Limits of a street ported motor
05-27-08, 11:44 AM
#1
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Limits of a street ported motor
I was just wondering how far you can push the limits. There is some kid running around town with a street ported 6 port hitting 11k on the tack. I cant imagine its going to last very long. I have a street ported 4 port, and on occasion I take mine to 8k at the most. Is this pretty safe, or should I stay within the 7k redline of the original motor.
Also, what type of power should I be putting out with my set up. It has dual webber carbs, 38mm down draft I do believe and RB header and exhaust. Car runs really strong. I ran a guy in a 94 Impalla ss with intake, exhaust, tune and 373 gears, and I took him by just over a car through the 1/4 He had claimed to pop off a 14.3 at Xmiles an hour. Is this about right? Low 14s? The car is somewhat stripped. It has a bolt in cage but no door panels, no carpet or panels in the back, and most of what was under the dash had been removed. I also think it might have an aluminum fly wheel, but I have not confirmed it yet. My friend has one on his gsl se and both motors get back to idle at about the same time. I remember my old steel one in my 12a car took like 2 minutes to get to idle from a rev. lol Oh yeah, gears, still has the 391s of the gsl in it.
Also, what type of power should I be putting out with my set up. It has dual webber carbs, 38mm down draft I do believe and RB header and exhaust. Car runs really strong. I ran a guy in a 94 Impalla ss with intake, exhaust, tune and 373 gears, and I took him by just over a car through the 1/4 He had claimed to pop off a 14.3 at Xmiles an hour. Is this about right? Low 14s? The car is somewhat stripped. It has a bolt in cage but no door panels, no carpet or panels in the back, and most of what was under the dash had been removed. I also think it might have an aluminum fly wheel, but I have not confirmed it yet. My friend has one on his gsl se and both motors get back to idle at about the same time. I remember my old steel one in my 12a car took like 2 minutes to get to idle from a rev. lol Oh yeah, gears, still has the 391s of the gsl in it.
05-27-08, 01:14 PM
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redline depends on what parts are in the rotating assembly, and how fast you wanna kill it...
if you're running the heavy heavy 74-85 13b rotors with a stock flywheel, stock redline is for you, it'll go higher, but keep it under 7500, and it'll be happy
an rx8 engine is good to 9300 from the factory....
if you're running the heavy heavy 74-85 13b rotors with a stock flywheel, stock redline is for you, it'll go higher, but keep it under 7500, and it'll be happy
an rx8 engine is good to 9300 from the factory....
05-27-08, 01:17 PM
#4
For RPM, I would keep it below 7k unless the engine has had the proper mods for higher RPM operation. The guy in town is going to kill his engine by spinning to 11k, not to mention the possibility of the clutch/flwheel coming apart and cutting his feet off. Also, it depends on intake/exhaust/porting, but usually peak power is like 6-7k, so spinning higher just means that you are making less power while wearing your engine out faster.
05-27-08, 02:09 PM
#5
Yeah not even an ITO street port could make power at 11K. Either someone is lying about what RPM's they are actually running or someone is seriously revv happy. A street port, depending on port size, should make power to 8K at most but you need the poper internals to do it, ie. 3 window bearings, hardened stationary gears, ported oil galleys, and one of the most important is a well balanced rotating assembly just to name a few
05-27-08, 04:44 PM
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Yeah not even an ITO street port could make power at 11K. Either someone is lying about what RPM's they are actually running or someone is seriously revv happy. A street port, depending on port size, should make power to 8K at most but you need the poper internals to do it, ie. 3 window bearings, hardened stationary gears, ported oil galleys, and one of the most important is a well balanced rotating assembly just to name a few
05-27-08, 05:43 PM
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well, it pulls rather good and consistent up to 8k when I take it there. I usually shift between 7 and 7.5 though. So now that we have that question answered, what about the other stuff?
05-27-08, 08:05 PM
#10
OMG here we go again with rev'ng it below 8K. 
Thats not true. Shift only when it stops pulling. It will be past 9K. Im using SE rotors (same as the old school) and I dont have any issues in the past 10 years. I never babied my motors and I drive my cars like I stole them.
Thats not true. Shift only when it stops pulling. It will be past 9K. Im using SE rotors (same as the old school) and I dont have any issues in the past 10 years. I never babied my motors and I drive my cars like I stole them.
05-27-08, 09:22 PM
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81 Gs
I use to run my 4 port 13b to 10,000 rpm EVERYDAY. I would typically get 120,000 plus thousand miles out of my rebuilds. The assembly was never balanced. I had a Mazdatrix 17 lbs flywheel, Racing Beat 550 Holley and the Racing Beat exhaust. I injected my oil into the intake under the Holley so it wasn't premixing with the gas in the float bowl. Then I put the blower and nitrious on it... I remeber those days well...
05-27-08, 09:38 PM
#18
I am just going to use a dyno graph from a LS2 engine, since that was what google gave me.
As you can see, full power is about 460 @ 6100rpm. If you shift slightly beyond that point your RPM will drop. Lets just say that if you are doing 90mph in 3rd gear, shift at 6100 RPM, the next gear (4th) will bring you to to a lower RPM but at the same speed. Lets just say that it drops it 1500 rpm. You are now making about 400ish hp at 4600rpm. That is less power than if you held it until at least redline. The goal of shifting is to make the most power per gear allowable. If you make more power after your peak 6100rpm versus shifting at your car after the peak, then you are not using all the HP your car can muster.
Did I confuse? Basically, every time you shift, you want to be in the RPM band that makes more power than where you are currently at pre-shift.
As you can see, full power is about 460 @ 6100rpm. If you shift slightly beyond that point your RPM will drop. Lets just say that if you are doing 90mph in 3rd gear, shift at 6100 RPM, the next gear (4th) will bring you to to a lower RPM but at the same speed. Lets just say that it drops it 1500 rpm. You are now making about 400ish hp at 4600rpm. That is less power than if you held it until at least redline. The goal of shifting is to make the most power per gear allowable. If you make more power after your peak 6100rpm versus shifting at your car after the peak, then you are not using all the HP your car can muster.
Did I confuse? Basically, every time you shift, you want to be in the RPM band that makes more power than where you are currently at pre-shift.
Last edited by Jeezus; 05-27-08 at 09:41 PM. Reason: 4600hp? I ment RPM :)
05-27-08, 09:43 PM
#19
I use to run my 4 port 13b to 10,000 rpm EVERYDAY. I would typically get 120,000 plus thousand miles out of my rebuilds. The assembly was never balanced. I had a Mazdatrix 17 lbs flywheel, Racing Beat 550 Holley and the Racing Beat exhaust. I injected my oil into the intake under the Holley so it wasn't premixing with the gas in the float bowl. Then I put the blower and nitrious on it... I remeber those days well...
05-27-08, 10:07 PM
#20
I need a new user title
Actually, you just want to maximize the area under your power curve. Typically that means shifting such that you're making the same power before and after shifting, but not always (depends on the shape of your power curve).
05-27-08, 10:37 PM
#23
Limitations are carbs size and tuning or going mad with EFI. As Wacky as aforementioned...rotaries can easily turn high RPM's. My 12A will still pull hard above 8000 with a modified Nikki....13B will effortlessly rev to 9000+ with no popping or hesitation on a 48 IDA.
My new streetport carb will be a 60mm Terminator IDA-style with custom chokes....going for 210rwhp easy...no nos, '85 rotors, stock steels....etc....
My new streetport carb will be a 60mm Terminator IDA-style with custom chokes....going for 210rwhp easy...no nos, '85 rotors, stock steels....etc....