Question about Boost/Volume

Blown F-150 · #1 10-10-2008, 06:04 PM

I have a question that might have been asked before, but I couldn't find anything on.

So, I am in the process of getting everything together to run a 3.40 pulley on a P-1SC. My question is, since I am running LT's and have lost approx 2lbs of boost across the rev range and am gong to a "12lb" pulley and only expect to see a net of 10 lbs, does that mean my engine (stock) could handle a smaller upper pulley like a 3.20 for example and be fine because I will still only then have 12 lb's of boost?

I am under the assumption that it doesn't have as much to do with the PSI going into the motor as much as the volume of air that counts. In other words I think that even though I will only have approx. 10 lb's of boost with the LT's, etc. that the motor is still at it's limits on what it can handle.

Clear as mud?

ONELOWF · #2 10-10-2008, 06:21 PM

Yer making my head hurt!

See kaboom10's post in this thread.Boost on 2001 5.4?

I believe the answer is that the more air you can safely flow the more fuel you can flow with the air, so more beans!

Blown F-150 · #3 10-10-2008, 06:45 PM

I've was following that thread as well, The chart in there is great to compare compression ratio's vs Boost. I really would like to build a motor and not have to worry about it, but I just bought a '95 Mustang GT convertible and have already spent too much on it.

So I still am wondering if PSI is the limiting factor or the Volume of air? Would a 3.20 pulley be safe because I will still only make 12lbs of boost, or would I just be pumping in too much air for the pistons/rods to handle when it fires?

RBFC · #4 10-11-2008, 02:29 AM

The limiting factor seems to be combustion chamber pressure. This is a combination of your pistons' profile, your head design, and your boost pressure. They're all inter-related, since they all combine to produce the final chamber pressure.

The ring lands (the grooves in the pistons where the rings sit), the rods, and the pistons themselves appear to be the weak links. The ring lands tend to deform, allowing the ring to come loose from its seated position. The rods can only withstand so much force before they break.

With your long tubes, you'll probably encounter the bottleneck for air flow at your exhaust valves. Unless you've done some head/valve modification, the exhaust valve will contribute to creating the back pressure (boost) at the power levels you typically read about here.

Remember that HP is a product of air flow through an engine. To create HP, you must cause a more powerful explosion of the fuel/air mixture in the cylinder. The more powerful this explosion is, the higher the pressure it can create. (I know this is a painful review of S/C basics, but we can get carried away with the quest for power and end up with a dead truck sitting in our driveway...)

So, if you can get good HP with 10psi of boost AND long tube headers, is it really worth it to go the extra 2 psi for ~20 RWHP and take much more risk? With a good dyno tune, you shouldn't have to worry too much about kabooms. Of course, if this is not your daily driver and you have an extra built short block lying around (+ a couple thousand $$$), go for the big boost!

Lee

tarajerame · #5 10-11-2008, 09:14 AM

depends on how much power you are putting out now. psi also creates heat so would the extra 2 psi make more power to negate the increse in intake charge temps?

425rwhp seems to be the window ledge for the stock non SVT blocks.

If you are putting down like 375rwhp with your current mods then I would just run the 10# of boost and start building a long block and get the smaller head pulley for when you get the built engine installed and broken in

Z7What · #6 10-11-2008, 09:11 PM

Boost isnt your limit, the HP numbers are. Boost is only a measurement of restriction of air.

Wayne

Blown F-150 · #7 10-12-2008, 05:14 PM

Thanks for the knowledge guys. I guess I'm gonna stop at the 3.40 upper and get a good tune. I do plan on building a good motor for a high boost application. I would like to do 19psi with a roots style blower. I don't think the rest of the truck would hold up as a DD beyond that.

RBFC · #8 10-12-2008, 05:41 PM

Quote:

Originally Posted by Blown F-150

Thanks for the knowledge guys. I guess I'm gonna stop at the 3.40 upper and get a good tune. I do plan on building a good motor for a high boost application. I would like to do 19psi with a roots style blower. I don't think the rest of the truck would hold up as a DD beyond that.

With the HP levels that 19psi can deliver, you might want to consider upgrading the following components on your truck:

1. Driveshaft: factory ones are only rated to 99 mph, and cannot handle a large amount of torque

2. Rear end gears: can take some of the stress off the transmission

3. Fuel delivery system: the stock items cannot deliver enough fuel to feed that boost level on the 5.4

4. Transmission: eventually, this would be a great idea. big $$$, but the stock tranny isn't really made to withstand that kind of power.

Good luck,

Lee

Blown F-150 · #9 10-12-2008, 06:53 PM

I Have some if that lined up.

My curent granny is supposed to have been built to handle 500hp. But I plan I. Going to a 4r100w my buddy wrecked his 7700 and I hope he buys it back so I can have it as a donor truck motor to build, tranny, etc

I will have to get a drive shaft, anyone know how much one is?

I have 4:10's sitting in box waiting for me to find instAll kits and my buddy to install them.

I know this all isn't going to happen right away, but I am slowly accumulating the parts.

As for fuel, ihave a 255lph to install when the pulley goes on. I am sure I will have to replace the entire fuel sys when the real motor goes in.

Blown F-150 · #10 10-13-2008, 11:48 PM

Sorry guys I read that last post and it is pretty badly typed, I was doing it from my stupid iPhone while I was waiting for turkey.

I can't wait till I can up the truck to 12 psi and finally a tune! I should have don it a while ago, but I've been putting it off.

I'm going to do a little research on pistons and heads, I bought a pistons but I already sold them to a friend because they would have put me above 9:1 and he is going to run N/A with NOS.

I don't really have a budget set yet, but I know I will try and piece it together slowly and do the build it myself other than the required machining.

Thanks for the great explanations and I will keep trying to learn as much as i can!

RBFC · #11 10-14-2008, 11:09 PM

Quote:

Originally Posted by Blown F-150

My curent granny is supposed to have been built to handle 500hp.

Yeah, this was good....

My granny used a walker, and couldn't get a quick 60 ft. time to save her ass. That must be one hell of an old lady there!

Good luck,

Lee

justjames80 · #12 10-14-2008, 11:49 PM

Quote:

Originally Posted by Blown F-150

I don't really have a budget set yet, but I know I will try and piece it together slowly and do the build it myself other than the required machining.

Thanks for the great explanations and I will keep trying to learn as much as i can!

SHM has a book about building modular motors. Good idea to pick up a copy because the torque sequence is very detailed.

Blown F-150 · #13 10-15-2008, 04:23 PM

Would you know of any online store that would carry it, I tried to find it locally with no luck.

Thanks

CobraKit · #14 10-16-2008, 08:02 AM

Some of the issues with higher boost is that it requires a very good tune by an experienced tuner, boost experience that is. Also, the magical 12psi boost limit on NA 5.4 is also attributed to the hypereutectic pistons, thin ring landing for emissions and sometimes the cast crank. Pistons/rings probably number one after you need a good tune. I had about 30,000 miles of 12psi boost on my 120,000 motor when oil started coming out the exhaust. Uponn tear down, noticed the rings were all bad and the exhaust guides were wasted as well. Luckly the rings and top of piston didn't fail. OBTW the bottom end and cyclinders looked great. Could have reused all the bearings, No I didn't!!!

Blown F-150 · #15 10-16-2008, 02:33 PM

My truck doesn't see to many miles in a week like it used to. So I hope that after the tune and upping it to 12LBs, which will most likely be around 10 lbs, that I will have enough time to start building a replacement longblock. I'm still waiting to hear if my buddy can buy back his '01 7700 that was written off. It only has 120,000kms on it and I think it would be a great candidate for a motor.

I should be able to afford the Tune and tuner by the end of next month. I am counting down the days!

I have been in contact with Justin @ VMP, so he will be providing me with the tunes and xcal3.

If anyone knows where I can get a good Mod rebuild book or DVD. Let me know I will be building 5.0 with mild ported heads for the stang in the coming weeks and am going to use it as my learner project for doing the 5.4. I know one push rod and the other is DOHC, but I think it will still be a good starting point. I have build 100's of ATV and boat motors, and probably double that in Sled motors, so I feel confident I can handle this.