I have a set of 1.6 Comp Pro Mags now but am thinking about replacing them with some 1.7 Comp Hi Tech ones. What are some of the cons to running such a rocker? I'm running the Patriot Golds so the extra lift won't be a problem. Thanks for any input you might have.

 

There have been a few that have stepped up to 1.7rr and have reported gains of 10-13 more HP. I see nothing wrong with it at all just be sure you have GOOD valvesprings that can handle the added lift and most of all be sure your piston to valve clearence is adequate....

 

IMO almost all aftermarket cam grinds take into consideration that LT1 owners are going from 1.5 to 1.6, you will need to recalculate for the 1.7's and make sure you do not run into PTV clearance issues.

 

I would be careful if your not running 7/16" studs the extra leverage of the 1.7 is going to cause a lot of stress where the rocker mounts to the stud as well as on the rocker body itself.

 

I was under the impression valve timing and duration are what caused PTV issues not lift as a valve is only at full extension when the piston is at the very bottom of travel

 

Whenever you change anything or mill the heads, it is considered correct to check PTV clearence on a cam. I am not a valve timing event guru, but there plenty of grinds that are near, if not over the 0.600" lift based on a 1.6 ratio rocker.

If we break it down to.....

0.600 / 1.6 = 0.375"

0.375 X 1.7 = 0.6375"

Which may not seem like alot but some cars have tight tolerences and depending on cam lobes and actual specs, PTV should ALWAYS be verified and not Assumed.

One other point I see with HIGH lift grinds is the stress on rocker bolts, stress on pushrods, valve guides, and rockers. Is the gain worth it? I would say no. I would put a cam with more duration or more overlap before I care bout lift. I ran into that with my 383 LT1 and swapping from a LT4 Hotcam to a customer Bauer lift cam (due to emissions) 224/224 .605/.605 @ 110 and I jumped up high on the lift, lost a little duration on the exhaust and the car made like 10-15 hp more. Never ran the ET that it should have. BUT with emissions I couldnt consider GM847 or something like a 23x/24x which is what it needed. We had hoped the ported heads would take advantage of the extra lift and it did, just was not going to turn the world on fire.

 

It depends on the cam. Don't forget the effect it will have on the ramp rate. With many of todays cams already very having aggressive ramp rates, 1.7s will make it even more aggressive and harder to control the valves at high rpms. On a hydraulic roller you can only run so much seat pressure before you crush the lifter plunger, so the cam has to be made for 1.7s. On a solid roller with insane spring pressures this is not as much of an issue, since the valves are kept more under control.

This is coming straight from LE, and is the reason why I have to sell my current LE4 HR cam and have a new one specced for me.

 

The lift is very important. Many people look at the peak lift number but not the lift at the lower end of the cam. The place where it will contact is usually 5-15 degrees before and after TDC. This is where the valve is usually the closest to the piston. Peak lift has virtually nothing to do with it. Mine was the closest at 9 degrees ATDC, I was at .043 on the intake. Put a checker spring on it with the head bolted on and the cam degreed. Then put a dial indicator on the valve stem and push it down till it contacts the piston. That is your PTVC. Check this from TDC and about 20* each way ATDC,BTDC. Talk to your cam/valvetrain company and they will recommend a PTVC number. Hydraulics are usually in the .100-.125 minimum area.

 

Agreed, I was going to say the same thing. I contacted Lloyd about running 1.7's with my current cam and he said the ramp rate was too great on the cam to run them. Best bet would be to give him a shout.

 

how about 1.7's with the hot cam?

 

I don't see a problem with that.

 

What do you think the hot cam with trickflow 21* heads and 1.7 rr's will put down With 11/1 compression with all the bolton's?

 

340-ish with your stalled auto unlocked, just a guess. Dyno's don't show accurate numbers on stalled cars so I wouldn't even think or worry about numbers, all about track times.

http://forums.land-and-sea.com/showthread.php?t=567

BTW: Tuned I put down 362rwhp with my stall locked. Before tuning with the stall locked I put down 353rwhp and went straight to the track and did 11.80's at 114 just like the 6-speeds with 390-400rwhp. That's how much stalled auto dyno numbers mean lol.

 

I sure hope I get more than 20 rwhp from a nice set of heads and a 1.7 rocker swap. I put down 318 cam only through my stalled auto with no electric water pump and stock TB

 

Was the converter unlocked or locked for those pulls?

Just a guess, only one way to truly find out!

 

Like said I am not a Guru but for me and the aft formentioned post about ramping rates, I would take a cam in the .580-.590's all day with compared to something in the .625's as it beats up the valve guides and controlling the valve can be a PITA if you still wish to run Hydraulic lifters.

Stick w/ the tried and true method of 1.6's and have the cam ground differently if you feel that you "need" more lift.

On stock or up to a hotcam I would not be opposed to 1.7's but compared to larger or custom cams, stick with what works. In most cases heads have a 23 deg. valve which is ultimately the issue, I hear there is new stuff coming out but I dont follow it as much as I used to. To me that is worth all the $$$

 

It made 300 unlocked and 318 locked and 461 unlocked on a 150 shot with a pcmforless tune pulling 12 degrees of timing

 

Well I guess I'll ask Lloyd about the lobes that Joe O used for the cam. I have a feeling they might be a little aggressive. The lift would go from .544 to .578 so no problems there with the Patriot Golds. I appreciate the comments so far. Feel free to add any more concerns I might encounter. Thanks again, Rick.

 

The real question is why would you run a hotcam with 21* TFS heads? Not enough cam to take advantage of those heads and won't perform any better then ported stockers.

 

My guess of 340 was unlocked. I think my guess is probaly pretty close because 40rwhp with the heads and completion of bolt-ons seems about right atleast to me. So locked my guess is 360. If you were to ditch the hotcam for a nice custom grind in the mid 220's on the intake and low to mid 230's exhaust you could probaly add another 20 or so to that.