1.7 rockers with renix cam?

[mendelmax]

Hi guys.

I'm considering getting 1.7 rockers, to install them on a renix cam, stock 7120 head on a 0.040 overbored stroker.

Now, would changing these rockers require changing springs also, or could I leave stock ones? The cam profile seems to be pretty mild, so I think that might work, but I would like to hear your opinions.

The reason for doing it this way is that I would like to have some more aggressive cam timing, but I don't want to remove engine and disassemble it (lack of time). So I thought that this seems like a nice bolt-on that could fix some problems with my friends motor (low compression + mild cam + long cam duration = suks at high RPM).

Any thoughts?

[TurboTom]

1.7 rockers won't really change anything but the lift. It will change the duration very slightly, but not the same as a cam change.

Your statement on your friends engine seems backwards

[SilverXJ]

x2 on TurboTom's post

[mendelmax]

Yeah, I know it will only change lift, but considering how mild the profile is, it seems that for a long time the valve is open but it's flow sucks, that's what I meant in my "reverse statement".

1.7 vs. 1.6 means about 5% more lift at all angles.

[gradon]

I say go for it if you're gonna buy RRs anyways. Do you feel like pulling off the timing cover and advancing the cam a few degrees(less o-lap, more dcr comp=more low end torque, less top end hp)?

[mendelmax]

Yeah, timing advance is also on "to do" list. I believe it's far too retarded, because whole torque curve on the dyno suffers. I plan to advance it about 4* (one teeth) and check on the dyno how it changed the characteristics. I strongly believe, that it can give me more HP (long story), though theoretically it should promote torque at cost of HP. We'll see if my thinking is right.

The main problem is that the rig has a bumper welded to the body, so I can't change whole cam with the engine inside, but I can take the timing cover off and play with the chain. That's why I'd rather take these 1.7 rockers than a cam change. This would also move the 0.050" lift further, so that despite cam advance, the 0.050 IVC could remain in the same place, meaning no HP loss due to cam advance.



The only important question here is whether stock valve springs will work with renix cam nad 1.7 rockers. Anyone knows for sure or at least has some thoughts on that? I'll just add, that it has auto tranny, so it probably won't ever run higher than 4600 rpm.

[gradon]

The 87-95 cam is .424" lift in/ex. Using the 1.7s will change that to .451". The stock springs are good to .43" lift, so it looks like throwing on the 1.7s can't be done w/o a spring change. . . Sorry about the earlier "go for it".

[mendelmax]

hmm, these are not good news

I guess I'll have to do it the proper way then...

But here again a question rises- assuming the funds are limited, would you choose:
a) renix cam + performance springs + 1.7 roller rockers
b) sport cam (ex. compcams) + performance springs + stock rockers

[lafrad]

I would guess, with all the other precautions most people are taking on these forums, that the stock rockers and a performance cam are NOT a good combination...

[mendelmax]

That's exactly what I thought. I'm afraid, that with the extra friction the valve stems could bent easily with the performance style cam and stock rockers. And getting a cam + springs + rockers = 700-900 USD + shipping to europe and 25% tax. That's a hell lot of money for this kind of upgrade...

[lafrad]

start with reneix cam, stock rockers, and performance springs.

Upgrade from there when funds become available

[lafrad]

FWIW... I'm doing something like that... aftermarket cam, stock rockers, performance springs... with a 1.7RR upgrade in a few months....

[mendelmax]

start with reneix cam, stock rockers, and performance springs.

Upgrade from there when funds become available

I guess that will be a way to go. We already got a 0331 head to replace current 7120 (we got it almost for free, so that's why we took it despite the crack risk), so I will persuade my friend to fit some performance springs there before installation.

Now the question is- what type of springs to use, and what seat pressure will be fine for this setup? Any recommendations? I guess that the seat pressure should be lower than with typical performance cam, since pushrod inertia is smaller, and the profile still won't be too wild... Am I right?

FWIW... I'm doing something like that... aftermarket cam, stock rockers, performance springs... with a 1.7RR upgrade in a few months....

What cam are you going to use? Aren't you affraid of using both high-ratio rockers and a performance cam? Won't you damage the cam/pushrods with the extra pressure?
I've seen so many people complaining about cam failure, that adding extra 5% stress seems risky...

[gradon]

P5249464. See if Advance Auto can still get them for $8 a pop.

[lafrad]

I'm going to be going with Stock valves, retainers, locks, and the Crower "beehive" springs: http://www.jeepstrokers.com/forum/viewt ... f=5&t=1433

They have a significant "bump" at the seat pressure, but the spring rate is extremely conservative and the pressure at max lift isn't much more than stock. This should be kinder/gentler on the most stressful part of the cam (the max lift/sharpest radius) while controlling the valvetrain much better overall throughout the whole travel. Since the max load on the valvetrain won't be much greater than stock to start with (30# at peak lift), most of the stock components should be fine. the *ONLY* thing I'm worried about is the extra stress on the valves on set down. I guess thats the chance I take.

The springs also have up to 0.550 - 0.600 lift available on stock install height (depending on who you talk to about coil bind safety) so there is plenty of room on them for a 1.7RR swap.... that adds 10-20 lbs at "open" pressure to the valvespring... a little more to the cam... hopefully its well broken in by then