1.5 or 1.6 ratio on new RPM heads?

[wsutard]

Since I am ordering all new parts for my Performer RPM 440 heads should I consider going with a 1.6 ratio over a 1.5? If I do go with 1.6 would I need to change my cam and spring selection of Comp Cams XE285HL and Comp springs?

I'm sure this has been debated on here before, I just couldn't find it in the search.

These heads are going on a fresh 440 street build looking to punch +500HP/TQ. No racing. I am going to have my machine shop spend $500-$600 on porting and polishing my heads.

My thought process is that it seems like it wouldn't be too much more to go with 1.6 vs 1.5 since I have to order the entire valve train.

Is the work required to use a 1.6 ratio on RPM heads so much that it makes it not feasible?

Cost is a big factor, I'm not going to skim on things but I will try to get the best deal possible, evidence the new RPM bare heads I purchased for $250 each.

OK, school away.

 

[wyrmrider]

Does that cam use Comps newer MOPAR size lifter design- check durations and list against comp's online lobe catalog
I'd use 1.6 on the intake only
one problem with roller rockers is that the fulcurm sits too low
do the mid lift drill and see- you will need spacers under the fulcurms, longer bolts and longer pushrods
I'd use oil through the pushrods pushrods to oil the ball and cup
rockers with a cup on the adjuster with ball and ball pushrods work better
have you checked out cnc programs for those heads or is your machine shop set up with a flow bench and has experience on those heads
what flows do you expect- given the flows you may want to adjust the cam,, size and lobe spread- centerline
power is in the heads, duration sets your rpm range with bigger heads you may not need the duration or have to rethink gears, converter etc
get your compression, intake and exhaust info together
on the street you need tight quench- do not ignore this or the rest is futile
with a race BBM you can use race gas and keep the rpm way up- pinging on the street is a disaster

 

[lewtot184]

if check any 1.5's you buy they'll probably measure at or very close to 1.6. 1.6's will go around 1.65. all this needs to be compensated for with the valve springs and higher ratios have negative effects on aggressive cam profiles and break-in. the 1.5's may yield close to .580 at the valve. so what does that do to springs? it's all a stack up of stuff and has to be thought thru. going to a higher ratio rocker may only yield 5-6hp.

 

[plymouthman72]

I am not sure if the big blocks suffer from this but on my 340 small block, I had to machine out the push rod holes on my rpm heads when I went to my 1.6 rockers as they wouldn't clear the sides due to the change in angle. just something to keep in mind.

 

[wyrmrider]

good point on the ratios lewtot
ratios are all over the place from different vendors and stock is usually less that advertised
if you do not have your rockers dialed in the ratios will be off also
remember you are going from an arc of the center of the roller to a line of the valvestem
the ratio varies from less at the seat to maximum at tangent- mid lift hopefully- to less ratio at full lift
hard to get everything right without a trial assembly with the trusty dial indicator
I see that comp cam card lists spacers with the rockers- anyone know if these are for the shafts or for under the fulcurm?
The stock rocker stands are height set for around 400 lift and are off a little even with a stock Magnum cam
you add a .100 to the lift and move the calculation point from the tip of the valvestem to the center of the roller rocker you have some adjusting to do
not as easy as a Chevy.- but raising the rocker on a chevy moves the center of the roller off the center of the valve- add longer valves and... no free lunch

 

[wyrmrider]

you may have to clearance the heads and block, especially with larger dia pushrods
check the retainer/ keeper to stem seal- you have to check everything
I've used the no longer available ERSON 1.75 Iron rockers and big pushrods- lots of grinding

 

[wsutard]

OK, you all convinced me that 1.6 is just too much work for my first experience with building heads. I will consult with my machine shop around what works best.

 

[moparcrazy]

1.6 forsure !! if it works for your build, they cost is the same 1.5 or 1.6 and 1.6 potentially gives you more POWER for the same $$ No Brainer to me??

 

[wyrmrider]

1.6 forsure !! if it works for your build, they cost is the same 1.5 or 1.6 and 1.6 potentially gives you more POWER for the same $$ No Brainer to me??

I'ts a no brainer if the engine is on the engine stand and he is doing a trial asembly
most of the time the 1.6 fit but sometimes they do not
if the heads are on the block he can eyeball the clearance
What stem seals- VITON?
with that lift Iron rockers work just fine with some lash caps on the valves
plan on spending the time to dial in the rocker geometry/ pushrod length no matter what you do
Do you have the cam? If single bolt mild locktite is your friend
One thing to think about everyone is 1.6 and one size shorter duration on the intake plot the lift curves
you do not build cylinder pressure till the intake is closed and shorter closes it earlier, and less overlap
cheers

 

[wsutard]

I'ts a no brainer if the engine is on the engine stand and he is doing a trial asembly
most of the time the 1.6 fit but sometimes they do not
if the heads are on the block he can eyeball the clearance
What stem seals- VITON?
with that lift Iron rockers work just fine with some lash caps on the valves
plan on spending the time to dial in the rocker geometry/ pushrod length no matter what you do
Do you have the cam? If single bolt mild locktite is your friend
One thing to think about everyone is 1.6 and one size shorter duration on the intake plot the lift curves
you do not build cylinder pressure till the intake is closed and shorter closes it earlier, and less overlap
cheers

It will be on a stand with trial assembly.
Im working on the cam now, deciding between hydraulic and solid. im leaning toward solid, just dont know which one. Im looking for low end punch. for the hydraulic I was considering the Comp 285HL.

 

[440fish]

On my 493 i have Harland Sharp 1.5's and as Lewtot alluded to they measure close to 1.6. "More isn't always better" and for a street build i'd stick with 1.5.

On the cam i want with a solid Comp XE 274S. Very responsive yet pulls into the upper rpms. I also have Edelbrock rpm heads with 74cc chambers for good quench. I am a fan of solid lifters for the simplicity and better high rpm performance. Adjusted mine at 7500 miles and NONE were out of tolerance. To me there's no downside to the solids anymore due to modern machining and they sound so cool.

If you were closer id say come on by and take you for a spin.

 

[wsutard]

On my 493 i have Harland Sharp 1.5's and as Lewtot alluded to they measure close to 1.6. "More isn't always better" and for a street build i'd stick with 1.5.

On the cam i want with a solid Comp XE 274S. Very responsive yet pulls into the upper rpms. I also have Edelbrock rpm heads with 74cc chambers for good quench. I am a fan of solid lifters for the simplicity and better high rpm performance. Adjusted mine at 7500 miles and NONE were out of tolerance. To me there's no downside to the solids anymore due to modern machining and they sound so cool.

If you were closer id say come on by and take you for a spin.

Comp recommends 9.5:1 CR for that cam. What are you running at?

 

[Kern Dog]

I ran that 285 cam in my 440/493. It was a good performer until it wiped a lobe! The replacement also went bad. Now, I am no idiot...I used the cam lube they provided, I made sure that I had fresh oil in the engine and I did the proper break-in. I even checked with Comp Cams to make sure the Edelbrock valve springs would be compatible. This was in 2006. Since then, I learned that the regular engine oils are inadequate for high lift, high performance camshafts. Now, on every break in, I use a bottle of the Comp Cams supplement, Joe Gibbs oil AND a generous slathering of the cam lube.

 

[wyrmrider]

EDM lifters
we used to put the lifters in a vblock on the mag chuck grinder and grind a flat almost to the face
like the Buicks did
puts oil all over the place whereas the EDM puts it where it's needed- almost like with the XKE jags where the cams were drilled and holes on the leading edge of the ramps- that was in the late 50's - nothing new

 

[wyrmrider]

If I had the engine on the stand I'd
GO to Jones Racing cams and fill out the cam request card- best advice you can get
You can get a lift curve up to a point with the cam, need more you have to up the lifter ratio
Mike's program will tell you which to do and can advise compression ratio vs intake close, etc
Very few tech guys have 40 years of experience

 

[rumblefish360]

OK, you all convinced me that 1.6 is just too much work for my first experience with building heads. I will consult with my machine shop around what works best.

No matter the rock a ratio, it’s the same amount of work. Consult with your machinist. Let him do the work.

 

[lewtot184]

to up the rocker ratio thinking it's a power boost may or may not work. the power increase for the most part is marginal. for a fast rate/high lift cam i'd do 1.5's and MEASURE everything; especially with iron heads! edelbrocks are lift friendly but just because edelbrock says their springs will take .600 lift doesn't mean they're compatible with a .600 lift cam. my thoughts are to use the higher ratio rockers to enhance a lower lift/gentler profile cam or use them with solid lifters were you know you'll loose a little lift due to lash. I don't get to heavy in the .904 lifter thing. I drive my cars and long term reliability means a lot to me. one of my cars has an old fashioned slow ramp solid in it and I darn sure don't need any more power with a modern fast rate cam. everybody has to pick their poison.

 

[RT K_line]

I tried 1.6 rockers on my Eddy RPMS but they hit the push rod opening so they would have to be opened open if you use them. I don't think you need them though I'm using isky iron rockers with a small duration high lift cam without any rocker issues. I did have multiple retainer failure from sub standard parts but never a rocker issue. Going with titanium retainers now.