Discuss Head Work

[marcz2893]

So i was thinking about doing some head work on my lt1 when i do the headers and ORY. I was thinking about 1.7" roller rockers, but I've heard that will need new springs, pushrods, valve covers and some additional mods. Has anyone had any expirience with this or know what exactly this upgrade will need? Also would there be any of this work for 1.6" roller rockers? Any help would be appreciative.

[Viper]

are 1.6 rocker arms worth it? read more inside

Rocker Arms 101 - Everything You Need To Know - Vette Magazine

[marcz2893]

Ok so the springs used in the aritcle are rated for .600 lift. with 1.7"RRs that will generate .595" of lift. So i would need even beefier springs. but this did help alot! thanks.

[Dynamic396]

If you also change to springs that will support it, I'd run 1.7's, no problem. You'll pick up a decent little gain from it without affecting much else. The LT1 springs suck anyway, so you'll want better ones anyway. I would also switch to 7/16" rocker studs at the same time. Assuming you have a stock camshaft, you won't be anywhere near .595" lift with 1.7 rockers, so don't worry about that.

The one thing that I will also say is that if you plan on upgrading your camshaft later down the road (highly recommended), 1.7's would be extremely aggressive on most of the common grinds that guys are using in the LT1's. I say that to keep you from having to buy another set of lesser ratio rockers later on to make reliable use of a better cam later on.

[marcz2893]

Originally Posted by Dynamic396

If you also change to springs that will support it, I'd run 1.7's, no problem. You'll pick up a decent little gain from it without affecting much else. The LT1 springs suck anyway, so you'll want better ones anyway. I would also switch to 7/16" rocker studs at the same time. Assuming you have a stock camshaft, you won't be anywhere near .595" lift with 1.7 rockers, so don't worry about that.

The one thing that I will also say is that if you plan on upgrading your camshaft later down the road (highly recommended), 1.7's would be extremely aggressive on most of the common grinds that guys are using in the LT1's. I say that to keep you from having to buy another set of lesser ratio rockers later on to make reliable use of a better cam later on.

ok that helps alot. So just to be clear, 1.7" is too much for a bigger cam? (that i will be doing in the future), as of right now i just have time and money for a bolt on setup. Would 1.6" be better then? Also, would u recomend any specific manufacturer or site for the rockers and springs?

[ShowNoMercy]

I would stick with a 1.6 rocker unless you are 100% you won't get a cam later on. As pointed out, with a aftermarket cam you don't need the added lift from a 1.7 and it becomes overly aggresive.

I like comp cam pro mags, I believe they have been superseded by the new ultra pro mags, also great rockers. A steel full roller rocker will always be a little louder than a aluminum rocker, but I like steel. It makes me feel safer.

Lately I do quick google searches for cheapest price and then give it to Summit for them to match/beat.

[marcz2893]

ok, and yea there will be an engine rebuild once i get out of school. thanks for the help

[Dynamic396]

Most guys are using camshafts ground with the Comp XFI lobes, either off-the-shelf, or custom grinds, and I have nothing at all against them. They just have very aggressive ramp rates and are very "square" over the nose. It takes some careful valve train parts selection and setup to make them work well (and reliably). You would really be pushing things, in my opinion, to run a 1.7 rocker with an XFI lobe in a street application. They were designed around 1.6 rockers and beehive springs with their lighter retainers - and work very well with them.

The other thing that comes into play here is that you really don't NEED 1.7 rockers with stock heads and a decent camshaft. Even the best ported stock head is not going to make use of the additional lift of a 1.7, so at that point, you're just adding additional stress on your valve train, with little or no benefit from it.

I chose to use 1.7 rockers on my current 396 build, but it was carefully planned. I am intentionally using a camshaft (GM847) with slightly less aggressive lobes over the nose (duration at .200" tappet lift), but with a little more lift, as compared to a comparable XFI lobe. I am also using AFR 210 heads that continue to flow crazy numbers to well over .650" lift, so I wanted the extra lift that a 1.7 would provide to feed those extra cubes. Plus, I'm using $400 Pacaloy valve springs, titanium retainers and extremely lightweight valves to control those very fast opening rates.

Everything has to be a carefully planned package...

[95 Firehawk]

I mostly agree with what was said about 1.7's, however a 1.7 can be used with aggressive lobes so long as you aren't planning to spin the motor so high. A 1.7 will lift the valve 6.25% higher in the same amount of time as a 1.6 (faster acceleration), and also apply 6.25% more force on the pushrod side of the rocker (F=MA), if they're both at the same rpm. If you slow the valve train down by the same amount that the rocker adds, you will get the same acceleration and force on the valve train. So if a said valve train can handle 1.6s at 6800 rpm, the same valve train will apply the same forces as 1.7s at 6400 rpm (6400 x 1.0625 = 6800). Like Dynamic said, everything has to be planned properly. If you choose a cam that needs higher rpms, you will be pushing it with 1.7s, but if you choose a cam that you will be shifting closer to 6200, you will be fine with 1.7s, even with aggressive lobes (with proper supporting components, of course).

As mentioned, this also goes hand in hand with the heads you are using. Makes no sense to have the additional lift (and stress) if your heads can't take advantage of it.


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[marcz2893]

SO with the 1.7" RR i realize that it will limit my options. But for now with the stock cam, would 1.6" be worth it? Getting the 1.7"s, FOR NOW, i think is my best choice, in the future with a cam, i know it will take a specific cam/lobe type, but i'm prepared for that.

[Dynamic396]

Originally Posted by marcz2893

SO with the 1.7" RR i realize that it will limit my options. But for now with the stock cam, would 1.6" be worth it? Getting the 1.7"s, FOR NOW, i think is my best choice, in the future with a cam, i know it will take a specific cam/lobe type, but i'm prepared for that.

I wouldn't hesitate to run 1.7's on a stock camshaft if you put a good set of studs, springs and retainers on it, too. They'll put you at around .510"/.521" lift and you'll pick up a degree or two more effective duration at the valve. Not a bad mod for a couple of hours with the valve covers off, really. But, down the road, it will definitely limit your choices, especially if you intend to stay with stock heads.

Sure, you could limit rpm to keep valve train forces in check if you wanted to run an XFI-like lobe profile like Firehawk was saying, but why...? The reason you're putting the camshaft in there in the first place is so that you can spin it a bit and make some power up top. Plus, even with the 1.6 rockers that they were designed for, the XFI's, for the most part, are generating lift numbers that a stock head will never make full use of this side of hundreds of hours of porting, valve and flow bench work. And all for what...? Buy a set of good heads and move on.

Don't get me wrong. I'm not saying that 1.7's can't be run with a large camshaft. Heck, I'm doing it...! But, you'll just have to be very careful with valvetrain component selection to make sure you haven't created a ticking time bomb. Plus, evaluate what you will have in the end. If you take two of the middle-of-the-road XFI grinds for the LT1, the 268 and the 280, you'll see that with the recommended 1.6 rockers the 268 has lift specs of .570"/.565" and the 280 has lift specs of .576"/.570". To make even moderate use of these lift specs on a stock head, it will require some pretty extensive porting and valve work. Now you add the 1.7 rockers and your 268 is now .606"/.600" and your 280 is now .612"/.606". Even with a proper set of springs, retainers, valvetrain geometry and everything it will take to make it hold together, there's no way that a stock head will make use of these numbers, no matter what you do to it.

I'm not trying to beat up on the XFI grinds. They are good cams, and work well in the right setup. They are just very aggressive over the nose, making valve control a big issue when using them. Adding 1.7 rockers just makes things that much worse, and unnecessarily, I would argue.

Having said all of this, if you wanted to run 1.7's, you could simply have a camshaft custom ground to match your 1.7's when the time came for a cam swap. The cam grinder that I use has over 8500 cam profiles to choose from, so spec'ing out the perfect cam is not hard to do.

[marcz2893]

maybe i'll hold back for now. get the cam heads and valve train as a package and do the entire top end as a unit. at least then i am not matching parts based on what i already have but a designed unit. thanks for all the help dudes, and hopefully faster times r in the near future.