Rocker experiment.

[dfarr67]

I've got a FIRST TPI on the 383 chev and was wondering if it was worth trying out 1.6 ratio rockers on the four corners as these runners have a 90deg turn, have 1.5's on all now. I was intending to go intake only all around, pretty mild Erson roller cam.

Erson_383_HydCam.xls

firsttpiintm8.jpg

[BOOT]

Too many factors other than the intake track to consider to try and equal everything out, for example sbc head runners aren't all the same like other engines. An argument could be made that indifferences make a broader power band, unless you want a narrow power band and test and R&D everything to get that. You'd have to test each possible rocker combo to truly know what is best, some cylinders may like a larger exhaust while other want smaller but then two sizes larger intake rockers.

All that to considered the TPI intake is well known at a disadvantaged, just increase all the intake rockers at least. If the four corner intakes improve more than the inner four, I'd still want all 8 improved. Still then who says an increase on the exhaust wouldn't help some if less than the intakes?

IDK bout the First intake but I rem reading the rear runners(6&8) were starved at high output but again I'd still take any improvement from the other 6 cylinders.

Even another angle to consider is some say the force of springs cancel each other out as one open and closes, so if you start randomly changing those forces to open n close diff valves.

Plus you have to consider pushrod length changes, do you want run diff length on each or intake & exhaust?

Just try 1.6 on all but maybe check with the cam manufacturer 1st because I'm no cam expert and idk how aggressive it is.

[MadBill]

The applicable philosophy is that rather than aiming for cylinder power equality, it is better to tune each to its maximum potential without regard to how its neighbors perform.

[andyf]

Are you assuming that the engine will make more power with more rocker arm ratio? I think I proved that isn't always the case with this article: http://www.hotrod.com/articles/trying-f ... m-testing/

The bottom line is that if the engine doesn't need faster valve action then changing the rocker arm ratio is just a waste of time and money. The engine only needs what it needs. In your case maybe it will help but then again, it might not matter at all or it could even cost you power. As long as you're willing to spend money to get nothing you'll be okay. Just don't assume that adding rocker arm ratio is going to make more power. That is not a good assumption.

[MadBill]

Are you assuming that the engine will make more power with more rocker arm ratio? I think I proved that isn't always the case with this article: http://www.hotrod.com/articles/trying-f ... m-testing/

The bottom line is that if the engine doesn't need faster valve action then changing the rocker arm ratio is just a waste of time and money. The engine only needs what it needs. In your case maybe it will help but then again, it might not matter at all or it could even cost you power. As long as you're willing to spend money to get nothing you'll be okay. Just don't assume that adding rocker arm ratio is going to make more power. That is not a good assumption.

Very true in general. In this case though, given the "..pretty mild Erson roller cam" it probably has less than 0.500" lift with the 1.5 ratio and so the bump to say 0.530" with the 1.6 arms would likely be good for perhaps 10 hp. As per your article, spring coil bind height, valve-to-piston clearance, etc., would need to be verified and positive results are by no means guaranteed.

[dfarr67]

I should have mentioned that this cam does have the 4-7 swap as I thought cyl 7 might be a problem with this manifold and the option did not cost extra. The heads are AFR vortec so my thinking is with this cam they could very well use the extra lift Erson wanted to go bigger but as a MAP truck engine I thought smaller is better. Also I'm finding the Comp Utltra is expensive, tough to find used steel, I have two and was thinking- what if....

[NewbVetteGuy]

Are you assuming that the engine will make more power with more rocker arm ratio? I think I proved that isn't always the case with this article: http://www.hotrod.com/articles/trying-f ... m-testing/

The bottom line is that if the engine doesn't need faster valve action then changing the rocker arm ratio is just a waste of time and money. The engine only needs what it needs. In your case maybe it will help but then again, it might not matter at all or it could even cost you power. As long as you're willing to spend money to get nothing you'll be okay. Just don't assume that adding rocker arm ratio is going to make more power. That is not a good assumption.

Andy: Real Question: Does the increase in HP that comes from a higher ratio rocker primarily come from the faster valve action or getting the valve into "better air" where the head flows better and the slight duration increase that comes along with the extra ratio?

(When I look at that particular test, the TFS Airflow PowerPort 240cc head's advertised flowchart on the intake side shows 326 CFM @ 0.600" and 334 CFM @ 0.700" (and there's only a 1 CFM flow improvement on the exhaust valve from 0.600" - 0.700" lift); the air flow chart doesn't even continue past 0.700" valve lift, I'm assuming because it goes "dead" at that lift and doesn't provide more gains. Your starting valve lift @ a 1.5 Ratio was 0.668" in that test, 0.713" with a 1.6 ratio rocker, 0.735" with a 1.65 rocker, and 0.757" with a 1.7 ratio rocker. Looking at the head's airflow #'s I would expect an improvement going from 0.668" lift to 0.713" and very little going beyond that because the head doesn't seem like the airflow improves after that point; that's exactly what we saw.

Theory: If that test were done with a cam with less valve lift and each successive rocker ratio increase resulted in getting the valve into better air with more CFM, the results would've been different and would've shown HP increases. If a bigger head would've been used that showed a bigger increase in CFM moving from 0.700" to 0.800" of valve lift; the results would also have been better and the 1.7 ratio rocker would've shown the best results, assuming that the valve train was kept under control with the now very aggressive valve motion. (An aggressive solid roller with valve lift already near the heads' max flow is a test that, by definition, will show very little improvement from rocker ratio, right? -It's a worst-case test for rocker ratio; a "classic" (read: lazy-lobed) hydraulic roller profile with 1.5 ratio max valve lift well below the head's max CFM airflow would be a best-case test of rocker ratio increase.)

The parameters of the test seem to be a near worst-case that would show the least benefits of rocker ratio increase.

Adam

[NewbVetteGuy]

I've got a FIRST TPI on the 383 chev and was wondering if it was worth trying out 1.6 ratio rockers on the four corners as these runners have a 90deg turn, have 1.5's on all now. I was intending to go intake only all around, pretty mild Erson roller cam.

Erson_383_HydCam.xls

firsttpiintm8.jpg

What heads?

My pretty uneducated guess is that if the head flows significantly more air at the newer higher lift #s, you'll see a benefit from the 1.6 ratio rockers.

I like your idea for a test to improve the airflow by increasing the rocker ratio just of the crappy flowing runners in the FIRST intake (especially the back runner). If the intake is the actual bottleneck, though, the extra lift, shouldn't provide any advantage, though, right? (only the slight duration increase at most lifts that you get from the higher ratio; although a slight duration increase I would THINK would help...)

(I'd be happy with just dealing with the difference in cylinder to cylinder air flow by tuning the per cylinder air-fuel ratio with my FIRST intake, but my Holley HP EFI doesn't support it; no idea yet if it supports per cylinder ignition timing with the coil-near-plug harness, but even that would be better than nothing, IMHO.)



Adam

[NewbVetteGuy]

The AFR Vortec 190cc heads' airflow seems to stop increasing inflow beyond 0.550"@ 279 CFM, and @ 0.500" flow 276 CFM http://www.airflowresearch.com/190cc-sb ... nder-head/

You're already at 0.510" valve lift with 1.5 ratio rockers and 1.6 would only get you to 0.544", so maybe +2 CFM at your new max valve lift. (+4 HP?)
-The faster ratio means you have slightly more duration across quite a bit of the valve lift curve and spend a bit more time in "good air" / get into good air faster.

My guess is a pretty modest increase in going with a 1.6 ratio rocker; if you were moving from 0.400"-something lift (253 CFM) to 0.500" of lift with those heads (276 CFM)-you're seeing a 23 CFM increase across a 0.100" lift increase and I'd expect a much bigger increase than moving from low 0.500"-something to mid 0.500"-something where you see only a 3 CFM increase per 0.100" of increased lift.

Having said that; that intake is about the midrange torque production and not being an impediment to making power to 6,000 RPM on a 383 SBC and a higher ratio rocker lets you keep the cylinder pressure up and make a bit more power, so why not; a more aggressive valve lift profile seems to line up well to the objectives for a 383 build using a FIRST intake, IMHO.

(I've got a 227/228 (272/280) more aggressive, Mike Jones roller in my SBC 350 with a FIRST intake on a 110 LSA (107 ICL); my Profiler 195cc heads showed only a 1 CFM flow increase on the intake side from 0.500"-0.600", but 7 CFM on the exhaust side, but I went with the 1.6 ratio RRs anyway so not super dissimilar build. -I found a "poor-man's" calculation to estimate the new duration @ 0.050" by switching to the higher ratio rockers (assumes a linear increase in lobe lift from valve open / close up to the new peak / max lift, so it's definitely a short-cut calculation) and it estimated that my new duration is 230/232 @ 0.050" with the 1.6 ratio RRs).) -Erson could probably just tell you the actual new duration @ 0.050" by going with a 1.6 ratio RR as they obviously know the full details of lobes.



Caveat: I'm a super newb at all this stuff so if anyone experienced contradicts anything I've said here; go with what the other guy says as a general rule.


Adam

[Newold1]

What is the Spec on your Erson Cam?

The 4,7 and 2,3 swap will help with that plenum arrangement in that manifold but if the expense of a new cam is too much now that's another time and place.

[dfarr67]

Alot to digest here.

Erson tried to talk me into 'give the engine what ti wants' while I agree to a certain extent, it went into a working truck not a lighter car, so I erred on the cautious side. Not that the cam suggested was a bottom of the page cam, the ecu is an older design so that is where my concern about going to knarly. The full LS cam conversion for the gen1 SBC costs $$ so didn't do that just got the good steel core. I just wondered 'what if' I left too much on the table and could recover a bit with an easy fix.

PART NUMBER 110995-47 GROSS VALVE LIFT INT. 0.510
GRIND special GROSS VALVE LIFT EXH. 0.510
ENGINE SBC INTAKE OPEN 37
ROCKER RATIO 1.50 INTAKE CLOSE 73
ROCKER RATIO 1.50 EXHAUST OPEN 83
CAM LIFT INTAKE .340 EXHAUST CLOSE 31
CAM LIFT EXHAUST .340 OVERLAP@ LASH 68
LOBE SEPARATION 112 INTAKE PHASE 108
ADV. OR RET. DEG. 4 ANGLE or CENTERLINE
INTAKE "LASH" DUR. 290
EXHAUST "LASH" DUR. 294 EXHAUST PHASE 116
INTAKE DUR @ .050" 222 ANGLE or CENTERLINE
EXHAUST DUR @ .050" 226
JOURNAL SIZE 1.868 INTAKE OPEN @ .050 3
INTAKE CLOSE @ .050 39
TDC 45 EXHAUST OPEN @ .050 49
EXHAUST CLOSE @ .050 -3
HEEL TO NOSE X OVERLAP @ .050 0
W / .010" CLEARENCE X

HEEL TO NOSE X
W / .010" CLEARENCE X

HOT LASH INTAKE 0.000
HOT LASH EXHAUST 0.000

DEFLECTION INTAKE 0.010
DEFLECTION EXHAUST 0.010

E110995-47 DAVE FARR
RH290/340 CUSTOM HYD
RH294/340 ROLLER
112+4

[NewbVetteGuy]

What is the Spec on your Erson Cam?

The 4,7 and 2,3 swap will help with that plenum arrangement in that manifold but if the expense of a new cam is too much now that's another time and place.

Newold1: Dumb question: Why does the cam+firing order swap help with an intake of this style?


Adam

[dfarr67]

I've done a little porting to the intake- but I was not happy with the number 7 arrangement (last cyl on driver).

NCTpi25.jpg

[Carnut1]

Just a guess but I would think due to plenum design #2 and #7 could use the higher ratio for a bit more time, duration and lift to get the charge around the turn into the runner. Thanks, Charlie

[MadBill]

Ah. # 7, which with the standard F.O. fights with #5 for air, also has its entry restricted by the distributor cut out. The 4-7 part of the F.O. change moves that battle to #2 vs. #1, where neither has the added burden of an entry restriction.