Ok, so I finally got my 250 ready to fire and break the cam in. I borrowed an engine run stand to do this on. Now, about the engine, it's a 0.040 over flat top (307 pistons) 255 with a lumped and ported head with 1.84-1.60 valves, and a Comp 268H cam and kit. It has a full Pertronix ignition with an Ignitor II, their wires, and Flame Thrower coil. I have a set of long tube headers and a Holley 600 carb, and am going to get an Offy 4 bbl intake. I plan to intall these after the break in.

For the break-in though, I wanted to use the stock intake/carb and exhaust manifold as to not run an untested Holley 600/Offy on a fresh motor. Well, once I got through the initial snafus, like little leaks and capping off all of the vacuum ports, it fired up and sounded great...problem is, which I was afraid of, it runs lean, and it won't hold at a steady 2000-2500 rpms without a little variation in the throttle. It sputters and wants to die out if I try to hold it at a steady rpm. After about 6-8 minutes of break-in, I had to shut it off because of temperature. It had a radiator with electric fan running the whole time, plus it has a 180 thermostat. But once the temp got into the 215-220 range, I let off of the throttle, which immediately made it die. I checked the temps on the engine with a laser temp gun, and it showed the most heat in cylinders 2-5. Numbers 1 and 6 were cooler. I figured it was better to let it cool down and finish another day.

I originally thought it could have been the filter or a clog, but it was clean, and the lean condition makes more sense, as this combo probably doubles the factory horsepower.

I haven't bought the Offy intake yet ($280) since we have other priorities going on right now, like getting ready to move to Northern Michigan. Is there any way to fatten up the stock 1972 Rochester Monojet so I can finish the break-in period? Or would it be better to go ahead and get the Offy intake? I can't take the engine run stand with me, but I have about 2 months before I'm moving. I would just like to know the engine is broken in and in running condition so I can install it in the truck and make it easier to move 500+ miles away.

Thanks in advance.

Be sure your ignition timing is where you want it before tearing into the carb.

If the timing is retarded, the engine can run hot.

Maybe tape the choke partially closed.

Good point. I'll double check the timing when I try it again. I was by myself and with one hand on the throttle, I couldn't do both. I'll get my dad to come over to help with an extra hand. Thank you both.

I think I may have found the retarded timing problem. It seems I couldn't go anymore advanced the way it was, so while I was out today, I stopped by my buddies shop to look at the parts car I got some p/s brackets and pulleys from. I took a picture of the distributor from the top down to see where it was clocked. When I got home, I looked at my distributor, and it seems that the spark plug wires were one off all the way around, and with it advanced all the way that the distributor would turn, it was still way retarded. I fixed all the wires and put the distributor in the same spot as the stock one, which puts the #1 spot on the cap right in line with the #1 spark plug. I haven't started it yet, but it seems like that could have been a big factor. Thanks for the heads up about the timing stokersix and Tom. If not for that, I wouldn't have thought to look at a stock distributor clocking. I'll post back once I fire it up again.

Do you have headers? I found once I installed my headers my stock carb couldn't keep up and it ran a bit lean. It even backfired when I let off the throttle at speed a little. Nothing too drastic but I could tell I didn't have enough suck for the blow I was able to do.

Now with an 8007 and offy it runs great!

Here's a tip on the offy: On the bottom there are two plugs that are there for manufacturing. They have to put the plugs in so the pathway inside can do a 180 there. For a stock system using exhaust gases they work fine. When you put water through it they leak. Most people on here recommend welding aluminum plugs in. I cheated. I used epoxy over the Offy plugs and so far they haven't leaked at all. Just regular old Autozone 2 part epoxy off the shelf. You'll never see it and this way you don't disturb the fluid path underneath.

You're also going to need to heat the intake or you'll get fuel pooling. My intake felt very cold to the touch until I heated it.

Right now it still has the stock intake/carb and exhaust manifold on it. I wanted to get the cam broken in before I put the 4bbl and headers on it. I agree about the heat plate. I plan on getting the heat plate from Langdon's when I install the Offy 5416 intake.

Smart move going with Langdon on the heat plate. By the time I was all said and done I had more into my home-made plate than his pre-made one would have cost.

For the heater lines I did mine like this:



I got new heater hoses, went through the fender, ran them to the brass T with hose barbs threaded into it, and ran one set out behind the engine and the other into the heater core. Works really well and everything is nice and tight. Plus it opened up a lot of room on that side of the engine bay.

...and I think the brass looks pretty cool which is always important in these endeavors.

It really tidied everything up by running the lines behind the engine. If you get the lengths right you'll clear the headers and linkage just find. Word of caution: Make sure there's no interference with the linkage no matter how you run them. Mine got hung up once when I was testing everything out. Ended up nearly wrecking the car! Got stuck at WOT and would not let go until I shut the engine off and physically moved things around. Really scary.


I had a tough time sealing my heat plate to the bottom of the intake. After trying RTV, etc, I ended up with a combination of RTV and a rubber gasket I made. Another trip to Lowes and I got this:

http://www.lowes.com/pd_31448-143-PP25547_0__?productId=1082957&Ntt=rubber+gasket&pl=1&currentURL=%3FNtt%3Drubber%2Bgasket&facetInfo=

I then cut it to match the opening and OD of the heat plate, punched holes in it for the bolts to go through, and RTV'd it top and bottom between the heat plate and intake. It's the only way I could get it to seal. Now that it's on and not leaking I'm NEVER taking it off!

Pic of it on the intake:



Couple of things to note: Notice how I trimmed the ears? That's because the Langdon headers were interfering with the Offy intake. I split the difference and now they come close to touching but I left about 1/8" clearance between the two pieces for expansion/contraction. Also you can see the "plugs" on the bottom of the offy that I epoxy'd closed. Literally just sealed them. works really well and no leaks. Now the brass fittings: they're much larger than Langdon's. Probably didn't need to be but I didn't want to mess with reducing the hoses. Heater core still gets plenty warm for winter driving and intake seems to be working well enough for now. I might look at throttling it down a bit this summer but it's fine up to about 70 degrees ambient so far.

Finally in the first pic you'll see the Offenhauser and emblem look like a different color. It's bare metal. I painted the whole thing and took a file to the raised letters. Nice little trick and really sets it off. Looks like it could be stock but isn't.

Engine bay looks great George. I like the stock look of the engine and manifold.
My 250 is actually going to look like a 216, with the gray painted engine and the oil bath style air cleaner. We'll see if I can fool anyone. lol

Only one problem I see. did you weld up Or epoxy the plugs On the bottom? Because they may end up leaking on you if you didn't. Because that Intake was not ment for water. Only Exhaust heat. Other The that it Looks Great.

see this tech tip on Langdon's website:
http://www.langdonsstovebolt.com/tech/repairing-coolant-leaks-in-inlet-manifolds/

Has anyone used the pellets and it worked ok?

So I got the timing taken care of. I feel like a goof. I didn't have the distributor quite loose enough to advance more. I ended up putting the plug wires back to how they were, and once I spun the housing farther counter-clockwise, it was fine. I had to look up timing online, and I found a picture of a stock distributor and saw how it was clocked...vacuum adv was facing forward. That's when I decided to loosen the distributor hold down a little more.

So it fires and runs good, but still is a little lean, since it runs much smoother when I put my hand over half of the carb. It still won't try to idle, and it still slowly gets hot, but that must be the tiny radiator and some air in the cooling lines, since the top hose goes a little high then down to get to the radiator. The timing is about 12 degrees at idle and about 32-36 degrees total with the vacuum port plugged.

It does sound good and boy is it snappy.
I'm thinking about ordering the Offy intake while I still have the run stand (and while Summit still has them in stock!).

Will get a video soon.

Just read though the thread and the 1st issue I saw was the carb...that carb is to small for all the mods done to the engine...that's why it was not running properly. Running lean on break in will cause more heat and cause it to run unevenly. Run it with your radiator cap off to get the air out. Air pockets in the system could cause a head gasket to blow. The engine won't run right till some more fuel is added as well as cfm. Timing should be set around 8-10 without vacuum, 20-25 with vacuum and no more than 36 degrees full advance or you risk detonation. And it looks like you've got the same cam specs as the one put in my 292! lol! Will be interesting to see how they sound as far as lopiness...mine will be a little smoother because its larger. The offy is an ok manifold, but the clifford is better quality. TJ

Good points TJ. That was my original assessment too. It's nice to have some confirmation. Do you have similar mods to your 292 too, like increased compression and head work?

I really like the range of that cam, 1200-5200 rpms. I'm going to have a pretty tall OD, with 3.42 rear gears, a World Class F-body T-5 5 speed with the .63 5th gear, and 28-29" tires, my highway cruise rpm (72-75mph) should be in the 1800-1900 rpm range. So hopefully, it'll like the lower rpms for cruising as well as 5000-5500 rpms for when I feel the need to let her sing. lol

I'm going to go ahead and order a 4 barrel intake, too. The exhaust manifold showed really hot spots in the 2-3 and 4-5 exhaust ports. I know they get hot, but the lean condition I'm sure played a part in that, and I have too much money in this thing to mess it up before I can drive it.

Thanks for the comments and suggestions.

I have some threads on my 292 if you want to see it. 292 Custom 6 going into my 66 c10 is the title. But yeah, more compression, lump ports, bigger valves, comp 268 cam, ross forged aluminum pistons, zero decked...all the good stuff. lol Left some room for boost as well. The cam attitude changes on mine..yours is something like 1200-5500 and when on mine it'll be more like off idle -5000. I liked the cam for the more mid range torque...be a nice cruiser, but won't loose all it's power when ya drop a gear to pass. Putting a tko600 behind mine. TJ

Sounds good. I browsed a little and saw your thread too. It looks good and should be a strong running motor. I'm guessing I'll have about 85-90% of the power and torque that you're going to have. On the Comp Cams Camquest dyno simulator, my engine showed 270hp and 300 ft. lbs. of torque. From other combos that I've seen, I think that might be close. I'm sure yours will be at least in the 310hp 350tq range. They both should be fun though.

Thanks, Yeah they sure will be fun. Mine should be around 310 hp and 330 torque. I'm throwing 5-10 pounds of boost around though. lol Haven't even started the new engine and I'm already wanting more power! haha! TJ

Cool. I thought about a turbo setup, but I was on a bit of a budget and figured that could be something down the road.

I always liked this video of a turbo inline Chevy II...

This video is what got me to hot rod my 250. It's got a nasty little sound to it.

Yeah those two sound sweet. The turbo one I've looked at many times. lol Never get tired of it.

Yeah, I know what you mean. I've played the bottom 50+ times myself.

So, we moved my wife and 2 oldest daughters up to Michigan over the weekend, and I came back to WV with our twins on Tuesday. I figured I was close enough to Akron to make a pitstop..............to..................Summit Racing. lol

I picked up the Offy 5416 4bbl intake for the 250. I could have ordered it and gotten it in a day, but it was good to break up the trip, and I've never been there before. One could spend hours and thousands of dollars there. lol

Anyway, got the intake, now I just need a nice, free day to put it on along with the headers and stuff. Video to come of that.

Sweet! Shoulda picked up some turbos to. haha

So I got the intake on and soon realized that the long tube headers don't fit with the Offy intake. Of course it wouldn't. I should've known. Two steps forward, one step back.
Anyway, I separated the manifolds and used the exhaust manifold and got everything bolted up. After fixing a few leaks, the (swap meet special) carb seemed ok, but the choke wouldn't open up, and started to run rough. Even though I rebuilt it, it was so old that a lot of the gaskets had to be wire-brushed off, and I don't know how the adjustment screws were set.
So, I did what I should've done from the start, I ordered a new carb for it. It should be here later today. New Holley 1850SA (aluminum) 600 with manual choke. Of course it's calling for rain on and off today and tomorrow. And, we're supposed to move in a week or so, and I still have to start packing up the garage/shop and bolt the front-end parts onto the truck so I can move it on the car trailer.
Hopefully, this carb issue will be over once the new one comes.

So, since I can't use the Flowtech long tube headers with the Offy intake. What headers do you guys with Offy 5416's use? I figured I'd get a set from Langdon's for $277. Is that the best choice?
Thanks

You probably just need to dent the header pipes in a few places to clear the intake.

Be sure to fit the headers on engine to clear the chassis and the ground , first.

Thanks. That very well could be the case. It was hard to gauge with it on the stand. It's a borrowed stand and isn't user friendly to the inline sixes, as it has plenty of obstructions too.

Well, the engine is finally broken in and runs and idles well. Has a nice lope and starts easy now. New carb made all the difference.

2 part epoxy. Just went right over the plugs then painted it all. No leaks at all.

The heat plate, on the other hand, was a real PITA to get to seal to the manifold. I ended up getting a 6"x6"x1/8" piece of rubber from Lowes, cut it into a gasket, then used RTV on both sides. snugged up the bolts to hold it down, let it cure overnight, then cranked them down.

It was such a pain that I will NEVER take it off again! Had to re-do it about 4 times before it sealed up.

My heater hose trick with the brass fittings looks cool but was a) expensive, and b) also took some shenanigans to make work. Once I got them threaded into the plate I had to grind them flush on the back side so everything cleared the intake guts. Had to make sure the position was right before cutting them too. Also had to use RTV on the threads to stop them from weeping.

Lots of RTV around on this set up. Nothing would seal up without it. Now that it's done I've driven it about 1,000 miles with no issues and no leaks.

...plus the brass helps the look of the engine bay. Compliments the brake booster, master, and carb. Even added some brass plugs on the thermostat spacer (needed that for the fan thermostat switch). Eliminating the mechanical fan quieted the engine down under the hood dramatically. Now it's just the sweet, loud, obnoxious sound of the 2.5" tube going through the Flowmaster 10 series.

It's a weekend toy that I've built to show off a bit and drive fast. I wanted to build a car that was all around good at everything: speed, corners, looks, and comfort. The kids these days call it "pro-touring" or some such nonsense but I'm missing two pistons for that crowd.

If denting the tubes doesn't do the trick my Langdon headers bolted right up for the most part. I did have to trim the ears on the offy around the mounting holes (I haven't figured out how to have two chunks of metal in the same place at the same time yet...) and had to trim a bit around the temp sensor but other than that it clears my power steering bracket and everything else fine. Big difference in power too!

I ceramic coated mine with VHT. Not the preferred method but it's holding up well and looks good.