At the moment I have 650rwhp 599rwtq with full exhaust and tvs setup. Was thinking of going e85 but don't want to blow motor. I've heard stock block can handle 650-700rwhp and be ok. Anything above it's possible to break anytime. Thanks
What's my stock 03 Cobra motor capable of handling without pushing it past limits?
- Thread starter d1sc46
- Start date
Stock block is good to 1000hp. The internals, with your pistons being the weak point, are good to around 850rwhp (just to be on the safe side). There are guys who have pushed well beyond that though. With a proper fuel setup and tune, E85 will only help you obtain your power goals.
Last edited:
What gas are you on now? Wouldn't it make your motor more safe running E85?
I'm currently on 93. But wanted to upgrade this winter to e85, but will not be cheap lol.. Thanks for info
I've heard you really don't want to go much north of 700 rwhp. Curious what kind of longevity testing your basing the 850 on.
Strength wise the stock motor can support over 1000whp. You'll stretch the headbolts and blow the gaskets before you overpower the forged pistons, rods, and crank.
That being said it is safe in short bursts. Heat is the killer in these engines. The forged pistons are set with a tight piston to wall clearance for emissions reasons. When you put serious heat to it for extended periods the forged pistons expand too much and drag the skirt on the cylinder wall resulting in a burned piston. Combine that with the known poor coolant flow to cylinders 7&8 and you see why heat is the killer.
E85 / E98 is an alcohol and burns cooler. Less heat on the pistons = more tolerance to extended pulls.
That being said it is safe in short bursts. Heat is the killer in these engines. The forged pistons are set with a tight piston to wall clearance for emissions reasons. When you put serious heat to it for extended periods the forged pistons expand too much and drag the skirt on the cylinder wall resulting in a burned piston. Combine that with the known poor coolant flow to cylinders 7&8 and you see why heat is the killer.
E85 / E98 is an alcohol and burns cooler. Less heat on the pistons = more tolerance to extended pulls.
Interesting… So I installed the cooling mod linking the two heads in the back via the freeze plug on the driver side head + I'm running E85, so what do you think I'm capable of making safely? I never do 5th and 6th gear pulls…
It'll take all you can throw at it. The 700whp number is common because people push the limits with 93 octane. One bad batch of pump gas and they detonate the motor to hell. The same inconsistent octane / AFR problem is found in E85 which is why ethanol test kits are so popular. Keep it safely rich, cool, and don't let it detonate and it'll last for quite a while at any power level.
so safely rich - I keep it under 12.0 at WOT (gas equivalent) - 11.7-11.9 or so. Would you consider that safe?
Gas equivelant 11.5 MINIMUM. You're talking about pushing it hard with big boost so I'd suggest 11.0-11.2 if you want a long healthy life with stock pistons. The extra HP gained by leaning it out comes at a price... HEAT.
Change the pistons to something with some more PTW and ring gap clearance and you can run it a bit hotter / leaner without fear of dragging a skirt. Stud the heads and the sky's the limit.
Lower IAT's is basically free power. You haven't specified your setup but big boost with roots / twin screw blowers comes with high IAT's. Consider a small dry shot of N2O to cool it off if you're going to push >25psi.
Change the pistons to something with some more PTW and ring gap clearance and you can run it a bit hotter / leaner without fear of dragging a skirt. Stud the heads and the sky's the limit.
Lower IAT's is basically free power. You haven't specified your setup but big boost with roots / twin screw blowers comes with high IAT's. Consider a small dry shot of N2O to cool it off if you're going to push >25psi.
I'm at pretty high altitude in Colorado… live at 7000, drive between 5000-8000 feet. DA's in the summer reach 9000 sometimes. So I run a 2.75 pulley on my whipple 2.9 and its pegging my overlay boost gauge around 20-21 psi max. Its E85, return fuel system, AFCO heat exchanger, cooling mod for the heads. I have it currently running between 11.7-11.9 AFR (gas equivalent). I test my fuel a lot because is can be inconsistent in Colorado. I've seen a few stations pumping out 72%. But I always try to run 85 or better.
I haven't dyno'ed it up here, but in Florida it had a 3.5 pulley at 19-20 psi and it made around 680-700 to the wheel. Pretty conservative.
Users who are viewing this thread
