How much vacuum does a TPI really NEED?

[Caveman]

I'm looking at cams for my SBC, and have 90% of the parts lined up (still need a fuel pump/sending unit--- & a different tank maybe.)

I want to go large-ish (street/strip) and was thinking maybe a flat-tappet Mother Thumper...

But how far can tuning go to compensate for low idle vacuum?

[Matt Cramer]

Re: How much vacuum does a TPI really NEED?

How long is a piece of string?

The real issue isn't the manifold, but the sort of electronics controlling it. What are you running in that department?

[Caveman]

Re: How much vacuum does a TPI really NEED?

I was thinking of meddling about with that MS piggyback thing for TPIs that EFI-DIY came up with a while back...

I realize that the stock TPI tuning capabilities wouldn't really be feasible once I go past a certain point with cam duration.

What I'd like to understand is this; how big can I go with a cam on the stock TPI tuning (MAF setup) before I get into trouble?

Conversely, if I spring for the DIY Mega piggyback setup, what capabilities would that open up from a camshaft duration point of view? Or does it even matter once I've gotten that far?

[Matt Cramer]

Re: How much vacuum does a TPI really NEED?

EFI-DIY's setup pretty much replaces the stock ECU, well, leaves it a gutted shell to put your own gear in. I've tuned an MS on a car that pulled about 10" of vacuum at idle myself, and that was on speed density - if your idle is really choppy you can tune the idle to go strictly off TPS readings and transition to MAP as the RPM comes up.

Not sure about the minimum for MAFs, though.

[Caddyman]

Re: How much vacuum does a TPI really NEED?

Why do you want a maf sensor?

Its easier to plumb the intake/air filter, easier to wire, easier to tune, and doesn't require all the "slowing" or "buffering" from the weird GPS signal with a big cam.

Just go with the MS unit. Its too easy.

Even I did it.

[SpiderGearsMan]

Re: How much vacuum does a TPI really NEED?

code 24 - maf signal low