Box Stock

Hemi predator gas build

Thanks Yak, I was concerned because we drop into the high 3k rpm range in the tighter turns I'd hate to have it ping itself to death. Probably start it with a 9 or 10 heat range plug?
 
I just use the 3910x plug... If you get any higher in comp. You can add 10-20% xylene to bump up the octane rating...if needed...
 
I'm not a fan of the 3910, but that is a 10 heat range plug I guess it'd be safe to start there. I won't be able to run the xylene, we generally don't have tech but I don't want to cheat the fuel and at the event that is combined with the GC race the sniffer will catch it. I guess if I have to, its easy enough to fatten up the head gasket thickness.
 
rkcarguy said:
My ARC flywheel I mounted on this engine is set at 32*. I'm running premium pump gas and around 10:1 compression. Will this be ok or should I back that timing down?
Click to expand...
Premium fuel 32* 10:1 compression ratio should be no problem. I have a different engine 10.9:1 and it will exist on regular fuel and is plenty safe on Premium.
 
Ok, thanks Kart43. Our "spec gas" is premium Chevron from the station just down the road from the track. In my other engine "tinkerings" I've always found no problem with premium pump gas up to around 11:1 if careful, but this is the first time I've had to consider the air cooled aspect.
 
I started working on my intake last night. I want the intake to match the D-shape port perfectly, so I spent about an hour tapping one end of the 1" aluminum pipe elbow into a D-shape with a little brass mallet and it actually came out really nice. The available material of the 1" pipe(about 1.040" inside diameter and 1.315" o.d.) matches the D-shape nearly perfectly by the time you get it shaped right.
The fun part is, the outside diameter doesn't leave much room for the bolts, so I'm going to have to shave the heads down on some allen head bolts and use them, maybe even insert the rearward bolt before I weld the flange to the pipe and it may remain captive within the flange.
On the other end, I'm going to try a 22mm Mikuni and a 26mm "Chonging" Walbro copy and see which one performs better on my track.
 
http://s874.photobucket.com/user/rkcarguy/library/?sort=3&page=1

Here's a few new pictures of the intake....well the pieces of it, and the carb. Intake will be welded soon, inside and out, and then I'll finish port matching and polishing the whole thing. In an attempt to compromise between loss of flow and cornering forces giving me float issues, I didn't use a complete elbow, this intake will angle the carb back about 60 degrees.
 
I'm getting ready to build my own header. With the broad power range I need for our sprint track(4-7.5K RPM), what would be a good tube size to go with?
In the past I have played with quite a few tube sizes and found the .840" inside dia tube to work the best, however this is a far hotter motor than the GK-65 and BP build I played with in the past. Keep in mind I have 19 turns to exit and only 2 short straights in the format we run the track in typically. Getting off the turns has been key.
 
I went from a .880 to a .930 and race studio shows it picked up from top to bottom.

low end came in earlier and upper end was improved. Power stayed about the same.

This is methanol btw
 
Just out of curiousity I went out and calipered the inside diameter of the WF header, .795" ......interesting. I can't say that the WF feels like it starts to choke before I find the rev limiter so I think I'm going to start with my .840", I have two flanges so I can make a 2nd header with a larger pipe and try both.
Another interesting fact, the actual direction of the exhaust port is not square with the flange surface, but the flange is 30* off in an upward direction. I mitered the end of the tube where it will weld to the header flange to match so the flow goes straight into the header from the port instead of being kinked at 30*.
It comes out being almost level/flat when viewed from the back.
 
Doing some calculations this afternoon in comparison to the world formula:

I have ~3% more displacement.
~6% higher compression ratio
Larger valves, but not opening as far
Higher rev limit
Same carb and slightly bigger exhaust.
 
I was wandering thru the hardware store of all places, and found their metals rack had 3' chunks of 1" x.060" tube in it, .880" inside diameter for $11. Bought it and ran it thru the bender, will be building a .840 and .880 header to see how they both perform.
 
By the math, the .880 has ~10% more area.....boy I sound like Al:) .....than the .840, but I guess it depends on the V/E I get out of the engine. 70% V/E means the .840 is adequate, but If I'm above that the .880" will be the answer. Anyone have any idea what kind of volumetric efficiency #'s we get out of these?
One thing I am doing which I've deemed very important, is really paying attention to the port matching. I am port matching everything to everything, carb to intake, intake to motor, motor to header, so everything is a smooth transition to the fingers touch to provide the best velocity I can get.
 
Header should be larger than the exhaust port, the exhaust should actually step into the exhaust pipe. the step disrupt the backflow of pressure.
 
All of us know the pipe doesn't match the D-shaped opening. I actually will partially weld the pipe to the flange where it aligns nicely, and then use a combination of a small mallet and various tools to form the pipe to better match the flange opening.
Kart 43, you mean shouldn't step? I know that when an intake is smaller than a port, the tumble of air off the step "to bigger" is far worse for flow than smaller to bigger.
 
No I mean the exhaust port should step into the header as in the header is larger than the port. The slight ridge prevents pressure reversion along the walls of the pipe, if you could slightly enlarge your bolt holes you should lift the pipe to make the floor(inside radius) flush, and have most of the step at the top. Exhaust flow is much different than intake flow.
 
The hemi port is pretty big, probably take a >1" inside diameter tube to have a step. Due to the way I miter cut my pipe though, there will be a step at the top because of the angle of the flange in relation to my pipe unless I fill it in with weld.
 
I'm thinking I need to brace this block before it hits the track guys. I have a big ole beast of a TIG machine but I don't want to warp the block/bore and have to start all over with this one. What about making a bolt on brace that would pick up all 4 motor mount studs, the gas tank "wings", and whatever else I can weld a tab onto and get a bolt through?
 
rkcarguy said:
By the math, the .880 has ~10% more area.....boy I sound like Al:) .....than the .840, but I guess it depends on the V/E I get out of the engine. 70% V/E means the .840 is adequate, but If I'm above that the .880" will be the answer. Anyone have any idea what kind of volumetric efficiency #'s we get out of these?
One thing I am doing which I've deemed very important, is really paying attention to the port matching. I am port matching everything to everything, carb to intake, intake to motor, motor to header, so everything is a smooth transition to the fingers touch to provide the best velocity I can get.
Click to expand...
this is from Nine Sheets, my collection of Excel spreadsheets. 1st time I've had the opportunity to use this. The formatting of spreadsheets on Bob's is a little haphazard, but I hope you can read it. Percentages are different going from big to small versus small to big. In any case, the actual numbers are there too.

Tube Wall Internal Area of Tube I.D. Area
O.D. Thickness I D of tube Area in Sq. inchs D3 ver D4
1 0.06 0.880 D3> 0.608212338 5.40% D3 Area Bigger
1 0.08 0.840 D4> 0.554176944 -8.88% D4 Area Smaller
 
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