How much boost difference 302 vs 408

[restomod]

I was wondering if anyone knew how much difference there would be in boost between a 302 and a 408? I have a 8" crank and a 3" sc pulley. Trying to get a rough idea of the boost at 5800 rpm. That would be the rpm limit since I can only spin the sc to 55000 rpm.

[Hustler]

12-13 psi is my guess from another post of someone elses 396ci setup, though he ran an intercooler so you might see less boost, he was showing 13psi.

http://www.superchargerhelp.com/showthread.php?t=5731

[fanglemeister]

If monitoring boost after the intercooler it would show less boost, if monitoring before i/c it should show more boost than non-intercooled.

A Novi 2000 spinning at max rpm is supposed to be able to move 1700 cfm of air, and/or make up to 27 psi boost!

Running a simulation in Engine Analyzer software, by my calcs at 5800 or so the 302 should make @ 18 psi and the 408 @ 14 psi.

No computer models were injured during testing. <grin>

[restomod]

Thank You both for the info. Here is another question. If I were to use a larger sc pulley and then increase the engine accordingly, would I still make 13/14 psi? Would there be any advantage to move my rpm higher or just leave it where it is?

[Hustler]

Well your intake manifold, engine stroke, camshaft should dictate what the optimal rpm band should be. I probably wouldn't spin the piss out of a 408. Is this a street motor or a pure drag motor? Either way you will still see the same amount of boost. Remember you will still be moving the same amount of air, boost does not equal power. Boost is a measure of backpressure. The smaller the space is the air has to move through the engine, the more restrictive the airpath is. The resistance the airpath creates really is what boost is measuring. So many things come into play that dictate how much boost will show up. How quickly you can pump the air in and out of the engine will vary the amount of boost you will ultimately show.

I only put up that list as a general reference, by no means can it be taken for verbatim. Everyones engine is different, everyone runs a different camshaft, intake manifold, blower, turbo, heads, headers, x-h pipe, mufflers etc. Unless you duplicate someones setup exactly its hard to say this will make x amount of boost, only rough guesses.

Using boost as a reference to your own engine can be worthwhile, it can tell you if mods are restrictive or are opening the airpath when you change things out. Unfortunately you can't reference boost directly with other engines.

[restomod]

Thanks again for the info. The car is for both, but more for the drag strip. I have to drive my car 65 miles to the track since I don't have a trailer.

One other question, do you think I'm crazy for running 12:1 comp? I'm using 118 octane racing fuel. I had originally set up the engine for nitrous with a large cam (258 deg at .050" on 114 lsa) but decided to go with a SC. I'm using a blow thru system with a 750 cfm.

[Hustler]

Hah, now I understand why you want to know how much boost it will make. That is touchy, 12:1 is a lot. That will be a lot of cylinder pressure regardless of octane and conservative timing. I forsee lifted headgaskets. I don't think I would try it personally, I just think you will spend lots of money on fixing things that could be prevented now. That money could have been spent towards different pistons. I've seen people get the evil eye talking about 10:1. Especially if you are going to drive this on the street, I would have to say yes, you are crazy.

[restomod]

Geee, Thanks :laugh:

[Hustler]

If you really want some direction as to how realistic that is, go to www.stangcrazy.com and go to the renegade section and ask those guys what they think. They run higher compression because they are limited in what they are allowed to run on the engine. So they might give you some better insight. Those guys have done it all. Maybe the websites name has some correlation to your agenda ;)

[restomod]

Thanks, I feel at home already.