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How much to bore block, .045 or .084 power gains?
https://www.slantsix.org/forum/viewtopic.php?t=42255		 Page 2 of 2
Author:  dustertech2000 [ Thu Oct 14, 2010 2:56 pm ]
Post subject: 
i too have my slant bored .030 over and i'm running 1.60 exhaust 1.80 intake valves and have had head off twice with in 10k and no problems
Author:  Rick Covalt [ Thu Oct 14, 2010 3:36 pm ]
Post subject:  Valve clearance
The original head we ran on Ryan's Dart had 1.55 exhaust valves & 1.750 Intakes. The bore had to be notched in order for the exhaust vales not to hit. It was only .030 overbore.

Rick
Author:  Joshie225 [ Thu Oct 14, 2010 4:40 pm ]
Post subject: 
When I was running Ford 300 valves in a +.030" bore engine I had the exhaust valves cut down to 1.45". Once I got the compression ratio of that engine up a bit (.100" each off block and head) it ran really well. I guess Reed's head must have the valve guides in the right place!
Author:  ceej [ Thu Oct 14, 2010 5:05 pm ]
Post subject: 
My bore is 3.445", or .045" over. I tagged the bores with the valves running the 300 Ford set up. (I had the machine shop put the engine together, so don't look at me that way!) :lol: Yeah, they fixed it.

Notched the bores, and turned down to 1.45" diameter as above, Face cut the O.D. Clayed, and adjusted the reliefs where I was tight. Now I clear.

The alignment dowls were not in the right place in the block. This moved the combustion chambers aft slightly.

hint: With the recip assembly out, bolt the head to the block, and turn it upside down. Verify the combustion chambers are lined up with the bores. Adjust as needed! :wink:

0.125" off the deck, .040" off where I started with the head to make 45cc chambers. Now at 48cc with a fresh cut on the valves after bending the exhausts and installed new guides.
7.005" 198 conn rods, 4.475" Stroke, Really small pin height metric pistons for a Toyota four banger.
This build was prior to the K-1. If the Wisco build had been available... :roll: ...it would have saved me a ton of cash.

CJ
Author:  Reed [ Thu Oct 14, 2010 5:17 pm ]
Post subject: 
Well, all I can say is that the guy that built the head for me (Bud's Machine and Engine in Lakewood, WA) had the head for about four months and charged me over $500 (in 1999 dollars!). He does first class work, and I know he had to mess with the valve stems, so maybe he cheated them a bit and moved them a touch inboard. :shrug:
Author:  sandy in BC [ Thu Oct 14, 2010 5:51 pm ]
Post subject: 
If you dont want the valves to hit the deck ....radius around the valves in the head and leave it uncut. Take all your compression cut off the block deck.

No bore notch with 1.72 intakes ....160 off the deck . Bigger cam than you run.....
Author:  ceej [ Thu Oct 14, 2010 9:53 pm ]
Post subject: 
I was referring to the exhaust valves...
The intakes weren't a problem because the guide centers are closer to the center of the bore. They're a bunch bigger too.

The problem with moving the guides with the 300 valve head is that they are extremely close together. Maybe Fopar measured the distance between the valves in his head? They are a tight fit.

There is shrouding with a valve that big by the bore itself. The engine builder valve sizes make more sense. I won't be using the Ford valves in my next build. What valves are you running Sandy?

CJ
Author:  LUCKY13 [ Fri Oct 15, 2010 5:36 am ]
Post subject: 
I think one thing everyone is over looking, but it has been said in a round about way, is with the bigger bore, even with smaller valves, the head is going to be able to flow more simply because the valve is not crowed so much by the small bore.


Now with the right machine work you can still get good flow by notching the block and doing the right combustion chamber work. Of course this would be with someone that really knows what there doing to gain this extra flow. It also aids in better cylinder fill and air/fuel distribution in the cylinder. Is it a hugh gain, no. But there is more going on than just power. Even fuel mileage and drivability can improve if all is done right.


Myself I say its worth going for the bigger bore. It helps in all this even without getting down to the technical workings of air/fuel flow and fuel distribution. If you take and work the cumbustion chamber to help it match the bigger bore it can help even more. There is a lot going on in a cylinder that even the pro's dont understand sometimes. It may seem like a little to reach for the extra bore, but sometimes a little can mean a lot in ways we dont understand. Plus even at the bigger bore you still have room to rebore later when it comes time for another rebuild. The bigger the bore, the better the head can work and this is one area we are hurting on with the slant. I would go for it.


Jess
Author:  sandy in BC [ Fri Oct 15, 2010 6:40 am ]
Post subject: 
CeeJ: Chev 1.72 intake / 1.50 exhaust

Exhaust have 3/8 stems .... Intakes 11/32

I also used Chev springs , locks etc.
Author:  1974duster kev [ Fri Oct 15, 2010 5:59 pm ]
Post subject: 
I think someone needs to test the theory run a car or dyno then bore it with no other changes, then see if there was any gains on the track or dyno.
Just a thought, Kev
Author:  Joshie225 [ Fri Oct 15, 2010 6:19 pm ]
Post subject: 
1 cubic inch of displacement is worth about 1-1.25 ft/lbs of torque. Boring a 170 +.040" makes it a 174. If the engine makes 5 ft/lbs more torque at 5252 RPM it will make 5 more HP. If the engine is already choked for air flow the peak HP likely will not change at all and the peak torque RPM should be lowered slightly.
Author:  slantzilla [ Sat Oct 16, 2010 1:41 pm ]
Post subject: 
Bore it out to the biggest size you can and be done with it. Why bother boring anything less than max? It's a freaking Slant block ferchrissakes. If you should ruin a wall later sleeve it or go buy another $5 block. They grow on trees anyway. :roll:

BTW, the biggest gain does indeed come from unshrouding the valves. Bore itself doesn't really do squat, other than give good ring seal again.
Author:  Reed [ Sun Oct 17, 2010 9:26 pm ]
Post subject: 
Sorry, I forgot that the motor has been bored .060, not .030.

:oops:
Author:  66aCUDA [ Mon Oct 18, 2010 5:57 am ]
Post subject: 
Quote:
Bore it out to the biggest size you can and be done with it. Why bother boring anything less than max? It's a freaking Slant block ferchrissakes. If you should ruin a wall later sleeve it or go buy another $5 block. They grow on trees anyway. :roll:

BTW, the biggest gain does indeed come from unshrouding the valves. Bore itself doesn't really do squat, other than give good ring seal again.
Big D is right slant blocks are cheap to play with.
Reed sounds better. :D
Frank
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