BBC piston to valve clearance

[C101971]

Tried some digging but didn't quite find the answers I am looking for. I have a mk4 454 2 bolt main, bottom end is factory, running iron closed chamber large oval port marine heads, 1.7 roller rockers torker 2 intake, sniper efi. 3k stall powerglide, 4.11 gears with 28 inch tires. I am planning for a hyd roller cam.

With my setup listed above for reference, keep in mind my motor is disassembled except the crank, rods, pistons are still in it, I plan on keeping the bottom end stock. What I want to know is how much space does the valve have before it breaches safe clearances? I will not be running stock springs. I read lots about .550 before coil bind but I am building my heads, not pushing factory limits. I just want to figure out what measurements I have to work with so I can narrow down my options. I can't test for compression cause the motor is not assembled and I am aware that contributes to cam selection. I plan on keeping it N/A, and will be using factory thickness head gaskets, my block has not been decked and my heads are brand new.

Or if people could tell me about their similar setups and what your clearances were for stock bottom end w/ iron heads

[kwmech]

It would depend on the bottom end and the cam you are planning on running.

[AussieinNC]

Stock lower end with stock pistons, I use the basic rule of thumb for minimum clearances is 0.080 for the intake and 0.100 for exhaust. I usually clay test at least one cylinder on each bank.

Much more important with these engines is coil bind at max lift.....I assume you will be using new springs....

If you buy a roller cam, by the kit that also includes recommended springs and follow the installation instructions to the letter.

[C101971]

Originally Posted by AussieinNC

Stock lower end with stock pistons, I use the basic rule of thumb for minimum clearances is 0.080 for the intake and 0.100 for exhaust. I usually clay test at least one cylinder on each bank.

Much more important with these engines is coil bind at max lift.....I assume you will be using new springs....

If you buy a roller cam, by the kit that also includes recommended springs and follow the installation instructions to the letter.

Yes I will be using new springs, I just didn't want to base everything off stock springs

[C101971]

Originally Posted by kwmech

It would depend on the bottom end and the cam you are planning on running.

Came out of a 79 c20 I believe, factory small oval port, if that affects what the bottom end would have been. I am leaning towards the lunatic voodoo

[AussieinNC]

Your "new heads"...

Are they small port or rectangular port?

Lunati Voodoo cams are a good product, try and find a full kit including lifters and springs etc.

Having a stock bottom end will limit the longevity and drive ability of the engine if you hit it with too much cam.

Big blocks produce tons of torque....if this is a street driver, the small port heads have sufficient flow to match the torque curve of the BB....

Try spinning it past 4500 and you will find trouble, especially with those cast factory pistons....

Have fun...

[Ironangel]

What heads do you have, numbers? If your pistons are factory 454 pistons they'll most likely be a flat top with valve reliefs. With that said you kinda need to do what AussieinNC said and call one of the cam manufacturers and let them tell you which cam profile will give you what your heads can flow. They'll supply the cam, lifters, push rods, rockers, springs, and valves that will all play well together with what you already have, a factory 454 truck motor...If your heads are "peanut port" heads they'll make killer stump pullin torque from idle to 5000 rpm and be done, great towing heads. If they're old school closed chamber oval ports they'll flow north of 6000 rpm. If you choose a reasonable lift cam in the .550" to .580" range of lift you should have ample VP clearance and still make lots of low end power out to 5000 rpm...Call some cam company's, I've ran Comp, Lunati, and Clay Smith cams and have no regrets on their products...Mike

[C101971]

Originally Posted by AussieinNC

Your "new heads"...

Are they small port or rectangular port?

Lunati Voodoo cams are a good product, try and find a full kit including lifters and springs etc.

Having a stock bottom end will limit the longevity and drive ability of the engine if you hit it with too much cam.

Big blocks produce tons of torque....if this is a street driver, the small port heads have sufficient flow to match the torque curve of the BB....

Try spinning it past 4500 and you will find trouble, especially with those cast factory pistons....

Have fun...

Heads are large oval port

[C101971]

Originally Posted by Ironangel

What heads do you have, numbers? If your pistons are factory 454 pistons they'll most likely be a flat top with valve reliefs. With that said you kinda need to do what AussieinNC said and call one of the cam manufacturers and let them tell you which cam profile will give you what your heads can flow. They'll supply the cam, lifters, push rods, rockers, springs, and valves that will all play well together with what you already have, a factory 454 truck motor...If your heads are "peanut port" heads they'll make killer stump pullin torque from idle to 5000 rpm and be done, great towing heads. If they're old school closed chamber oval ports they'll flow north of 6000 rpm. If you choose a reasonable lift cam in the .550" to .580" range of lift you should have ample VP clearance and still make lots of low end power out to 5000 rpm...Call some cam company's, I've ran Comp, Lunati, and Clay Smith cams and have no regrets on their products...Mike

I will have numbers from it later today, can't remember them off heart. The factory pistons had 2 valve reliefs and a very shallow bowl in the center of each piston I remember. Will be giving lunatic a call on Tuesday.

Thanks for the info!