My next engine mod will most likely be 1.6RR's, but I have one question.

What do they do to the TQ curve? (With the stock cam)

I know that they add more lift, and I know that more lift generally makes the TQ curve more peaky. So does the low end and very high end TQ suffer in favor of a higher peak TQ in the middle RPM? Or do the low and high RPM stay the same and the curve is just raised between those points... Or is it something else entirely.

Please help. I would like this answered and I won't order the RR's until I know what it will do to my curve.

Thanks in advance,
Dan

 

Sorry but I cant see moving to 1.6 rr's doing a "in your seat" difference in your car. I think if anything it will free up some hp, somthing around 10-20hp. Useually thats not a big enough difference that you will feel.

Added lift will probably, help you uptop in the power band more then anything. So I wouldnt worry about it impacting your torque curve.

Great mod. Let us know how it goes.

Mike

 

Well, I'll take another 10-20 hp.

I'm just looking for real data that people have seen when adding 1.6 RR's to a stock cam. My thoughts are that it is going to slightly hurt the low end and high end in favor of the midrange, but maybe the LT1 reacts differently than most small blocks.

Dan

 

Anyone?

Thanks,
Dan

 

You're pretty close to the mark Dan.

Expect low speed torque (below 3000rpm) to drop a tad, but from there on up the engine will be stronger.

You're always robbing from Peter to pay Paul with engine stuff. Just have to decide if under 3000rpm or 3000rpm and up is more important to you.

-Mindgame

 

Thanks Mindgame. I figured it must do something like that because with all the aftermarket cams and 1.6 RR's, the TQ curve definately has a more curved shape. It's like duration shifts the curve left to right, and the rockers (or lift) define how peaky the curve is.

I can understand that having the higher lift will help with breathing up top, which is certainly needed on the stock LT1 with such a "stump puller" stock cam. I think I could sacrifice a little low end. I have plenty to spare. More top end sure would be nice at the track since I never drop below 4000 RPM after 1st gear WOT.

I'm assuming that the loss of low end TQ is due to the slightly larger overlap between the intake/exhaust valves allowing more unburnt fuel to escape into the exhaust?

Thanks,
Dan

 

You'll get a pretty even power increase. Adding duration is what hurts low end, not necessarily adding more lift. 1.6's do add a slight amount of duration (amount of time the valves are open) due to the valve opening wider. Don't expect any real losses in low end with 1.6's.

BTW, a pcmforless or madz28 tune would wake your car up about as much as 1.6's would, especially if you're still running rich like you were on the dyno run. Might want to get a tune first before rockers.

Jason

 

Agreed, the term "loss" is vague in my previous explanation.

Very small and likely not even noticable to you.

-Mindgame

 

Can 1.6 RR be run on stock springs?

 

Yes, just check your clearances... especially coil bind!

Also keep in mind that you are accelerating the valve quicker now which means you need that much more control of the valve. The springs may work fine for a while, but your best bet is a new spring or a shimming to get a bit more pressure.

Also consider the mileage on your current springs. May be best to change them out while you're there.

-Mindgame

 

Well right now my car has 24k miles its a 96 though but just wasn't driven much. I was looking to get the Gold self alligning ones i believe they are from Crane or Comp not sure. I'm planning on having the heads port/polished and the springs and valves changed anyway during the winter when the car is hibernating and i was going to do a cam swap along with that. I just figured if i'll get the roller rockers then i might as well get them now since its a fairly simple bolt on.

 

Actually, I have a madz28 tune. The tune was already in my PCm when I dynoed. I'm running rich with the tune. I need to get it reprogrammed again to get it straightened out.

I don't know if this makes sense, but I think I'm actually running lean at partial throttle, and that is causing my PCM to add too much fuel during WOT because the car is too lean during partial throttle.

Dan

 

I have 1.6's with a stock cam. I don't have a baseline dyno graph
but you can see the graph w/1/6's in my sig.

 

I haven't dynoed it since I put my rockers on but I know it picked up 4 mph in the 1/4. I was sold.

 

Going to 1.6 rockers will not affect duration. Valve events will still occur at the same point of crank rotation.
I noticed no loss of low end but I did notice a gain in mid/high rpms.