My father-in-law said he would buy a set of roller rockers for my 383. The question is, which size to get? My choices are -

all 1.5's
1.6 int & 1.5 exh
or all 1.6's

My cam is hydraulic, non-roller. Specs are -

int exh
214 224 0.50 dur
440 460 Lift (1.5)
112 Lobe center

No intake work other then removeing the air dams behind the butterflies. Screens will be removed and lid cut. Cast iron heads with intake and exhaust ported and polished with 2.02" intake valves. Stock exhaust. I also have 19# Ford/Bosch yellow top fuel injectors.

 

It depends on the intake to exhaust flow ratio of the heads. I like to use mid-70s and the determining factor.

It's the exhaust flow that's the real bottle-neck. that's why so many cams you see advertised are split-duration cams, to prop up the exhaust flow.

If the exhausts flow mid 70s (percentage wise) of what the intakes flow, go with the same duration on both intake and exhaust. 1.5/1.5 or 1.6/1.6 With the 1.6/1.6 you'll have slightly less vacuum and the idle will be raunchier because of the increase in duration and overlap the higher ratio rockers create.

If the exhaust flows less than the mid 70s, go with split ratio rockers and put the higher ratio on the exhaust. 1.5/1.6

Another consideration is how restrictive your exhaust system is. With a stock setup, definitely run 1.6s on the exhaust. With full-length headers, gutted or no CAT and free flowing mufflers, let the exhaust port flow of the heads determine the rocker ratio.

Make sure your springs can handle the additional lift that 1.6s will give too. With 1.6s, you'll increase valve lift in the area of .030".

Just my thinking.

Jake

 

Get a full set of 1.6's and see whether the engine prefers the split-ratio or not.

Your cam already favors the exhaust with 10* @ .050 and some lift, so maybe you'll do better with 1.6 on both...but there's only one way to know.

 

If the iron heads use stock style holes to guide the push rods you will need to machine the heads to use rockers with ratio greater than the stock 1.5:1.

 

Excellent Point! I completely missed the cast iron head part in his original post.

Yes, if your heads have slots that the pushrods go through they'll need to be elongated if you opt for 1.6s.

I ended up with a handfull of bent exhaust pushrods when I didn't check to verify that the machine shop elongated both the intakes and the exhausts.

All the bent pushrods were exhaust and I ended up having to pull the heads AGAIN to have those slots elongated since the shop had only done the intakes.

One more point, you may also need screw-in studs if you're currently running the press-in variety. The press-in studs have been known to often pull out.

Jake

 

The heads have screw-in studs and guideplates. I don't think I will have a problem with the pushrods. The heads were done by a guy that has been building high perofrmance race engines for the last 35 years. The heads were just refreshed a little bit ago and the springs should be able to handle the rockers. I am going to go back to the guy that just refreshed them and make sure.

I allready have a set of Crower 1.5 roller rockers. There shouldn't be any problem mixing rockers from two different manufacturers would there?

 

[SNIP=Insane1]
I allready have a set of Crower 1.5 roller rockers. There shouldn't be any problem mixing rockers from two different manufacturers would there?[/SNIP]

Not a problem.

Jake

 

Nope, those valves couldn't care less!

 

Since the heads are no problem and you have a non roller cam going to even 1.7:1 RRs would be a good way to increase effective cam intensity. Since valve lift with 1.7:1 RRs would be around .52" you could still use single springs with dampers.

With stock iron heads mixing rockers is preferred for smooth idle but with your heads 1.7s on int & exh would be preferred.

Ask your machinest if you need to upgrade the springs for that much lift. If so TPIS makes a spring that will handle it.

 

Not trying to be a jerk or anything but it seems every shop has a guy thats been building "high performance" engines for a number of years.

Just saying you can never be too careful, and never take anyone who you are doing business with fully on their word without prior reasons to trust them.

 

Except in this case he is the owner of the shop and I have seen many of his race engines running at the local track. I have known him for at least 23 of those years

I tell you what, he can sure wake up a little Ford Pinto motor with his head work on there. Those little pony cars go around a 3/8's mile track almost as fast as our street stocks can!

Oh, one other thing I forgot to mention. Hope this doesn't throw a monkey wrench in the works but this motor also has to pass Ca. smog laws.

 

With that cam on a 383 you should be able to go with 1.7:1 RRs and still easily pass the sniffer.

Remember, you don't need an EO number on parts that are in side the engine.