[Jake Harsha]

I Hydro-locked and blew up the bottom end of my Ramjet 350. Block is cracked, but the heads are still fine.

I ordered a GMPP 350 HO long block to replace it, but the 350 HO has the plain jane stamped rocker arms and I'd rather keep the roller rockers from the Ramjet motor. Thing is, the rockers in the HO are 1.5:1 and the rockers in the Ramjet are 1.6:1. The cams are as follows:

Ramjet 350:
Cam lift: I 0.431" / E 0.451"
Cam Duration: I 196 degrees / E 207 degrees
Lifters: 1.6:1

350 HO:
Cam Lift: I 0.435" / E 0.460"
Cam Duration: I 212 degrees / E 222 degrees
Lifters: 1.5:1

I believe the pistons are the same between the two engines, but I haven't looked yet.

My question is this:

Will I be able to keep the cam that's in the HO and and use the Ramjet heads/roller rockers with the 1.6:1 rockers, or will I need to swap cams as well to avoid piston/valve contact?


Thanks,
Jake Harsha

[johnsongrass1]

The tells me you should be okay. But I would check the clearances anyway, just to be sure. Guide boss to retainer clearance as well as coil bind, depending on the springs used, would be my biggest worry. Just check them all closely.

[Jake Harsha]

Originally posted by johnsongrass1
The tells me you should be okay. But I would check the clearances anyway, just to be sure.

The [what?] tells you? Is there a chart for this somewhere online?

"Guide boss to retainer clearance as well as coil bind, depending on the springs used, would be my biggest worry."

How does a fella go about checking these things?


Thanks,
Jake Harsha

[1BAD80]

Knowledge Base has the info needed.

[jimfulco]

Jake, your roller cam is rated at .431/.451 with 1.5 rockers. The flat tappet cam may be a little much, especially on the exhaust. The Chevy book says stock Vortecs are good up to either .470 or .475, but the 1.6's will put your exhaust at .491, where the roller cam exhaust is at .481. They may have modified the valve guides/seals, but I can't imagine GM going to that much trouble. Another thing to watch is the holes where the push rods pass through the head. I've heard that they may need to be enlarged to keep the push rods from rubbing when 1.6's are used.

[Jake Harsha]

Originally posted by jimfulco
Jake, your roller cam is rated at .431/.451 with 1.5 rockers. The flat tappet cam may be a little much, especially on the exhaust. The Chevy book says stock Vortecs are good up to either .470 or .475, but the 1.6's will put your exhaust at .491, where the roller cam exhaust is at .481. They may have modified the valve guides/seals, but I can't imagine GM going to that much trouble. Another thing to watch is the holes where the push rods pass through the head. I've heard that they may need to be enlarged to keep the push rods from rubbing when 1.6's are used.

After giving it some thought, I'll probably swap both the Ramjet heads and Ramjet Cam onto/into the new block, leaving the valves in the same heads, so the pushrods shouldn't be a problem. I want to preserve torque and maintain vacuum to operate the brakes.

Can you see anything preventing me from going this route?

Thanks for all the info,
Jake

[USA1]

I just got off the phone with GM performance parts. I was wondering if 350HO block was machined for roller cam. Yes it is, they also said both engines have the same vortec heads, so clearance should not be an issue other than the valve covers. He said to use the tall valve covers with the roller rockers, but it appears to me that both engines have same covers. They say you can do what you are wanting to do.

[Jake Harsha]

Originally posted by USA1
I just got off the phone with GM performance parts. I was wondering if 350HO block was machined for roller cam. Yes it is, they also said both engines have the same vortec heads, so clearance should not be an issue other than the valve covers. He said to use the tall valve covers with the roller rockers, but it appears to me that both engines have same covers. They say you can do what you are wanting to do.

Thanks!
I'll be using the same valve covers as have always been on the Ramjet heads--but they do look the same as the ones on the 350 HO heads (except the ones the came with the RJ are chrome--the ones that came on the 350 HO are ugly black--unlike the picture).

I got to thinking about how the fuel system works and I don’t even know if the engine would run at all with a lower-vacuum cam in there because the intake vacuum regulates the fuel supply return. As intake vacuum increases, it closes off the fuel return line. That’s how it regulates the fuel pressure in the rail.

My buddy said I should get the RJ heads decked to make certain they're O.K. before putting them on. Do you think this is necessary?

The engine never overheated or anything--just did it's best impression of a wet-vac. Would that ever tweak a head? -Or would the head gasket blow long before that would happen?

I was thinking an alternate method might be to just place the heads flat against eachother to make sure neither was warped...

Thanks again,
Jake

[USA1]

Hydrolock can do some strange things. It probably would be a good idea to have the heads checked by a good machine shop. It would be cheap insurance. It could have bent valves or pushed valve seals out of place. As far as decking goes, some new heads aren't exactly flat to begin with, so having them checked may save trouble in the long run. I'd hate to put everything back together just to find a sealing problem right off the bat, or even 6 months down the road. Most machine shops don't charge much to pressure test and check for square. You would probably be OK using the heads already on the HO motor.

[Jake Harsha]

Originally posted by USA1
You would probably be OK using the heads already on the HO motor.

I know, but then I'd lose the roller rockers and I can't see taking a step backward like that... I suppose I could change out the rockers between heads, but knowing me, I surely screw that up and end up with something too tight or too lose and then have more problems.

I figured if I could just change everything whole-hog that'd be alot easier.

I'll definitely get the heads checked before I put them on.

Thank you,
Jake

[USA1]

The roller rockers will work on either set of heads. According to GM both sets of heads are identical.

[jimfulco]

You should check your old heads with a straight-edge to make sure the deck surface is flat. Sometimes heads from a perfectly good engine will come off warped. This is because repeated hot-cold cycling changes the stresses in the casting, especially in the lighter castings. I've heard that even brand new Chevy heads are sometimes not flat. Me, I'd just use the heads that are on the engine. I'd still make sure the push rods don't hit the side of the pushrod holes closest to the rocker studs with the 1.6's.

[Terry Petty]

Originally Posted by Jake Harsha

I Hydro-locked and blew up the bottom end of my Ramjet 350. Block is cracked, but the heads are still fine.

I ordered a GMPP 350 HO long block to replace it, but the 350 HO has the plain jane stamped rocker arms and I'd rather keep the roller rockers from the Ramjet motor. Thing is, the rockers in the HO are 1.5:1 and the rockers in the Ramjet are 1.6:1. The cams are as follows:

Ramjet 350:
Cam lift: I 0.431" / E 0.451"
Cam Duration: I 196 degrees / E 207 degrees
Lifters: 1.6:1

350 HO:
Cam Lift: I 0.435" / E 0.460"
Cam Duration: I 212 degrees / E 222 degrees
Lifters: 1.5:1

I believe the pistons are the same between the two engines, but I haven't looked yet.

My question is this:

Will I be able to keep the cam that's in the HO and and use the Ramjet heads/roller rockers with the 1.6:1 rockers, or will I need to swap cams as well to avoid piston/valve contact?


Thanks,
Jake Harsha

Jake-
Take the ROLLER cam and lifters, timing chain and gears, rocker arms and pushrods out of the cracked RJ350 and put them into the 350HO. There will be NO clearance issues whatsoever. 350HO has the exact same cylinder heads as the RJ350 so no need to change anything.

IF you left the flat tappet cam in and put on the 1.6 rockers, you would have .490 lift on the exhaust and that would put your valvesprings into coilbind (destroy the heads, maybe worse if you drop a valve). ALSO, if you left the flat tappet cam in, your lobe centers are 3 degrees off and you would also have more duration, thus you would have to have your computor controller for the F.I. "reflashed" for optimal performance.

HOWEVER, the two engines have different pistons. The RJ350 has hyperutectic pistons with offset pins for 9.4/1 compression. The 350HO has plain old cast aluminum pistons that are good for 9.0/1 compression (the difference must be in either the piston dish or the head gasket as they are different part numbers).

Put it in like that and run it. IF you want to get even closer, put a set of .015" felpro steel shim head gaskets the rubber coated ones or the stainless steel with spray coppercoat. With a steel head gasket, use the teflon on the threads and the top of the bolt where it meets the head. One last step would be to lay the steel head gasket on the head and if you can identify the coolant by-pass ports drill them out if possible so you don't have problems with air bubbles. Or just drill a 1/16" hole in the thermostate. Or leave the thermostat til last and fill coolant up to the intake so that the thermostat dips down into the coolant to get it to open. Otherwise, you might have an "airlock" on the new motor and sieze it.

Todays oil sucks for flat tappet cams. Put in the roller and forget it. IF there is any chance you can return the 350HO, I know where you can get a BRAND NEW 4 bolt main block for less than 700.00 GM part and just put the guts into it that you have.
Terry Petty

[Hippie]

The original post is 7 years old...............

[Terry Petty]

Originally Posted by Hippie

The original post is 7 years old...............

I'm new here. I don't know how old the posts are I will try to look for dates in the future. I assumed the site would only post current events.
Thanks for telling me.