Ok guys its been a very long time since I've posted but I've been busy with college studies and what not.... but anyway I have since purchased a 503hp motor which has a 12.5:1 compression ratio. This is way to high for me to be able to drive it as a everyday car. So I want to detune it ugh I had that sound of that but I have to. I have the 462 camel hump heads with a sweet port job which our 64cc. So is there anyway to do this with out changing the pistons? I've heard of high rise gaskets to raise the heads up but I dont know. I would like to beable to keep the same ones so when I race it I can change gaskets or something and go back to the 12.5:1.

Ok well I cant think of any other way so heres the other question. I have no idea if the crank has been turned or not and when ordering a rebuild kit which will get me the 10.5:1 pistons I want and also all the bearings needed. The problem is I have to order the bearings correctly I dont know if its a std, .010, .020, or .030. How can I measure it? Thanks for the help in advance.
-Mike

 

You could get a thicker head gasket,But thats not going to put you into streetable terms.

As far as the crank, the bearings in the block should be marked.


503 HP is a ****load out of a NA smallblock, It must have a Monster Cam. Your going to have a hard time drivin that everyday as it is



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 15.26 @ 87.0
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

The only way to get a compression that high is with a domed piston. You would have to take them out and put flat tops in. Also in doing this, the cam would have to be changed as it would be very soggy on the bottom end.

 

Installing thicker head gaskets most likely will not reduce the octane requirement as much as the drop in compression ratio might suggest. The thicker gaskets tend to reduce the turbulence of the mixture in the cylinder as the piston approaches TDC. The octane requirement is somewhat dependent on this mixture turbulence in the cylinder, greater turbulence being better.

Are you really sure that you'd want to replace the head gaskets to go race and then again to drive on the street??? It's quite a bit of work. As has already been suggested, I'd go with the flat top pistons and a smaller cam.

Norm

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1979 Malibu w/some cornering tweaks and a few other interesting things

 

Ok guys heres everything I know about the engine I have...

Its a 350 engine casting 3790010

--Heads are a 69-70 462 Camel Hump heads with Crane gold race extruded billet aluminum roller rockers
--Comp Cam Magnum series 305H dur: 253 exhaust/intake lift .525
--12.5:1 Speed Pro domed racing pistons
--Victor Jr. Intake
--800cfm double pumper
--Hooker Comp Headers (1 3/4", 3" collector)
--new stock crank and rods if I remember straight
--High volume oil pump
--120gph carter fuel pump
--MSD HEI modulator
--ACCEL super coil
--Taylor 8mm Spiro wires
--Bosch Platinum +4 plugs
--91Z28 Serptine pulley setup w/ 1LE AC bypass

and thats everything...

so here if I was to buy one of those Summit 350 engine rebuild kits with 10.2:1 flat top pistons I think everything would be good.... however again I dont know if the crank was new or not and if it wasnt it was probably turned.. so when ordering bearings I would have no clue.

So to get around this would it be ok to reuse the old bearings? I forgot the rule of thumb on bearings as my engine class I took was about 4 years ago in highschool. The engine has only been used for drag racing and has about 4-8 runs in the quarter.

Any info would be great, Mike


[This message has been edited by IROCU69 (edited May 22, 2001).]

 

You definatly got to take that cam out. Get flat tops, and a dual plane manifold. As previosly mentioned a thicker head gasket isn't going to cut the octane requirements because you are opening up the quench area, which will make it waste gas and require high octane anyway or it will detonate. Also with a wide open quench area you lose alot of power.

That cam is wicked! Way to wicked.

The intake manifold isn't a good idea on a toned down street motor. A good dual plane or even a dual hi-rise would be sweeter with 9 to 10 compression and a cam specc'ing in with upto a 5,500 to 6,000rpm powerband.

The carb is a little to big also. A 700cfm with vacuum secondaries and an electric choke would make it more streetable and gas friendly, not to mention easy to start in colder whether.

Selling off the parts you remove could very well offset some of the expense. The pistons are very likely for an overbore and if in good shape could get you some cash. They probably are forged also.

If you get forged flattops and a street friendly 'nitrous' cam, you probably could put out just as much power in the street friendly setup on the bottle. (Just a thought)

You probably have some very steep gears out back since that engine seems like a drag setup.

Since your motor probably already has an overbore, you might want to check into seeing how much because changing the pistons will at least require a hone job, and if it's worn to the point of falling out of spec and you're already .060" over, the motors life is pretty much over and might be more cost effective to sell the whole motor and get a different one.

Just some ideas/pitfalls.

 

Another thing that came to my mind that might be considered half-assed but something I would do would be to bring the piston up to TDC, tape around the rings so no chips fall in there, and use an end-mill to mill the domes down. You have to get them all equal, but it will bring the compression down without losing quench and won't require taking the bottom apart. With aluminum heads instead of the iron, you could even get away with running 89 octane.

 

Hey thanks that helps a bit. But does anyone know about reusing bearings???

-Mike

 

You could save some money by getting your combustion chambers thermal coated.

I wouldn't waste time changing the crank and pistons. Just run the compression. That cam is not too big for the street. I ran a 242 @ .050 duration 108 LSA cam in my daily driver 350 for years. Gas mileage blew, but who cares about that. Vacuum was a little low, and the brake pedal was kind hard, but it was livable.

I would get the heads coated, change head gaskets, and run the bottom end the way it is. If it ain't broke, don't try and fix it.

 

Yeah, I agree, either live with it, or buy a H*nda to ferry you around while your baby sits, waiting for the weekend. You paid for the horses, might as well enjoy them sometime.

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No guts, no glory.

 

So keep the bottom as it is eh... well if I do that I have to run 115 octane fuel and at 4 bucks a gallon here in MN I cant afford that. I'm a college student... trying to pay off my loans before next fall semester.

So.. can anyone just tell me if I can reuse the bearings they only have 20 miles on them.. or should I buy new ones pleaseeeee let me know.

Thanks, Mike

 

Buy new bearings, they don't cost that much.

You will have to pull one of your old main bearings and the size will be stamped on the bottom of them if they are undersize.

 

Yes i just spoke with some friends of mine at work that do a lot of car work and they told me the same thing. So I guess now I'm looking at just buying a set of Speed Pro 9.8:1 forged flat top pistons. I'll buy some new bearings and rings and more or less hone the cylinders while I'm at it.... so now heres the next question..

Does anybody have a recommendation on a company to buy rings and what kind of rings to buy??

Thanks again guys, Mike

 

anything? I'm thinking of buying the summit 350 rebuild kit with hypereutectic 9.73:1 pistons. Or should I get the 10.3:1 pistons. You see I finally went to a speed shop and found out that my engine was zero decked leaving the pistons dome clearing the block by 1/2" and we found that the heads have been milled to about 62cc. So with 9.73:1 pistons at 64cc... would that be like 10.3-10.5:1 compression with these heads I have?

-Mike

 

If the pistons are in good shape and are solid dome, the pistons can be fly cut down to reduce compression. But with the cost of getting that work done, you might as well get new pistons. The HP gain from 9.7 to 10.3 is very minimal, probably 5-8 HP. I would go with the 9.7 since you’re heads are already milled down. It’ll be more forgiving octane wise.
Bearings that are in good shape can be re-used, but they’re cheap so you might as well change those out too.
The only way to find out if the crank has been turned down or not is to take a dial caliper and measure it.
As far as rings are concerned, I prefer Speed-Pro plasma-moly rings. They’re very durable, but are higher priced and is also the choice piston rings of Lingenfelter and Duttweiler, Joe Sherman, etc. If you want a slightly cheaper alternative, go with the Speed-Pro moly top rings. I haven’t used the Childs and Alberts but have had friends go back to Speed-Pro’s after using them.
Since you’re already working with a speed shop, why not work with their engine builder and have them work with parts they know? The smart thing to do when building an engine is to work with a reputable builder/machinist, tell them what your goal is, get their feed back on what parts and modifications they recommend and then go from there.