SN95 New Heads

[Blakeknight]

Hi, I’m new to building engines. I have fixed my dad’s old 1995 GT. I want to rebuild top end of motor. It has a ford F303 cam in it now and I want to keep that.

SVE 185CC CNC CYLINDER HEADS - 58CC CHAMBER​

That’s the title of aluminum heads I plan to use. They are from LMR. I want to switch to 1.7 rocker arms if that’s something I should do. But I have zero idea what size rollers or rods I need. I’m absolutely clueless. How can I tell what can pair with my cam and head to cheaply rebuild the top end? Thanks guys I really hope I can get some help.

 

[bird_dog0347]

You will need to upgrade the valve springs on those heads I'm 99% sure to use them with the F cam and 1.7 rockers, possibly even with 1.6 rockers and you WILL need to measure for PTV clearance. You'll need the pushrod length checker tool from LMR as well to know what length pushrods to order.

 

[gkomo]

Not to side track the thread but could be useful information, but what determines if you use 1.6 or 1.7 RR's?

 

[LILCBRA]

Not to side track the thread but could be useful information, but what determines if you use 1.6 or 1.7 RR's?

A couple different factors that I can think of off the top of my head. First, rocker ratio effects valve lift. So, if you want higher lift from your camshaft, you can increase the rocker ratio. As I'm sure you know, increasing lift increases the amount of air and fuel that is allowed into, as well as the speed it enters, the combustion chamber and exhausted afterward. You take the cam lobe lift and multiply that by the rocker ratio to find valve lift.

For example:
A camshaft with .333 lobe lift will give valve lifts as follows;
1.6 rockers: .333 x 1.6 = .533
1.7 rockers: .333 x 1.7 = .566

The limiting factors on lift include coil bind on the valve springs and piston to valve clearance. So when building an engine, or swapping to a different set of heads, these are 2 of the factors you have to consider.

You'd take your head flow data to help determine what kind of valve lift you'd want.

Hope this helps answer your question.

 

[gkomo]

A couple different factors that I can think of off the top of my head. First, rocker ratio effects valve lift. So, if you want higher lift from your camshaft, you can increase the rocker ratio. As I'm sure you know, increasing lift increases the amount of air and fuel that is allowed into, as well as the speed it enters, the combustion chamber and exhausted afterward. You take the cam lobe lift and multiply that by the rocker ratio to find valve lift.

For example:
A camshaft with .333 lobe lift will give valve lifts as follows;
1.6 rockers: .333 x 1.6 = .533
1.7 rockers: .333 x 1.7 = .566

The limiting factors on lift include coil bind on the valve springs and piston to valve clearance. So when building an engine, or swapping to a different set of heads, these are 2 of the factors you have to consider.

You'd take your head flow data to help determine what kind of valve lift you'd want.

Hope this helps answer your question.

Helps a lot, thank you.

I only asked because it seems like most people go with 1.6RRs. On my last Fox when i had my 331 built the builder put in 1.7RRs so i was just curious. It was a TFS stage 1 top end kit, and i'd have to go back to my build sheet (if i still have it) to see what pistons were used. It was a stock 302 block with the stock crank, but everything else was changed/new.

 

[Noobz347]

I only asked because it seems like most people go with 1.6RRs.

This because it is the ratio for the OEM lifters.

For example:
A camshaft with .333 lobe lift will give valve lifts as follows;
1.6 rockers: .333 x 1.6 = .533
1.7 rockers: .333 x 1.7 = .566

This is the key piece. If the coils on the springs are fat enough to provide tension all the way to the top of the cam lobe then they might be too thick to allow travel to the top with rocker arm with a higher ramp multiplier (rocker ratio).