I have quit a rare and weird set up it is a 1979 short block 350 four bolt with a GM performance stock stroke crank with pink rod and Trw forged .125 dome pistons and I have a set of stock reverse flow 96'Lt1 alum.68cc heads and a GM performance intake for the heads a 600cfm edelbrock crab as far as the cam all I know is it was some kind of GMpreformace hydraulic cam with .435 lift all this is a 1850Lbs v-8 pulling mini rod tractor this set was working great until last Tues. when I wiped out #7 cam lode and all I had was a stock .375 lift cam I put it in and it was sounding o.k. to be stock I hooked to the sled and went to take off and all it did going down the track was pop and crack from about three grand up but when not under a load it revs fine what my question is what is making it do this and what kind of other cam can I get that will give the low end like this stock cam was tiring to and the nice revving of that performance cam

Wow another externally plumbed set of reverse coolant heads on a Gen 1 block, and I thought I was the only person that crazy.

The SBC is famous for digesting cam lobes, so much so, back in the early eightys there was a class action law suit on the subject, along with Turbo 250 transmissions behind 305s and 350s, Q-jets held on with 3 of the 4 required bolts, the Olds diesel fiasco and other consumer displeasures resulting from GM's cost savings activities.

The Root Causes are the lack of positive cam retention added to the effects of wear of the cam's hard overlay, same for the lifter, and wear of the cam bearings and lifter bores. These finally come home to roost along with the lack of ZDDP anti-wear agents in modern oil designed for engines with roller lifter cams and catalytic converters. The ZDDP while a great boundary lubricant clogs converters so it went, old engines with sliding lifters lost what little protection they had for an already marginal environment.

Replacing the cam and lifters as well as cam bearings and carefully checking the lifter bores and bushing them if necessary is required, along with a cam button to take up the fore and aft thrust movements. Or better still for this block is an aftermarket roller cam. Or replace the entire block with an 87 up with the factory roller set up which includes solution to unresolved thrust moments with a retention plate like eveybody else has used for decades.

Bogie 

not its not that bad the worst part was getting the four water ports blocked off so the coolant wouldn't go into the oil but other than that i was pretty easy until i wiped out this lobe have you ever heard that the stock lt1 heads have to much spring pressure since it is a roller cam head and it is compressing the hydraulic lifter are just compressing and not letting the valve hardly come open and that is why i'm getting a miss fire at higher revs under a load is this true if so do i have to change them to a gen1 type spring and will this really work if i do that this is what summit and jegs both told me tonight and was just wonding i have never heard that before and a friend told me that my timing ignition is off or not adv. enough in the up revs but i have a msd hei distributor 8501? i think any help would be greatly appericated i have a pull tues and like to have it fixed

Well the reverse coolant LT1 engine's heads are designed for a roller cam set up and depending on exact time of manufacture leading toward the LT4, you might find LT1 heads with factory installed 1.6:1 roller rockers. However, none of these factory engines ran so much cam that the springs are so powerful as to collapse a hydro lifter.

The inability to kick the valve open at least on the cylinder where you lost a lobe, is just that, no lobe! If there are other cylinders that barely move the valve, you might be looking at other wiped lobes or lifters.

A cam that's loosing it lobes often makes the engine run like the ignition timing is off. Guess how I learned that. You're going to have to pull the cam so you're going to get a look at all the lifters and lobes.

Part of the problem is that modern oil whether mineral or synthetic has been neutered of what you might call dry lube components. These are or were things like Zinc Dialkyl Ditho Phosphate (ZDDP) which was used as stabilizer, cleanser, and most importantly forms a high pressure chemical boundary lube that is very useful in places like the cam lobe to lifter interface where forces and dimensions are such that it's difficult to maintain an oil film in that space. Modern oils have removed this material because its a powerful pollutant and is poisionus in the environment. But, and the oil companies are going to reject this notion, but there really isn't anything that makes a good substitute. The factory and this is everybody's factory, responded to the removal of ZDDP from oil by installing roller cams. Now there are folks who will say this was done for improving available power by eliminating a frictional loss and while that's true to a small extent, I think you can bet warranty issues with these rubbing parts and no ZDDP in the oil was the bigger driver.

So where do you go. Well the simplest solution is a roller cam, it's just the factory roller doesn't retrofit to older blocks without a lot of cost and difficulty and aftermarket rollers are expensive and usually ground with pretty aggressive duration and lift. You could hunt down a 880 Vortec block which would give you four bolt mains and factory roller capability. There's gobs of them in trucks from 96 to 02 or whenever GEN 1 production ended.

Or rebuild from what you have, but it's important to keep the cam bearings, lifter bores, oil pump/distributor drive spot on dimensionally. Plus you've got to run a cam button. All of this is to keep the shaft from moving around which drags the lobes sideways across the lifter face. We're trying to minimize the loads so the lubrication doesn't have to work so hard.

You also have to check the pushrods for strength, wear and length. The heads you're using are aluminum which pushes you into a thicker head gasket, the heads were never meant to be on that block so there can be other dimensions stacking up on you. So you need to make sure the pushrods are of proper length to keep rocker and valve stem geometry correct. If this gets too far off you'll eat parts like there's no end to them. Also, this just keeps going doesn't it, the LT1 heads used a self guided rocker with a shall we say widely spaced sheetmetal pushrod guide. You can't run the factory guide without the self aligning rocker, it's too wide to keep the push rod where it needs to be. If you go with non-self aligning rockers the guide needs to be replaced with a "hot rod" part that has narrower push rod slots and the pushrods need to be hardened to prevent wear when they rub the guide plate. You also cannot run LT1 pushrods they're shorter because the roller hydraulic lifter is taller than the flat tappet. So you have to start with a push rod that has at least the length for a flat tappet engine. Like I said earlier, you need to check on this length to make double sure that the rocker geometry is right.

A Franken Mouse I built a few years ago uses LT1 reverse flow heads on an 880 Vortec block with the LT1 injectors and rails mounted thru Moroso spuds to a GMPP LT1 4bbl intake with a Turbo City modifed 2 inch TBI throttle body housing sitting atop an adapter plate with an LT4 HOT cam. It both SMOGs and scares me to get on it. I ran coolant lines from the front and rear vent connections increasing them to .5 inch pipe. The lines come together up front to an aluminum collector with a conventional thermostat and return elbow to the radiator. To do this the serpentine belt system had to come off as there wasn't space for its adapters and the forward return plumbing. With the hood up, the factory carburetor style aircleaner almost covers everything so well, you can't tell at a glance what you're up against. Obviously a set of FB385 heads on an 880 block would be easier to do, but sooo common. 

The next trick would be to use those heads and reverse flow a standard block. I figure that if you started with a short water pump with a set of long pump adapters. Drill and tap the pump's outlets for fittings. Do the same to the adapters. Install with a plate to block the pump flow to the block at the adapter. Rout the pressure coolant into the heads thru the vent locations, enlarged of course. Coolant would flow into the block, it would then return through the hoses and fittings of the long pump adapters to a collector with thermostat and back to the radiator. Or you could collect coolant at the soft plug locations and return it to the radiator. The latter would help even out cyclinder to cylinder temps so the fronts didn't run cooler than all the others. This would put a smile on Smokey's face, just the kind of thing he'd do.

Bogie

thanks for all the help but i am running out of things to try besides put a new cam in i have done alot more asking aound and was told that the cam might not have enough advance ground in it since it is a older truck cam and that i might want to try another cam like the comp cams 256 or the 268 but i am looking more torwards the edlebrock preformer cam but i am un sure on which to use and be the best for my setup i do have a new edelbrock 14054 carb with the GM performance carb intake made for the Lt1 heads (24502592)and with the trw .125 dome pistons i know i have all the componets for a strong motor High compression motor but i just can't get this miss firing or like a sputter out of when it is under a load i have tried changing the timing curve to reseting the valves and it all don't change a thing but if you just rev it up not under a load it seems fine so i believe the only thing i have left is to change the stock cam because a guy told me that with high compression motors a stock cam will not work becasue of the lack of lobe over lap but am unsure on the right one for what i am doing the one i wiped the lobe off was working great but i can't find an #'s stamped in the end of it but the #'s casted in it is GM20 in one spot and the 2182 in another but that is all there is no it i believe is has like a .434 lift and a 216 dur. at .050 or 262dur at .006 but i'm not for sure it seems bigger than that when it was in the motor these #'s are just my guess from what i have been able to measure and figure as far as what happened to the lobe i believe it came from an over rev deal

One of your problems is way too much compression. Your estimate of 68 ccs for the LT1 combustion chamber is way too big, unless you've done something to open them up. The factory puts these at 54 ccs and that checks out pretty close when I measure them. In fact I've got a set on the bench I just spec'ed out at 52 ccs straight from GM.

I figure that with 54 cc chambers a .054 thick head gasket, a .125 dome on the piston and zero crown clearance, you're running a compression ratio right around 16 to 1.

Chances the missfire you're feeling is detonation. This engine will have to run 100 plus octane racing fuel and for a cam forget anything from the factory. Ultra high compression is used to compensate for extremely long overlap cams, these tend to bleed a lot of mixture through the exhaust and loose a lot of mixture density. The compression is jacked up to compensate for the density loss. With a short timed/short overlap cam running against a lot of compresson does is to trap too much mixture significantly increasing its density. This leads to detonation and preigniiton as the trapped mixture overcharges the cylinder for the operating conditions the fuel can tolerate.

You need to look at cams with off the seat durations above 250 degrees when measured at .050 inch of lift. LSAs of less than 110 degrees. Overlaps of 30 to 60 degrees. Lifts over a half inch.

For the ignition, you'll want a lot of static lead say 14 to 18 degrees with a short and fast mechanical advance dumping in 25 to 30 degrees by 2200 to 2500 RPM. You may find yourself having to back the total mechanical down by limiting the reach of the counterweights. The best timing solution is to lock the distributor's flyweights and use an MSD adjustable timing computer PN 8981. This is far more adjustable, accurate and stable than any mechanical device.  

The other choice is to back the compression down to around 10 to one or a bit less, this would allow the use of factory cams and distributor.

thanks for all the info so far and i can understand where you are coming from this is and does sound like the most reasonable reason and i will get another cam what type would you suggest for what i have and the type of sport i am doing i am using the v-power c-12 race fuel and with the other cam it seemed to do great but do you suggest somthing diff i was using the blue cam two from the local race track but i was getting alot of dirt like they was not filtering it from the pump and it was was getting to be a pain refiltering as i put in my tank and this vp seems good and all but i am open for any suggestions thanks for all the help so far  

Can I drag you back thru a discussion as to what youre doing with this engine, the vehicle weight, overall gear ratios, tire size, type of transmission, stall ratio if an automatic, etc, etc?

Bogie

well lets see it is a mini rod pulling tractor it weights 1850lbs with me on it and the sled weights about 10 grand i have to pull it about 200 feet as the weight goes up and for a trans i have a  turbo 350 truck trans with a BnM shift kit with a 1800-2100 stall with 5:38 12 bolt truck rear with 31x15.5-15 V-cleat tractor tires and i will never get out of first gear pulling and should be tacking about 5-6 grand i hope and i am mainly looking for a cam with great low end torque because i am starting with a load on me more or less like the big pulling tractors that pull in the mid west thanks for all the help this is the first hp motor i have put together and all was good till i wiped out the cam but i can't figure out what kind of cam it was because there are no #'s stamped in the end of it all it had was a GM20 and a 2182 forged stamped in it  in it  all i know it was a GM hp cam with a lift of .43's and a dur. of like 220 that is all i knew since was a buddy's he had in a truck he had thanks again

Ya know, there's a couple experiments to do here, one is to run a big port/valve head with a "milder" cam such as you're doing with the LT1/4. The other test would be to run a smaller ported head with a longer cam.

What I'd be searching for is really high port velocity without the ports/valves being so small they gasp the motor at 5-6000 revs. A longer duration cam with lots of overlap and high lift would combined with smaller ports could combine to really work flow inertia to help load and unload the cylinder with mixture thru exhaust.

A head that works hard in the upper rev range would be good, the Fastburn/Vortec/LT1 or LT4s whether GM or aftermarket would be good.

You might consider filling the lower intake port with epoxy say the bottom 20%. This would force higher velocities and push the rather sluggish flow on the bottom of the intake up into the main flow zone. The intake needs to be filled a reasonable way up to make a streamline on the bottom of the port so fuel woun't puddle along the bottom of the runner ahead of the head's port.

Bogie

i get what you are saying i my self have never done anything that extreme before but have read it in a book or two so i am kind of worried about doing something like that i may try that but  what type of cam would you suggest for it as i can see a stock cam is to small i was thinking about going with something like a circle track cam  something like the isky .465 lift and 221 dur and the put a set of bleeder lifters in but i have never tried a set and don't know how well they work or a guy told me that he would suggest a compextreme cam with .432/.453 lift with a 206/214 dur i know the dur and the lobe sseparation has alot to do with the bleed off but i am un sure what will be to much i also know that the more dur i have the less low end toque i will have but wouldn't the extra compression help on that since it can't bleed all it off just a question i thought of bogie thanks for all the help you are the on'y that has given me anything that sounds like a reasonable answer