6.5L rebuild adventure finally begins
08-30-2008, 12:58 PM
#46
Three Wheelin'
I guess I over looked this thread when it started. I am not an expert, but can provide some answers to some questions
I don't know about the strokers only producing 330-350 rwhp, but would suspect as speculated they are just stroker short blocks without the cams and head work to get the extra hp. Based on what has been done before, getting to @400rwhp should be straight forward, but includes 968 valved heads and at least GT cams. Based on my build in progress experience, you can add $5k to the cost with just those items.
The 500+rwhp stroker motors do not have forced induction.
Off the top of my head, all of the following are stroked and bored @6.5L, none are forced induction, all are @500rwhp (possibly even in the order of their appearance):
Joe Fan
Mark Anderson
Tom Falkenbeg (Don Hanson's old race car)
Louie Ott
John Veninger
All of the above
I don't know about the strokers only producing 330-350 rwhp, but would suspect as speculated they are just stroker short blocks without the cams and head work to get the extra hp. Based on what has been done before, getting to @400rwhp should be straight forward, but includes 968 valved heads and at least GT cams. Based on my build in progress experience, you can add $5k to the cost with just those items.
The 500+rwhp stroker motors do not have forced induction.
Off the top of my head, all of the following are stroked and bored @6.5L, none are forced induction, all are @500rwhp (possibly even in the order of their appearance):
Joe Fan
Mark Anderson
Tom Falkenbeg (Don Hanson's old race car)
Louie Ott
John Veninger
All of the above
To get good horsepower, you must provide the engine with the best breathing capability (valves, ports, intake, exhaust) and have a cam and valve train that will maintain that good breathing at high rpm. Increase compression ratio to the limit of the fuel you'll use. Horsepower is torque x rpm. The torque has to be maintained at the higher rpms. Cubic inches alone does not guarantee a high output motor. In general terms, cubic inches determines the amount of torque. The breathing capability of the whole package determines where in the rpm range that torque will be available. Torque at high rpms = high hp.
08-30-2008, 01:04 PM
#47
Three Wheelin'
Based on my research the key point here is that @400-420rwhp is often achieved with a stroked/bored motor, including head/cam work.
The jump to 500rwhp is the result of intake work. Mark & Joe have effectively one-off carbon fiber intakes with throttle bodies. Tom F., Louie O. and John V. all use throttle body intakes with adapter plates. Engine management varies from stock (possibly with Sharktuner) to DTA to Motec.
Devek did claim to produce a 500rwhp motor by modifying the stock intake, as I recall. I don't know where that motor is or if the result ever made it to be a product that could be sold.
The jump to 500rwhp is the result of intake work. Mark & Joe have effectively one-off carbon fiber intakes with throttle bodies. Tom F., Louie O. and John V. all use throttle body intakes with adapter plates. Engine management varies from stock (possibly with Sharktuner) to DTA to Motec.
Devek did claim to produce a 500rwhp motor by modifying the stock intake, as I recall. I don't know where that motor is or if the result ever made it to be a product that could be sold.
08-30-2008, 01:05 PM
#48
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Thanks for the reminders that it takes more than just 6.5L to make big power, but THAT is a good place to start FOR SURE! Was thinking last night how if the 928 had been released originally w/ the 5.0 300HP+ motor that was planned the GTS's would have ended up at 6.5L and been making 450HP+ and we would probably still be able to go down to the dealer and look at new ones for sale today!
For example, I always think of boring but not stroking. This would "save" the cost of a crank and the heads/cams/intake would probably be up to the task, but you "only" get to a 5.4L motor (from 5.0L) and the expected result is not enough for the cost. If you decide you want the crank later, you need a different set of rods, so an expensive "throw-a-way" for the later upgrade at @$1.5k
You could build a stroker shortblock and save $5k by not doing the heads and intake, but again you may only get to that @350rwhp result and still have spent $10k. Of course the later upgrade doesn't have you throwing away parts, except gaskets, etc.
The other often overlooked value of a stroker motor is that it is a rebuilt motor. The "standard" supercharged motor is not rebuilt. Of course in this topic's case, the candidate motor has only 28k miles on it, so probably didn't need to be rebuilt anyways and 928 motors don't necessarily need any work just because they have many miles on them.
Living in emission states definitely raises the value of building a stroker motor vs. having to de-install a SC periodically, otherwise for the street SCs seem like a great idea.
Personally I am still waiting for SC 928s to be proven on the track in race conditions. I believe Carl F. is planning on racing his soon.
08-30-2008, 01:06 PM
#49
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08-30-2008, 01:34 PM
#50
Race Director
strokers are NOT the most cost effective way to make more HP...but for those of us in the Republic of Ka with are smog laws, its the only option that will pass bi-annual smog inspection....no way around it until a SC kit gets CARB approved, which is pricey...
08-30-2008, 01:35 PM
#51
Three Wheelin'
Naturally, I don't know the details of Devek's work. Here is how I'd do a high output 6.5L motor using the stock intake. There are a few things known to help. Extrude hone the intake. Space out the side plates as far as you can. Remove the flappy valve. Use a larger throttle. This all on top of ported heads with 968 intake valves and better valve springs. Ti retainers. Proper cams with more lift and duration than GT cams. If your goal is really 500+ hp with the stock intake, then compression ratio about 12.5:1 and race fuel. John Speake SuperMAF and SHARKTUNE it. I cannot believe the number of highly modified engines where people put in a lot of $$ and they won't spend a few more to get it properly tuned. Often they end up with a box of oily pieces. Properly tuned for a street driven modified engine is not adjusting a RRFPR. Spark timing is very important. I know, I'm too **** about it. This will get a 500+hp NA 928 motor that is barely streetable.
08-30-2008, 02:38 PM
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I look forward to getting you guys some fresh numbers in a month or so (hope hope) when the motor is back in the car and we get it on the dyno.
The head is being ported and matched to the new larger valves last I checked, so I assume we'll be into assembly and sharktuning at some point in September here. These things always take longer than you'd expect. Latest delays were in getting the 968 valve seats from Porsche - they sent us enough for 6 cylinders, but for some reason we needed 8...
I'm staying away from race fuel and stratospheric compression. This thing is gonna look surprisingly stock, especially in the engine bay, it's gonna have a factory cat still on it (gasp), and it will be tuned to the best pump fuel we can get in California (which is crap, but that's what we've got). Tuning will be biased slightly towards extra torque than all-out top end HP. I'm hoping for roughly 400 hp at the rear wheels, but it's the ~440 ft-lbs (pray pray) that I really want access to.
The head is being ported and matched to the new larger valves last I checked, so I assume we'll be into assembly and sharktuning at some point in September here. These things always take longer than you'd expect. Latest delays were in getting the 968 valve seats from Porsche - they sent us enough for 6 cylinders, but for some reason we needed 8...
I'm staying away from race fuel and stratospheric compression. This thing is gonna look surprisingly stock, especially in the engine bay, it's gonna have a factory cat still on it (gasp), and it will be tuned to the best pump fuel we can get in California (which is crap, but that's what we've got). Tuning will be biased slightly towards extra torque than all-out top end HP. I'm hoping for roughly 400 hp at the rear wheels, but it's the ~440 ft-lbs (pray pray) that I really want access to.
08-30-2008, 04:27 PM
#53
How close is an ethanol station to SB?
08-30-2008, 04:40 PM
#55
Three Wheelin'
08-30-2008, 04:47 PM
#56
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Stan,
To get good horsepower, you must provide the engine with the best breathing capability (valves, ports, intake, exhaust) and have a cam and valve train that will maintain that good breathing at high rpm. Increase compression ratio to the limit of the fuel you'll use. Horsepower is torque x rpm. The torque has to be maintained at the higher rpms. Cubic inches alone does not guarantee a high output motor. In general terms, cubic inches determines the amount of torque. The breathing capability of the whole package determines where in the rpm range that torque will be available. Torque at high rpms = high hp.
To get good horsepower, you must provide the engine with the best breathing capability (valves, ports, intake, exhaust) and have a cam and valve train that will maintain that good breathing at high rpm. Increase compression ratio to the limit of the fuel you'll use. Horsepower is torque x rpm. The torque has to be maintained at the higher rpms. Cubic inches alone does not guarantee a high output motor. In general terms, cubic inches determines the amount of torque. The breathing capability of the whole package determines where in the rpm range that torque will be available. Torque at high rpms = high hp.
08-30-2008, 04:49 PM
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I doubt that. If the heads were ported and the pistons were notched for the valves you would produce way more HP with a 16v. I imagine you could run a much larger cam with the 16v than the 32. If you want HP your going to need a much larger carb. your going to be looking at close to 800/900 cfm to support 500 hp
08-30-2008, 05:14 PM
#58
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I doubt that. If the heads were ported and the pistons were notched for the valves you would produce way more HP with a 16v. I imagine you could run a much larger cam with the 16v than the 32. If you want HP your going to need a much larger carb. your going to be looking at close to 800/900 cfm to support 500 hp
Not sure why you think 2 valves are better than 4 though, seems clear to me that essentially all new motor development in the past 20 years has found value in more valves than 2. I wouldn't think they are doing it to increase the cost without return.
By the way 928s don't use carbs.
08-30-2008, 05:57 PM
#59
Three Wheelin'
I doubt that. If the heads were ported and the pistons were notched for the valves you would produce way more HP with a 16v. I imagine you could run a much larger cam with the 16v than the 32. If you want HP your going to need a much larger carb. your going to be looking at close to 800/900 cfm to support 500 hp
08-30-2008, 06:29 PM
#60
TECHNICALLY, The cam ramp and total lift is MORE limited in the 2V setup as it exists than in the 4V. If you were to remove the bearing size issue in the 2V, then maybe, at least, it would be cheaper (no cam toothed gears in the middle).
The 2V heads are limited in port size and shape, as well as valve size by the combustion chamber size, as well as the castings.
The 4V heads are also limited, but at a much higher value. More work can be made on them.
.... at least I think so...
The 2V heads are limited in port size and shape, as well as valve size by the combustion chamber size, as well as the castings.
The 4V heads are also limited, but at a much higher value. More work can be made on them.
.... at least I think so...