Topic: Highest HP - UNDER 750cc & Stock compression

[754]

How high are you guys revving your RC 315 motors?
 As I got older and the cops started curtailing all our fun , I started short shifting a lot... surprising how good that 836 would pull from 4 to 7 K..
 I have a set of stock  cylinders  with fresh bore job , 1st or end over. If I build that  I will not be using a hot cam .. real mild cam.....maybe..

[PeWe]

392 pistons in a K6 or earlier will improve if using stock cam or slightly "hotter" possible drop in cam.
+0.5mm and +1mm set sold by Cruzinimage.  $120US

[Don R]

 Shucks, there was a guy on here that made 80 or so HP with a 400F.  L0L!

[754]

So far it looks like no one is stepping up to the challenge. .

[johno]

Frank he's calling the challenge, were just waiting for him to post the dyno hp numbers to see if its worth a challenge 

[Plzhalpimlost]

Frank he's calling the challenge, were just waiting for him to post the dyno hp numbers to see if its worth a challenge 

Ha! Franks getting anxious — he’d hate to see a stock bike come close to his big bores and challenge his beliefs

I was hoping y’all would be giving me some numbers to aim for, but hey I’ll have my numbers posted by the end of the year.

Though I was trying to BEAT a record, not start one!


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[scottly]

Though I was trying to BEAT a record, not start one!


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Then remove your silly stock compression limitation.

[PeWe]

392 head must give more hp, the chambers and ports look much better than previous K heads.
Pistons to match.
CycleX write that 392 chambers are 24cc.
http://www.cyclexchange.net/Engine%20Parts%20Pistons%20Page/890cc/890cc%20Pistons.htm

[dragracer]

I'm just here for the comments.

I'll just hold onto my big bore records for a while- any challengers to those known numbers??

[MRieck]

Frank he's calling the challenge, were just waiting for him to post the dyno hp numbers to see if its worth a challenge 

Ha! Franks getting anxious — he’d hate to see a stock bike come close to his big bores and challenge his beliefs

I was hoping y’all would be giving me some numbers to aim for, but hey I’ll have my numbers posted by the end of the year.

Though I was trying to BEAT a record, not start one!


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My 75F makes a verified 106.4 RWHP if you want a target to aim for.

[MRieck]

392 head must give more hp, the chambers and ports look much better than previous K heads.
Pistons to match.
CycleX write that 392 chambers are 24cc.
http://www.cyclexchange.net/Engine%20Parts%20Pistons%20Page/890cc/890cc%20Pistons.htm

.....and earlier heads are 22cc's. So.....if you fit an early head with an F2 piston............

[PeWe]

Frank he's calling the challenge, were just waiting for him to post the dyno hp numbers to see if its worth a challenge 

Ha! Franks getting anxious — he’d hate to see a stock bike come close to his big bores and challenge his beliefs

I was hoping y’all would be giving me some numbers to aim for, but hey I’ll have my numbers posted by the end of the year.

Though I was trying to BEAT a record, not start one!


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My 75F makes a verified 106.4 RWHP if you want a target to aim for.

A really good target, indeed!!!
Stock Mike Bike

[PeWe]

392 head must give more hp, the chambers and ports look much better than previous K heads.
Pistons to match.
CycleX write that 392 chambers are 24cc.
http://www.cyclexchange.net/Engine%20Parts%20Pistons%20Page/890cc/890cc%20Pistons.htm

.....and earlier heads are 22cc's. So.....if you fit an early head with an F2 piston............

Using various Honda stock parts   must be a challenge in the hunt for more as long as it has only one cam.

[NitroHunter]

Great question. Only other “rule” would be N/A. No forced induction.

Besides, what kind of knucklehead would even think that putting big turbo boost onto stock pistons (and running 143mph) would be a good idea? Lunacy to be sure. 

[PeWe]

Great question. Only other “rule” would be N/A. No forced induction.

Besides, what kind of knucklehead would even think that putting big turbo boost onto stock pistons (and running 143mph) would be a good idea? Lunacy to be sure. 

Stock pistons from another Honda?
Stock CB1100 rods....

[754]

Nope he ran stock 750 pistons with a stack of gaskets, to lower compression.
 Then he ran a 10.10 in the 1/4 mile... actually  a 10.0×..
 All with stock pistons..

 That is over 120 horse on stock pistons..

[grcamna2]

This thread could be cool to see what can be had with razor sharp tuning.  It will need people to actually do dyno runs.  And since dyno's are not very accurate comparing from one to another, the interesting part is gonna be the amount of increase, not the total number.

subscribed,
balancing the improvements and fine tuning,this will be good 

[NitroHunter]

Actually Frank the 10.10 run on the event winning final round pass served as the backup to the 10.00 semifinal run. Tom Loughlin DRAGBIKE USA made me pull the head at the track to verify the 736cc displacement for the class record.
Yes PeWe, that motor was genuine old SOHC unmodified stock pistons, rings, and rods. And 5 base gaskets to raise the cylinder deck and keep the slugs down in the hole. Lower compression on the cheap.
I modified a top end oil return passage spacer dowel and O ring to use in the base oil supply passages.
I'm sure the key to successfully running almost 2 years without twisting those stock rods into pretzels was staying on the safe side of detonation through a combination of low boost, good fuel and modest ignition timing. ERC 110 was the gas I ran until that Spokane Dragbike race, where after consulting with ERC they sent me a special 118 blend so I could really stuff the manifold pressure for a few runs. As this was intended to be the last runs on this motor I really wanted to push it to the limit and hopefully still have it one piece when I came home. 

[HondaMan]

A lot of people want higher compression  along with a hotter cam.

What I have always noticed about cams is: you need to bump the piston domes higher if the cam duration is [generally] longer to get the original compression numbers back. This is due to the overlap characteristics of all but the turbo-specific cams. The old CB750 "Racing Kit" that Yosh used to make had pistons advertised as 9.2:1 or 9.8:1, while those engines I saw with the 9.2:1 pistons and the "90 HP" cam (as they called it then) had compression numbers similar to stock, around 130-140 PSI cold cranking. When I build stock 750 bores under the "85 HP" cam (today available as the Megacycle 125-00) the compression comes out around 125. It goes up a little with the flat-topped 836 pistons installed, but that's just because of the volume. To date, I have not built an F2/3 stock-bore engine with the Megacycle 125-00 cam, at least that I can remember? So, I don't know what those compression numbers might be.

[PeWe]

My almost stock K2 has 170- 180 PSI with Cruzinimage 392 61.5mm pistons and K7 cam. Head chambers differ some.

I hope I can get 2 Dyno times within a month. The minimum numbers to beat here.
The higher numbers by Mike 

[Plzhalpimlost]

A lot of people want higher compression  along with a hotter cam.

What I have always noticed about cams is: you need to bump the piston domes higher if the cam duration is [generally] longer to get the original compression numbers back. This is due to the overlap characteristics of all but the turbo-specific cams. The old CB750 "Racing Kit" that Yosh used to make had pistons advertised as 9.2:1 or 9.8:1, while those engines I saw with the 9.2:1 pistons and the "90 HP" cam (as they called it then) had compression numbers similar to stock, around 130-140 PSI cold cranking. When I build stock 750 bores under the "85 HP" cam (today available as the Megacycle 125-00) the compression comes out around 125. It goes up a little with the flat-topped 836 pistons installed, but that's just because of the volume. To date, I have not built an F2/3 stock-bore engine with the Megacycle 125-00 cam, at least that I can remember? So, I don't know what those compression numbers might be.

Why do they/you call them 85/90hp cams? That seems pretty dang optimistic for a 750 with a cam thrown on. What changes needed to be made for a 125-00 to make 85hp? I have no expectation of seeing those numbers with the 125-NR.


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[bear]

Great question. Only other “rule” would be N/A. No forced induction.

Stock pistons from another Honda?
Stock CB1100 rods....

Not all CB1100 rod's are equal Per. They need to be the M4 units in my opinion.
Pistons? RC45 or XR250, take your pick. The RC45 units are a beautiful thing but XR's are as tough as old boots.
Both won't stand up to the stock bore rule I'm sorry to say but they are Honda Stock.

[PeWe]

A lot of people want higher compression  along with a hotter cam.

What I have always noticed about cams is: you need to bump the piston domes higher if the cam duration is [generally] longer to get the original compression numbers back. This is due to the overlap characteristics of all but the turbo-specific cams. The old CB750 "Racing Kit" that Yosh used to make had pistons advertised as 9.2:1 or 9.8:1, while those engines I saw with the 9.2:1 pistons and the "90 HP" cam (as they called it then) had compression numbers similar to stock, around 130-140 PSI cold cranking. When I build stock 750 bores under the "85 HP" cam (today available as the Megacycle 125-00) the compression comes out around 125. It goes up a little with the flat-topped 836 pistons installed, but that's just because of the volume. To date, I have not built an F2/3 stock-bore engine with the Megacycle 125-00 cam, at least that I can remember? So, I don't know what those compression numbers might be.

Why do they/you call them 85/90hp cams? That seems pretty dang optimistic for a 750 with a cam thrown on. What changes needed to be made for a 125-00 to make 85hp? I have no expectation of seeing those numbers with the 125-NR.


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Maybe crank HP?  Stock had 67.

[johno]

yep !

[mark ward]

Frank, you make a great point; right down to the idea of the 'cut-seat'. When I ran my current K1 in stock form, back in '76; I ran 13.40. And with stock, flat seat, and 8" extended forks (from previous owner); it's easy to see that better 1/4 mile times can be achieved with even minor chassis mods. That 'seat-sliding' had it's greatest detriment during launch, and 2nd gear shift, (obviously).