Supercharger vs. N/A build!

[Phill Pollard]

Originally Posted by olddog

Be warned that Ford started with Speed Density. It uses a MAP sensor in the manifold to estimate what the air flow into the engine is at a given throttle position. It does not work well with big cams, as the vacuum can be lower at idle than it is at off idle with such a cam. Second it does not automatically adjust for altitude changes. When you turn the key on the ECU saves the MAP sensor reading and assumes that is the atmospheric pressure. It does not update again until you turn the engine off and restart. So if you drive 4000 feet up a mountain, its no better than a carb, however turning the engine off/on is much easier than changing jets.

Olddog,

Your statement isn't entirely true. You were good up until you gave the 4000 feet comment.

Speed Density systems actually DO compensate for altitude on the fly without having to turn the key on/engine off (KOEO). They do it by sensing the manifold pressure (via the MAP) every time it sees WOT (via the TPS or Full Throttle switch on a minimum function system).

So on your way up that 4000' mountain, every time you push the throttle to the floor the ECM sees atmospheric pressure (since man vac drops to 0"Hg) and notes it as BARO.

I have seen ONE instance where a customer drove his car over a very long distance with a *gradual* rise in elevation without ever having to floor the gas pedal and he got a CEL out of it. That's one instance in over 25 years of EEC work so it is rare.


Hope That Helps,

Phill Pollard

[olddog]

Originally Posted by Phill Pollard

Olddog,

Your statement isn't entirely true. You were good up until you gave the 4000 feet comment.

Speed Density systems actually DO compensate for altitude on the fly without having to turn the key on/engine off (KOEO). They do it by sensing the manifold pressure (via the MAP) every time it sees WOT (via the TPS or Full Throttle switch on a minimum function system).

So on your way up that 4000' mountain, every time you push the throttle to the floor the ECM sees atmospheric pressure (since man vac drops to 0"Hg) and notes it as BARO.

I have seen ONE instance where a customer drove his car over a very long distance with a *gradual* rise in elevation without ever having to floor the gas pedal and he got a CEL out of it. That's one instance in over 25 years of EEC work so it is rare.


Hope That Helps,

Phill Pollard

Phill,

Thanks for the correction (I don't want to put bad info out). I never studied Speed Density in great detail, but read a bit. I do not recall anyone ever pointing out that it will correct the Baro at WOT (not doubting you). That is not intuitive that they could do that because vacuum would not necessarily drop to zero at WOT. At high rpm WOT, I would expect there to still be a bit of vacuum. Otherwise the claims of a bigger TB increasing power is BS.

Rick

[olddog]

I'm guessing factory rods are in it now. Since your buying pistons anyway, get a complete rotating assembly for a 347" stroker build. ~$1200 or so.

That extra 45 cubes will be worth in the ball park of 55 Hp 60 torque.

[Cobrat24]

Originally Posted by olddog

I'm guessing factory rods are in it now. Since your buying pistons anyway, get a complete rotating assembly for a 347" stroker build. ~$1200 or so.

That extra 45 cubes will be worth in the ball park of 55 Hp 60 torque.

As much as I would love to do this, I am already over my budget just with the additional labor to pull the motor and pistons and all the work that comes with that. Especially now that everything is out and bare.

[ct clint]

Ok if no one else is going to say it i will. That needs to come out b hot tanked and flushed out. Check bores for true Ness if good deglazed. I like to deck them also. Crank needs to be inspected good time to polish it if it's in speck. Spend the money get rotating assamably balanced. If u are using new heads they should be pulled apart cleaned and inspected. U will be surprised what u find they are mass produced not built buy loving hands. You can fit your parts together right and did your math it should be good. In the best motors round things are perfect round and flat is flat. Do some math on how much air will flow through the headers. Yours may be fine u only need to push out what goes through the carb. Sorry for the rant but don't waste money do it right. There are far smarter guys on here then me I am sure they will add.