It was the Chevy Pistons Trev. They were supposed to be forged,
It's easy enough to tell a forged piston from a cast one but I'd need to see more of pics of them. but they distorted around the valve cutouts with only 6psi of boost and no nitrous. There were no signs of degradation or melting. They just seemed to go soft under mild load. I've taken Rover cast pistons past this much power on nitrous only.
They may not have suffered in the normal way from signs of a lot of heat but there's plenty of signs that EXCESSIVE heat was the cause!!!!
I can say with a great degree of certainty that either the bore was too tight or the ring gaps weren't big enough, as the piston crowns have been DRAGGED UPWARDS and there's ONLY 2 ways that can happen;
1) The excess heat caused the rings to butt up and they locked in the top of the bores, so that when the piston tried to move down again, the rings tried to lift the crown off.
2) The excess heat expanded the crown more than there was adequate clearance for and in the process the crown momentarily seized at the top of the bore and as the rest of the piston tried to move down it lifted the crown before breaking the seizure.
It could even have been both at the same time and you can actually see the seizure areas quite clearly, to prove number 2 certainly happened. They distorted and hit the heads and scuffed the bores. On left hand side there may be a hint of melting but I was running 12 degree's of retard for 6psi of boost with AFR showing mid 11's. The sharp edges on the valve cutouts on top of the piston are pristine with no signs of metling.
Excess heat caused by blowers causes different damage to heat caused by nitrous, so it's easy to be mislead when you've not had much experience of blower related damage.Maybe the rod failure was just bad luck.
NO that would be as a result of the piston/s seizing/locking up in the bore/s and suggested that the seizures occurred just before TDC and then continued through to after TDC, subjecting the rod/s to immense force breaking the seizures. The old engine did have 180,000 miles on it. And it was only 1 rod. All the others were fine.
That indicates that the one damaged piston/rod was running hotter than the others, causing the piston/ring to expand more than the others. I'm only going to run the blower to about 75% so as not to stress it too much, and then use nitrous to top it off for my final power adder.
You'd have more success with nitrous alone as it doesn't heat the air charge like a blower does but at least adding nitrous to the mix with the blower will certainly help.
I can say with 100% CERTAINTY that the rod failure was NOT due to excess power and was ENTIRELY DUE to the piston seizure. Mainly because the blower is not very controllable. Once I've spooled up about 20 feet off the line the blower is all or nothing. But if I keep the boost down a bit I know I can control the extra power very smoothly even with old FRED
Another overriding reason for nitrous..... UNRIVALLED CONTROL.I only need ONE power ramp. Thats for 1st gear only as I'm at WOT straight off the line and I dont need to back off for gear shifts with the auto box and ratchet shifter. Although my ign retard control is fixed so I have no ability to alter that during a run.
That's far from being desirable, that's for sure.The engine is at peak torque rpm very quickly off the line which is where I shift gears. The down side I've experienced with the low revving Rover has been after the 1/8th mile marker where I'm in top gear (normally running around 6 seconds to 107mph) and then slowly moving above my peak torque rpm where the engine then starts to just soften off. I'm wondering if at this higher rpm I should be adding timing back in?? 6 seconds to 107 and then the slow haul to 131mph in another 4-5 seconds.. It seems like a lifetime from inside the car??
There's a whole bunch of potential reasons for that but I wouldn't start playing with timing as my number one option, as that could cost you another engine.I'm so close to a 9 second ticket that I can almost taste it
I knew how that felt for a good while. Remember I was THE FIRST to run a 9s 1/4 in a Street legal Rover THREE POINT FIVE LITRE engined car, although I was never officially credited with it, just as was never officially credited with being quicker than Steve Green and many other accolades I should have had, just because I didn't go around kissing certain people's asses. But this 0.3 of a second is not that easy to find, especially on my old stock 4.6 with nowt more that Omega's and a better cam.
You would have run a 9 LONG AGO 'IF' you'd stuck with the nitrous ONLY and acted on my advice, just as MANY other people have achieved their dreams and goals by doing so.
Switching to a blower MAKES NO SENSE as it SOAKS UP POWER to drive it, whereas nitrous is FREE POWER.
If you'd spent ALL that money that you spent on the blower on building a motor to MY SPEC and had ME fit and set up the nitrous system for you, 9s would have been A BREEZE.
The ONLY good thing about a blower, is the noise it makes but the noise doesn't make the car run any quicker. I've got my 60 foots down into the 1.45 second area so I'm not sure I can improve much more than that with the stock back end and suspension. So I'm thinking I need the engine to run a little bit stronger after the 1/8th mile marker for just 2-3 seconds. Thats why this engine was put together. I'm hoping I can pull hard off the line and stay in my 1.4 60 foot times, but then have the engine run harder for another few seconds. I really hope this works because I'm past the point of financial return now with the Rover V8. If this set up runs a 9.99 I'll be happy and then I'll pull it out and sell it so I can put the money towards a Chevy engine for next year.
It's VERY UNLIKELY that improvements in the second half of the 1/8 will give you a 0.3 secs gain from where you are now. You'll need AT LEAST a 0.1 gain in the 60ft followed by ADDITIONAL 0.1 gain in the 330 ft to even have a chance of making a further 0.1 gain from there on.
The ONLY car combo that might pick up 0.3 in the last eighth ONLY would be a turbo combo.
Your best hope is to get SOME nitrous in EARLY and keep it flowing strongly through to the 1/8, so you get the 0.1 sec improvements in all sectors.
Come and watch my Swedish Pro Mod customer next weekend at the Pod and with a bit of luck he'll produce some impressive times and show a few people what a CORRECTLY DESIGNED & FITTED WON nitrous system can do, despite being on a TOTALLY UNSUITABLE engine.