increasing compression on Saito 4S..!?
04-28-2012, 07:04 AM
#101
Senior Member
RE: increasing compression on Saito 4S..!?
ORIGINAL: canardlover
SrT:, many thanks for your viewpoints which I appreciate a lot...
...regarding your second post on the pushrod length/angles I must take some time to really absorb what you said before responding. Shortening the PR is very simple I think I could take it out, shorten it and have it back in again in 15-20 minutes - no sweat..
..provided I am fully convinced I should shorten it. Please allow me to come back on this item...Thanks..!
SrT:, many thanks for your viewpoints which I appreciate a lot...
...regarding your second post on the pushrod length/angles I must take some time to really absorb what you said before responding. Shortening the PR is very simple I think I could take it out, shorten it and have it back in again in 15-20 minutes - no sweat....provided I am fully convinced I should shorten it. Please allow me to come back on this item...Thanks..!
Of course you do realize that all this is "splitting hairs" as far as potential performance loss/gain.
The only thing that would make me seriously consider shortening the PR is if there was not enough adjustment left
04-28-2012, 07:30 AM
#102
Thread Starter
RE: increasing compression on Saito 4S..!?
In my simple trigonometric world I would prefer to have these two lines being perpendicular to each other at "half open" valve position to achieve maximum valve opening..?!?!
...!! I now sat down at the drawing board and found out that "net lift" increases rather dramatically when the angle increases from "square". Now, this explains why Saito has chosen to have the inlet valve PR pointing forwards rather than the exhaust PR which points slightly backwards. I hereby humbly apologise to Saito for insinuating they had "suboptimized" the engine.......!!..and this indicates that they also consider - as expected - that inlet valve lift is more important to engine performance.So what I should do is to shorten the PR as much as the increased sideways movement will allow. And my measurements with pushing down the valves at TDC(fire) and TDC(overlap) shows that there is still plenty of clearance to the piston crown even for this engine.
SrT (and others) do we agree on this "net lift" topic...?!?
And then about "valve acceleration" I think we can conclude that this also should have a minimum at "square" angle..Right..!?
SrT: thank you so much for forcing me/us to dig deeper in this area....
04-28-2012, 09:32 AM
#103
Senior Member
RE: increasing compression on Saito 4S..!?
ORIGINAL: canardlover
Yes indeed you are correct but the ''operation'' was so demanding that I hesitate to repeat it....[
].. Next time I think I will rather try to preheat the cylinder unit, push out the bronze valve guide and work from above.
You will reap a LOT of benefits by also streamlining the exhaust port bowl. You have increased flow in the intake bowl, by doing likewise on the exhaust bowl you will positively influence scavanging, thereby further increasing the intake flow.
].. Next time I think I will rather try to preheat the cylinder unit, push out the bronze valve guide and work from above.Why not make the flow divertor part of the valve guide itself? [X(]
04-28-2012, 01:44 PM
#104
Thread Starter
RE: increasing compression on Saito 4S..!?
ORIGINAL: SrTelemaster150
Why not make the flow divertor part of the valve guide itself? [X(]
Why not make the flow divertor part of the valve guide itself? [X(]
[/quote]
Excellent idea SrT, should we not pass it on to Saito....!?!?...
..!Honestly I have played with the idea to silver solder a brass insert to the valve guide which has a flat underside - should be doable....Cheers..
04-28-2012, 05:34 PM
#105
Senior Member
RE: increasing compression on Saito 4S..!?
ORIGINAL: canardlover
Excellent idea SrT, should we not pass it on to Saito....!?!?.....!
Honestly I have played with the idea to silver solder a brass insert to the valve guide which has a flat underside - should be doable....Cheers..
ORIGINAL: SrTelemaster150
Why not make the flow divertor part of the valve guide itself? [X(]
Why not make the flow divertor part of the valve guide itself? [X(]
Excellent idea SrT, should we not pass it on to Saito....!?!?...
..!Honestly I have played with the idea to silver solder a brass insert to the valve guide which has a flat underside - should be doable....Cheers..
I think that the Saito valve seats were integral W/the valve guides @ one time.
04-29-2012, 04:14 AM
#106
Thread Starter
RE: increasing compression on Saito 4S..!?
I think that the Saito valve seats were integral W/the valve guides @ one time.
05-06-2012, 11:31 AM
#107
Thread Starter
RE: increasing compression on Saito 4S..!?
The modified .82 engine with a head space of 1.05mL giving CR=13.8 and a squish band of 0.65mm has now been run in benchtest and showed a marked improvement in power as compared to the results on the stock engine(9,500/2,700 rpm) in post #65 above.
Both modified engines .72GK and .82 were run with the same 13x8 prop. and the .82 has now "overtaken" the .72GK so the performance order is now restored:
.72 GK gave 9,500/2,400 - sweet running..
.82 engine gave 9,800/2,200 - harsh running..[]..some detonation..??
Using the .72GK as reference the modifications on the .82 has gained some 400+400rpm=800rpm gain. Why the .72 has "lost" some 400rpm since post #65 is probably a combination of warmer wheather and less nitro in fuel (5%) and both engines now have velocity stacks fitted.
However, I am not at all happy with the .82 due to harsh running and vibrations so I took it apart and put the piston back in the lathe and shaved off another 0.15mm from the crown.This increased head space to 1.10mL with corresponding CR=13.2.
As you see from the "balance act" pics the .82 is still markedly "under-balanced", the crank counterweight can only balance out the lightened conrod but not the wristpin, piston, ring and scuff pads. Further lightening of piston and conrod done - see pic. but this skeleton .82 piston is still heavier than a stock .72 piston...[:@]...More later after new bench test..
Both modified engines .72GK and .82 were run with the same 13x8 prop. and the .82 has now "overtaken" the .72GK so the performance order is now restored:
.72 GK gave 9,500/2,400 - sweet running..
.82 engine gave 9,800/2,200 - harsh running..[
]..some detonation..??Using the .72GK as reference the modifications on the .82 has gained some 400+400rpm=800rpm gain. Why the .72 has "lost" some 400rpm since post #65 is probably a combination of warmer wheather and less nitro in fuel (5%) and both engines now have velocity stacks fitted.
However, I am not at all happy with the .82 due to harsh running and vibrations so I took it apart and put the piston back in the lathe and shaved off another 0.15mm from the crown.This increased head space to 1.10mL with corresponding CR=13.2.
As you see from the "balance act" pics the .82 is still markedly "under-balanced", the crank counterweight can only balance out the lightened conrod but not the wristpin, piston, ring and scuff pads. Further lightening of piston and conrod done - see pic. but this skeleton .82 piston is still heavier than a stock .72 piston...[:@]...More later after new bench test..
05-09-2012, 02:40 PM
#108
Thread Starter
RE: increasing compression on Saito 4S..!?
OK folks I am at the "end of the road" regarding the .82 engine. Still got 9,800/2,000 in bench test and still with rather rough running. The tick-over is nice though, had it going for some time at 1,600-1,800 but 2,000 is stable. All on 5% nitro, 5% castor, 10% ML70 oil-balance MeOH, brand new OS F plug and 13x8 prop.and large plastic spinner.
Ran the .72GK at the same time under identical conditions - even the prop nut/washer was the same.....and it gave 9,400/2,100 with much less vibrations....
...sweet..!
That´s it for now from my "tinker shop"....the .82 now goes into the Kelly F1 Racer and the .72 into my Ultra Sport.60.....sack time..
Ran the .72GK at the same time under identical conditions - even the prop nut/washer was the same..
...and it gave 9,400/2,100 with much less vibrations.......sweet..!That´s it for now from my "tinker shop"....the .82 now goes into the Kelly F1 Racer and the .72 into my Ultra Sport.60.....sack time..
