????? about Boost

[Wrecked Em]

Is there any difference in running 18# of boost with a TA49 and 18# of boost with a larger turbo? I am speaking of identical builds only the turbo being different. I do understand that there will be lag and such, but as far as power, is there a difference?

This will lead into my next round of questions....

[Steve Wood]

depends.., if you are running on straight gas and the larger turbo is sufficiently more efficient so that the charge air is much cooler at the same boost than the 49's...then the air will be more dense meaning that there are more molecules being pushed into the cylinder...the n the car will make more power if the a/f ratio is set properly.

It is more likely that you would see more difference at a higher boost level where the 49 is straining to keep up and charge is considerably hotter due to the inefficiency of the compressor map at that point.

I mentioned on straight gas because spraying alky provides chemical intercooling and the difference is less as long as the turbo can supply the quantity of air required.

[Pyro6]

If you are supplying a bigger turbo, aren't you supplying more air? Which means you need to supply more fuel for the balance?

[Steve Wood]

it only supplies more air if the engine will take it.  But, if it does ingest more air then it will need more fuel.

But, the clinger here is to define more air.  We have to consider what more air is.  For our purpose, more air is more dense air which is more air molecules per volume of measure.  Ten cfm of air at 200 degs temperature has less "air" than does ten cfm at 100 degs.

People get hung up on boost which in itself does not mean a whole lot when comparing between turbos, or even different engines.

I knew a guy once that bought a 276" stage engine.  He put his TA49 on it and it would only make 18# of boost whereas it had made 28# on his 231" engine....drov e him crazy because he did not understand the relationship between volume and boost.....neve r even got to density

[TSM Girl]

[shadow=indigo]Ya know, it is so nice to see my car running for once. ok, back on subject..[/shadow]

[Steve Wood]

[shadow=indigo]Ya know, it is so nice to see my car running for once. ok, back on subject..[/shadow]

I know the feeling well...I always am amazed how well a Buick runs after not driving mine for awhile

[Wrecked Em]

Thanks Steve. I was assuming there was efficiency involved. I understand your example with the 276 engine as it deals with restriction in the system.

That is why my hot air car makes more power with less boost after install a ported intake and GN1 heads. I am making more power at 13# now than I was before at 19#.

[Steve Wood]

yes... simplistically boost is resistance to flow so better flowing heads will allow more air to get in before the pressure begins to build up

thermally, aluminum heads are less efficient than iron so we can up the compression and/or turn up the boost to make up for the loss.

[Steve Wood]

If you remember when turbos often were listed by cfm potential, Joe Lubrant once posted this formula which seems to work

theoretical horsepower is:  CFM x 0.069 x 10 = maximum horsepower that the turbo can theoretically support.