Dyno testing 308 P6 cams, borgo hi comp pistons

Do we bow now or later !!! I'd say both of your educated guess's were pretty good .
Don was the airbox closed on all the runs or did you leave it open ?

 

Great numbers!

I've seen quite a few dyno set-ups without large fans for cooling the whole lot, and given the way the 308 gets its' air from the outside, I suspect that at 250km/h there may be quite an effect on what is happening with fresh air between the scoop and the engine.

Does anyone have any figures regarding this?

It'd be nice to know what kind of pressures exist in the engine bay at speed when doing away with the stock filter set-up, as well as underbonnet temps at speed, which may also influence the HP-figures negatively if hot air is taken in.

 

Don, completely forgot to ask, but was this on a dynojet or a mustang dyno? was too tired after watching qualifying last night to ask

 

Mark's bhp chart was amazingly accurate. Bow to Mark lol

 

Just throwing this out there, but I have often wondered if Ferrari's 'optimistic' factory hp quotes might have in part had something to do with the ram cold air effect. With the chassis dynos it is pretty difficult to replicate this effect, heck for that matter I guess that would be the case for any dyno. I still doubt that Ferrari actually ever setup a proper dyno test with some sort of fan set up to replicate the ram/cold air effect for any 'official' dyno (or at least a dyno that they would ever quote to the public), but perhaps they threw in a 'rough' hp figure for the effect into the already 'rough' hp equation that helped equate to an even more optimistically quoted hp figure. Not that familiar with other Ferrari models of the era but perhaps the cars with a cold air induction setup might seem to have more optimistic hp quotes than the F-cars sans the boxes from around the same era.... Just a thought.

 

The increased filtering surface would certainly help, but you're doing damage by sucking in hot air. I don't have figures at hand, but I think you could roughly calculate 1% per 10 degrees, certainly not insignificant.

 

Good to know Don. Carobu's P6 run which yielded 277bhp was performed without an airbox. Russ Turner has proven with dyno runs that an airbox sucks away a good 10bhp+ from the wheels, he has actually shown more but he is using a stock airbox. I suspect you would easily be over 220 at the wheels without the box, but what is the point in testing them like that considering we don't drive without the airbox.

 

typically on older cars with 5 speeds, dynos runs are taken in 4th gear as close as possible to 1:1 gearing reducing the the torque multiplying effect. running it 3rd gear will give you a higher reading. im suprised your dyno guys says to use 3rd

was this an inertia or load bearing dyno you used?


hf

 

hey Don, can you tell us at what rpm peak bhp was made, and what torque figures were at what rpm?

 

Sorry to bump an OLD thread, but inertia dyno's, specifically DynoJet's don't really care what gear you are in. Just so long as the run takes enough time to get enough sample data. Older dynojets only get a signal about twice per drum revolution. You'll see very little difference between 3rd, 4th or 5th gears, but the run will take much, much, longer. The output of a dyno jet is based entirely on the work it takes to accelerate a drum of known mass to a speed. Third gear will accelerate faster, but to a lower speed. 5th gear will accelerate slower, but to a much higher speed. For the most part the equations work themselves out. We regularly dyno lowered powered cars in 3rd because it takes less time and builds up less heat so results are more repeatable.

I don't know where the concept of needing a 1:1 ratio to get the least drivetrain loss came from, but the last time I saw it explained the person actually thought 1:1` bypassed the gears in the transmission! That doesn't happen.

Turbo cars can be different though. Mostly because of the previously mentioned heat levels. A 4th gear pull will spool the turbo sooner because there is more load on the motor, it will also take longer and put more load on the intercooler. Back to back 4th gear pulls are barely repeatable. Once again, 3rd gear to the rescue. Haha.

 

Not on a 308 or most (all?) modern transmissions but on a lot of old stuff high gear (3rd or 4th) just locked the input shaft to the output so no gears involved to get 1:1 and no gear losses in high "gear"....which wasn't a "gear" at all I guess but did give the highest hp to the wheels. Nothing modern is made that way that I know of.....my '84 4sp H-D XR1000 (XL sporster trans which was a 1940s trans design I think) still worked this way, not sure if it changed when they moved to 5sp but that is probably the most modern example I can think of....so there was time now long gone by...... and any transmission where the output shaft is aligned with the input shaft is most likely a design relic from that time as that is the only reason to malign them I can think of.

 

Wow this was a long time ago. I’m not an expert on gearbox designs but you are probably correct with the interia dyno jets (they now make load bearing ones too) that the differences between gears one step away from the closes 1:1 are negligible.

On a load bearing dyno it may be beneficial since there is much more resistance than just spinning up a drum and measuring the acceleration. With the added dyno brake, the transmission experiences elevated forces. The gears closes to 1:1 distributed the torque forces more evenly to minimize deflection in between the lay and output shafts for proper meshing. These plays a roll on loads on its bearings bearings as well which is a major contributor for power soak in manual gearboxes. The helical gears by nature produces end thrust.It also helps in reducing any flex of the transmission case with can reduce misalignment and inefficiencies.

We used to dyno a whole slew of cars at my university, even with low powered cars the forces were high. When strapped and weighed down with additional 200lbs over the driven wheels , even a sub-100hp will throw chunks of its molten rubber off its rear tires. There’s a good reason many shop dont run a load bearing besides the higher cos of the unit.

I know you are adept at building 600-800hp monsters. More likely you would have a clue if you are missing a few ponies here or there

I say more of a concern is risking splitting cases or distorted them enough to cause problems with the gears themselves. Just like Murray did during those crazy 80’s turbo days?... an they ran straight cut boxes without end thrust. You may have to call up Weisman eventually?

all the best!

 

Inertia Dynos are fun for bragging rights at Sunday get togethers of car/Moto enthusiasts. They are not suitable for serious engine work.

 

Its a bit harder to tune EFI when you can't sustain any given condition...but that is why God gave us data logging. I've never had any real trouble tuning an engine on an inertia dyno other than it can take a few back to back run to get enough data or heat sometimes. The biggest issue is when the engine is anywhere close to the dyno's upper rating the runs can be so fast that its hard to be sure what you're seeing it like fuel/timing wise is what it will really like down the front straight. For sure its easier and more certain when you can actually control accel rate but I'd take any dyno over no dyno every time

 

When tuning, dynos should be used to replicate actual operating conditions. An inertia dyno can be used just fine to simulate actual acceleration rates. If you are having trouble reaching a particular load cell on the fuel map then try a different gear or throttle position. My dyno has proportional braking that can be used to hold the car at a set speed or rpm, like for tuning cruise speeds but it’s not really necessary. 5th gear works fine for tuning those cells.

Aaron

 

We use an engine dyno for WOT and steady state.. However that's only step one. I've found that I still need to spend a couple hrs of actual on the road tuning. Throttle tip in, highway cruise, country back road cruise, city driving etc... Esp since the lack of gears in the 308's mean there's lots of cross over between load cells. One day I'll figure a way to let the ecu know what gear it's in for additional maps.

Engine dyno rooms are also temperature controlled... That's not really applicable to the street... Great starting point though to work out the kinks. Typically 3 days on the engine dyno and 3 days of road tuning.

 

I too have found that the public dyno (road use) is the only way to get the final tune. A good data logger really helps too.

 

I cheat... Besides a data logger..I have a driver.. Though at times he can get a little too spirited and the nausea factor goes up. Only once have I had to use the 'kill' function in real time... To be fair it was a redline SNR sensor issue.

And I'll also go out with the client for a check and tune based on their driving habits... Almost never need to fix anything, mostly tip-in as everyone has a slightly different way of going from a dead stop. And aftermarket ECU's are not adaptive like the big boys.

 

They are.

 

Input torque is input torque no matter the rate of acceleration. Slowing down rate doesn't put more torque through the box but it can elevate engine/trans temps.

 

No