Reaching into my bag of "Questions I'd ask the developer of the AM 4.3L V8 if he suddenly showed up on a car forum that I frequent," I came up with this one that I've been wondering about. Hopefully Mike can share some perspective. Please keep in mind that I always come across as a bit of a smart aleck, but I'm sincere in wanting to know your thoughts.

- It has been speculated that the 4.3 didn't make all of the advertised 380 hp...part of this is internet lore, but the rest is based on dyno testing and comparison to similar cars. Dynos have shown that the car makes 290-310 hp at the wheels depending on the type of dyno (this would require 20-25% drivetrain loss to make 380hp at the crank, which is high for a modern manual). Comparisons with 300+ hp, 3500 lb cars shows the Vantage to be slower than or equal to cars making much less hp, including the BMW e46 M3 (333 hp), 335 and 535 (300 hp), Infiniti G35 coupe/sedan (306 hp), Lexus IS350 (306 hp), and some others, all of which weigh the same or more than the Vantage. Is there any truth to the speculation (perhaps some of the horses escaped) or is it more that the engine makes less usable power across the power band than these other cars?

On a similar note, the 4.7 showed significant improvement in instrumented testing...sometimes beyond what was believable. It was tested in the 0-60 in around 4.1 which could be possible, but more importantly, there's an Autocar test online that shows the 4.7 beating, shockingly, a 997 GT2 and Lambo LP5640-4 in the 0-100-0 test. I'd like to believe that is true, but it seems more likely that they had a ringer...or that it managed to corral up those horses that escaped from all of the 4.3s. Any info you can share on this Mike? Thanks!

 

I dynoed my car at 307 rwhp before doing my mods. Assuming 20% loss, that puts my old car at just over 380 hp at the crank.

I'm not Mike, nor am I an expert, but it appears to me that the power-to-weight ratio is only part of the equation. That ratio doesn't take into account things like the longer gearing Aston chose to get higher top speed numbers, the relatively high rotating mass the engine must push around, or the fact that while the car has 380 bhp at the red line, it is very peaky and has much less at lower rpms. It seems to me that it is these other factors that are the main culprit here.

 

I too believe it is the rotating mass that is the reason for such a high drivetrain % loss. Its also why the engine has such a lazy throttle respons (pretty terrible in stock form). I am curious to hear DragonMikes response of course ... 290+ for a loading dyno is healthy where as for dynojets it's more like 300+.
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Depakote settlement

 

Tahoe - Aston are very straight laced when it comes to reporting crank horsepower figures - to the decimal point, what was recorded during official sign-off tests appears in the literature.

If any auto maker supplied cars straight from the production line to press event it would be a 'flying pig' moment....!

Racer X sums up perfectly why the 4.3l doesn't feel like 380BHP.
The Vantage 'S' is same BHP as previous level 4.7L, a differential ratio change and closer gears reduces that 'bogging down' feeling dramatically. Imagine how those gearing mods would transform 4.3L... Performance 'feel' is won and lost in the differential ratio and power to weight ratio stats...

 

Mike, what about rotational mass of both the engine itself and the drivetrain as well?
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Hyde Park Residence 2

 

It's funny you mentioned the Vantage S Mike. I was just about to post that I recently read an article stating that the 7th gear in the Vantage S enabled Aston to select more aggressive ratios for gears 1-6 and therefore get better acceleration numbers.

 

Yep.. these too.

Let's say the car is in 4th gear about 3000 rpm - you want to overtake something and put your foot to the boards. The sluggishness here is differential ratio, gearing and power to weight ratio- as the inertia / mass is already spinning. Whilst yes - getting the thing moving from lower speeds / standstill is all about overcoming rolling resistance and engine inertia.

 

I think that's the more annoying of the two. I wish there was a quick fix. 0-60 times are rather pointless in real world application, aren't they? Isn't 60-120 mph really a more useable range anyway?

 

Better gearing would help a lot in that situation. I was interested in such a mod a while back and I recall Stuart saying that RSC was working on a crown wheel and pinion set. Not sure if RSC is still open to this or not, but Stuart can chime in.

 

Yes they are a little pointless, especially when the 0-60 screams off the line at 5000 rpm - yes, in gear times much better measure.

 

0-60 is a terrible measure for most cars I think. to get the best 0-60 times is usually abusive on the machinery.....and launch control is part of this silliness. who the hell engages a mode that often takes several steps and really, is only good for the dragstrip? Try a wheel spinning chirruping launch from a light and everyone thinks you're a d-bag .

 

I still believe changing gearing is the band-aid solution, not the true cure. The cure is still rotational mass reduction. A few weeks ago, I would have agreed with you 100% on this matter, but after installing the new rotors I now realize it is rotational mass that is the problem.

Now, I have no problem accelerating in 4th gear now from 3000rpm anymore, where as before it would just bog and I would have to downshift into 3rd. Even in 5th gear now I can plan my foot and the car will move forward smoothly. On the hwy I do not even have to downshift from 6th anymore, I have all the pulling power I need. This was certainly not possible before. Its not as fast as I would prefer, but its definitely an improvement to say the least.

Also, for clarification ... inertia is ALWAYS a factor unless you are talking about static steady rpm conditions. Yes the effects become less accelerating from a higher base rpm/speed , but it still exists. Anytime you change rotational acceleration/velocity/deceleration ... inertia is rearing its ugly head ... unfortunately.

I genuinely believe more mass reduction will ultimately solve the problem completely. In fact, with the current setup I actually think the stock gearing is now perfect (where as before I did not). Gears 3-6 are very close, so the additional 300rpm has made a big difference in those gears allowing you hit the powerband perfectly in the next gear.

Perhaps this the biggest reason why the torque sensation is so much higher in the 4.7L, its the reduced rotating mass of the engine internals & flywheel clutch assembly combined. Aston Martin even alludes to this in their literature (as has Mike breifly). I am sure this is contributing to the jump in torque specs for the 4.7L vs. 4.3L.

To take the subject one step further ... the V12V carbon rotors weigh only ~9.5 lbs! LESS than 10 pounds (a 12.5lb reduction from the V8Vs rotors), AND most of that mass is in the center hub because the carbon disc itself weighs next to nothing. This is certainly NOT helping the traction on the V12s (or lack there of). If you were to reverse this and put the carbon rotors on the V8, and the stock 22lb rotors on the V12 ... the difference between the two wouldn't be so drastic (not possible of course, the carbon rotors require completely different calipers).

I have a feeling the only way to properly reduce rotating mass is to do ALL the components together, simply doing one item will not be enough (as Michael found out with the LTW flywheel on its own). You have to go through the entire drivetrain and remove as much weight out of all the components before you can really get a significantly faster revving engine. I have started that process with rotors. It in itself is not enough IMO, but it is a good starting point ... there is still more to be done.
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WASHINGTON DISPENSARIES

 

I agree that reducing rotating mass is a great way to improve performance, but it sounds like a lot of $$$ to do the ECU reflash, replace the cats and exhaust, AND change out all the components that add to the mass bogging down the engine. Maybe gearing is a "band-aid solution" as you say, but it could also give more bang for the buck. Also, I can't help but think that, at some point, it makes more sense to just upgrade to a used 4.7 instead of doing all this modding to a 4.3. Buying a 4.7 would likely be more expensive than all the mods, but you would also have a newer car with higher resale value. My two cents.

 

Racer_X - At first glance it may seem like a lot of money but in fact its actually quite a bargain. For the record I am not doing this to try and turn it into a 4.7L or etc. I am doing this project for the fun/enjoyment of trying to max out the car's HP/L output because NA high revving small displacement high HP/L cars are just so much fun to drive. In many ways, its an "underdog story" ... everybody loves an underdog story .

With that said ... 4.7Ls are on avg $30-40k more expensive than their 4.3L counterparts. The 4.3Ls have essentially bottomed out in price, where as the 4.7Ls still have a ways to fall.

If you can get significantly superior performance for less than $10k in costs, then it actually comes out as a bargain. Obviously I do see your point of course (and I agree), for those not wanting to heavily modify their cars, it is simpler to just buy the 4.7L. This is not about trying to save money, its more about having fun with the car and treating it like a science experiment from which we can all learn from.

(I have only spent ~$5k in parts & labor so far to achieve current results)
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BONG REVIEW

 

Okay, got it. Well then, I wish you luck with the rest of the project. You're doing pretty good for only spending $5k!