changes (heat/humidity). My bike gets slower every pass as the temp and humidity increase sometimes a tenth or two every pass, makes it difficult to come up with a dial-in time. Not concerned about speed looking for consistency. Yes the lower end has welded MK2 crank, main cap support plate , trans is backcut and billet second gear

Southpaw wrote:

Injected wrote:

This thread morphed into engine building after I posted that 1075 drag bike example, which in all fairness was not a good example to post. Drag bikes are like snowflakes, no two are alike.

Thats ok all this info has my wheels turning, as i said im learning so all the info everyone is sharing is greatly appreciated.
So let me pose a question, would it be better/easier to put a J head on this motor vs. having port and valve work done to the Z1 head?
Would also love to hear everyone's thoughts on this: I have been told I should go up to a 1325 CC engine as it will be more consistent throughout the day with weather changes (heat/humidity). My bike gets slower every pass as the temp and humidity increase sometimes a tenth or two every pass, makes it difficult to come up with a dial-in time. Not concerned about speed looking for consistency. Yes the lower end has welded MK2 crank, main cap support plate , trans is backcut and billet second gear


 

As far as the head is concerned it depends on if you can get a J head cheap enough, but yes starting off with J head is easier on the porting guy.

I have a Z1 head that flows 110 CFM with 37/31 valves and is OK for my 1327cc setup with 40mm Lectrons (38's would be ideal but 40's good for hot days) The big block with 1327 can be punched out as big as 1428 without changing the liners.

My setup is not idea either, with those carbs I should be running a bigger valved head and more CC's. I just slapped together a engine on the cheap that will hopefully be fast enough to work that pro built chassis.

A big CC engine might be more consistent but I am not convinced. That 1075 setup I posted was very consistent as that guy won the points championship at my local track 3 years in a row.

The only thing about going to a bigger engine is the carbs will now be too small, plus you have to run bigger cams in these big engines (460/480/500) On my head I am running 460/480 lift cams and static compression is about 16:1

Just so happens i have a J head. Would that actually need to be ported? I thought the stock J flows more than a stock Z1

wrote:

Just so happens i have a J head. Would that actually need to be ported? I thought the stock J flows more than a stock Z1






 

Only 6 CFM more than a stock Z1/KZ head. Those numbers listed are just the intake flow and as you can see just going up in valve size does not really change the flow that much. The GPZ has bigger valves and bigger ports, but its still not a drag bike head.

 

75-85 CFM is street bike flow, my 1200 street bike head flows 96 int/73 exh with 37/31 valves, that has been ported about mid way to keep some lower end grunt.

If you really want it to perform you should big valve it and port it. 39/33 would be ideal to push it past 110CFM. I guess it depends on how much $$$ you want to throw at it.

Injected wrote:

A big CC engine might be more consistent but I am not convinced. 
 

Totally agree with Injected on this.  

And, Southpaw, along with a big CC motor, comes some other issues, especially if you're running a small tire chassis.  If your track has reliable hook from week-to-week, that's a plus.  If not, you better be on top of your clutch tuning.  Also, the condition of your rear slick becomes a real issue.  And, is your chassis stout enough to handle the extra power?  A big motor can turn what was a decent handling bike into something evil.  

You may want to focus on honing the combo that you're currently running, at least in the short term.  As you gain valuable tuning experience, you'll find that consistency you're looking for.  Just a thought from somebody who's been down the road....

Mike
 

wrote:

wrote:

A big CC engine might be more consistent but I am not convinced. 








 

Totally agree with Injected on this.  

And, Southpaw, along with a big CC motor, comes some other issues, especially if you're running a small tire chassis.  If your track has reliable hook from week-to-week, that's a plus.  If not, you better be on top of your clutch tuning.  Also, the condition of your rear slick becomes a real issue.  And, is your chassis stout enough to handle the extra power?  A big motor can turn what was a decent handling bike into something evil.  

You may want to focus on honing the combo that you're currently running, at least in the short term.  As you gain valuable tuning experience, you'll find that consistency you're looking for.  Just a thought from somebody who's been down the road....

Mike

Well said. 

Not sure if you noticed but he is running a 5" slick (more like 5.5") bike in question looks to be a Z1 back half conversion.
Pretty sure M/T and Goodyear no longer sell those tires  

M&H list a 4"x18" but they seem pricey and I don't know anyone who has tried one.

My 650 drag bike uses a 5" Goodyear, so not looking forward to the day its no longer any good. My chassis on that bike is also a stock frame conversion but running a tiny engine so not too worried about torque.

People have run those 5" tires (early Kawasaki V&H) into the low 9's as far as I could gather, but those engines were no bigger than 1260cc.

I agree that more power needs a stiffer chassis and a wider tire to be effective, guys have run real quick on 7" tires ( Walt Timblin went low 7's @ 200 mph at Atco 25 years ago) The tall 18" tires seem to have a high speed potential under the right conditions (Timblin custom chassis was very rigid) According to my math, for a 550 lb package to generate those kind of numbers takes about 300 HP at the rear wheel.

Car tires are a complete other realm!

Getting back to the matter at hand, at 750 lbs package weight you would need about 180 HP at the wheel to run a 9.40 which is totally achievable with a fully built NA engine in the 1260-1327cc range.

Injected wrote:

I agree that more power needs a stiffer chassis and a wider tire to be effective, guys have run real quick on 7" tires ( Walt Timblin went low 7's @ 200 mph at Atco 25 years ago) The tall 18" tires seem to have a high speed potential under the right conditions (Timblin custom chassis was very rigid)

Car tires are a complete other realm!


 

Yes, Walt Timblin is quite the master chassis builder and is still going strong, I believe, to this day; as is Paul Gast.  Two icons of the sport.  

And, yes, car tire chassis present their own set of "challenges", speaking from experience.  

You're right, Injected - the selection of 18" motorcycle slicks is very, very limited.  I'm seeing just two options - the M/T 7" and that 4" M&H.  I'd imagine that it's driven by lack of demand.  Seems as though the trend over the past 20 years has been towards the no-bar Busa's and ZX's with their 17" rear wheels and 12" over arms.  A whole different beast, for sure!

And Southpaw, I hope that you can get your combination squared away.  Finding that week-in, week-out consistency is the key to successful bracket racing.  I think that you're on your way.  Just keep chipping away at the process, eliminate variables, and don't be afraid to ask questions.

Mike