Stud or Pedestal Heads/1.6 or 1.7 RR's
- Thread starter erniet17
- Start date
samickguy15
Member
Get studs. Pedestal mounts are inherently weak and are more of a hassle to adjust. Stud mounts are strong and easy to adjust.
1.6 rockers are basically stock. 1.7's will give you more lift. Alot of people recommend keeping the stock cam and using 1.7's for mild upgrades such as intake and headers. If you're springing for heads though you may as well get a cam to match. What all are you running?
1.6 rockers are basically stock. 1.7's will give you more lift. Alot of people recommend keeping the stock cam and using 1.7's for mild upgrades such as intake and headers. If you're springing for heads though you may as well get a cam to match. What all are you running?
Jason 302
10 Year Member
65ShelbyClone
Founding Member
I agree on both points.
I have Cobra 1.7s and pedestal edelbrocks in my '68 and I wish I had gone with studs. It's nothing radical so the pedestals are fine, but studs are in fact stronger and easier to adjust. My cam is also designed for 1.7s.
oz
Founding Member
If you are replacing the cam and can get whatever lift you want, there is no need to use 1.7 rockers. It is always better to get more cam lobe up front rather than using a non stock rocker ratio. 1.7's cause more valvetrain stress and non ideal rocker to valve tip geometry.
In summary, assume 1.6's and size your cam to get the lift you want.
In summary, assume 1.6's and size your cam to get the lift you want.
oz
Founding Member
5spd GT,
Can you explain your statement about lift not effecting PV clearance? I disagree but want to fully understand your statement first before commenting further.
Can you explain your statement about lift not effecting PV clearance? I disagree but want to fully understand your statement first before commenting further.
What 5spd GT means is that piston to valve clearance is determined by the valve timing events, when they open and close and how long they are opened and closed. Duration is the number to look at because the valve is never fully open to peak lift when the piston is always at the top of the bore. Even the stock cam would have valves hitting pistons if that were the case, which is why valves get bent when your timing chain breaks. So, the lift numbers are worthless in this determination, it is all about when the valves open and close and how long they are open, which is determined by the duration.
It is the period of overlap that causes piston to valve contact, as Fast63 was getting at.
The period of overlap is when both valves are opened. The exhaust valve is closing and the intake valve is just starting to open.
When the valve is opened up all the way (peak lift), the piston is down in the bore a good 2 inches.
http://www.youtube.com/watch?v=ec0tczrYuYc
This video shows the intake stroke and then the piston comes up and compresses the air and ignites. It then shows the piston going down (power stroke) and the exhaust valve begins to open. Then the video quits.
What it does not show you is after the exhaust valve (left valve) goes full open, it begins to close and the piston is chasing it up the cylinder bore. It is this point near the top of it's travel that the exhaust valve is closing and the intake valve is starting to open.
If you want to read more about valve events, click the link in my signature.
The period of overlap is when both valves are opened. The exhaust valve is closing and the intake valve is just starting to open.
When the valve is opened up all the way (peak lift), the piston is down in the bore a good 2 inches.
http://www.youtube.com/watch?v=ec0tczrYuYc
This video shows the intake stroke and then the piston comes up and compresses the air and ignites. It then shows the piston going down (power stroke) and the exhaust valve begins to open. Then the video quits.
What it does not show you is after the exhaust valve (left valve) goes full open, it begins to close and the piston is chasing it up the cylinder bore. It is this point near the top of it's travel that the exhaust valve is closing and the intake valve is starting to open.
If you want to read more about valve events, click the link in my signature.
65ShelbyClone
Founding Member
They don't have studs. Pedestal heads work with the stock rockers because the stocker heads are pedestal mount.
oz
Founding Member
While I agree that it's good to advice to inform that duration and event timing have the biggest effect on PV clearance I don't think it's good advice to tell someone that lift 'doesn't matter'. It does matter - especially when 1.7 vs 1.6 ratio rockers come in to play. There WILL be a difference in PV clearance with increased lift - say, for instance, when you use 1.7 rockers instead of 1.6's with a given cam since duration does not change - only lobe ramp rate... The difference is about 6%. Is it a huge difference? No, but it is something to at least consider.
5spd GT,
It is not the valve overlap that 'causes' PV clearance issues but rather 'when' this event occurs that is the problem. Semantics I suppose.
The best advice is to check the PV clearance with modeling clay any time you build an engine - especially if you are not going with one of the more typical combos. This is even more important if you do not plan to degree your cam because if the grind is off even a few degrees, PV clearance could be compromised.
5spd GT,
It is not the valve overlap that 'causes' PV clearance issues but rather 'when' this event occurs that is the problem. Semantics I suppose.
The best advice is to check the PV clearance with modeling clay any time you build an engine - especially if you are not going with one of the more typical combos. This is even more important if you do not plan to degree your cam because if the grind is off even a few degrees, PV clearance could be compromised.
While I agree that it's good to advice to inform that duration and event timing have the biggest effect on PV clearance I don't think it's good advice to tell someone that lift 'doesn't matter'. It does matter - especially when 1.7 vs 1.6 ratio rockers come in to play. There WILL be a difference in PV clearance with increased lift - say, for instance, when you use 1.7 rockers instead of 1.6's with a given cam since duration does not change - only lobe ramp rate... The difference is about 6%. Is it a huge difference? No, but it is something to at least consider.
5spd GT,
It is not the valve overlap that 'causes' PV clearance issues but rather 'when' this event occurs that is the problem. Semantics I suppose.
The best advice is to check the PV clearance with modeling clay any time you build an engine - especially if you are not going with one of the more typical combos. This is even more important if you do not plan to degree your cam because if the grind is off even a few degrees, PV clearance could be compromised.
Just check out the link I sent you and it should clear it up for you
The period of overlap is when piston to valve contact occurs.
Edit:
Even a stock camshaft's lift at .444"/.444" would hit if it had a steep lobe ramp rate, with late exhaust valve closure and early intake valve opening events.
If you are able too, install a camshaft, rotate the crank to spin the camshaft to its peak lift. Then remove the valvetrain/heads, and see where the piston is
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