Well, three weeks after she was suppose to be done, my 383 is finally going to be in my hands monday afternoon. I am very excited. When it is all said and done, I am hoping for low 12s, with the help of sub frames and lca and relocation brackets. I hope to have her in by next weekend. It is going to take alot of chip tuning, but hopefully it will be well worth it. I think fuel delivery may be a slight problem as well, but if I can increase the pressure, she should be able to do it. I'm gonna data log much of the break in period so I can at least get an idea of what she's gonna do when at WOT as well. I really hope the 2bbl tbi will hold up....we will see. Once I get some numbers, I will post more engine details-assuming I have respectable numbers that is Wish me luck guys, I'm hoping to take the tbi step foward.

 

Your car should be deep into the 12s depending on how stout you built that stroker motor.

Hate to say it but your limiting factor will be fuel delivery with the 2 barrel TBI. You might be able to get by with the larger 454 TBI unit and some good tuning as a minimum. A healthy 383 needs breathes lots of air (and needs the fuel to go with it!!)

A carbed application would see a minimum 750 CFM double pumper and the ones pushing 500+ HP use 850s

If you find that the 2 barrel system is inadequate for your setup you will need step up to a Holley 4-barrel 750 CFM TBI with 65 #/hr injectors and in order to use it you will need to ditch the factory ecm and go with the Commander 950

 

Yeah, my 383 should be pretty healthy-you can find some of the specs in my sig. Hopefully airflow isn't too much of a problem, as the engine is set up for low to mid power for the most part. I don't plan on taking her past 5,000 rpm until I am absolutely confident it's safe. One day, when I can afford it, I would like to go with a multi port injection of some sort like the stealth ram. But when that happens, I'm probably going to make a few changes to the engine as well so she can pull higher rpms. For now, I really want to test the limits of the 2bbl TBI. We've seen 320hp in a few, but anything higher than that is theory and speculation. Hopefully I can break new grounds.

 

I'm really rooting for you because I'd love to see someone here push the envelope with TBI.

You will really have to optimize your car with that motor to reach your goals... otherwise I'd be suprised if you make it into the 12's. You are going to have to set it up to get good weight transfer ala drag struts and traction via a set of slicks... you will also have to get your weight down to something like 3000 lbs with driver...

It looks like you are trying to keep the revs down. Why is that? I think you are selling yourself short by shooting for whats going to be about a 400 hp motor when you could for about the same cash outlay build nearly 500 hp.

With your motor, a 900cfm 4bbl TBI, a performer RPM intake, a bigger cam with less LSA I think you'd looking at 450-480 hp and still make gobs of low end torque.

 

<-------
EXACTLY...

 

 

The Holley 670 unit should allow airflow enough to support 400+ fwhp, incl intake losses due to the air cleaner, and possibly as much as 5-10 % higher still (i.e. 420 to 440 fwhp). Sure the 4bbl TBI unit would be better, but airflow won't be your problem.

The cam & heads are certainly up to the task of flowing enough air for 400+ fwhp.

The 85 #/hr injectors are probably good for 300 fwhp reliably with the stock fuel pressure, so it's an understatement to say that fuel delivery will be a problem. It will be a BIG problem. You are going to need, IMO, 33% more fuel volume to get near 400 fwhp and I think that means 77% more fuel pressure. So starting at an assumed 11 psi fuel pressure (stock) you will need 19.5 psi.

I doubt your engine will be happy running 19.5 psi under all load conditions, so you are probably going to have to use the vFPR... in addition to the ECM tuning. The vFPR has been discussed here as well as on the CFI forum.

Be careful with that motor especially when you get on it --- if you run very lean (which you will if you don't bump-up the fuel pressure), you run the risk of punching a hole in a piston.

FWIW you might learn from Tom400cfi -- he's been running a 400 sbc using a Crossfire intake and two std single barrel TBI units, along with the vFPR. His setup is probably the closest to what you have (near 400 cid, TBI powered, aftermarket cam, two TBI bores), or what you will need when your engine arrives. He's also using a tired motor and has run 13.2 at 4000' altitude, so in a fresh motor at sea level, he's probably into the 12s as is. That's not far off of where you want to go.

HTH.

 

Well, heres what I'm looking at. I want the car to be plenty streetable while making good power. She's gonna require a lot of air as most 383s do, but I don't have $1000+ to invest in a 4bbl tbi or multiport system right now. And I'm NOT switching to carb. I'd still be running my 305 if she hadn't have blown. As far as reving the engine goes, it's simply until I'm 100% confident she has the air and fuel needed to rev past 5,000rpm. The heads are definetely set up to rev. The cam is there too, all I would need to do is switch to 1.6 rockers, which would give me .544/.544 lift. The reason I went with LSA of 114 was to keep the computer a little happier.
As far as fuel goes, i'm not too worried about it actually. In theory, two 85pph injectors are good for 340hp. I'm gonna crank the pressure up pretty good, probably integrating a VAFPR inline. The delphi injectors should hold up pretty nicely as well, and if I did my math right, I need fp of 25psi for 400hp.
As far as times go, I'm very confident that as long as fuel delivery is good to go, low 12s are very achievable. There are other guys on this site running very similar combinations less injection running 12.3-12.8s at 109-114mph.
I am going to test the 2bbl TBI system for all it is worth, and we can finally have some hard evidence as to how much power it can support. If I can't get what I need outta her, then the old 'maro will sit yet again until I can afford to change fuel injection. But we will know the limit at least.

 

We go by rwhp not fwhp, just thought ide let you know, lol

 

Yeah, it ought to be pretty easy to tune with that cam... I'm betting it will idle at 16-17". 11" is enough to keep enough resolution to tune with although tuning gets more difficult. Keep in mind that that 670 cfm TBI unit is flow rated at 3" not 1.5" like 4bbl carbs... This means it flows substantially less air. I havent seen flow specs on the vortec performer but the standard performer intake flows less than your heads. There is not doubt its going to make great low end torque but not nearly as much power up top as if you allowed it to breath better. I'd be willing to bet that your down close to 40 hp just between the intake and tb unit. The cam duration is close enough but the lobe seperation is going to hurt also to the tune of about 10 hp.

 

The intake is of nice design, though not really any different runner wise from the non vortec version. I am running a 1/2" spacer as well as an injector pod spacer, so maybe that will help a little. As far as the TBI goes, I did fine sand the bores and gave them a polish if that's worth anything. I have toyed around with the idea of having them bored out a little, though if I remember right, there is next to no side wall left to do so. I'll have a little time to check it out this weekend, but I also recall the adapter plate bores just barely clearing the intake. Maybe some work could be done on the intake as well. Who knows... The ram jet 502 makes 500hp with the 48mm throttle body, so there is hope.

 

i think it's a good idea to limit rpms on this application for two reasons:

first, there's the question of reliability. the lower you rev it, the longer it'll last. who wants to stick all that money in an engine only to have it puke a rod after 20,000 miles?

second (and more importantly), is the issue of airflow. a 383 will already require more airflow at any given rpm than a 350. as you rev it higher, you even further increase the airflow demand.

i'm thinking the 383 would be better with 90 pph injectors rather than 85s. that'd leave more headroom for increasing pph through raising fuel pressure. the less he has to raise fuel pressure, the better, and if it does end up being a tad rich, you can always adjust for it with the chip. i also think he definitely needs to think of a 454 tbi.

i've been trying to find out what the "true" cfm of the various tbi units (small block, 454, holley 670) would be if flowed at 1.5". with that, you could easily calculate what the cubic inch/rpm limits of each are.

the other thing i'm trying to figure out how to calculate is the effect of increasing fuel pressure on pph. knowing that, you can calculate the maximum horsepower your tbi is capable of supporting.

can anyone help?

 

NewFlow = OldFlow * (sqrt(NewPres / OldPres))

RBob.

 

i'm sorry, i don't follow.

 

Well, the largest injector for the holley unit is 85pph. They make a 90pph, but that is for the single tbi unit, and i believe the voltages are different. I am using the Holley 670, which is basically the same as the 454 tbi, except the injector pod is smaller thus having a little less restriction. Like I said, I am toying around with the idea of boring it out a little more. I think 670 cfm at 3" turns out to be roughly 550 at 1.5".

As far as the equation "NewFlow = OldFlow * (sqrt(NewPres / OldPres))", My example would be like this:
New Flow=85pph * (squareroot of (35psi/21psi))=109.73pph

The "OldPres" is what the injector was rated at. New holley injectors are rated at 21 psi. I believe stock gm injectors are rated at 12psi. The "NewPres" is what you are raising the psi to, in my case, 35psi. Old flow is what the injector's pph is at the old pressure.
Holley injectors supposedely run better at higher pressures as opposed to lower pressures, and I can vouch for that from using the 57pph on the old 305. Before anyone does this on their 305 though, realize it took a lot of chip tuning.
As far as achieving that pressure, I am going to do this: Set the AFPR on the holley unit to around 12psi. That will be my minimum and idle pressure. Then I am going to place a vacuum referenced regulator inline. This will raise the psi when under more load, i.e. WOT. Not sure which one yet, as I am having a hard time finding one, but it will obviously need to have a range between 12psi to about 40psi. Any suggestions?

 

By the way, I am going to follow Jon's advice and wait until I install the Walbro 255 fuel pump. There is no way I would try to get 35 psi out of the stock one.