The Stovebolt Site Forums The Shop Area Engine Shop A REAL Power Problem

I have an 87 full size 1/2 ton 4X4 with 3.73 gears and a 700R4 trans and 31 inch tires. Many of the newer ones come with 31-32 inch tires as stock with the same gears and tranny such as 285/16 or 17 inch tires. I had a good running 350 TBI that burned no oil and ran smooth. I am the second owner of the truck. I love this truck so I opt for a modest built 250 for better economy. They, the shop, bored it .040 over, .010 on the bearings, balanced it, put in 1.84 intakes instead of the 1.74s size plus ARP rod bolts. The cam is a 240 cam from Comp and the valves clatter even after adjustment. Supposed to have about .060 more lift than stock or there about. I have the paper on it. One is quite loud. Less than 200 miles on it. Had a 600 Holley, waaaaay too big, but its what I was told to put on it and it ran too rich even after jetting it down. Adjusted the timing and such, new distributor, total MSD ingition system including the red wires. I removed the 4 bbl which had lousy power anyhow and I'm still getting about 8-8 1/2 city and 11 hwy with the stock one bbl that I rebuilt. My friend does that bad with his 454 with MUCH more power. Been at this 41 years. This is far worse than the 350 V8. Everything is new on it. It can't get out of its own way. Does not like hills. It slows down when it sees one. The idle is so so. Supposed to be noticable according to Comp. Please help!!! Should I have put in a 292 instead or go back to the 350? It weighs about 5300 lbs actual weight. Should I have put on a smaller 4 bbl like a 450 - 500 cfm or is it just too small for this rig? Any info would help. Thanks guys! Henry

My advice is to chuck the Comp cam as far as you can and install a direct replacement 250 camshaft. It will have a bunch more low rpm power and way better idle. Your heavy truck could have used the 292, but what you have will work OK. Hoe

Thanks Joe, I agree with you on chucking the Comp cam. I did not ask for one, they just installed it. It seems that Comp has some serious problems with quality. Actually the power has gone down. I have a good friends' son that wants a 250 for a smaller rig so I may sell it to him and put in a balanced 292. Much more torque and with OD should not do bad on fuel within reason. Just love the ole' bolts and their sound. I had a 292 years ago and it ran real well. Had a 3/4 ton 2WD with a 4 speed. Wished I had kept it. My Dad had one similar and it had hwy gears with a 3 speed and got 20 hwy with a stock set up. Anyhow thanks again Joe I really appreciate your input. This is STILL the BEST site yet for Stovebolters!

Hey Joe, BTW, a REAL nice 37'. Thats a sharp looking truck. Fun to drive I bet. Henry

Thanks Henry, it is fun to drive! I think most people forget how small a 250 really is cubic inch wise, and install way to big of a camshaft. Even the so called RV cams will raise the usable rpm level to high for general around town driving. They claim they are good for towing, but when towing, you need as much low rpm torque as you can get, so why would you want a bigger cam that moves the torque up the rpm range? Mine has Wolverine Blueracer camshaft, Adv. Dur. 260Int 270Exh .464"I .490"E lift. This cam is not much over stock, but even it idles like crap and I really doubt it runs any better. I know the off idle power is less. I run Rhoads bleed down lifters so the vacuum will stay high at idle, it has 19.5" now and only 17 with stock lifters. The stock cam was around 19.5 and had a lot smoother idle. One of these days I goin back to it. I need to run this at the dragstrip first so I have some numbers to compare to when i change it out.

Joe

I dunno, but you swap a 350 for a six & now you are bothered by lack of power?

Hey 64 Fleetside, Under normal stock conditions, obviously a 350 will have more hp than a smaller 6. However, I have owned Chevy inlines in a 1/2 ton and a 3/4 ton truck and they would leave this one in the dust. One of those with the 250 integral had the 700R4 and the other one had a 292 with a 4 speed. Neither were light trucks. Especially the 63' 3/4 ton. This one runs like it a 4 cylinder. Not only did I have the things done as mentioned but the block was decked and the head was milled .030 and they used low dished pistons. It has about 9.25:1 compression instead of 8.5. Should run really well. You have to put your foot down and wait for it to slowly build RPMs. Something is definately wrong. Can't even climb a normal hill without dowshifting it. Its as Joe mentioned, its over cammed plus, Comp seems to be the cam for inlines that do not work well or last more than a couple thousand miles according to some posts here. I'm going to the shop and have them put in a stock cam. I have changed carbs and no difference. The plugs are black, running too rich. Almost like soot. Both carbs are new/rebuilt. With the larger intakes it should scoot within reason. It idles so so, and chews up fuel like a dragster almost. But in general you are right. I still have a 350 in my 90' full size van. Runs great, just not too efficient. I love the sixes over 8s. SBC are so common. Oh well, not much fun for me but thanks anyhow. Have a nice week. I'll post how things work out.

Your OD may be the key, the torque curve prolly doen't match too well. The six lugs down 'cause your truck is heavy & the 250 doesn't have the torque at that RPM. That's a big cam in a small six.

Hey 64, You are right. I am going to go to the shop tomorrow and talk to them about this problem. Its too big a cam as you said. It is under warranty and I told them that I wanted mpgs more than power. Unfortunately I toasted the computer so I don't have lock-up. Just the 4 gears in the tranny. Have to get another computer asap. The oil and temp gauges don't work because the computer is out. They are wired through it. I don't like not having my gauges working. May have to get some after market ones. The overhaul was rather pricey, so they need to make it right. I'll know tomorrow I hope.

A smaller cam should help vacuum also, low vacuum gets the power circuit going & things go rich. A 390 Holley is a good size. You can run a 700R4 to lock up w/o a comp, mine is wired to lock in 4th only, thru a vacuum switch also. Seems like I got the diagram off of z28forum or bowtieoverdrives.

Hey Thar 64Fleetside, Both you and Joe are right. I left the truck at the machine shop for two a one half days. Guess what? The Comp cam has a flat intake lobe on the back cylinder. Soooo they ordered a stock cam which will be in on Monday. Its too big a cam and its junk on top of that! They could not adjust the lifter slap out and others are somewhat noisey. Just over 200 miles on it. The thing is that I sold the engine to my friends son which I have know for years. At least he will get a sweet engine when its done. All I was trying to get was more mpgs with a reasonable amount of power. I was thinking of going with a 292 being a long stroked engine for more bottom end. With 3.73 gears and OD it would no doubt run really good. The thing is mpgs. They were not known for that though some did well like my Dad did years ago. Do you think that an engine like this balanced 250 with a stock cam but adding roller rockers would be good enough? Maybe headers and a 2 bbl from a sbc? Or should I stay with a 1 bbl or 2 single bbls? I sold the 4 bbl manifold. I could find another one on Ebay or some other site. 64, you are right about a smaller cam. Those RV cams for these are just not a good idea. Makes it load up badly. Stock sure seems to be the best. Smoother idle too. BTW, where did you get the lock-up kit from? My computer is fried from the TBI that was there. That would do the trick. Sure would like that info. I need the lock-up. Thanks so very much for the replies. Have a great weekend! Henry

Sorry to here about the cam going flat, true it wasn't the beat to start with, but you still don't want them going flat. Make sure they break it in using the proper oil, it must have a high Zinc level or the next one could very well go flat to. When building the next motor, you may want to save some money on the balance job. I have been told the in-line is a naturally balanced engine due to its design. Plus, if your not going to wind it up to 6000, whats the point, it could save a hundred bucks or so. Joe

Hi Joe, Thanks for the info. I'm sure with the new cam it should run better. They used cam lube and I have 10-30 Castrol oil in it right now. I'm going to change it in a couple of days. I sure do not want the next cam to go flat like this one. It seems that others stovebolters has th same problem with that brand of cam and not with the others. Either way it will be fixed and running much better. Do you think the 292 would be a better way to go instead of a 250. With milled head and decked block should it do somewhat better and get similar mpgs? Either that or how about a 305/327/350? Would either of these work? Thanks Joe. Henry