1rwhp per c.i. = streetable. True or False Thread.
- Thread starter Pokageek
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edit - I did a little research and as it seems, production cars, (a little off topic but I'd like to address), most of the cars over the 1- 1 ratio are DOHC - yes true. That's a whole nuther subject too..
I know the DOHC cobra's aren't up there, unless you count the positive displacement blower equipped 03/04 Cobra, but that of course is not N/A
The 96-98 Cobra's get around 250rwhp, or in that range, and they have 281 cubic inches and rev near 7,000 rpm. So they make less than 1rwhp per cubic inch.
Same for the 99/01's, but they dyno around 270-285rwhp I think. Maybe closer to the 281 cubic inches. Either way it is very close to 1rwhp per cubic inch.
I think you can reach in the 1.1-1.2:1 ratio, if you aren't too picky...but I think 1:1 is a pretty good rule of thumb for a daily driver for sure.
Shamus O'toole
New Member
Grady, Awesome post!! You have def. done your homework on what you wanted out of your car. Great job in my eyes and not an easy accomplishment. It is def. easier to tune a car for WOT then for drivability as you have. Once again great job!!
VIPRETR
New Member
Honda S2000 DOHC 2 litre 240bhp. Thats approx 122cu. inches, 190rwhp, for a 1.6-1 ratio. ( If my calcs. are correct ) Not sure if this fits Grady's criteria, with the soft bottom end and being biased towards the track. i.e. harsh ride, too much in town shifting, and high RPM's on the highway. I know it's apples to oranges but I thought I'd give an example of a highly efficient, stock motored vehicle that def. beats 1-1 ratio.
) Not sure if this fits Grady's criteria, with the soft bottom end and being biased towards the track. i.e. harsh ride, too much in town shifting, and high RPM's on the highway. I know it's apples to oranges but I thought I'd give an example of a highly efficient, stock motored vehicle that def. beats 1-1 ratio.
WHITE94COBRA
New Member
I am going to elaborate more, but i'm at work late tonight, i'll talk about this more in the morning.
There's a long list of modern EFI cars whose engines are putting out at least 100hp/liter (1.64hp/ci) at the flywheel naturally-aspirated but they all have the following in common:
4 or even 5 valves per cylinder
DOHC per bank of cylinders
Peak HP comes at more than 7000rpm
and they may also have at least one of the following:
Variable length intake manifold
Variable intake valve timing +/- lift
Variable exhaust valve timing +/- lift
The last three are used to fill out the torque curve at low rpm so that these engines have good street manners despite having peak torque coming in at sky high rpm.
Now you might be wondering where our 5.0 engines come into the equation. Since the 5.0 has none of this modern technowizardry, I think it would be safe to say that peak HP should be not higher than ~6000rpm (I'm talking naturally-aspirated here) if the engine's going to perform reasonably well at low revs. That means 400hp or 80hp/liter (~1.3hp/ci) at the flywheel (or ~1.15hp/ci at the rear wheels) will be a realistic maximum for good streetability. Anything more and the idle is likely to be lumpy and the engine will feel soggy below 2000rpm.
4 or even 5 valves per cylinder
DOHC per bank of cylinders
Peak HP comes at more than 7000rpm
and they may also have at least one of the following:
Variable length intake manifold
Variable intake valve timing +/- lift
Variable exhaust valve timing +/- lift
The last three are used to fill out the torque curve at low rpm so that these engines have good street manners despite having peak torque coming in at sky high rpm.
Now you might be wondering where our 5.0 engines come into the equation. Since the 5.0 has none of this modern technowizardry, I think it would be safe to say that peak HP should be not higher than ~6000rpm (I'm talking naturally-aspirated here) if the engine's going to perform reasonably well at low revs. That means 400hp or 80hp/liter (~1.3hp/ci) at the flywheel (or ~1.15hp/ci at the rear wheels) will be a realistic maximum for good streetability. Anything more and the idle is likely to be lumpy and the engine will feel soggy below 2000rpm.
Thank You for the kind words
I do want to tell everybody the focus of what I was able to accomplish should be more on what others before me did than my individual efforts
I looked at combos that obtained results that were close to what I desired and asked their owners very specific questions about them.
I was very specific with my questions when talking to peeps like Ed Curtis for parts selection and various Tuning Gurus when planning out my combo.
Simply Put
I sought out the knowledge of those who did what I desired
cause
They be the folk that had the fruit of success I desired
Thats the thing thats so great about the internet
The info is so easily available to everybody
Grady
BlackVert
15 Year Member
my definition of streetable is similar to grady's ... a/c, power steering, no idle searching or bucking, no worries about stalling out on cold or hot starts, or coming to a stop at a stoplight.
as to >1 rwhp per cube being streetable ... absolutely it is possible, but it is not an overnight thing. when a 302 is putting down 350 at the wheels (or a 410 putting down 450), it can get pretty agressive, and that is when the above issues start coming into play.
like grady said, it comes down to how much time you can devote to the tune. for me, the tuning process is just beginning. i have my idle at 1200 when in drive, it starts right up either hot or cold, and idles solidly at 1200 when at a stop light. as time goes on and i get the injector slopes and injector timing right, i should be able to lower the idle rpms to closer to 850 and still have a solid idle with no startup issues. but it is going to take a while.
as to >1 rwhp per cube being streetable ... absolutely it is possible, but it is not an overnight thing. when a 302 is putting down 350 at the wheels (or a 410 putting down 450), it can get pretty agressive, and that is when the above issues start coming into play.
like grady said, it comes down to how much time you can devote to the tune. for me, the tuning process is just beginning. i have my idle at 1200 when in drive, it starts right up either hot or cold, and idles solidly at 1200 when at a stop light. as time goes on and i get the injector slopes and injector timing right, i should be able to lower the idle rpms to closer to 850 and still have a solid idle with no startup issues. but it is going to take a while.
It depends a lot also on the compression, look at those cars making more than 1.xx WHP, take a look on their compression ratio , you will see that most of them are on or above 9.5:1, they need more than 91 octane gas, otherwise they start to backup timing to avoid detonation, it would be interesting to see one car on regular gas, you will see how much HP they loose.
Actually most of them are running CR's of 10:1 or higher and indeed they require premium fuel to get maximum performance. With knock sensor timing retard the performance of most, if not all of those vehicles, would be degraded if they used lower octane fuel.
A good case in point is the new BMW M5; 5.0L V10, 500hp@7750rpm, 368lbft@6100rpm, redline 8250rpm, 12.0:1 CR.
Same displacement as our 5.0 engines, but maximum torque comes in at higher rpm than our engines make maximum HP.
