Probably a dumb question, but...

[DarkoNova]

Is it possible to get somewhat of a lopey idle with forced induction and still make massive power?

Originally I was going to just go heads/cam/intake on my LS1 because I've always loved muscle cars with the big lope at idle. I've also always loved the sound of a supercharger whine.

I'd prefer to have the lumpy idle, but I know a stock bore/stroke LS1 has more power potential with forced induction.



So is it possible to at least get a "rough" idle with a blower?

Matt

[Procharmo]

I'm not an expert so I will expect some additional comments. The lumpy idle is caused by the cam opening and closing the intake and exhaust and allowing both to be opened for an instant. I believe this is called overlap. At idle this overlap causes the engine to momentarly die and then come back hence the lope.
Overlap on a boosted motor will mean some of the air/fuel charge will be blown out of the cylinder before full compression is acheived. However I would imagine that would be even more the case on a N/A motor. Lope at idle may also mean efficiency at WOT. Less lowend torque more high end horses.
I think most centrifugal blower owners initially want drivability for the street and then power. Thats why blower/stockish idle cams have been used. However racers have used lopy cams and Prochargers to great success. Please listen to the vid below. This is the best sounding Procharged motor I've heard period. Too bad its a full on drag set up and not Protouring but he has 5.72ET 1/8 mile. Probaby 950 hp from a SBF with an F2.

[DeltaT]

If you don't care about cruising mileage and don't need to worry about emissions, sure! My friend has a 355 with a solid roller, like 255/[email protected]" on a 110LSA, along with an intercooled Procharger D1SC. Basically a classic old 69 Firebird hot rod but the centri kicks in from the midrange up and really cranks. But cruising on the highway he's lucky to get 10mpg, and as for emissions, ha!

My only problem with this idea is that you can have both - excellent street manners and mileage, and kickass upper end power, especially with an LSx at the core.

Maybe you could wire a switch to turn off one (or even 2) fuel injector(s) to get a really raspy idle when you wanted to psych someone out...

Jim

[shmoov69]

There are guys doing it both ways sucessfully. I went with a small overlap cam and low compression and it is fine. Just miss the sound of the old engine before boost.

[DarkoNova]

That Mustang sounds awesome.

I want the Nova to be a cruiser, and one of the reasons I chose an LS1 was for efficiency and mileage.

So there's no way to have the whine of a supercharger, a somewhat rough idle, and decent mileage (5th gear is .64)?

It's tough to choose between N/A and forced induction.

Matt

[DeltaT]

Decent mileage is possible, but good mileage probably isn't. Depends what mileage you really want vs. the sound you love. Can't optimize both ;(

Personally, I'd rather have hi mileage and incredible power, even if it had a stock (wimpy?) sounding idle.

Go FI and you will never regret it.

Jim

[Blown353]

My Procharged 353 uses a 242/254 @ .050 cam, 114 LSA. It was designed and spec'd for my engine combination by a guy who at that time nearly exclusively built Procharged engines, now he's doing turbos too.

My engine has a very healthy sounding idle (although somewhat muzzled running through large cased Magnaflows)... and it still makes plenty of power. Engine has about 2 psi of boost at 2000rpm at WOT with the Procharger and it ramps in pretty quick from there. Many guys told me my cam was just too big (based on more "oldschool" thinking about boost and cams) but quickly changed their mind when I took them for a ride.

Too small of a cam with forced induction can hurt the top end efficiency of the overall combination too as the valves just aren't open long enough.

Since you mentioned mileage... I get 18-19 mpg at 80-85 mph, and 22-24 mpg at 65mph with my combination. Car is tuned to be in the 50's for timing and 15.5:1 AFR at freeway speeds. Car is geared so that the cam is happy in 5th at around 55mph, any lower RPM than that and it starts to buck a bit. I geared the car to have the cruise RPM just over where the cam "cleans up."

I also helped build and tuned a 427 small block Ford with an F1R; 847hp on 91 octane pump gas and the cam was pretty stout too, pretty nasty idle. I seem to remember the cam being 25X/26X @ .050 with mid .600's on the lift. However the engine had an awesome torque curve from 4000-6700, not at all what you would expect from a centrifugal and especially with that big of a cam. It would have made more power if we spun it to 7200 but we ran out of injector. Need to change injectors and go to the dyno again.

Bigger cams are starting to be used more often with great success on turbo combinations as well. It used to be that everyone ran short duration no-overlap cams with small A/R exhaust housings for quick spoolup. Now, you see more and more people running larger cams coupled with larger than usual A/R turbine housings and these combos are working very well in the real world. The larger cam makes more HP off-boost than a small no-overlap short duration cam. The larger cam makes more off-boost HP, and more HP means more exhaust volume to spool up the turbos; you still get quick spool as you do with a pipsqueak cam and small A/R housings but the bigger cam and bigger A/R housing makes way more power up top because of the less restrictive larger turbine housings... and they have some "sound" at idle.

Again, it's all in the entire combination. Everything must be accounted for and planned out... but if you do, you can have a little lope at idle with your boost and things will run great.

[DarkoNova]

Hmm, I think I'll just get the supercharger and find a reputable forced induction shop and see if they can recommend a cam that'll still make gobs of power and have a nice idle. When I was planning on sticking N/A, I was only shooting for 500 whp. I figure with good heads, headers, maybe an electric water pump, and the blower, I can get that easily and still get a rough idle.

We'll see, though.

Matt