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Old 01-19-2011, 06:19 AM
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Default How to increase TORQUE in a big block ??

With the demise of the 8.1 and the supply of 8.2's limited to a very expensive Mercruiser, alot of folks will be forced to rebuild their 454, 496, or old 502 or replace with a rebuilt longblock.

Since most folks [other than the raceboat crowd] will usually be between 2800 to 3500 RPM at cruise speed, if I were to install a rebuilt big block, I would want to maximize torque in this RPM range so that the engine could work a little less and I could keep the secondaries closed and get better fuel economy.

What can be done to increase the torque of these engines, and/or to flatten the torque curve ? Notice I said torque, NOT horsepower. Going from 330 to 415 hp doesn't do much good if you have to stay spooled up north of 4200 RPM to get the extra horsepower.

Please address changes for carbed engines, TBI engines, and MPI engines. I suspect that signficant changes to an MPI engine could require remapping the fuel injection software, but I don't know much more than that.

So, Billinstuart and other gas engine gurus, school me !

And yes, I know that going to diesel would give me plenty of torque and better fuel economy, but please humor me.
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Old 01-19-2011, 06:41 AM
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I'm no engine builder, but would a different crankshaft that allows for a longer stroke be the first step?
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Old 01-19-2011, 06:46 AM
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I do not know; that is what I am trying to find out.
It seems to me, though, that is you change the crankshaft to give it a longer stroke, you would also have to install shorter pistons or extend the cylinders [obviously not practical] to accomodate the longer stroke, otherwise you would slam the piston into the head, depending on the existing compression ratio.
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Old 01-19-2011, 06:55 AM
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Yes you can stroke the motor, but parts and labor costs increase quickly.
Why do you not want to increase hp..........it does the work?
You can build in more hp @ the rpm you are looking for and will (in all cases I have ever seen) increase torque.
A good engine builder can get you the #s you need
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Old 01-19-2011, 07:07 AM
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If the starting platform is a 454, the easiest way to more torque is probably to bore and stroke it to 489 or 496 and then camming it up to take advantage of the additional displacement. If one isn't already part of the package, installing a roller cam will also help. Next up would be working the cylinder heads for more flow - or simply installing better flowing heads.

Intake and exhaust system attention will be necessary at some point but not critical in an application where the engine is spending most of its time below 4K RPM. Unless, of course both are already woefully restrictive.

Certainly, the key is the camshaft. For example; I have a 489 on an engine stand that is just about ready to go into my old car. Dyno numbers show peaks just shy of 500 HP, and just a bit over 600 Ft/Tq. Impressive part, to me, is that it is making 500 Ft/Tq by 2000 RPM and is still making 500 Ft/Tq just past 4500. If I recall, torque peaks around 3700. Only down side is that it will probably end up idling around 750-800 RPM - a bit high for no wake speeds.

If the platform is already a close to 500 CI engine, cam and heads, followed by induction and exhaust.
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Old 01-19-2011, 07:10 AM
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Ok, on the engine torque thing, let me start by saying that other than racing applications it has been my experience that bore beats stroke 2:1. Some engine builders and machinest would disagree and thats their oppinion. The way to increase torque without a major change in engine blue print is to change the cam, and if carburated, go down in size on the carb. There are alot of camshafts on the market that address torque. Iskendarian, Ultra Dyne, and Comp, just to name a few. These cams are designed with just a slight increase in lift, and the duration adujusted to leave the valve open for optimum performance increase for the application. Changing the cam and carb are a couple of the easiest ways to increase torque, and can be done efficiently by a good marine or auto mechanic with the the engine remaining in the boat. These cams should be advanced at minimum 4 degrees when installed. I think starting here would be the way to go. There are alot more things that can be addressed about Hp and Torque, so many in fact that a 1000 page book could be written on the subject. I have been building performance marine and racing engines since 1979 and will be glad to help with any further questions. Once again there are a hundred different oppinions on the subject, Im just throwing this one out because its a simple start.
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Old 01-19-2011, 07:18 AM
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Buy a GM Performance truck engine. They've already figured it out.
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Old 01-19-2011, 07:28 AM
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To properly answer the question some sort of budget figure or goal would help. As others have noted, changing the cam would be the simplest step. a cam that is about 210 degrees on the intake and 230 on the exhaust will lower the torque peak into the 3500 area. Going to 200/210 should bring it down to about 3200. Power in an engine is all about cylinder filling. A small cam fills the cylinders better at low RPM, but sacrifices top end in the process. A roller cam will make a minor improvement as will changing over to the Comp Cams beehive valve springs. For reasons I still don't understand, the springs can add about 20 lbft of torque in the midrange.

Big blocks come with two types of heads; the rectangular port and the oval ports. The lower flow velocity of the rectangular ports hurts their performance in the lower RPM ranges, so be sure you have the small port heads. Changing from fuel injection to carb or vice versa is not going to have much effect. An engine needs a given amount of fuel for any load and in the ranges most marine engines run, either system works.

Adding stroke is the best way to gain lots of torque, but it is also expensive. You can build most big blocks into 540s with little problem. Here's an article on a build up Hot Rod did that produces 650 lbft at 4200. That is torque in anyone's book.
http://www.hotrod.com/techarticles/e...ine/index.html
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Old 01-19-2011, 07:31 AM
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"Why do you not want to increase hp..........it does the work?
You can build in more hp @ the rpm you are looking for and will (in all cases I have ever seen) increase torque."

Horsepower does not do the work, torque does, at least in an inboard engine. If you are increasing horsepower at a specific RPM, by definition you are increasing the torque.

Horsepower = Torque x RPM/ k

k is a constant; Torque is in pound-feet, and RPM is in revolutions [or rotations] per minute.

So to increase horsepower, you either increase torque, or you increase RPM. In order to build in more horsepower in the 2800-3500 rpm range, you must increase the torque since the horsepower range is already fixed in this example.

When engine sellers, builders, re-builders, manufacturer's, etc. state the horsepower of their engine, they are stating maximum horsepower. Maximum horsepower is produced within 5 % of the maximum RPM for the engine. If the builder just manufactures the engine with a higher maximum RPM capability, it will increase the maximum horsepower, but if the user does not operate the engine at this higher RPM that extra horsepower is nver reached nor is it ever used.

If you have 454's rated at 330 hp, the only time you are using the 330 hp is when it is at 4200-4300 RPM or higher. When you are at 3200 RPM, you are using considerably less horsepower.

I am looking for engine changes that produce more useable horsepower in the RPM range that most boaters use their boat- 2800-3500 RPM. This REQUIRES increased torque. If it produces more torque at, say 3200 RPM, then you could cut the RPM down to 3000-3100 and get the same speed as at 3200, resulting in 1) less fuel burned, and 2) longer engine life.
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Old 01-19-2011, 07:39 AM
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FWIW, the 454 330hp have the oval port heads and a cam that is about 220/230. The 454 magnums came with the rectangular port heads and bigger cams.

I agree - it is all about torque and where you want to be able to use it. I have a street vehicle with an engine that is nearly identical to the one described in the Hot Rod build up. Except, I kept the cam a little smaller at 232/242 and the low end torque is astounding.
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Old 01-19-2011, 07:40 AM
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Increase displacement and cam appropriately. Cheapest way to increase displacement is boring. For more get a stroker crank set with the appropriate rods and pistons.

This is not rocket science.

If there is a 1/4 or 3/8 mile circle track near you visit the pits on race night and find out which shop does most of the engines for the top dogs. You can often find that information from the stands if you read the advertisements on the cars. Part of the price for an engine is usually a mention on the car. With that information in hand visit the shop and talk to the boss about your needs. There are a lot of benefits to getting engine work done locally.
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Old 01-19-2011, 07:53 AM
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Your desire makes sense.....but power costs money. I've often heard "how fast can you AFFORD to go".
You can spend a small amount during a re-build and replace the cam and carb, netting a small amount of increase. You can spend a little more and replace the heads and exhaust during a re-build and get a little more power/torque. You can spend alot by increaing bore/stroke (which is crank/rods/pistons), and increase compression at the same time and net a huge increase. It all depends on your financial comfort level.

With the exception of exhaust or a mild cam change, any other changes to a MPI engine will need re-programming.....and this is best done on a dyno where they can monitor exhaust readings, knock sensors, etc.

On my last boat we built 540's and used smaller heads (ported 308's) and higher compression (9.8/1) with a cam (298/306 adv, 244/244 @ .050, .610/.632 on a 114LC). Airflow was restricted by the EFI intake which held back HP...but might have increased TQ. Fully dressed with my exhaust on a dyno they were making 670/lbs TQ at 3,400, peaked at 697 at 4,300, and was still carrying 580 at 5,600. Horsepower peaked at 630 turning 5,200. Other than the fact I had to run 93 octane and it cost alot to build, this is what your looking for......how much power can you afford/justify building????


edit: apparently I was typing for awhile....Kerno mirrors what I'm trying to say above.
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Old 01-19-2011, 07:58 AM
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1) Kerno is right, we do need some budget boundaries for this. A Generation V 454 reman from 1800runsnew.com is $3095 with 4 bolt mains, plus shipping. Lets use $3500 as the limit for a local quality rebuild, unless someone has a better suggestion.

2) To further refine our options, lets look at things that can be done when the engine is still in the boat [like cams], AND look at things to be done as part of a rebuild.

Also, my specific question is focused on getting more lower end torque without burning more gas, so that should be considered. My question is not about going faster, it is about cruising on plane at lower RPM and extending engine life a little. I would not mind sacrificing a few knots from the top end to attain this.
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Old 01-19-2011, 08:21 AM
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Unfortunatly, boring a block typically only gains a small handful of cubic inches. For instance, boring a 454, which has a 4.250 bore, .030 over only nets just over a 6 cubic inch displacemet increase and going another .030 results in a total of 468. At some point the block runs out of sufficient cylinder wall thickness - compromising reliability/longevity/rebuildability). Boring does bring another benefit - better air flow because the valves are now that much farther away from the cylinder walls.

There are a lot of ways to do this, just depends on how much you want to gain, and how much you want to spend. I can't imagine that anyone is going to really "notice" a 10 or 20 Ft/Tq gain, but 50 would be apparent.

Yeah, factory rectangular port heads on a "small" big block hurts low RPM torque because they can't produce enough velocity through the ports for good filling at low RPM. Those same heads on a big displacement block are a different story.

Kern, that 232/242 cam in a 540 must idle almost like a stocker.
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Old 01-19-2011, 08:45 AM
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Quote:
Originally Posted by Captain Crispy View Post
"Why do you not want to increase hp..........it does the work?
You can build in more hp @ the rpm you are looking for and will (in all cases I have ever seen) increase torque."

Horsepower does not do the work, torque does, at least in an inboard engine. If you are increasing horsepower at a specific RPM, by definition you are increasing the torque.

Horsepower = Torque x RPM/ k

k is a constant; Torque is in pound-feet, and RPM is in revolutions [or rotations] per minute.

So to increase horsepower, you either increase torque, or you increase RPM. In order to build in more horsepower in the 2800-3500 rpm range, you must increase the torque since the horsepower range is already fixed in this example.

When engine sellers, builders, re-builders, manufacturer's, etc. state the horsepower of their engine, they are stating maximum horsepower. Maximum horsepower is produced within 5 % of the maximum RPM for the engine. If the builder just manufactures the engine with a higher maximum RPM capability, it will increase the maximum horsepower, but if the user does not operate the engine at this higher RPM that extra horsepower is nver reached nor is it ever used.

If you have 454's rated at 330 hp, the only time you are using the 330 hp is when it is at 4200-4300 RPM or higher. When you are at 3200 RPM, you are using considerably less horsepower.

I am looking for engine changes that produce more useable horsepower in the RPM range that most boaters use their boat- 2800-3500 RPM. This REQUIRES increased torque. If it produces more torque at, say 3200 RPM, then you could cut the RPM down to 3000-3100 and get the same speed as at 3200, resulting in 1) less fuel burned, and 2) longer engine life.
My bad, I thought you were asking how to increase your torque with out adding Hp

Quote from your original post : What can be done to increase the torque of these engines, and/or to flatten the torque curve ? Notice I said torque, NOT horsepower.

I stand by its the hp that does your work
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Old 01-19-2011, 08:59 AM
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Quote:
Originally Posted by Captain Crispy View Post
1) Kerno is right, we do need some budget boundaries for this. A Generation V 454 reman from 1800runsnew.com is $3095 with 4 bolt mains, plus shipping. Lets use $3500 as the limit for a local quality rebuild, unless someone has a better suggestion.

2) To further refine our options, lets look at things that can be done when the engine is still in the boat [like cams], AND look at things to be done as part of a rebuild.

Also, my specific question is focused on getting more lower end torque without burning more gas, so that should be considered. My question is not about going faster, it is about cruising on plane at lower RPM and extending engine life a little. I would not mind sacrificing a few knots from the top end to attain this.
Now I got it.
Do you have room in the front of the engines to pull the cam?
If so there are lots of good combos for good in frame builds if the short block is in good condition, that said a good engine is more than the sum of its parts.
Assembly is a major factor, I have seen many good piles of parts add up to terrible results.
As mentioned a good local builder with a good machine equipment and the ability to use it will give you more than you can use.
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Old 01-19-2011, 09:05 AM
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Is there any particular reason forced induction designed specifically for the 2800-3500 rpm range is not feasible?
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Old 01-19-2011, 09:06 AM
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Actually, the "easiest" way to increase torque may be to supercharge the engine. Unfortunately since you are talking about a carbureted engine, even a low pressure supercharger would probably require significant engine mods.
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Old 01-19-2011, 09:14 AM
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Quote:
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Actually, the "easiest" way to increase torque may be to supercharge the engine. Unfortunately since you are talking about a carbureted engine, even a low pressure supercharger would probably require significant engine mods.
I just love it when the shadetree mechanic Bubbas go install a supercharger and immediately go melt a few pistons. Or a monster sized shot of nitrous and throw a few rods through the oil pan !

Gotta love them 'bolt-ons'
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Old 01-19-2011, 09:34 AM
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[quote=Captain Crispy;3473925

Horsepower does not do the work, torque does, at least in an inboard engine. If you are increasing horsepower at a specific RPM, by definition you are increasing the torque. [/quote]

Say what?

Torque is nothing more than a twisting moment. You can have all the torque in the world and have no power produced or work done.

Horsepower by its very definition is a measure of work performed.

Horsepower of course is based on torque but torque alone won't do anything.
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