Been a long time folks, back for more help. Looking for induction and head work ideas for the little 250 in my coupe. Is there enough 'meat' in the ports to properly blend the throats to a 1.94/1.6 valve combo? Port lumps, or just cut the head bolt boss out and let her go? How about manifold/carb ideas? Current setup is approx 9:1, Schneider custom grind 218/228, .490/.505 hydraulic, stock head, Clifford split shorties, Clifford manifold with Rochester 4GC. Muncie M-20 and 3.36s. Made a couple mid 9 second 1/8 mile passes, would like to get into the 8s.
Turbocharger! Look at the 12bolt.com site, he has several articles about the later Chevrolet six. 40 years ago I built a 250 with a 194 head cut .060, Holley 2 barrel on a Clifford intake, and Clifford headers. Cam came from J.C. Whitney and all I remember about it was the lift .509/.509. Mallory dual point with a Judson coil and ignition box. I had problems keeping the flywheel bolts tight, and clutch wear was terrible. But it was a fun project. I wonder IF the lump ports are really needed with a turbo or supercharger? I am Butch/56sedandelivery.
Well I am not familiar with your coupe but with the 6 and the 3.36:1 gears I am going to suggest that you are geared a little tall for 1/8 mile passes. A gear change would be beneficial something in the 3.7-4.1 range would be the first thing that I would do. Longer headers and switch to a little holley or even a big 2 bbl. I would not do the big two bbl if I were driving it on the street. I probably would not cut the ports, if you have room in the chambers and cylinders for the bigger valves then I would work on the bowls and maybe only do minimal work to the ports. Think of it like a sinus, your nostrils are small compared to your mouth. But they open up into a cavernous sinus, you can draw more air through your nose then through your mouth (unless you have an obstruction). That is because you open up from a small opening to a large cavern and what it does is increase velocity passing though your nostrils, with increased velocity comes increased volum. By keeping your port work minimal but increasing the bowl size you will in effect increase port velocity. Am I making any sense to you?
I think the lump ports are a good idea either way because it does multiple things in one shot. It removes the head bolt boss obstruction in the center of a shared intake port. It enlarges the short turn radius & helps define the bowls. The intake port is already cavernous cause it shares the port area & bowl area of the other siamesed cylinder. Leo Santucci's book is a really good read. More cfm means more boost. thanks.
250 Chev 6's are notorious for twitching crankshafts. From my experience, the 240 Ford is a far superior engine - short stroke/larger bore (3.18"X4.00") - 12port head - easily adaptable to 1.94"intake/1.60"exhaust valves - Offenhauser or Clifford manifolds readily available - major cam manufacturers have whatever cam you could want - SBF bellhousing bolt pattern. Problem with Chev head is their wonky siamesed intake ports which creates turbulences under the intake valves. Those wanting to at least partially remedy this will remove the bolt boss and fab and install a port divider to, in essence, produce a 12 port head. Easier said than done! And then the intake manifold must also be modified to take full advantage of this port modification.
An old trick was to start with a 3864883 head from a 194 mill the head .060 and you had 10 to 1 with stock pistons.
Thanks for all the advice guys, now how the hell do I reply to everyone at once? Gotta keep the 3.36s as this is damn near daily driven when the weather is halfway decent. I have Santucci's book and after reading it 5 times or more Im still nervous about hitting water when opening the throats to match the larger valves, or equally as bad cracking a head from adding bolt in lumps. This supposedly has the 307 chevy flat tops with stock 250 head but I have not had the head off to verify. If it does, Ill be cutting the head to get closer to 10:1, if not, itll get a 194 head with .060 off. Turbo would be awesome, 292 would be great too, but I like the little motor's lack of big grunt, being able to shift it at 5500-6000 and not break parts all the time. She just needs to pull a little harder above 4000. Anyone have experience with single vs. multiple carb? Would love a pair of 2gc's or better yet triple 1bbl's....
I see you are from Mooresville. Start asking around, Chester and Lancaster were the last dirt tracks around here to stop running the 6 cylinders. You should be able to find some help and maybe some parts. Most of those guys ran two carburetors. A lot of them liked the Predator, but I have never ran one of those, it may not be streetable. Good Luck!
Self racing in Durant Oklahoma has huge experience with the 250/292 engine built for drag racing. Their cylinder head work on this head is as good as anyone out there. Larger valves are not a problem. Pushrods can be, so use aftermarket ones. Roller rocker arms are another improvement. Machine the heads for screw in rocker studs. Study the Chevy vortec head chamber to know how to improve the inline 6 chamber. We did remove the head bolt boss as did Self. The 250 cast crankshaft can be a problem. Don't expect them to live long.
It goes without saying the 302 is an older, 4 main bearing engine. But as far as beating goes. They ran them in ready mix trucks, dump trucks, deuce and a half Army trucks and lots of other beat upon stuff. I ran as much as 22 psi boost in mine without breaking it. One has exceeded 300mph in a streamliner at Bonneville. So they are pretty tough. Still if it was me I would want a 292 unless you must use a vintage engine
Been an inliners member for many years now.What I did on my last 250 was use 307 V-8 pistons, deck the block .030" and use 1.840" Hi perf" 305 V-8 intake valves and 1.550" Manley exh valves for sbc (summit has those)in the old 60cc chamber head. I tapered the sleeves in the intake ports and did normal port work otherwise.Used a comp cams "280" cam-they may still make them for the 194-250 engines- Clifford headers and a 3X1 offy intake-I like multi carb setups-you can make more power with a 1X4.I used Crane"gold" roller rockers.Engine ran just fine pretty much daily for 50,000 miles until I sold the car.
I have ran a single 4 barrel on my 292 but never could get the plugs to show even fuel distribution. Now I run 2 600 cfm four barrels on the same motor, plugs look good and with 8 inch slicks I had to drop tire pressure almost 2 lbs to get it to hook up. My dyno is the seat of my britches but I bet it`s putting out 25 or 30 more hp. With a 250, I would be tempted to run two 2 barrels
Contact Tlowe here on the HAMB. He is the 12bolt.com guy. Talked to him Saturday, great guy and knows his stuff.
Regarding your question around lumps - I don't have my flow sheets handy but we did 3 flow tests on my 194 head....stock, bosses removed and then with lumps installed. The lumps definitely help and no need to reinvent the wheel there. I was able to get 1.94 / 1.6 valves in with no issues but again on a 194 head. Milling the head helped and a good point of reference is for every .010" off equates to .1 increase on compression ratio. I'm running a 3x1 offy intake (non-progressive) and love it. Plugs look good and consistent across all cylinders. As papastrk mentioned push-rods can be an issue. I ran into this and had Smith Bros. make me a custom set. Tom Lowe (and others) offer heads already setup and ready to go which might not be a bad route to go. It took me awhile to find a machinist that not only understood what I was wanting to do but was willing to do it.
Contact Twisted6 here on the HAMB, he is mentioned in both of Leo's book and actually created the bolt-in lump concept mentioned in them over 15 years ago. He has constantly innovated and updated the design over the years and has by far the best one's on the market and his holds more inline records than anyone's. That speaks for itself!
Here are some pictures of a head Tom Lowe built for me. It is for a 153 Chevy Four which is 2/3 of a 230 six. Bore spacing and chambers are the same a s your 250. This has lumps and Tom did some port work. It is shaved .035" and has 1.86" intake and 1.60 exhaust valves. I can't remember what springs he used. He installed screw in rocker studs. They will take 1.96 intakes. He does good work for a good price. he makes a lot of aluminum parts too. With roller rockers you'll need to increase the room inside the cover. https://picasaweb.google.com/sixpic...authkey=Gv1sRgCO-O3sen0Ir4_wE&feat=directlink
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