stevesxm

if you were to do nothing at all other than replace the stock rockers on a 502 mag mpi with 1.8 roller rockers, what would you expect to see for a gain ? just trying to do a cost/benefit analysis...

1BIGJIM

iTrader: (1)

Just as a warning, I tried this a couple years ago. On my application the push rod rubbed against the bottom of the guide plate. I ended up not taking the chance for a couple of HP.

stevesxm

why didn't you just clearance it ?

Griff

IMO, Not worth it.

1BIGJIM

iTrader: (1)

Actually I started grinding down the guide plate and just decided it was to much work for the unknown. My engine was not stock, and I also did not want to take the chance of hitting a piston with a valve.

Even if you gained 15 hp you probably would not even notice it. Over my 30+ years I have tried almost everything I thought would make more HP CHEAP. As I get older I started to realize there are no short cuts.

jeff1000man

YEP

stevesxm

well... cheap is a relative term. i have seen two back to back test session done and published that showed about a 5 % net gain. from a " stock" 350 chevy motor with some work done at 390 hp to 402 with the addition of just the rollers , to 412 with the rollers plus the added ratio. thats 22 hp over 390 or about 5.6 % . now assuming that the heads and intake on this motor don't flow at the maximum with the existing cam which we actually do know to be true, then the added lift and reduction in friction should yield a similar sort of gain... or about 24 hp. at about 400 bucks to do it with no loss of reliabilty and a significant increase in efficiency thats less than 16 bucks a hp. not a bad trade off. and my guess ( and i mean guess ) is that this motor is likely to respond a little better to this than the one s i read about because this cam is milder and likely to react better to the slightly better lift and duration...

at any rate, thats my theory but thats why i was asking someone like bill who would be authoratative on the subject.

jeff1000man

You were stating no loss of reliabilty etc. If you are increasing the amount that you are flexing the spring from where it was desgined, you are decreasing it's lifespan. You shouldn't have a piston clearance problem, since those are flat top pistons. Since this is also not a carbed engine you are going to have a leaning problem and since the only way you are going to see the HP gain is to rev it more, I am saying this is just like pissing in the wind, but some guys have to learn the hard way.

we have guys asking questions like this all the time on this board using research from a street engine or a small block or something that is irrevelvant to what we do in the marine environment.

What we were saying is that the HP gain you are talking about 415-435 is not going to Net anything except wasted money, shorter lifespan on a valvetrain that no one knows the hours on, and a potential problem. Your not going to gain anything except a conversation and a little speed when you are out of gas at the end of the day and headed for the pump.

Good luck anyway though since you seem to be convinced.

Don't forget to check your springs to make sure that they are not in a bind from opening a little further than they were installed to do.

jeff1000man

I have tried this experiment with a 1.76 one time, but it had no effect on the overall performance of the boat, and the springs were set to the adjustment. I didn't just change it the way it was.

Griff

12 of the HP is just from the switch to rollers. Also, SBC's turn a lot more RPMs than BBC's. There may be big difference in the gain between 5000rpms and 6500rpms. That has to be taken into consideration.

As far as clearancing guide plates.......My machine shop said they wouldn't even redrill the holes bigger because the steel the paltes are made of was so extremely hard.