How much compression with a Magnum?

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Penfighter

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I am putting together a '96 SMPI 5.2 and I am wondering how much compression can be run on regular or premium gas. On 340s we could run 10.3:1 with premium without detonation-even with a lot of advance timing. Surely some of you Dodge Boys have tried to stretch the compression on these Magnum engines.
The stock compression was 9:1 using regular gas. However, I am using 62cc EQ heads which should raise compression to 9:4-9:6. So how much extra compression can the ECU compensate for?
Will the port injection make the air/fuel/cylinder temps noticeably cooler to aid reducing the detonation?
I will be using a cam with about 210* duration and .515 lift (no razzing about the small cam please. This is a work truck). Which LSA will help best to minimize detonation to keep the hyper pistons going in it from cracking up?
Air will flow well with a hi-performance intake and long tube headers so the engine will finally be able to breath. Should I go with one or two stages cooler spark plugs on these engines?
 
I can't answer your questions, but are you sure about your CR with those heads? My 5.9 magnum using those heads and a .028 gasket with stock replacement pistons will be 9.1:1. I also have a stock deck height putting my pistons .06 in the hole. I use the keith black calculator, and take into account the 11.23 cc dish on my new pistons.

I would think a 5.2 would be even less compression, so I'm curious if maybe you are using flat top pistons or deck work
 
What's your source for factory compression numbers?

I seem to remember them crowing back in the day about low compression for "regular" gas.

8.8 is what I want to say, IIRC.

I run 87 in my 2000 5.9.

Pings under WOT or lugging only- doesn't go away until the second tank of 93.

...so I just don't do too much WOT and run 87.
 
Peyote said:
I can't answer your questions, but are you sure about your CR with those heads? My 5.9 magnum using those heads and a .028 gasket with stock replacement pistons will be 9.1:1. I also have a stock deck height putting my pistons .06 in the hole. I use the keith black calculator, and take into account the 11.23 cc dish on my new pistons.

I would think a 5.2 would be even less compression, so I'm curious if maybe you are using flat top pistons or deck work
Click to expand...


Shepard and others have stated stock compression is 9:1 on a 5.2. Some older 318’s I have seen ran slightly less. Also, EQ states that with their heads have 62cc chambers (though some say they are 58cc) and 172 cc intake port volume. I have seen stated the 5.2 had factory 62cc chambers and also 64cc chambers depending on who you believe.


All I have ever seen in a 5.2 or 318 were flat top pistons.


I saw in Silvolite’s catalog the 5.9s also run the 9:1 compression so Peyote’s calculation is right on—even though his pistons are dished and have a shorter compression height than the 5.2 piston.


I cannot find my calculations or a piston manufacturer statement, so Peyton’s response indicates either I did not enter something in right or when I did the calculation I went with a 60cc “average”.


Still, the object of this build is to run the highest compression using 87 octane fuel. So, can the engine get by (no detonation) running a 9.3:1 or 9.5:1 compression using 87 octane on the SMPI engine? If not, what do I need to do to/change on the engine so I can run this high compression?


And YY1, the old tired engine ran fine, no pinging at WOT—even with a cylinder with bad rings. Assuming your ECU is timing the engine correctly and no one changed any of the innards of your engine, I would think you have deposits in the cylinder chamber that are raising your compression and causing the detonation. Of course, maybe you could run a plug one or two stages cooler and see what happens. I would try cleaning the cylinder chambers first before swapping plugs.
 
My stock heads were/are 62cc, I think the stock 318 CR is 9.2:1 and the 360's is 8.8.

The fact that you're planning to run a cam larger than the stock 5.2 cam with stock pistons could well mean that 87's in the cards.
 
Interesting that the cr ratio of the 5.2 was a little higher than the 5.9. Don't forget that also carbon deposits in the first 10k Mike's are supposed to bump the cr up by .5...do I believe that, no, but there is probably an increase to a lesser degree. In other words if you are trying to get your cr right up to the edge of detonation, it's a good idea to leave yourself a little wiggle room. And in terms of actual performance to me it's just not worth it. But to each his own, if you really want to be right on the edge, I've always heard to keep it under 9.5:1
 
OP, which pistons are you using? Silvolites or? Using the higher 1.81" CH (compression height) pistons will raise CR about a point over the more stockish 1.74" CH pistons. If you are using the KB's with the 1.81" CH, then you need to pay attention with a Magnum block as the pistons will be right at the deck. Your valve lift ought to be OK with the KB reliefs but check valve-piston clearance.

BTW, DON"T take the factory or catalog CR numbers as correct; they are always high by some amount. Real CR's ran in the 8's at best, and as low as the low 7's in the old 318's with the low CH truck pistons.

Examples: With 62 cc combustion chamber volumes, and bored .030" over, if you used the KB's with a .039" thick head gasket, you'll end up around 9.7 SCR. If you used the lower 1.74" CH with a pure flat top, you'll end up near 8.8 SCR. (These numbers are per the Pat Kelly calculator.)

And don't be particularly fearful of the hyper pistons; detonation can kill a forged piston as well. The 9.5 SCR limit is a safe, conventional wisdom limit for iron heads.

A narrower LSA will minimize detonation but will lower low RPM torque. IMHO, adjusting LSA for this is not the way to do it: pick the LSA for the application and adjust cam timing to manage the dynamic CR, and be ready to manage ignition timing to perhpas a level leve that is below the absolute optimum for peak power.

What is your general use and objectives for this engine and truck? No issue on the cam from me! I ran a 192/200 (@ .050 lift) duration cam once for torque; it was a real stump-puller and good for mileage.

And for fuel.... well I ran 10.3 on the street for a long time but 87 was always marginal at best.
 
nm9stheham said:
BTW, DON"T take the factory or catalog CR numbers as correct; they are always high by some amount. Real CR's ran in the 8's at best, and as low as the low 7's in the old 318's with the low CH truck pistons.

Examples: With 62 cc combustion chamber volumes, and bored .030" over, if you used the KB's with a .039" thick head gasket, you'll end up around 9.7 SCR. If you used the lower 1.74" CH with a pure flat top, you'll end up near 8.8 SCR. (These numbers are per the Pat Kelly calculator.)

And don't be particularly fearful of the hyper pistons; detonation can kill a forged piston as well. The 9.5 SCR limit is a safe, conventional wisdom limit for iron heads.

A narrower LSA will minimize detonation but will lower low RPM torque. IMHO, adjusting LSA for this is not the way to do it: pick the LSA for the application and adjust cam timing to manage the dynamic CR, and be ready to manage ignition timing to perhpas a level leve that is below the absolute optimum for peak power.

What is your general use and objectives for this engine and truck? No issue on the cam from me! I ran a 192/200 (@ .050 lift) duration cam once for torque; it was a real stump-puller and good for mileage.

And for fuel.... well I ran 10.3 on the street for a long time but 87 was always marginal at best.
Click to expand...
It shouldn't be assumed that they will all be larger either. Underguessing your CR is not better. Too much cylinder pressure in a truck that sees real use is a bad idea.

Peyote said:
Interesting that the cr ratio of the 5.2 was a little higher than the 5.9. Don't forget that also carbon deposits in the first 10k Mike's are supposed to bump the cr up by .5...do I believe that, no, but there is probably an increase to a lesser degree. In other words if you are trying to get your cr right up to the edge of detonation, it's a good idea to leave yourself a little wiggle room. And in terms of actual performance to me it's just not worth it. But to each his own, if you really want to be right on the edge, I've always heard to keep it under 9.5:1
Click to expand...
It depends on the cam among other factors. If you're planning to run a stock 318 cam it can be very sensitive at just over 9:1. No- the performance of having high CR is not worthwhile if your primary goal is streetability. I'll take lower CR any day of the week if it's a lower HP application which most attempts at a "torque motor" end up being.
 
Infecteddog said:
My stock heads were/are 62cc, I think the stock 318 CR is 9.2:1 and the 360's is 8.8.

The fact that you're planning to run a cam larger than the stock 5.2 cam with stock pistons could well mean that 87's in the cards.
Click to expand...


What am I forgetting? The extra duration opens the exhaust valve sooner to cool the cylinder down/releases the pressure sooner? Seems to me that would be too late.
 
Penfighter said:
I am putting together a '96 SMPI 5.2 and I am wondering how much compression can be run on regular or premium gas. On 340s we could run 10.3:1 with premium without detonation-even with a lot of advance timing. Surely some of you Dodge Boys have tried to stretch the compression on these Magnum engines.
The stock compression was 9:1 using regular gas. However, I am using 62cc EQ heads which should raise compression to 9:4-9:6. So how much extra compression can the ECU compensate for?
Will the port injection make the air/fuel/cylinder temps noticeably cooler to aid reducing the detonation?
I will be using a cam with about 210* duration and .515 lift (no razzing about the small cam please. This is a work truck). Which LSA will help best to minimize detonation to keep the hyper pistons going in it from cracking up?
Air will flow well with a hi-performance intake and long tube headers so the engine will finally be able to breath. Should I go with one or two stages cooler spark plugs on these engines?
Click to expand...

Ok, here goes...lets see if I can answer this without starting a riot or derailing the thread.

"On 340s we could run 10.3:1 with premium without detonation-even with a lot of advance timing. Surely some of you Dodge Boys have tried to stretch the compression on these Magnum engines."

If you are referring to running premo "back in the day", that was a bit hotter than todays 91 octane mule piss. That said, on the west coast, we dont get much 93 which I have heard is the norm in the midwest, we typically get 91. My rule is 9.5 max on Iron and 10 on aluminum. That is assuming aftermarket iron, not factory crackers. The EQ/Indy heads are iron but are extra thick so they seem to tolerate a bit more, probably to better cooling, but thats an educated guess, not scientific proof.

I have checked many Magnums and all are between 8.8-9.3 factory. it all depends on how deep the pistons are, .040-.080. 5.2's seem to run almost half point more than 5.9, just observation.

EQ wont raise comp 1/2 point but a skinny gasket will. You will be safe with EQ and .028 gasket.

As far as compression and pcm, it wont care. What will matter is LSA of the cam. That plays a huge part in how it runs and how much tuning you need to do for it to run correctly. You can run quite a bit of duration and lift as long as the LSA is 114 or close. You will loose low idle with less than 114. we commonly run 215-217 @.050 and .533 lift with flashed pcm, large injectors, 850 cfm TB, combine that with EQ and you will have tons of torque, good MPG and lots of pull to 6K and still idle at 950-1000.

NGK 4291 .050" gap. Just make sure you have big wires, copper cap/rotor, better coil and the plugs. Make a giant diff to actually light all the mix and not 3/4's of it. On a stock magnum I would bet it might make 10 hp. It improves MPG, idle quality, extends rev by few hundred rpm and starts better. save the .035" champions for the riding mower....

These things are available on our site along with lots of info on magnums, pm if you want info. Evan

"
 
Don't forget that the Magnum engines have a shorter deck height, too. That will allow them a little higher compression right from the rip.
 
nm9stheham said:
OP, which pistons are you using? Silvolites or? Using the higher 1.81" CH (compression height) pistons will raise CR about a point over the more stockish 1.74" CH pistons. If you are using the KB's with the 1.81" CH, then you need to pay attention with a Magnum block as the pistons will be right at the deck. Your valve lift ought to be OK with the KB reliefs but check valve-piston clearance.

BTW, DON"T take the factory or catalog CR numbers as correct; they are always high by some amount. Real CR's ran in the 8's at best, and as low as the low 7's in the old 318's with the low CH truck pistons.

Examples: With 62 cc combustion chamber volumes, and bored .030" over, if you used the KB's with a .039" thick head gasket, you'll end up around 9.7 SCR. If you used the lower 1.74" CH with a pure flat top, you'll end up near 8.8 SCR. (These numbers are per the Pat Kelly calculator.)

And don't be particularly fearful of the hyper pistons; detonation can kill a forged piston as well. The 9.5 SCR limit is a safe, conventional wisdom limit for iron heads.

A narrower LSA will minimize detonation but will lower low RPM torque. IMHO, adjusting LSA for this is not the way to do it: pick the LSA for the application and adjust cam timing to manage the dynamic CR, and be ready to manage ignition timing to perhpas a level leve that is below the absolute optimum for peak power.

What is your general use and objectives for this engine and truck? No issue on the cam from me! I ran a 192/200 (@ .050 lift) duration cam once for torque; it was a real stump-puller and good for mileage.

And for fuel.... well I ran 10.3 on the street for a long time but 87 was always marginal at best.
Click to expand...


Before we go any further, I want to thank all for adding to this discussion.

What I find amusing is it seems to depend on who's calculator one uses as to what the CR works out to be. Sure hope the one you chose is wrong as 8.8 would make it hard to reach the 350 HP on regular gas I bet $100 I could make with the 340's baby brother.

If 9.5 is the best regular can handle, then that is what I have to work with and the KBs are a no go. Maybe Grant Pistons have a comp. height between the Silvolites and KBs. I had hoped the SMPI would not only cool the air/fuel temp some and the finer mist of the injectors, as compared to carbs, create a smoother and more evenly distributed burn; the low quench heads; and the computer adjusting timing all would allow me to go a little higher CR without doing any decking.

Hughes 208/214 dur. with .523/.533 lift cam is what I was going with, unless I cannot reach +20 mpg with it; and then I'll have to go with a Comp 262 cam--which I will go with if I can make up the HP with a bit more compression (and it should be more durable).

For builds that are mostly stock, I use the hypers. Love 'em.

I was planning to use a 110* LSA cam to reach max HP at a lower RPM (<5500), but as per Comp this raises the chance of detonation--another reason I was concerned about detonation with 87 octane.

General use: in a van, to haul arse when I want to enjoy the vehicle, gas mileage of at least 20 mpg (with a 46 RE and 3.55 gears), must get 150,000 miles out of the engine, and must be able to tow 5500 lbs (to bring home the '69 Barracuda I want to/will build or a parts van).
Can you think of any more resrtictions/limits on this build? :toothy8:
 
I dont think 8.8 would be hard to reach 350 HP at all with good flowing heads. That's where it's all at anyway. In the heads.

Dig up IQ52's low compression 440 build. When I say low compression, I mean UNDER 8:1. You will be impressed.
 
If you really want to get to 9.5:1, the way to do it is use the kb Pistons and then shave that cr back to where you need it with the head gasket thickness.
 
Mmmmmm.... I just tried 3 SCR calculators with the same number inputs and they all came up within 0.1 point of each other. Most of the variations I have seen have come from entering data incorrectly; the best place to go wrong is to enter the piston valve relief cc's with a + where it should be a - or vice versa. The different pistons manufacturers will list the same valve relief as + or - in their specs, and people don't catch that subtlety; that is the most common place for an error. I've run the numbers on the 318 with the lower pistons multiple times and it always comes out at the same place; at least the Magnum block and head volumes help you quite a bit over the 318 LA. But high 8's is where it ends up for the lower CH pistons.

BTW, if you use the KB's and the Felpro standard head gaskets at .051" thick, then you will right around 9.5 SCR.

As for your goals: 20 mpg in the van is mostly a challenge of moving that big cinder block shape through the air at any speed without killing efficiency. Maybe a chin spoiler? Enginewise with the FI, it seems like an easy goal to get the efficiency; not counting the wind resistance problem you'll face. But I have never cammed or programmed one of those so I'll defer to others on that beyond any general cam experience.

Just a general comment on the cam for fuel efficiency: Higher lift, lower duration and wider LSA. Crane had a series of cams back in the early-mid 70's that they labeled their 'HE' grinds that they came out with in response to the Arab fuel embargo of '73. 'HE' stood for 'hydraulic, efficiency' (I think), and they featured the high lifts, lower durations, and wide LSA's. They did the job and made a wide torque band engine with good economy. So that makes me think you are on the right track with the cams (and is where modern OEM rollers have gone for that reason).

BTW, IMHO, the 350 peak HP WITH the 20 MPG in that van is the compromise you are going to have to fight and make a trade-off. For your broader uses, I'd forego the 350 HP peak number, which you will not use much in reality, and focus on the mileage/torque. That is also partly my personal inclination, but I have built a multi-use engine that towed too and I thought more about torque at lower RPM's and let the peak HP go where it would. That was the engine that used the 192/200 @ .050" cam, and the engine was run almost 100k miles before the forged pistons got to where the blowby was pretty atrocious LOL! You should have better durabiilty with FI and hypers in newer block metallurgy.

With the above said, then certainly don't push the SCR too hard and end up with detonation issues. If you do, you at least have the option to use premium. Keep the knock sensor if the system has one! I don't know enough about the Magnum MPFI to know how it will adapt to detonation. (IMO, Magnummopar would know much better on that.)
 
Penfighter said:
Before we go any further, I want to thank all for adding to this discussion.

What I find amusing is it seems to depend on who's calculator one uses as to what the CR works out to be. Sure hope the one you chose is wrong as 8.8 would make it hard to reach the 350 HP on regular gas I bet $100 I could make with the 340's baby brother.

If 9.5 is the best regular can handle, then that is what I have to work with and the KBs are a no go. Maybe Grant Pistons have a comp. height between the Silvolites and KBs. I had hoped the SMPI would not only cool the air/fuel temp some and the finer mist of the injectors, as compared to carbs, create a smoother and more evenly distributed burn; the low quench heads; and the computer adjusting timing all would allow me to go a little higher CR without doing any decking.

Hughes 208/214 dur. with .523/.533 lift cam is what I was going with, unless I cannot reach +20 mpg with it; and then I'll have to go with a Comp 262 cam--which I will go with if I can make up the HP with a bit more compression (and it should be more durable).

For builds that are mostly stock, I use the hypers. Love 'em.

I was planning to use a 110* LSA cam to reach max HP at a lower RPM (<5500), but as per Comp this raises the chance of detonation--another reason I was concerned about detonation with 87 octane.

General use: in a van, to haul arse when I want to enjoy the vehicle, gas mileage of at least 20 mpg (with a 46 RE and 3.55 gears), must get 150,000 miles out of the engine, and must be able to tow 5500 lbs (to bring home the '69 Barracuda I want to/will build or a parts van).
Can you think of any more resrtictions/limits on this build? :toothy8:
Click to expand...

The calculators are all based on same math equation, differences are from input errors and the fact that the pistons are not all the same depth in the hole, figure one with .040" in hole then another for .080" in hole...there is your difference. If you have an 8.8, simply use a .028" gasket and you are good. The amount of power made between 9 and 9.5 will be so minimal on a street build I doubt most dynos would pick it up..under 10 hp diff would be my guess. You will find more power in better ignition system than half point.

20 mpg from a van with a large cam will be pushing it but possible. I have built a number of magnum wranglers that with stock 5.2 nv3500 5 speed, 31" tires and 4.10 gears that got 21-22 on highway and they are a barn door at anything over 65 mph. With 2wd and AT I am going to guess closer to 18 mpg.

You need to stick to 114 LSA if you want your engine to idle at anything under 1500 rpm. Evan at 112 LSA you will be hard pressed to get idle under 1000 rpm. I had 6 pcm flashed this week and sold 4 FI cams as well. I can tell you from experience that you will need to stick to these parameters if you want results you will like.
I just got off the phone with Jim at Racer Brown Cams who is helping with our cam designs aand we both agree that split duration/lift cams are the old school way of doing things so our cams are all single duration/lift design. The reason they use more on exhaust is that LA heads as well as GM and Furd used to have crap for exhaust ports/valves. Chrysler being the leader in bigger valves/ports but still small. The EQ heads dont have this problem, you can see 3/4 of back of valve through port and exhause only has to move about 1/3 air intake does. a 1.62" valve is plenty to move spent mix when compared to what a 1.92, 1.97 or 2.02 will let in. Basically, you are adding stress and wear for no extra gain.
Now before people start stoning me, think about the physics of it. We are not talking about big cube race engines either, different animal, we are talking about mild build street/work horse. I would recomend a cam like this, 213* @.050" .520" lift, possibly .533" lift BUT on 114 LSA. This should get you your 350 or pretty damn close and a ton of low end so you can pull your load. Then you will want to upgrade ignition, get a 850 CFM TB and a set of 5.9 red injectors. Flash the pcm for it and you should b good. You can call the shop or pm if you want to talk about cams. Evan magnummopar
 
magnummopar said:
I would recomend a cam like this, 213* @.050" .520" lift, possibly .533" lift BUT on 114 LSA.
Click to expand...
Just curious: Any ideas on why the 112 does not do better at idle, or is it just the combination of that with the duration and too much overlap?
 
Thanks magnummopar for some detailed insight.

Please clarify that the 9.5 max with EQ heads was with regular fuel. I ask because I have read several Mopar builds, and the Chevies and imports do it for sure, can push 11:1 with premium/pump gas using aluminum heads.

Perhaps you can answer this: unless Dodge was using different piston manufacturers who provided slightly different pistons, how did the factory end up with such wide variance of compression (8.8-9.3) since the rod length has stayed the same and to my knowledge they never put larger duration cams in the 5.9s?

We use to run 110* cams with large durations (290+) in the LA engines built for the streets and still managed to idle at 750-800 rpms (but that was using 91-93 octane). So why do you say I couldn't idle at 750 rpms with a less duration 110* LSA cam? What is so different about the Magnums needing 114*? If the explanation is too long to write, tell me on the phone.

Better coil and wires are a must. Enough said there. A little disappointed that the best coil out there for this vehicle is the Accel 140021, but then again it is a street vehicle.

I was figuring gaining 15 HP from the higher compression (9.5), but after thinking about what you wrote, maybe I would get less than that and it would be better to stay with the 9:1 anyway.

I did find it odd that Racer Brown Cams and you state to go with a single duration and single lift cams. Comp states running different durations and lifts is the new way of doing cams; as does Engine Builder and others. In the past the big cam manufacturers didn’t even stock such cams and nowadays most cams offered are the split durations/lifts. I will be calling the shop to discuss with you why “old school” cams are the latest thinking.
 
nm9stheham said:
Just curious: Any ideas on why the 112 does not do better at idle, or is it just the combination of that with the duration and too much overlap?
Click to expand...

It only applies to factory injected engines, the factory pcm can be flashed to deal with a 112 to 110 duration at 50 but the lower you go, the higher idle you have to program into pcm. This is mostly beause its a MAP based system, not a MAF based system. MAP uses engine vac signal to determine throttle, load and fuel parameters so if you install a cam that pulls 25% less vac you have to compensate for it, more you go off "normal" the harder it is ot get a good idle.

The aftermarket FI systems typically have a much larger "grid" used in programming, think 720 dpi tv vs 1080 HDLP tv. The factory is a much finer "grid", more lines of code and more finely tuned. The aftermarket systems like FITech use a big grid, chunky style, program which will deal with lower vac signal much better but at a trade off of not being as precise in fuel curve. I think its like 3x3 vs 12x12. Atari 800 vs Playstation 3. A Mega Squirt system is like factory and a much finer "grid", 24x24 if I remember correcctly, thus why its able to run multi port, sequential MPFI either as piggyback or stand alone. If you use one of these, you can deal with smaller LSA much better than even factory pcm's, BUT they wont run a 44/46 RE or factory gauges in say Dak, Dur, Ram or Wrangler due to not having ccd buss.

Too much tech for a sunday :D
 
Penfighter said:
Thanks magnummopar for some detailed insight.

Please clarify that the 9.5 max with EQ heads was with regular fuel. I ask because I have read several Mopar builds, and the Chevies and imports do it for sure, can push 11:1 with premium/pump gas using aluminum heads.

Perhaps you can answer this: unless Dodge was using different piston manufacturers who provided slightly different pistons, how did the factory end up with such wide variance of compression (8.8-9.3) since the rod length has stayed the same and to my knowledge they never put larger duration cams in the 5.9s?

We use to run 110* cams with large durations (290+) in the LA engines built for the streets and still managed to idle at 750-800 rpms (but that was using 91-93 octane). So why do you say I couldn't idle at 750 rpms with a less duration 110* LSA cam? What is so different about the Magnums needing 114*? If the explanation is too long to write, tell me on the phone.

Better coil and wires are a must. Enough said there. A little disappointed that the best coil out there for this vehicle is the Accel 140021, but then again it is a street vehicle.

I was figuring gaining 15 HP from the higher compression (9.5), but after thinking about what you wrote, maybe I would get less than that and it would be better to stay with the 9:1 anyway.

I did find it odd that Racer Brown Cams and you state to go with a single duration and single lift cams. Comp states running different durations and lifts is the new way of doing cams; as does Engine Builder and others. In the past the big cam manufacturers didn’t even stock such cams and nowadays most cams offered are the split durations/lifts. I will be calling the shop to discuss with you why “old school” cams are the latest thinking.
Click to expand...

Comp of 9.5 is max with iron heads in my shop, 10 is max with aluminum. We dont have much 93 here, 91 is common. You might get 11 with aluminum on 93 but only if you had a huge cam which lowers static comp by hanging valves open at same time, thus lowering comp. With the cam size we were talking about, better play it safe at 9.5.

Your question about compression variances is not due to pistons, rods or heads, its machine differences in block, core shift, decking or crank boring varies a bit and can add up to .030-.050 prety easily. What you will find if you checked 10 engines, is they vary from say .040-.080 in the hole due to relation of deck surface to crank journal centerline, not much but enough to change by .2-.4 ratio.

Idle quality on FI engine is completely different than on carb, you cant just crank on a screw to raise idle on FI, the computer wont let you do that, it adjusts to its own parameters and how stuff is set up. Screw with LSA and engine vac at idle will change dramatically causing pcm to try and correct by artificially enriching due to low vac( it thinks you are stepping on gas)....hope this makes sense and doesnt sound snotty...:D

Cams all depend on heads and air flow compared to overall cylinder volume....math problem is you will. Old school was to make up for small valves/marginal exhaust ports by larger exhaust on cam. Notice they dont mess with EQ exhaust hardly at all? Because its big enough already and doent need a crutch from extra lift/duration on cam. Comp and other big guys are just following along with the popular vote..like high school. has nothing to do with reality. Look at modern cams on big $ race cars, most dont think that way anymore but big am company guys are too afraid off what others think to go against whats popular. Couple of articles in the mags and it will be yesterdays fad then everybody will do whats in the mags.
 
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