Ive got stock mid 80s heads now. Found a set of cobra gt40 heads with 1.7 rockers on craigslist for 350. Will I be able to use my stock pushrods? Any concerns with the 1.7 rockers? I'm not valve train edumacated. Mid 80s 306 Mild 484 lift erson cam Torker I intake Long tube headers 3 speed 4.10 gears
And also I'm not dead set on gt40s either. Anyone have any good gead suggestions for a cheap 300-330hp setup. Flywheel hp
Those are the ones you want. Make sure they are not P heads (four bars on front of Ps, 3 bars on front of non-P heads). The P heads have spark plug angles that interfere with the exhaust. Ps on top, regular GT40 on bottom, for comparison. Good for an easy 300-350 hp if you use the correct cam. Stock pushrods will work, but these are made stock for roller cams. Make sure you have springs that are compatible with your cam. Ask the guy what cam he was using, and you may have to swap springs out to make it compatible with your cam. Cheap, probably under $50 to swap springs.
I'm familiar with the 3 bar and 4 bar. He had a roller setup with a stock mustang cam. Springs are stock which shouldnt be terrible with my mild cam. Not sure if the 1.7 rockers will give me a fit though.
Should be OK. I ran 1.7 rockers on a flat tappet Edelbrock Performer Plus cam clone, with stock pushrods, and it ran great, but eventually ate the cam lobe due to the roller cam springs. If you are running a mild roller cam, the stock springs and 1.7 should be fine. Like always, every engine is different, so measure piston/valve clearance and verify you have no issues. It will be a fairly fun engine in the 300+/- hp range. I am still running the GT40 heads, but with a little bit more aggressive cam, and it is plenty fast for me.
Just a little word of cautionary advice here.. do NOT use stock spring pressures on any performance cam. And that rule applies even moreso as you start upping rocker ratios which causes valve and spring acceleration to increase in the process of adding lift with the higher ratio. Adding even .1 ratio to a rocker has the same exact affect as adding faster ramp rates and more lobe lift which ultimately requires about 10-15% increase in spring pressure over the stock ratio. Running 80 lbs of seat pressure would be a big mistake while trying to toss over 100 gram valves around at 6,000+ rpm with higher ratios. To add even more detail.. most people don;t realize that stock springs are a major part of the reason that factory cams fall over cliffs when over-revved. Basically, an engine doesn't have to severely float valves to the point of popping and backfiring in all directions.. or even bend valves.. to cause major power dives because they can easily bleed off cylinder pressures in a much more subtle fashion to make you think that the cam is just done. This is why rev kits can be so effective and reduce the need for excessive spring pressures as they help control the valve action much better. IMO, both of you guys should be running at least 110 lbs of seat pressure with 1.7 rockers and mid-range cams. Scoop's more aggressive grind could very well do with closer to 125'ish lbs. Also keep in mind that most cheaper entry level springs lose around 10% of their rated pressures within the first year too.
I've run the stock roller springs with 1.7 rockers in several 302's and 351's with zero problems. But if you're gonna rev it past 5 grand or so, then better springs wouldn't be a bad idea.
I would ck the push rods for correct length.A 1.7 will have a sharper angle than a 1.6,& if the rocker does`nt stay centered on the valve,this WILL cause excessive guide wear & you WILL soon be burning oil.(Just a word to the wise.)
Specs on my springs. DUAL W/DAMPER 1.440 Seat pressure 135# @1.800" Open pressure 320# @1.200" Coil Bind 1.125 Max Lift 0.600
Just a refresher on this. I pick up the heads todsy and drop them off at the machine shop tomorrow to work out a set of springs. Has anyone done gt40 heads with 1.7 rockers with flat tops w/ reliefs? Worried about clearance issue. Decided to be safe and get my hands on a pushrod length checker to see what I need.......if I can figure out how to use it Lmao.....
That is EXACTLY my setup. Mine might be 1.72, but not much difference. Ended up with around 9.5:1 compression and PLENTY of clearance. There is a lot of room for growth on my engine. Here are my pistons... Details of my build are here... http://scooper77515.fordmaverick.net/november2007.htm If your cam does not have a smaller base circle, stock pushrods will work. I used stock on all of my cylinders, but there was a slight lash at the top of the exhaust, which had a smaller base circle. I measured my lash and bought Comp lash caps P# 621-16 which are .080" thick. Before you bash the fact that I used lash caps rather than buying .080" longer pushrods, remember that the stock 302 came with lash caps.
Good to know. Just picked up the heads. It has crane 1.72 roller rockers. Looks like we have the same setup except I have a flat tappet setup and yours appears to be a roller.
How much lash should I have? I'm guessing I'll need a flat bar to mark the pushrod level with the head at 0 lash and then torque down and remark. Measure distance between two marks and that is my lash value?
