TFS Stage 1 cam on 1.7 rr's
- Thread starter Jo_885o
- Start date
i wouldnt even know, I was just wondering cause that could have been a option while the heads are being ported and off the block. The max lift on the heads are 540''
Michael Yount
Mustang Master
To find the resulting lift simply divide 1.7 by 1.6 (1.7/1.6) and multiply times the lift with the 1.6 rockers. Alternatively, simply multiply 1.7 times the cam LOBE lift.
As for p to v - peak lift has no impact on p to v. At peak lift the pistons are well down the cylinders with LOTS of clearance to the valve. The issue of clearance show up during overlap when intake is just opening and the exhaust is about to close as the piston passes through tdc. At that point, with the stage one your lobe lift is about .050", your valve lift is around .080". So changing from 1.6 to 1.7 results in valve lift of about .085" -- and reduction in p to v clearance of about 5 THOUSANDTHS of an inch. Assuming you measured p to v when the cam was installed (as you should have) all you have to do is deduct the .005" from it and you'll know your p to v. And if you didn't measure, then all you know is you'll have about 5 thousandths less than you have now. If it's all still going together, then be sure to measure p to v properly.
As for p to v - peak lift has no impact on p to v. At peak lift the pistons are well down the cylinders with LOTS of clearance to the valve. The issue of clearance show up during overlap when intake is just opening and the exhaust is about to close as the piston passes through tdc. At that point, with the stage one your lobe lift is about .050", your valve lift is around .080". So changing from 1.6 to 1.7 results in valve lift of about .085" -- and reduction in p to v clearance of about 5 THOUSANDTHS of an inch. Assuming you measured p to v when the cam was installed (as you should have) all you have to do is deduct the .005" from it and you'll know your p to v. And if you didn't measure, then all you know is you'll have about 5 thousandths less than you have now. If it's all still going together, then be sure to measure p to v properly.
giddyup306
Founding Member
- Oct 22, 2002
- 3,041
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You usually gain about .030" with 1.7's and more times than not you won't run into p/v problems. That only usually occours when you have ~300* of duration.
Michael Yount
Mustang Master
Once again guys - peak lift increases have absolutely NOTHING to do with p to v because the piston is WAY down the cylinder when the valve is open at peak lift. And you can't generalize on the durations that cause problems. Much less duration than that, for example, can cause a problem with the 86 flat top pistons, or with heads that have 2.02" intake valves. The only way to know if a particular engine/combo is ok on p to v is to measure. Even two engines with identical components can have significant differences in p to v due to tolerance stacking.
chevyboy_z28
New Member
jose, with those fly-cut pistons tho u should be ok...9 times outa 10 youll be set, but for a lil extra insurance, you could run a lil thicker head gasket. it may drop the compression a slight bit but shurely youll have that clearance. still tho you shouldnt have any problems.
chevyboy_z28
New Member
Michael Yount
Mustang Master
...running a thicker head gasket is bad way to solve any p to v problem. A thicker head gasket ruins the quench characteristics of the cylinder/chamber, and usually results in a detonation-prone engine.
He only said that cause i have fly cut pistons with th tw heads design valve reliefs at the top of the piston. Im still going to check for myself but i know i have or should have clearence, but thankz
Jo
Jo
chevyboy_z28
New Member
thats weird b/c alot of the LT1 guys will run an a set of Impala head gaskets as opposed to the stock fbody gaskets (ie the impala ones are thicker) to drop the compression slightly for a blower, etc. of course a 302 is a different engine, but the same principles apply. and surely if any detonation would occur it would be with the higher compression engine, also what do u mean it will ruin the "quench" characteristics of the cylinder/chamberMichael Yount said:
, the only change would be in p/v clearance, and actual compression. im not doubting whether what u say is right, it just isnt logically correct. elaborate a lil...hey maybe im wrong 
Michael Yount
Mustang Master
Yup - there's more to it than you think Devin. Quench is the term used to describe the piston's ability to squeeze all the air/fuel mixture from around the perimeter of the piston-to-head gap, into the combustion chamber. When that gap is bigger (e.g. - thicker head gasket), some of the fuel/air remains out of the chamber and in the 'gap', and there's less turbulent flow in the chamber. Those conditions are more likely to result in detonation - as temps/pressures build in the chamber once ignition begins, it's more likely that some of that air/fuel that's out in the quench zone, and not in the chamber, is going to self-ignite - the beginnings of the ultrasonic effects of detonation. I searched around for a layman's description -- Here's an excerpt, and then a link that goes into more detail.
"So what are the benefits of all this squishing and quenching? The benefits are small, but >> often important. Pump-gas engines that run on the ragged edge of detonation, for example, can greatly benefit from a tighter piston-to-head clearance to reduce rattle. (you get the OPPOSITE of this when you put in a thicker head gasket) That sounds contradictory since increasing compression should lead to increased detonation. All the engine builders we spoke to mentioned that tightening the quench (reducing the piston-to-head clearance) to get it under 0.050 inch will increase the static-compression ratio, but this tighter clearance also creates a more powerful squish effect. This additional turbulence creates a more homogenous “soup” in the chamber, reducing the harmful effects of lean air/fuel ratio pockets. With all other variables being equal, this contributes to creating an engine that is less prone to detonation. "
http://www.chevyhiperformance.com/techarticles/94138/
Lowering the compression ratio is absolutely a good way to allow boosted engines to run more boost, more timing, less fuel octane - and stay out of detonation. But the better way to do it is with a larger combustion chamber and tight head to piston gap. A thicker head gasket increases that head to piston gap - which makes one more prone to detonation.
"So what are the benefits of all this squishing and quenching? The benefits are small, but >> often important. Pump-gas engines that run on the ragged edge of detonation, for example, can greatly benefit from a tighter piston-to-head clearance to reduce rattle. (you get the OPPOSITE of this when you put in a thicker head gasket) That sounds contradictory since increasing compression should lead to increased detonation. All the engine builders we spoke to mentioned that tightening the quench (reducing the piston-to-head clearance) to get it under 0.050 inch will increase the static-compression ratio, but this tighter clearance also creates a more powerful squish effect. This additional turbulence creates a more homogenous “soup” in the chamber, reducing the harmful effects of lean air/fuel ratio pockets. With all other variables being equal, this contributes to creating an engine that is less prone to detonation. "
http://www.chevyhiperformance.com/techarticles/94138/
Lowering the compression ratio is absolutely a good way to allow boosted engines to run more boost, more timing, less fuel octane - and stay out of detonation. But the better way to do it is with a larger combustion chamber and tight head to piston gap. A thicker head gasket increases that head to piston gap - which makes one more prone to detonation.
chevyboy_z28
New Member
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