Hi, I had hardened 7.8" pushrods in my Chevy 350 V8 with camel hump heads and a Luminati cam
I upgraded the heads to Aluminium race heads with +100 valves and the engine builder put my same old push rods back in.
I have a new cam shaft which is almost the same spec as my old one but it is an XE268 Comp Cams Camshaft this time.
The performance is dire and it really lacks power. So I'm wondering if it is because the pushrods are too short.
Given that the valves are +100 on my new heads does that mean the pushrods should be 7.8 inches plus 100mm?
That would be approx 8.2" long, but I can only see Ford pushrods that length, Chevy ones are either shorter or much longer?
Can anyone help me?
Looking at the Summit Racing website it seems that +100 pushrods are actually 7.9" long is this right?
I would want hardened ones for use with guide plates
Its 100thou, not 100mm, you would need some fkn tall valve covers for +100mm on a pushrod .:lol:
Is it stock stamped steel rockers on a hyd cam?, is gross valve lift the same as the old cam?
You need to know if you have the desired valve/piston clearance with a duration/lift/cam change, you cannot guess here, that's why there is a cam spec card in the cam kit
Sounds like the valve stems are 100thou longer in the heads which, IIRC the lifters only have a work parameter of 20thou hence the reason for pushrod "trimming"
I was just thinking logically, if standard pushrods are 7.8" and my new heads have +100 valves in them, then running the engine with 7.8 pushrods is going to massively restrict the performance of the engine isn't it?
is that how it works, it would require +100 pushrods to match the +100 valves?
Or are you saying that having +100 valves requires shorter pushrods to compensate?
All else being equal, you'd do best to have +.100" pushrods.
As it is now, it wont make a massive difference as long as the rockers are adjusted to get the right lifter preload -and as long as there IS enough adjustment!. But it will wear valves & guides out faster if rocker geometry is wrong and performance will be mildly affected.
I would guess though that this isn't going to be the whole cause of poor performance.
No it soundn’t affect performance as they would have been adjusted to the correct lash. It just means the rocker won’t sit in the Correct place on the valve tip.
In a modded engine there are too many variables, the correct push rod length is the one that rolls the rocker across the valve top an equal amount (i.e doesn’t get too close to falling off one side. ). You do this but spinning the engine over manually with an adjustable push rod taking into account the lifter spring. You can then adjust the pushrod to get the correct ‘roll’ over the tip. That is then your correct pushrod length whatever that is.
Did your builder actually measure what pushrod was needed or did he just use what was there and not measure...?
Ive built loads of Chevy’s and never needed anything other than standard length or +100
Quick check, loosen one rocker and clean top of valve & rocker face with thinners etc. Cover valve stem with a marker pen/sharpie ink etc and refit rocker and adjust lash.
Turn engine over either by hand or starter for 2 or 3 turns only. Loosen rocker again and see where the clean patch is on the valve stem.
If it's in the middle than all is well. If its towards the rocker arm stud you need a longer pushrod, if its nearer the exhaust side you need a shorter pushrod. This is where an adjustable pushrod is needed, you adjust the length until you get the correct wear pattern, then measure the pushrod for length. Order a new set of rods in whatever length you have measured.
If the valves are 100thou longer you need a shorter pushrod . You only have 20thou of free float in a hyd lifter..."you" have stolen that +80thou because of the longer valves, if you slacken the rocker arm to compensate...you have just done that, compensate, its a band aid in my World.
Rocker geometry is important, but won't on its own be responsible for really poor performance. Was the camshaft dialled in, or was it just installed by using the timing marks?
I paid a mechanic to fit the new camshaft and new lifters and new heads for me. I believe that he dialled the camshaft in, but I don't know if it was dialled in for horsepower top end, or for torque low end (which I would prefer).
I didnt actually want the new camshaft I had a Lunati performance cam with a big lope before that sounded amazing and had really powerful performance,
but one of my camel hump heads had a crack and it was over heating and I had blown a head gasket, I originally went to him to fix a blown head gasket and he wanted me to do a full engine rebuild.
I didnt have the money, but because of the cracked head I needed new heads, he then told me that the engine would never run again unless I put a new camshaft in it because 2 of the lobes were worn.
I would also need new lifters etc... He was still trying to push me to tear down and full y rebuild the engine, but I didnt have the money.
As it was he tried to charge me about 4 times what he had quoted to start with. And I ended up also having to buy a Com Cams Extreme Energy EX268 Camshaft, new Aluminium race heads and new lifters and new head studs. (He said that head bolts were not long enough.)
He reused my old pushrods which are 7.8" and the old standard Chevy 350 rocker arms.
Before despite over heating due to the cracked head, the wheels would spin every time you touched the throttle and the limited slip dif would leave 2 black lines on the road.
After the work it doesnt wheel spin barely at all... It should have had more power after the work not less... But he doesnt want to know he said that if I couldn't afford a full engine rebuild then it is my problem not his.