I kind of agree if pistons were gonna be purchased no matter what then I agree 100%. But let's say 9.5:1 Is what he's capable of tuning to, don't see a point of buying new pistons and balancing for a half point or even maybe a full + point of cr. I could see maybe if taking it apart anyways a clean up milling of the deck and heads for a good surface plus a small cr bump.
Should i even bother with with getting a higher compression ratio?
- Thread starter DumpsterFire
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Like the plan!
Exactly
Bonus move
Ugly cam idea, except the split duration which I tend to favor.
With the Magnum head with the 1.92 intake valve should see a LSA of 106.
Find flow test sheets with the stock Magnum head and realize where the head flows levels out and drops. When I say drop, I really mean like falls like a stone. Some high lift flow loss will happen.
Lift the valve as much as possible or reasonable. It adds a few more HP. Is it necessary? No, but it helps.
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Why?
Agree, even small ish (RV) cam definitely gonna make the biggest difference especially with a little porting.
Cause he said so
junkyardhero
Well-Known Member
the oregon 2204 grind has... wait for it... a 106 intake! ;D
i don't like to speak in absolutes when talking cams so i was more giving just a general "this is about where you wanna be" for a street motor.
i've seen the test sheets agree on the flow point just falling off the face of cliff. i wanna say it's around .500 which conveniently coincides with the lift limitation on stock heads, non spring modified division. which is where the hughes kit comes in, giving you the ability to run a little more lift without expensive machine work and a stout spring to take advantage of modern aggressive ramps.
Newbomb Turk
Well-Known Member
Post 24 is 100% correct. What limits how much compression you can use on pump gas (or any fuel really) is your ability to tune.
Because you are asking I’m saying leave the compression where it is.
Because you are asking I’m saying leave the compression where it is.
Jim Lusk
Well-Known Member
Unless you need pistons it's not worth the cost, especially with the available fuel. I suspect my 440 is around 7.5 with a 284/.484 cam. While I haven't driven it yet, I think I will be happy with it. It's just a simple street cruiser.
Ok while we're talking 360 magnum and CR:
I'm looking to put one together for a different application than the OP ( a 3/4 ton truck used like one, towing etc) for a torque monster that is happy on cheap gas ... What's the sweet spot???
I'm looking to put one together for a different application than the OP ( a 3/4 ton truck used like one, towing etc) for a torque monster that is happy on cheap gas ... What's the sweet spot???
As in cam? or cr? OR?
Technically the most CR you can possibly run (Tune) for a given gas cam etc.. I imagine your cam choice is gonna be quite mild, can't really see much reason to go with a lot more cr than it has but if you over do it you can end up with a pinging mess especially in a truck that tows.
Plus if you have to run a higher grade of fuel your not gonna save much by any mpg gain.
Unless your use to pushing the limit of cr and know how which don't seem to be the case I would be cautious of anything over stock.
Add a good exhaust and tune and probably the best it's gonna be.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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You have a 5-speed and going into a Dart.
If you are running the NV3500; the ratios are;
3.49-2.14-1.38-1.00-.73 od and the Road gears with 3.73s are ;
13.02-7.98-5.15-3.73-2.72.
My guess is that you will NOT be running 28" tires, so I
I'll assume 27's or a lil less. If that's true, then your stone-stock 5.9 Magnum could be down on one cylinder, and still smoke thru first, and a good ways into Second.
IMO, don't spoil a good thing.* (see end of story)
For a Street driven vehicle;
Static Compression ratio is NOT a good measuring stick as to street-performance. It is only a tool.
Way more useful is the Dynamic Compression ratio, but still just a tool.
Even more useful is the Cranking Cylinder Pressure; again just a tool, but IMHO, it is the best tool.
Unfortunately, with the engine torn down, we cannot measure the CCP. But we can measure it all out, compute the Scr, and if we know the Ica of the cam, then we can pretty accurately figure the DCR, which will predict a pressure. And once we have that number, we can predict what gas it will want at WOT, and if we can run full timing in the thing.
And yes, we can run the numbers in reverse, after certain decisions have been made.
But Know this, Every time you slide a non-factory cam into the engine that has a later-closing intake event, as measured at the same way as the factory cam is, that engine with no other changes, will lose CCP. Which means the Compression ratios have ALL of them, gone down! This is unavoidable. With the lost pressure, goes the torque.
However , this does not always point to a lazy at low-rpm, street engine.
In your case, with the first two Roadgears being such large torque-multipliers, you already had a preponderance of EFFECTIVE Torque, so then, some can be sacrificed. Bookmark this.
Now, if that cam with the later closing advertised intake event, has a greater intake duration at 050, chances are that it will make MORE power at some higher rpm. And if the duration at .200 lift is greater than the factory cam, then FOR SURE it will make more power with increasing rpm.
So, in your case, with those two early gears in the NV3500, you could easily go probably two sizes bigger, and not suffer too much bottom end torque loss.
My notes say that the 5.9 M cam is: 250/264/110, but the factory installs that at Ica of 64*, which bleeds a lot of potential pressure, and kills the overlap. If you retime that cam to Ica of 51*, which is very near split overlap, that would bring the overlap back on-line, so headers are now a good option.
But more importantly this resets the compression degrees from 116 to 129, and the pressure to rise from about 139psi@800ft elevation, to 156psi.. That right there is a huge improvement, and I guarantee that you are gonna feel that, especially with headers.
This advancement has the side effect of reducing your Power stroke from 127* to 114*, So the theory goes that is gonna cost you steady-state fuel-economy. However, IMO, that should NOT scare you for a couple of reasons;
1) your Cruise gear is gonna be 2.72, which means that with 27"tires, 65= 2200, which means reversion is NOT gonna be an issue, and neither is the overlap.
2) And besides that; 127* was way to much in the first place.
3) And besides that, a bigger cam will quickly plummet that 114* downwards toward 100*, making it a worse option.
There are really only two problems with the stock cam, which are
1) the dreadfully long ramps, and
2) the dreadfully low .411/.430 lift
However; Your 2.14x 3.73 Second gear, is gonna get you to 50@5000rpm, in a heartbeat, so ask yourself, how much the more, is Third gear gonna matter to you, cuz yes, in Third gear, yur gonna nose over in the power department.
But-um hey, your Third gear with 3.73s is a roadgear of 5.15 ......... With 3.91s it would be 5.40 which is 4.8% higher, which is like adding the same percentage of Torque throughout the power band, whereas a bigger cam would trade away sub 3000 rpm torque, to get over-the-nose power.
With a manual transmission, you do not have the torque-multiplying feature of the convertor, so, because you will be in Second/maybe Third around town for most of the time, you may wish to think about, if you want to give away nearly 5% torque at low speed to get a few more horsepower at 50mph.
Now, having said all that;
IMO, if you installed a fast-rate of lift cam, aka High-intensity, aka hi-energy; with the same Ica of 51* advertised, then;
1) you would be no worse off than the factory very low intensity cam, in terms of pressure and Power-stroke, yet
2) with the greater 050 durations and higher lifts and especially the increased overlap(to be used with headers), now you have the same pressure potential as the factory cam has, but with the added potential for in the neighborhood of adding over 30 degrees of intake/exhaust durations at 050. That is a really really really big deal. Especially since the overlap is gonna gonna rise to say 45 or more degrees. However, if you get too greedy, cruising at 2200 will lose fuel-efficiency, and now you're looking at adding rear gear to get the cruise rpm up, to get out of reversion/overlap issues, to get your fuel economy back. But if you choose wrong, it could go back the other way.
So
What do you do?
Well, it's sortof a tight-rope act, and it depends on what you are willing to sacrifice.
1) In your case, the Scr of 9.0 can already produce 156psi@800 ft elevation, at an Ica of 51*, which should still burn 87 gas most if not all of the time . So you kindof want to stick with that Ica. But,
2) you could sacrifice some of that Power duration, and maybe loose some fuel-economy.
3) and if you install headers, you could really use a bunch more overlap. but
4) the really big deal is those super slow factory acceleration ramps. My notes say that this factory cam is 182/194 @050, which makes the acceleration super slow back to advertised. If I assume the Advertised is at .008 tappet, then the intake intensity is 68 degrees. Well crap I doubt there is a slower rate of lift in anybody's catalog, and we can easily jump that up to 48*, and with a little hunting maybe 44*. This costs you NOTHING except some new valve springs, and possibly new valve gear.
Ok so, how big a cam can you install in your 5.9M, with the same 51* Ica?
Well punching the calculator shows this gem;
256/129/111/260/42overlap, Ica of 51*, on a 108 Lsa. compared to the factory
250/129/114/264/37 overlap/Ica of 51*, on a 110Lsa.
Notice that Compression is still 129*, which is because the Ica is still 51*..
Notice I only gave up 3* of Power-Stroke.
Notice intake duration only increased 6*, and exhaust just 4*, but
notice that the overlap jumped 5* But here comes the big deal; with an intensity of 44* the 050 number jump to
212/216 exhaust, from
182/194.
Do the math; the intake is plus 30* and the exhaust is plus 22*
With each cam size being about 7*, These numbers are over 4 cam sizes bigger! where it counts. and, as it happens, the 42* of overlap is about the same as the old 340 cam which was 44*..
Finally, with this new cam size comes the difficulty of making the new higher lift-numbers work with your lo-lift heads.
The Cam I worked out is imaginary. But there are quite a few offerings of similar sizes from the various suppliers.
The point was not to point to a specific cam, but to show you what can be done, with the factory Ica.
Happy HotRodding
If you are running the NV3500; the ratios are;
3.49-2.14-1.38-1.00-.73 od and the Road gears with 3.73s are ;
13.02-7.98-5.15-3.73-2.72.
My guess is that you will NOT be running 28" tires, so I
I'll assume 27's or a lil less. If that's true, then your stone-stock 5.9 Magnum could be down on one cylinder, and still smoke thru first, and a good ways into Second.
IMO, don't spoil a good thing.* (see end of story)
For a Street driven vehicle;
Static Compression ratio is NOT a good measuring stick as to street-performance. It is only a tool.
Way more useful is the Dynamic Compression ratio, but still just a tool.
Even more useful is the Cranking Cylinder Pressure; again just a tool, but IMHO, it is the best tool.
Unfortunately, with the engine torn down, we cannot measure the CCP. But we can measure it all out, compute the Scr, and if we know the Ica of the cam, then we can pretty accurately figure the DCR, which will predict a pressure. And once we have that number, we can predict what gas it will want at WOT, and if we can run full timing in the thing.
And yes, we can run the numbers in reverse, after certain decisions have been made.
But Know this, Every time you slide a non-factory cam into the engine that has a later-closing intake event, as measured at the same way as the factory cam is, that engine with no other changes, will lose CCP. Which means the Compression ratios have ALL of them, gone down! This is unavoidable. With the lost pressure, goes the torque.
However , this does not always point to a lazy at low-rpm, street engine.
In your case, with the first two Roadgears being such large torque-multipliers, you already had a preponderance of EFFECTIVE Torque, so then, some can be sacrificed. Bookmark this.
Now, if that cam with the later closing advertised intake event, has a greater intake duration at 050, chances are that it will make MORE power at some higher rpm. And if the duration at .200 lift is greater than the factory cam, then FOR SURE it will make more power with increasing rpm.
So, in your case, with those two early gears in the NV3500, you could easily go probably two sizes bigger, and not suffer too much bottom end torque loss.
My notes say that the 5.9 M cam is: 250/264/110, but the factory installs that at Ica of 64*, which bleeds a lot of potential pressure, and kills the overlap. If you retime that cam to Ica of 51*, which is very near split overlap, that would bring the overlap back on-line, so headers are now a good option.
But more importantly this resets the compression degrees from 116 to 129, and the pressure to rise from about 139psi@800ft elevation, to 156psi.. That right there is a huge improvement, and I guarantee that you are gonna feel that, especially with headers.
This advancement has the side effect of reducing your Power stroke from 127* to 114*, So the theory goes that is gonna cost you steady-state fuel-economy. However, IMO, that should NOT scare you for a couple of reasons;
1) your Cruise gear is gonna be 2.72, which means that with 27"tires, 65= 2200, which means reversion is NOT gonna be an issue, and neither is the overlap.
2) And besides that; 127* was way to much in the first place.
3) And besides that, a bigger cam will quickly plummet that 114* downwards toward 100*, making it a worse option.
There are really only two problems with the stock cam, which are
1) the dreadfully long ramps, and
2) the dreadfully low .411/.430 lift
However; Your 2.14x 3.73 Second gear, is gonna get you to 50@5000rpm, in a heartbeat, so ask yourself, how much the more, is Third gear gonna matter to you, cuz yes, in Third gear, yur gonna nose over in the power department.
But-um hey, your Third gear with 3.73s is a roadgear of 5.15 ......... With 3.91s it would be 5.40 which is 4.8% higher, which is like adding the same percentage of Torque throughout the power band, whereas a bigger cam would trade away sub 3000 rpm torque, to get over-the-nose power.
With a manual transmission, you do not have the torque-multiplying feature of the convertor, so, because you will be in Second/maybe Third around town for most of the time, you may wish to think about, if you want to give away nearly 5% torque at low speed to get a few more horsepower at 50mph.
Now, having said all that;
IMO, if you installed a fast-rate of lift cam, aka High-intensity, aka hi-energy; with the same Ica of 51* advertised, then;
1) you would be no worse off than the factory very low intensity cam, in terms of pressure and Power-stroke, yet
2) with the greater 050 durations and higher lifts and especially the increased overlap(to be used with headers), now you have the same pressure potential as the factory cam has, but with the added potential for in the neighborhood of adding over 30 degrees of intake/exhaust durations at 050. That is a really really really big deal. Especially since the overlap is gonna gonna rise to say 45 or more degrees. However, if you get too greedy, cruising at 2200 will lose fuel-efficiency, and now you're looking at adding rear gear to get the cruise rpm up, to get out of reversion/overlap issues, to get your fuel economy back. But if you choose wrong, it could go back the other way.
So
What do you do?
Well, it's sortof a tight-rope act, and it depends on what you are willing to sacrifice.
1) In your case, the Scr of 9.0 can already produce 156psi@800 ft elevation, at an Ica of 51*, which should still burn 87 gas most if not all of the time . So you kindof want to stick with that Ica. But,
2) you could sacrifice some of that Power duration, and maybe loose some fuel-economy.
3) and if you install headers, you could really use a bunch more overlap. but
4) the really big deal is those super slow factory acceleration ramps. My notes say that this factory cam is 182/194 @050, which makes the acceleration super slow back to advertised. If I assume the Advertised is at .008 tappet, then the intake intensity is 68 degrees. Well crap I doubt there is a slower rate of lift in anybody's catalog, and we can easily jump that up to 48*, and with a little hunting maybe 44*. This costs you NOTHING except some new valve springs, and possibly new valve gear.
Ok so, how big a cam can you install in your 5.9M, with the same 51* Ica?
Well punching the calculator shows this gem;
256/129/111/260/42overlap, Ica of 51*, on a 108 Lsa. compared to the factory
250/129/114/264/37 overlap/Ica of 51*, on a 110Lsa.
Notice that Compression is still 129*, which is because the Ica is still 51*..
Notice I only gave up 3* of Power-Stroke.
Notice intake duration only increased 6*, and exhaust just 4*, but
notice that the overlap jumped 5* But here comes the big deal; with an intensity of 44* the 050 number jump to
212/216 exhaust, from
182/194.
Do the math; the intake is plus 30* and the exhaust is plus 22*
With each cam size being about 7*, These numbers are over 4 cam sizes bigger! where it counts. and, as it happens, the 42* of overlap is about the same as the old 340 cam which was 44*..
Finally, with this new cam size comes the difficulty of making the new higher lift-numbers work with your lo-lift heads.
The Cam I worked out is imaginary. But there are quite a few offerings of similar sizes from the various suppliers.
The point was not to point to a specific cam, but to show you what can be done, with the factory Ica.
Happy HotRodding
Last edited:
The sweet spot for either truck or car is.....it's already there. Don't eff with it.
Oh dear heavens!!!!
Did somebody just make sense in a few short words?
Common sense even?
Without a novel to write it out filled with piles of bullshit?
How can this be?
Truly a wizard of few words to often ignored for simple and sound advice while others shoot off the mouths and write baffling bullshit trying to trick into thinking they are smart.
How is this K.I.S.S. so often laughed at and disregarded as trash?
Start a new thread on your build ideas.
junkyardhero
Well-Known Member
i mean, i get it. i talk weird and i'm three raccoons in a trenchcoat.
so who's gonna take advice from three trash pandas who has weird phrasing?
Three gay rabid raccoons at that.
My post. Not directed at you.
junkyardhero
Well-Known Member
i know.
Then why did you quote me and add a disclaimer?
junkyardhero
Well-Known Member
i was commiserating
-
