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| 4.9L Cadillac Information (Page 8/11) |
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Will
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AUG 19, 12:02 PM
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| quote | Originally posted by Johns 4.9:
Hey Darryl,
Thank you for visiting my website. Estimating horsepower is a touchy subject. I hate throwing numbers out there. But my engines are built for road racing and autocross. I am more in to great handling and braking then I am about quarter mile speeds. So the square bore and stroke, 3.62, of these engines is never going to see high horsepower and high revs over 6200. The 4.9 engines is a good choice for a sports car but really not much of a dragster engine. So if your concerns are quick quarter mile speeds, you are better off with a different engine. But for handling and spirited driving, I like the torque and light weight of the 4.9 engine.
Cheers,
John |
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Spin some rollers so you don't have to estimate.
| quote | Originally posted by FieroWannaBe:
Stroke has very little to do with the ability of street engines to "REV" its has everything to do with airflow and camshaft timing, Neither of which this platform is designed for. What will happen, is with an identical top end, the lower displacement engine will achieve peak power and torque at a higher RPM. This has been proven time and time again the dyno.
Wear and tear is a factor, but it's affect on power production, as far as street engines are concerned, is effectively nil.
My point is, there is rarely ever a reason to not go with the maximum displacement possible. it makes reaching the desired power goal much easier, since engine speeds can be lower to achieve the needed airflow for a certain power level, provided you have the top end airflow (read: mass-flow) needed to reach that power level.
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92mm is the stock stroke of the 5.3, 5.7, 6.0 & 6.2 displacements of the LS family of engines... no one says they can't turn over 6200. RPM is all about displacement vs. airflow.
| quote | Originally posted by pmbrunelle:
Well if you're throwing out the stock heads and using custom-made billet heads, then the flow limitations of stock 4.9 (or stock-based) heads no longer apply to you. The sky is the limit.
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Heh... maybe yes, maybe no. I'll draw a parallel with a friend who wanted to turn a GenII V6/60 to 8000 RPM. Sure, the components are out there to build a valvetrain that will do it. A pushrod valvetrain that will turn that RPM is going to cost as much as the rotating assembly, though. The real kicker is that once the valvesprings are stiff enough to control the valvetrain at that RPM, there's a very real chance of breaking the rocker boss off the cylinder head. What do you do then? You're done. You've spent a lot of money and you're just not going to hit your goal. Full stop.
The same applies to radically upgrading any one part of an engine. Say OP does have 350+ CFM billet heads cut for the 4.9. Being designed from scratch, they would naturally have strong enough rocker bosses to turn 8000+ RPM, which is what the airflow in such heads would allow for a ~5 liter engine. Remember, GM put their first 350 CFM heads on a SEVEN litre engine and spun it to 7000 RPM. So now you have a top end that will flow air for 8000 RPM, you'll need a cam that will open the valves to allow the engine to make power at that RPM and a valvetrain that will turn that RPM. Since no one makes 4.9 cores, you're buying a billet cam. Is the timing chain up to turning that load at 8000 RPM? Is the rotating assembly up to it? You'll need rods & pistons, which is really rods & rod bolts & pistons & pins & locks & rings & bearings... What if you do all that and the oiling system in the block just can't move enough oil at enough pressure to keep the assembly lubricated? Dry sump? How much 4.9 is left after all that? It certainly wasn't a cheap swap at that point, and for the money spent there would be lighter options that would make more power.
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Johns 4.9
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AUG 19, 01:08 PM
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Not stroke, bore to stroke ratio. Physic still applies to a reciprocating engine. A Ford 302 will spin better because it has a shorter stroke and larger bore than the 4.9 engine. Almost the same displacement. A Ford 302 is 4" bore and 3" inch stroke. Less piston speed per stroke in the 302.
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Johns 4.9
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AUG 19, 01:13 PM
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FieroWannaBe
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AUG 19, 09:09 PM
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| quote | Originally posted by Johns 4.9:
Not stroke, bore to stroke ratio. Physic still applies to a reciprocating engine. A Ford 302 will spin better because it has a shorter stroke and larger bore than the 4.9 engine. Almost the same displacement. A Ford 302 is 4" bore and 3" inch stroke. Less piston speed per stroke in the 302. |
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The LS7 made peak power (6300) and torque (4800) at a higher RPM than any other previous GENIII/GENIV V8 from Chevy. It does that with a 4.0" stroke. It's 100% a function of the top end.
If I am trying to compute how efficient an engine is, I do not need to know at any time what it's stroke is, I need to know how efficiently it can move air.
Fords 302 has larger heads and cams available that will allow the engine to breath enough air to produce high power, and the cams have timing favorable for high RPM.
Nothing about the stroke of the 4.9L will limit its ability to make high RPM power, everything about the available camshaft heads and intakes will, and they don't change at all in the 4.5L.
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Warlordsix
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AUG 20, 07:48 AM
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Just wanna say....this is one of the best 4.9L threads in awhile. Great info and photos. Thanks to all who are commenting. Keep it coming!
Ernie------------------
'87 Fiero 4.9 5-speed
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Will
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AUG 20, 09:15 AM
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| quote | Originally posted by FieroWannaBe:
The LS7 made peak power (6300) and torque (4800) at a higher RPM than any other previous GENIII/GENIV V8 from Chevy. It does that with a 4.0" stroke. It's 100% a function of the top end.
If I am trying to compute how efficient an engine is, I do not need to know at any time what it's stroke is, I need to know how efficiently it can move air.
Fords 302 has larger heads and cams available that will allow the engine to breath enough air to produce high power, and the cams have timing favorable for high RPM.
Nothing about the stroke of the 4.9L will limit its ability to make high RPM power, everything about the available camshaft heads and intakes will, and they don't change at all in the 4.5L. |
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The LS7 has a 4.125 bore and 4" stroke... so it's NOT very oversquare.
NHRA Mountain Motors turn 8500ish RPM with strokes approaching 6 inches and are UNDERsquare.
Turning up and making power is about breathing, which is why the focus area in 4.9 performance is rightly on the heads and cam.
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FieroWannaBe
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AUG 20, 02:48 PM
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| quote | Originally posted by Will:
The LS7 has a 4.125 bore and 4" stroke... so it's NOT very oversquare.
NHRA Mountain Motors turn 8500ish RPM with strokes approaching 6 inches and are UNDERsquare.
Turning up and making power is about breathing, which is why the focus area in 4.9 performance is rightly on the heads and cam. |
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One cannot forget the intake. I believe it is where the real restriction lies in this engines, since they route the runners around the pushrods, forcing the air to accelerate twice, and then make the short radius turn into the valves. They air loses a lot of energy. You can see how the engineers curved the center ports in the head and intake to try to work around that.
The standard TBI intake has very small ports and a dual plane setup. It is set up for low speed torque, and short of re-fabbing entirely it is stuck that way. The Allante intake is very similar in setup to the TPI intake, very long skinny runners. Shortening them with and porting combined with a larger plenum will help shift the power curve, but it really needs to match the cam installed. I have a old 4.5l I decided to not swap years ago because after looking at all this, I just couldn't see it meeting my power goals per dollar spent. At the time 250whp NA seemed like it was almost too much work with available components at the time (2008-ish)
But it is possible, if the entire top end is designed with a common goal in mind. Cam, Intake, Heads.
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Reborn756
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AUG 20, 03:11 PM
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So, given all of the information presented thus far, it seems my idea of finding a machine shop to build a custom set of heads is the right direction. Now to find someone willing enough to eventually take my money and do it.
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- Darryl
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FieroWannaBe
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AUG 20, 03:19 PM
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the holes for the pushrods pinch the ports heavily.[This message has been edited by FieroWannaBe (edited 08-20-2020).]
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FieroWannaBe
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AUG 20, 03:23 PM
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| quote | Originally posted by Reborn756:
So, given all of the information presented thus far, it seems my idea of finding a machine shop to build a custom set of heads is the right direction. Now to find someone willing enough to eventually take my money and do it.
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It would be foolish not to acquire and dissect a set of factory heads first. Actually the project would be impossible without doing so.
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