How much boost can a stock 305 take?

 

As much as you're willing to risk

Assuming no smoke or problems to begin with, and a good tune, it would very reliably handle 12-13 psi intercooled without any problems. You could have some luck and get away with 14-16 psi for a long term. Beyond 16 psi you are definitely starting the timer, but even then there are some guys around that have done so without problems.

 

That seems a little high

 

Not if it's timed/tuned properly. But as ZZ3Astro said - - A decent overall engine and tune is critical. Even at 6 pounds of boost, if the tune is way off, it can destroy the engine. For instance, I thought I had my engine dialed in pretty well (it ran awesome) until I put it on a Mustang dyno and found out that I was detonating like crazy in the upper RPM's. But yeah, that's a bunch of boost to begin with, but note that ZZ3Astro said "intercooled" boost.

I'd personally limit myself to 5-8 pounds using pump gas on a stock bottom end. No real reason why....but you'd need to back off on a whole lot of advance at anything above that on pump gas. If nothing else it's a bit less stress. You'll feel a huge improvement nonetheless.

 

Boost pressure is just a measure of resistance. It can essentially be a higher reading depending on how restrictive your intake passages are, or it can be a lower reading depending on how large your intake passages are. Mind you, you will be flowing more air with larger passages and a lower boost pressure reading, so the measure itself is really meaningless. What stresses (weakens) engine parts is heat and detonation, so keep them in check. Remember that the LC2 engines all came cast from the factory like your 305, and were tuned for 15-psi when they left the dealership floor (lower static compression, of course). I've known guys that have run close to 30-psi on them for years, and have hundreds of passes, and they held fine because they controlled detonation and heat....

 

Probably can run alot more on E85 or race gas but will the bottom end hold? The general concensus these days is yes, with limited rpm and good tuning.

 

Seems high but I speak from 10,000 miles of experience turbocharging a stock 5.7 with the numbers I posted. I've always felt that the 5.0 is a bit more more durable so I actually consider my numbers a tad conservative.

You will hear stories about people blowing up stock engines with 7 psi and yet other people succeed with 20 psi on the same type of engine. The difference is the person 99% of the time. One cuts corners and tries to run a stock fuel pump, injectors, etc with a FMU. The other builds a supporting system of properly sized injectors, a good fuel system and a properly tuned fuel/spark control system. One blows up and the other lasts for years. Of course you'll only hear about the one that blew up, because that's more exciting to talk about on the forums.

As an illustration of this.. I have a friend with a Vortech on a stock engine. It's blow-thru and do you think he has a WB02 on it? Reminds me of the old days with an 8-71. Blast down the road, come back and remove the plugs. Oops looks rich, lets try smalller jets. Detonation? Couldn't hear that if we tried. Just have to run a conservative set of springs & weights. Oops got a head gasket. Damn that 8-71 is H-E-A-V-Y to lift off the lower intake! Been there

 

So what if it smokes at idle and makes a funny ticking noise under acceleration from the driver's side?


I'd be pretty surprised if it would be so limited that e85 would make a significant difference. I'd expect that the bottom end would fly apart before detonation limits things with a good tune.

 

this is a common misconception.
Boost is not a measure of restriction. An engine by itself is not a restriction . dirty airfilter, clogged catalytic convertor,throttle are restrictions.

 

Wrong. Boost is a measure of restriction, period. If you are claiming that it isn't a measure of restriction then you are going to have to prove that it isn't, not just label it a common misconception without any clarification....

Wrong. A stock cylinder head is more of a restriction than an aftermarket cylinder head. A stock intake manifold is more of a restriction than an aftermarket intake manifold. A stock camshaft is more of a restriction than an aftermarket camshaft. All of these items directly effect the amount of air that enters into the combustion chambers, and all of these items directly effect the amount of boost pressure being embellished. If these items were not a restriction, then boost pressure would not be effected when modifications are made to the intake tract, but it is of course effected, because boost pressure is a measure of the air tract's restriction....

 

I'm not getting into the discussion about boost pressure (OK I guess I am ), but I can tell you what I've found with my particular setup. The pulley that was provided with my Magnacharger should have provided 5 pounds of boost on a stock engine. My engine was far from stock before I put it on i.e. Comp cam, Dart heads, headers bla.bla...

Anyways, I only managed to get 2.5 pounds of boost with that pulley and had to change to a smaller pulley in order to increase blower speed/pressure. Of course, this is with a roots type blower, but the basics are the same as turbo, centrifugal blower or whatever. Biggest differences being where you see max boost pressures at.

If your engine has the ability to USE the boost, the pressures won't stack up as compared to an engine that can't breath as well. My install instructions for the blower state pretty much the same thing. The vast majority of power gain will be at those lower boost levels. At increased pressures they'll be gains since air is compressible, but they won't raise nearly as sharply as it was at the initial lower boost pressures.

A WBO2 is always a great thing to have with or without a blower. Tuning as far as timing and A/F ratios are a different ball game between roots type and centrifugal/turbo blowers though. There's no WBO2 that I know of that'll tell you if there's detonation occuring at the upper RPM range, or maybe I don't know how to use one properly since I'm a rookie myself at this forced induction thing...but I'm learning.

 

Exactly! The boost gauge tells us the resistance for that particular engine, as although the pulley is originally intended to provide 5-pounds of boost on a stock engine, if we open things up to allow it to breath better, then boost pressure inevitably goes down because it essentially makes it easier for the supercharger to force air into the combustion chambers (less resistance). The tighter the air tract, the higher the boost pressure reading, the more open the air tract, the lower the boost pressure reading. The reading tells us how hard the blower is working for that particular engine, the boost gauge is measuring resistance for that particular engine. It is just a measure of resistance....

 

what your really need to be concerned with is the amount of air the turbo can flow .15 lbs. of boost out of a gt 25 is far less air then lets say 15 lbs out of a t88 . bottom line is your timing has to be perfect an you have to have the right amont of fuel for the air coming in .then comes the real problem how much horsepower can your parts handle .i think assuming the tune is ***** on then the real question is how much horsepower a stock 305 can handle before you break the bottom end .

 

Definition of restriction is a " a limiting condition" . Is flow being limited if you see 10psi, 20psi, or 30 psi on the gauge???
If boost was a restriction than the more psi you make the less hp you make.
clearly this is not the case.

 

http://en.wikipedia.org/wiki/Turbocharger

a good read :

 

I'm not sure that I agree with the exact wording that either side of this has used, but getting past that you're wrong.

Yes, if you see 30psi on the gauge at the same airflow as another engine or combination sees 15, then that engine is a bigger "restriction" than the one that sees a lower boost pressure.

In your example, the same engine sees different intake pressure with different amounts of air trying to be forced through the engine. The engine can only flow X volume air, and if you try to force more the pressure has to increase, increasing the air density to get that amount through the engine. The volume stays roughly the same, the engine is a restriction to more flow, but if you increase the density you can increase the mass of air that you can force through it without it being able to ingest any more volume of air.

 

any given engine flows a given amount of air you cannot change that with forced induction like you said. when an engine flow 500 cfm of air than you clog the exhaust ,it now flows only 400 cfm of air, that is a restriction.
restriction is based on flow which a boost gauge cannot tell you.

 

Any given engine has a given displacement. The amount of air that flows varies greatly. The difference between the two is called volumetric efficiency.

 

hey one of my boosted engines did that. I put a set of valve seals in it which cleared up the smoke. As for the ticking noise it has right now, well, it always had that noise for over 30K miles and still runs fine with boost.

 

You asked a question you already know the answer to?

 

Dave, Mark,
You guys have a good understanding of how boost works. I am surprised to see two knowledgable people arguing it.

 

To be honest, I don't have the time to pay attention (or argue) around here that I used to, I don't know who dave is (who you are... i don't know, am I talking about you or addressing you in this... I think I'll settle with I'm going to go back and forth) and the fact is that most of what you've written is technically incorrect, and as far as the last post goes if you have a given volume air flow and a pressure you know (can calculate) the restriction, adiabatic efficiency... or if you know the volume flow at 2 pressures (atmo and after the turbo) you can calculate the volume flow, change in density (and again, adiabatic factors also)... or you can look at it a few different ways, but no matter how you slice it you are showing a restriction and it's not hard to calculate.

 

Dave, I'm not going to argue with you because you are wrong. Boost is most certainly a measure of resistance for the particular engine, and explaining why for you in the greatest detail will do very little because you simply refuse to see it. I have argued this same fact with you in the past before, whether on here or on other websites. Not only do you claim that boost pressure isn't a measure of resistance, but you are also very adamant about saying how blow-thru carburetors don't work, and how it takes $25,000 dollars to build a good turbo setup. You are wrong on all three accounts....