My car is getting close to being done and am really curious how much gains I will get out of it over NA. My buddys car with 8 psi picked up like 15 mph in the 1/8 but that seems crazy to me for 8 psi. The car is a full weight street car thats around 3600lbs or so. Since my motor has kinda high comp ratio(9.88 to 1) and not a full forged shortblock planning to keep the boost down. The motor is a very mild 408 sbc and has run a best of 11.89 at 115 NA. What kind of mph should I see with 7 psi?? What about rwhp increase?? I would guess my car has about 360rwhp NA with its weight and trap speed. The power adder is a D1SC Procharger.

Thanks!

 

Gains in going to low boost are pretty suprising tbh. I don't necessarily know the numbers or formulas to go figure everything out so you can compare $ to hp, but iirc, *most* N/A motors that we normal people build are around 80-85% efficient. That being said, once you reach 0 psi, just before going into boost, you're already increasing the power by 15-20% by making the engine 100% efficient. Assuming all things are perfect then adding nearly half normal atmospheric pressure would net ~40-50% more of an increase. Therefore IN MY THEORY, bringing you to somewhere ~55-70% increase in hp over what you have now. Assuming you will lose the same amount of power thru the drive train, you're looking at around 560-610hp to the wheels.

Lots of assumptions made there, but the take home is that you're boosting the motor's efficiency a good deal before you even see boost. That's how guys like wazslow have been able to make killer power on low boost (good heads, intake, etc). Imagine if your motor is only ~60% efficient N/A, then getting into boost would be all that much more.

 

I dont have a clue .

Just get it to the track so we can find out !

 

Haha...Thanks guys for the help. Just bench racing in my head until it gets done. Anyone else have any info they can add??

Dave...as soon as I get some numbers from the track I will PM you asap!

 

Rule of thumb IIRC with boost is 8% increase for every 1psi boost in an ideal world with no losses due to the turbo/blower adding the boost. So 8# would equal 64% increase minus the power it takes to turn the blower. I'd guess you'd add real close to 50% to your rwhp if the combination is right.

 

Usually in an NA setup your VE and manifold pressure don't coincide like your assuming. When reading boost your reading whats in the intake manifold, not in the cylinder. Same with a VAC gauge on an NA motor. Go for a ride in an NA car with a vac gauge and watch the gauge when you go WOT. The vac gauge will go to zero aka standard atmosphere. That doesn't mean your engine has 100% volumetric efficiency. You could still have 80% VE. So what your saying about the 15-20% increase in power just before going into boost is incorrect because your intake manifold (where you read boost from) always had 0 psi/14.7 psia/ 29.92 in. hg. (whatever you wanna call it) before you turbo'd it. It all comes down to delivering the air to the inside of the cylinder. Thats where valve size, runner size, cam profil etc. all come into play to increase your VE in the cylinder.

 

Yea, I don't doubt that. I was just trying to make the point that you're going from less than 100% VE to more than 100% VE, and then some when adding boost. So gains may be more than expected even with "low boost numbers."

 

360 hp with 7 psi will get ya about 160 more hp. (45%)

 

I'm really not trying to be a jerk but I don't think you see what Im sayin. There is no "and then some". Both NA and turbo will make the same HP until there is actually postive pressure in the intake manifold. Both NA and turbo will go from vaccum to 0 psi right at WOT there is no gain until the boost gauge reads above zero.

 

So most likely around 500-520rwhp. That would be cool for 7 psi for me.....

 

My truck with a 8.8:1 383 sbc n/a went mid 13's @ about 98 in the 1/4. Same everything with twin to4b's with 8 psi it went 10.91@123. Went from 88 to 100 in the 1/8th also. Not a bad hp gain there.

 

HAPPY THANKSGIVING !

Just to make a point about what it takes to turn a blower .

I had the same blower , ( literally ) and my truck and went 10.5 at 128 in the 1/4 on 15 psi .

When I put the turbo on it only took 12 psi to run that same time .

And it went 10 mph and 8 tenths faster on almost the same boost ( 16psi )

Calculators say it made 180 more HP at 16psi with the turbo . I'm sure it all comes down to efficiency , but I think thats incredible !

I made no other change other than put an S480 / 1.10 / 87 trim turbo on it and changed the cam .


Blower on 15psi made 720 according to calculators . ( that was basically spinning the D1SC to around 60,000rpm )

Turbo on 16psi made 900 according to calculators .





I wish I had more info on the blower numbers , because my motor made right at 500 on the engine dyno NA . ( pretty close to yours ) Problem is I never only ran 7 psi . I started around 10 to 12 psi .

But if I remember right , it would run right at 11 sec in the 1/4 on 12 psi . Calculators say 620rwhp . :noidea:

So I think you right about it making somewhere around 500 to 520rwhp at 7 to 8 psi .

 

Good info guys. So I would think with 500-520rwhp I should be able to run solidly in the 10's at 3600lbs. That will be plenty for a bit!

 

If all the parts match up pretty well you should run 10's. I was running 10.8-90 @ 540rwhp @3800lbs.

 

Thanks!

 

My buddies nova was running 12.0s at 111 on motor. I sold him my P1SC and tuned her up she went 10.89 at 125.90. 8 psi and 93 oct. pump gas non/ic with timing still pretty conservative weighing 3250 lbs.

 

Thanks Tbird thats some great info! Looks like he is picking up almost 15 mph like Greg O's car with 8 psi. What kind of total timing are you guys running witht your set ups?? What cubes and pulley is he running??
I would be stoked to pick up 15 mph in the 1/4. That would put me right at 130 traps.

Tell me about your ser up in your truck!

 

On a low comp/boost supercharger many like 30+ timing
Again, trial and error and tuning are necessary. I start conservative (rich and low timing) and work from there.

 

I am running a MSD 6530 box with 35 deg locked timing. Then pulling 1.3 deg per lb of boost. Should be right at around 26 deg at 7 psi.

 

On the dyno we ended at 22 deg. total cuz he was afaid of pushing the motor. Believe it or not the motor is 98 350cid from an escalade.
He put a mild cam ,airgap intake and carb and new valvesprings and it ran low 12s. So with the procharger when we reached 440 whp on the chassis dyno he was getting nervous that the bottom end wouldnt take it. Last time at the track he turned down the timing retard a bit I think it put him at 25 or 26 total .

MY junk. WEll I just relized I still have procharger in my sig. However I am building a twin turbo blowthru setup with the same motor. Hope to make an relatively low maintainence 1000hp.