While I hear what you are saying, we do not have agreement with respect to the issues.
MDross1, the OP, originally inquired about supercharging as it might apply to a big block Ford engine. The discussion covered a wide ranging group of suggestions and possibilities.
I entered the discussion and suggested the supercharged big block would be overpowering in terms of its power even at relatively low boost levels. I suggested the power would allow you to get out of control more rapidly and more violently than a n/a equivalent.
I went on to suggest a supercharged small displacement engine (302 cubic inches) would still be capable of significant power (700 to 800). I implied this would be less dangerous than the supercharged big block alternative.
Jason went on to say,
Quote:
Originally Posted by D-CEL
I disagree: 700-800 hp from 302ci requires A LOT of everything! Aftermarket block, Big flowing heads, High dollar rotating assembly, a big blower, race fuel and RPM. Yes it can and has been done, but the motor will be a peaky, high maintenance and temperamental (sounds like my X wife) Not the making of a good street motor.
And that is the beauty of the 385 series BBF. We can make those numbers naturally aspirated on with a stock block, an $800 Chinese forged crank, good alum heads and possibly on pump gas!
Jason
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As you can now see from my original posts and commentary I made no references to the block, heads, rotating assembly, blower size (although somewhat implied with Whipple), race fuel or rpm.
Jason believed the engine would be,
Quote:
Originally Posted by D-CEL
peaky, high maintenance and temperamental (sounds like my X wife) Not the making of a good street motor.
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In actual fact as we can see from Harold's performance nothing could be further from the truth assuming the engine was built correctly and the tuner knew what he was doing..
The Internet is capable spreading misinformation at a mind boggling rate. Truth and fact are always better. It allows readers to make informed decisions in their own build's component selection and build process avoiding costly mistakes and misspent funds which are always in short supply.
While we are talking about misinformation your own representation that the modular block was
Quote:
Originally Posted by itstock
...one of the strongest factory stock short blocks ever in production
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is also misleading. The engine was a force fit into the rear wheel drive product line because another engine had become cost prohibitive in the early 90's. Its original home was a transverse front wheel drive application in a Lincoln — which is how the bore centers got squeezed to 100mm. That tight bore spacing was necessary to transversely fit between the shock towers.
The block in terms of strength is probably several pages back from the leaders Detroit has offered over the years. When you look at the main caps, their fasteners and main web dimensions the engine pales in comparison to blocks like the FE, the 427 Chevy or the 426 Chrysler.
Shucks, a Modmotor even pales when compared to a stock 302 block. The fasteners, main caps, wrist pins pistons, connecting rods, and crankshaft all look like toys compared to a 302. The Modmotor's 10mm main stud is marginally larger than 3/8 inch. The 289 uses 7/16 main studs, the 302R uses 1/2 main studs and the 351's use 1/2" main studs. The "little" Ford Windsor blocks are massive compared to a Modmotor engine.
The Modmotor pistons are so small they do not look real. This is a picture of an intake valve from a Chrysler and a Modmotor piston;
Mod motor pieces are diminutive in size compared to any performance engine part we normally handle — including 302 components.
It is worth noting the width between the fenders on those early 90's FWD Lincolns that forced the 100mm bore centers also forced very narrow main webbing and main web anchors to the block structure — making the block a dicey choice at best as a performance engine.
It is a foregone conclusion in any engine build that the higher you target the engine's specific power output the stronger you are going to have to make the stressed components when you build the engine. Considering the age and casting technology of the time it is probably a prudent decision to use a block built with modern casting technology and benefiting from the decades of continuing product development done for the small block Ford engine.
Quote:
Originally Posted by itstock
Speaking specifically of the 302 block, 600hp WILL require an aftermarket block or you can count your blessings every time you don't crack the block (been there done that at under 450rwhp, not to say it HASN'T been done though, just not reliably).
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You don't have to buy DART, you can also buy Ford. More to the point however, blocks rarely if ever crack because of horsepower. They will crack because of torque, they will crack because of detonation, they will crack from cyclic failure as in a 24 hr endurance test on a dyno or in a car on a race track but they will not crack because of horsepower. When most builders experienced an engine failure, they look at what they used and simply use better/stronger parts rather than attempting to discover the real reason for the failure and then address that.
For decades engines were built, sold and or put into cars for immediate use. Infrequently were they ever evaluated on a dynamometer and tested for fueling let alone fuel distribution, spark mapping or lean spots in the power band. My suspicion is you have built one perhaps two 302s that failed and you can not explain the origin or mechanics of the failure — other than to say an aftermarket block will not fail.
The 700 RWHP threshold you have achieved in your Cobra was a direct result of the Ford calibration team's building the logic that was employed in your 03/04 PCM to manage the engine. The monies they spent on the engine management system for that one engine alone dwarf anything the aftermarket can even begin to approach — or you can do when you attempt to build a high specific output 302.
Engine failures are most often the result of poor engine management rather than ultimate strength failures in individual components. This is especially true in high performance aftermarket pieces which can frequently be overbuilt. You can however mitigate the failure due to poor engine management issues by using a Ford engine management system — vastly superior to aftermarket.
Your statement that,
Quote:
Originally Posted by itstock
twin screws/roots/rotors are notoriously HARD on engines, quite contrary to your statement.
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could not be farther from the truth either. When supercharged engines fail, in almost every case, it is a fueling or lubrication failure that precipitates the engine failure. The fueling failure is invariably traceable to error(s) in judgement made in the build and/or tuning process or a tuner that did not either appreciate or more likely understand the intricacies and nuances of the Ford calibration lab's engine management system logic.
Properly tuned and intercooled, the twin screw supercharged engine is as reliable as it n/a cousins. Your own 700 RWHP Cobra was in effect an 820 FWHP engine performing at 2.93 hp/cu in. A 3hp/cu in. engine is normally not looked upon as a reliable daily driver. Yours was because of the work the Ford engine calibration lab did to make it reliable.
The traditional roots style compressors (even intercooled) have a substantially increased downstream air temperature if the compressor is over sped. The attendant reduced engine reliability is directly attributable to that increased down stream air temperature (intercooler not withstanding), what Ford calls IAT2 or downstream air temp.
When you increase the downstream air temps the tendency to detonate increases which requires the spark map to be flattened out and the AFR richened to mitigate the conditions necessary for detonation. The higher the down stream air temperature the higher the temperature throughout the entire power cycle and the more likely detonation.
Additionally as that temperature rises, the greater the heat losses to the internals of the engine. As those heat energy losses increase the engine's thermal and volumetric efficiency is reduced with each increment of air temperature.
In all cases the roots style compressor will enter this destructive phase much, much sooner than the intercooled twin screw. Moreover, proper engine management logic/models can push out the twin screw detonation threshold even more.
For the inexperienced builder / tuner the tendency to push the spark map and push the manifold boost to recover the lost power quickly sends the engine into detonation with attendant massive destruction of pistons and cylinders. The old adage 'lean is mean' should be lean is destructive.
Again with proper engine management the twin screw compressors can deliver engine reliability performances equivalent to their n/a brothers but at substantially elevated power levels without the detonation issues of a roots style compressor.
The reliability issues you attributed to the twin screw compressor are in fact the very issues the roots style compressors experience but the properly designed twin screw system does not.
I have built supercharged engines for just shy of 50 years now. Properly architected and with a correctly designed engine management system, very high specific power output twin screw engines can be easily had without bad street manners, with excellent throttle response and fuel consumption. If you adhere to a regular maintenance schedule, as the owner you will wear out your supercharged engine instead of blow it up.
BTW I think it is always good when we consciously choose not to buy low priced Chinese knock off goods. We have talented design teams and engineers over here that can produce great product. When we buy Chinese knock off product we are cutting our own throats and most likely buying inferior product.
A for profit Capitalist economy ceases to sell what people cease to buy. Do it long enough and the only ones we will hurt will be ourselves.
Ed
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