Help with 340 compression + cam change

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AJ and wyrmrider, I've read your posts several times.

wyrmrider, I hear you saying to forget the 1.6 roller rockers to boost lift. Is this primarily due to cost/effect? Without any real experience it "seems" like they would boost lift #s while keeping pretty much the same duration. I am fine with my 273 rockers, but trying to understand.

AJ, I appreciate your analysis! I have long known it wasn't doing what it should. (I have the old Mopar bibles and have seen the charts on W/P and build levels and what it should do, even by the old standards.)
I do get a little confused here, I'll admit. I know it's all in the balance of parts, but I think you are saying you yourself would start with getting higher compression pistons in the motor, ...but also if just changing cams, saying that more cylinder pressure (XE275HL) with iron open chamber heads could possibly be too much without retarding the cam some. With closed chamber heads/good quench I understand how higher compression can work. Not sure what happens with higher compression and the X/J heads. Is it that with higher compression the efficiency goes up, and a bigger cam can work better as it bleeds off some of the compression at the right time?

I know I am resisting the idea of tearing it all apart for a number of reasons. Cost, and down-time, of course, but also that it is in such good condition and done with high quality parts etc. and I hate to mess with it if it's running well. So I either rethink things and consider a rebuild, or I am stuck with the "cam or no cam change" question.

Also I like a challenge, so wyrmrider (and others) when you say "8.5 motors can be made to run well" I am trying to figure out what that takes.


By the way, here are the specific cam recommendations I got:

Mike Jones-
280/280, 224/224 @ .050, with .495"/.495" and 108 LC, plus he recommended limited travel lifters.

Howards-
267/267, 220/220 @ .050, with .506"/.506" also at 108 LC.

Dwayne Porter was a bit more conservative saying maybe an XE 262 or Voodoo 701 or 702 at most, but suggesting I might think about getting different heads that would actually work much better for my purposes than the ones I have.
 
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This has been a great thread and I wanted to thank everyone who contributed!!!

I am pretty clear as to what direction I need to take. When I get to tearing the 340 down some, I'll find out exactly where the pistons sit, change the cam, change to some better springs, and at least put the thinner head gaskets in.

For now I am dialing in the new 650 AVS2, AF meter and seat of the pants tells me I'm real close.

I live 20 miles from Heartland Park in Topeka and they are open for the Friday nite test n tune sessions, so I'll play a bit more with timing and fuel first.

Again, thanks all!!!
 
I have no problem with 1.6 roller rockers per se but they require a B3 kit to work properly so it get's pricey -not needed for most street builds
IDK if Jones has .904 lifter grinds- ask him but his advice is usually spot on
let us know how the tune goes
did you post your cranking compression?
and again after the head gasket change
 
Working with 650 AVS2, set idle by vacuum (and A/F meter), needed 3 steps fatter in secondaries and silver (strongest) springs for rods. WOT A/F in mid 11’s, and motors seems happy. Still don’t have low rpm oomph I had with 750 but I had .043 pump nozzles in it so this may need more than stock .031’s.

Haven’t set a date to tear it down. Maybe a couple of weeks. I will ask Mike Jones about the .904 lifter grinds. Looking at a couple of Howard’s cams too, but need to check things first.
 
just a guess here
but an observation on recommendations

Mike Jones-
280/280, 224/224 @ .050, with .495"/.495" and 108 LC, plus he recommended limited travel lifters.

Howards-
267/267, 220/220 @ .050, with .506"/.506" also at 108 LC.

I would guess that jones is using a .842 profile and Howards a .904
you would have to see a complete profile to really know
with a high compression motor the longer duration might work
but with a 8.5 the shorter duration would be much better for dynamic compression
now jones could be using a profile with the nose rolled over limiting lift
a lot of heads can't use more than around .500 lift anyway which both of these provide
but how quickly they get to the high flow area of the head is what matters not just peak flow for a very short period of time/ duration
I know for a fact that jones 256 .904 cam has more area than any other 256 cam that I tested on the cam doc (way back when) but over 50 % bigger than the much longer DC 260 at .275 cam lift
you are better off with a solid lifter cam
I know jones has some excellent solid .904 grinds and his inverse radius rollers can't be beat
especially for low compression builds as you can get equivalent profiles to flat flank with much shorter seat timing
measure twice- cut once
 
Wyrmrider said:
you are better off with a solid lifter cam
I know jones has some excellent solid .904 grinds and his inverse radius rollers can't be beat especially for low compression builds
Click to expand...

I liked the look of that Howard's cam, but I will likely check back with Mike Jones in regards to other options as well.

I might consider a solid lifter cam ...I hadn't really thought about how a solid cam could be better for a low compression motor, but I see your point.
 
Just for info, download the Howard's lobe list and they show a couple of pages of nothing but .904 lifter profiles. You can get mechanical cams down to 212*@.050" and hydraulics down to 252/206 for this lifter size. Order through Summit or Jegs with a base PN, profile, and LSA (and ICL if you want).
 
Exactly NM
so does Lunati and Bullet Jones and Comp have more solid mopar grinds than Hyd
Engle grinds are time proven and wear well
Crower has non catalog grinds
but be sure to check with the grinder
two grinds with similar specs can be quite different
one race only requiring big springs for example
or one for a heavy valvetrain, or for endurance or a boat
going to the "bottom of the page" of a cam list almost never works
and
less is more
edm lifters is another benefit of solids
or side grind the hyd like the small v6 chevy lifters
 
midnight340 said:
I liked the look of that Howard's cam, but I will likely check back with Mike Jones in regards to other options as well.

I might consider a solid lifter cam ...I hadn't really thought about how a solid cam could be better for a low compression motor, but I see your point.
Click to expand...
IMHO, the way in which solids CAN be better is for the opening/closing ramps to be quick. But hydraulics have come a long way in that regard, and the traditional off-the-shelf solid cams have typically all been long duration, high RPM cams, that have not been appropriate for average street use, or for rally/road race. So that is why I posted about the Howard's .904 profiles. I am going to try the smallest duration of the high lift solid Howard's .904 profiles (FM2303586A) in my next build.... to try it for experience, and also because I am getting wary of the quality issues that crop up all too often anymore in 1-2 hydraulic lifters leaking excessively in a new set.

The way in which I like to think of the compression matter is that when you start out with lower CR, you are 'painted into' a performance corner. You're not going to significantly increase power without increasing duration, but with low CR, you can't help but hurt low RPM torque. Fine for revving the engine and flying down the drag strip, but it hurts all around street use at the low-mid RPM's. Starting with higher CR allows you more flexibility to keep low-mid RPM torque and get better high RPM HP. Some uses demand a wider torque band, and higher CR is the place to start for those.
 
pick the cam duration for your torque band needs -drags-road-street- wide ratio vs close ratio etc then build the cr to match
heads still determine how much power but as with cams too big can cut low end- think BOSS Fords
 
nm9stheham said:
Just for info, download the Howard's lobe list and they show a couple of pages of nothing but .904 lifter profiles. You can get mechanical cams down to 212*@.050" and hydraulics down to 252/206 for this lifter size. Order through Summit or Jegs with a base PN, profile, and LSA (and ICL if you want).
Click to expand...

Yes, I did download that lobe list from Howard's for the .904 lifters. (saw the cam you are thinking of using...) Also have looked around at other company's mechanical cams and see what you mean. Most are ground for way more duration that I would want.

Definitely will pull it apart and check where the pistons are before making any decisions. Also I likely need more spring than the Lunati singles I have if I increase the lift.

Wyrmrider said:
Exactly NM
so does Lunati and Bullet Jones and Comp have more solid mopar grinds than Hyd
Engle grinds are time proven and wear well
Crower has non catalog grinds
but be sure to check with the grinder
two grinds with similar specs can be quite different
one race only requiring big springs for example
or one for a heavy valvetrain, or for endurance or a boat
going to the "bottom of the page" of a cam list almost never works
and
less is more
edm lifters is another benefit of solids
or side grind the hyd like the small v6 chevy lifters
Click to expand...

I am going to be careful here, I definitely do not want to lose the torque I have now and will stay conservative on total duration.
 
Thought I'd add a bit of update:

Just talked with Steve Slavik at Lunati (for about a half an hour) about a solid tappet cam recommendation for the 340. He says I should run Lunati's Voodoo 264/272 solid lifter cam (235/243 at .050 with .525/.546 lift, 110/106 lobe center) maybe advanced a few degrees, and he recommended their beehive springs. This is their smallest of the catalog Voodoo mechanical cams.

I'll probably ponder this for a bit before ordering. Still thinking about the Howard’s 220@50/.506 lift 108 single patter hydraulic.

I've been running a Lunati cam and I like the idea of staying with them. Also Steve started at Ultradyne with Harold Berkshire so I feel he knows his stuff, and this is one of Harold's designs. I also like that, as I've always heard great things about his cam designs.

He said they would grind me a single pattern on 108 LC, but that this design would add top end and be about the same at lower rpm's on the street.

Although the cam info says "needs 10:1 compression" he said that he's not as concerned about that part as a lot of people. The cam is listed as 2400-6600 RPM range, and he says that he has always thought it should be rated as starting more like 2000-2200.

So I may order the cam/lifters and beehive springs, etc. as a package from Lunati. Steve assures me that this will wake up the motor! My 273 rockers/shafts are well beyond wear limits. I may have Rocker Arm Unlimited rebuild mine if it doesn't take too long, or look for a set with less wear, or just run these???

Anyway, at least I have the new timing cover painted to match the block. (Got mine from Rick's Mopars on ebay ...Rick Ehrenberg's ebay store).
 
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Mmmmm.... I vote NO on reusing the worn 273 rockers. LOL Makes no sense to 'ruin' this big change with poor parts!

IMHO you are definitely on the right track. Quite a change in the cam there, going from 214 to 235 @ .050". For sure ought to make it stronger up top. And the lower 'advertised' (measured at .015" or .020" lobe lift for a solid) ought to boost the low RPM performance; it won't be a barn burner at low rpm but for sure better. This cam ought to be quite different than that old slow ramp thing you had!

Make sure you look over the seals and retainers when you get the springs set up, and make sure you have adequate clearance between retainers and guides/seals; you lift is going up quite a bit.

Also, check piston to valve clearances..... put a pair of light hardware store springs on one cylinder (#1 is easiest) with everything installed and cam timed and lash set up. Slowly rotate the engine so you go through the overlap cycle on that cylinder, and starting at 30-40 degrees before that cylinder's TDC, and continuing to 30-40 degrees after TDC, stop every 3-5 degrees, and manually push down on each valve to see how much further they have to travel to stop on the piston. That extra travel is the PV clearance you have at each measurement point. Make sure it is adequate. It very probably will be, but with the light increase, and the higher RPM capability of this cam don't take a chance.

Be thorough on the break-in; these steeper ramps are going to put more dynamic loading on the lifter-lobe contact.

Sounds like a good move, IMHO.... hope you enjoy it, and are happy with the change.
 
mn9stheham, thanks for the advice and reminders, etc.

I pulled a head today, and the piston is down .045 from the deck, which with the gathered info punched into Wallace, gets me 8.62:1 with .023" gasket, so not as bad as I feared. Not sure what steel gaskets to use yet.

Honestly I'm still going back and forth between a solid and hydraulic, but have some good choices that I've zeroed in on (with good advice from several cam companies or engine builders.)

I talked with Mike at B3 for a while about his 1.6 rockers and geometry kit. Very nice guy, straight forward and was very helpful, and I can tell he knows what he's talking about. He was recommending using 1.6 with the Voodoo 702 cam.

I talked with Rocker Arms Unlimited about rebuilding (bushing and resurfacing) my 273 pieces, but the cost difference between that and some new roller rockers isn't all that great.

If I stayed with a (new) set of 1.5 rockers, what's the best source? Comp? Hughes? Or??

I'll post some photos when I get a bit further. Am going to weld me up a valve spring compressor tool tomorrow.
 
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FWIW.. 0.027" from Cometic is the thinnest head gasket I know of. Cometics ought to have the heads re-surface to a certain finish to hold well. There also is the .028" thick Mr Gasket 1121G.
 
nm9stheham said:
FWIW.. 0.027" from Cometic is the thinnest head gasket I know of. Cometics ought to have the heads re-surface to a certain finish to hold well. There also is the .028" thick Mr Gasket 1121G.
Click to expand...

Oops, the Mr Gasket .028” , so it looks like 8.53:1, (not great but at least not lower.) From what I’ve seen the Mr. Gasket head gaskets work well for people. (And in this case adds a calculated .210 to the compression.)
 
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Progress...
(edited)
Removed the springs/valves.
340 lightweight valves.jpg
valve stems seals.jpg

some of the valve spring spacers under the springs were broken, and this explains a couple of pieces found in the oil pan a while back...

I made up a valve spring compressor tool... which worked really well, once I put a socket over the spring and gave it a good strong hit to free things up...
valve spring compressor tool.jpg

not much carbon build up, and the cylinders all look really good.
View attachment 1715315857
piston:cylinders.jpg

more later.....
 
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