LameRandomName

SETUP

> 383 with 5.85 or 6.00 inch rods
> 8.0 - 8.5 to 1 compression
> AFR 227 LT4 heads
> Relatively mild cam, specs to be decided, idle speed probably under 1,000rpm
> LT4 Intake, with appropriate matching/smoothing
> Vortech X-Trim running ~ 1 bar or less of boost
> Mild converter (mid-2000 stall rating)
> Transmission - most likely a 4-speed automatic, possibly T-56
> 3.73 gears
> Heavy car (4,000lbs +)


THINKING

I'm thinking that this setup would result in a car that was fairly tame at lower RPMs (under 3,000), but that would rapidly build up to something in the 750hp vicinity between 3000 & 6000 rpm.

I'm also thinking that the fairly large compressor on the rather large heads, with relatively mild cam would result in good volume of air at lower RPM, making up for the size of the heads.

The intention is to kill power on the bottom end for better hookup without going to very large tires with the attendant driveline shock and to allow fairly tame "around town" driving, while still having a lot of power on tap at higher RPMs.

This is on a "toy" that does not need to be used for daily driving.


QUESTION

I'm basically looking for a "reality check" from someone more knowledgable about the characteristics of forced induction engines.

Highlander

for 750HP flywheel or rearwheel the x-trim is not needed..... Better go with a ysi-trim...

it will work a lot better on the street for that matter...

AFR 227 heads and a mild cam??? What do you call mild???

LameRandomName

The 750 figure was, to be quite honest, a wild-assed guess. I'm not actually shooting for a particular number, I'm shooting for a particular effect.

I know that I could make 750 with a YS, or maybe even smaller blower, but I'm trying to achieve a particular effect in terms of the vehicle's overall behavior, and it's in that light I wanted to have my thinking checked.

As to what I consider mild, it's hard to put a number to it because I would get a custom cam for this setup.

Having said that, in this context I would call a "mild cam" one which would be well suited to the AFR 227 in a NATURALLY aspirated motor.


To re-state, I am intentionally trying to shift the entire powerband up, away from idle, for the purpose of getting the car launched on lower power (in order to lessen shock loads) and then bringing in the big numbers above 3000rpm.

My thinking is that intentionally using oversized heads with an oversized blower (which should generate a larger volume of airflow) will both shift the powerband up, and allow me to make big power in the upper half of my RPM range, and do so with a lower pressure level than I would need to use on a smaller blower.

Highlander

The 227 are not that big for a 396.. A cam well suited for a 396/N/A in termos of duration will not be the correct cam to use on a supercharged engine... As a matter of fact.. I dont think that you will get a good idle with a cam suited for it...

I do agree you will have to pulley up the supercharger to get the desired effect and match it to the cam...

I believe that you will be a lot better with a YSi-trim than with an X-trim...

How much rpm are you planning on that engine??? the bigger the cam the more you will have to rev to get the correct power out of the setup... If you overly size the heads and the cam to remove low end you better be expecting to get to the super high end or it will be a mediocre performing engine with a bad combination...

Let me know what rpm range and hp range you are planning nad i guess some of the most awesome guys here can suggest a better combination...

LameRandomName

I'm thinking, no more than 7000rpm.

Like I said, I'm fairly unsure of the cam specs.

I believe that having a set of heads that is too big for the cam and a blower that's too big for the heads will work for what I want to do, but I'm really not sure what sort of cam specs will make it all happen.

I specifically want to use that pattern though...
heads too big for the cam, blower too big for the heads.



BTW, it's a 383, not a 396, although if at some point I come to believe that I would be better served by moving to an aftermarket block, I'll start with an Iron Eagle, which should let me get into the 430-ish area with good cylinder thickness. At that point I would have some really nice heads available to choose from, and I don't really think it'll be all that much MORE than what I would spend at a machine shop with the LT1 block, getting it ready for higher HP. I figure that careful selection of off the shelf parts will go a long way, and I'll be doing all the supercharger plumbing myself.

Highlander

the afr 227 unless they are ported to 240ccs i dont see them flowing like a good set of 18ş which would be my next move if i ever decide to. which means that for a 430CID they are too small...

Whith what you say, it would probably "do" what you expect.. but its a bad combination of things and it will simply make the engine very very inefficient and it will simply not run well.. it will not have a good low end to use on a daily basis, or even if its not a daily basis, it will NOT be a super enjoyable car...

I really dont have the experience to say much more.. all i feel is that its not the right combination... maybe im mistaken and i hope someone with more knowledge chimes in.

What is your RWHP goal??? a YSi-trim can get to 900-1000rwhp and can do 8s as has been done before... that will not be a street car anymore, the required fuel is different.. everything will be different. an X-trim would be a bit higher... so unitl you start getting in the 1000rwhp range which i dont think the ltx block can hold it i suggest you go with either a YS-trim or think in getting another block and change the setup...

engineermike

I'm a firm believer that a properly "mis-matched" set up can work especially well. Example: 5.0 mustang - very short stroke coupled with a long runner intake manifold makes good mid and top power.

I predict your combo will have a very good powerband, but maybe not what you're looking for.

The heads will not shift the powerband up much - they may lose 10 ft-lb down low versus 190's. The stroker will add bunches of low-end. The cam is the largest determining factor in low-end. My car, a 383 with AFR 210's, 224/236 cam, and T-trim, made 575 rwftlb at 3500 rpm (as soon as the throttle was opened).

To accomplish your purpose, I'd use the parts you listed, but stick with a 350 or 355, then get a large cam on an extra wide LSA. For instance, something in the 230/242 range on a 116 - 118 LSA will kill some bottom-end.

My honest opinion, though, is that you're going about this all wrong. Bottom-end power is how you win drag races. My old Bandit 1200 made 90 rwftlb at 6,500 rpm and ran 10.18 at 133 mph. My new ZX-10R made 80 rwftlb at 9,800 rpm and ran 10.06 at 145 mph. So, with way more hp, the ZX barely ran any quicker.

My point is, build the best combo you can, then figure out how to hook it. You're purposely building a combo with flaws. If you put the time, money, and energy into building a 700 rwhp motor, handicapping it so it won't reach its potential is just plain silly.

On my only clean pass in the car, I pulled a 1.52 60' with a Vigilante 2800, 3.42 gears, and 27X10-16 ET Streets. No wheel well mod's, no major suspension mod's, 7.5" rear, etc. . .

LameRandomName

Highlander -

I don't really have a HP goal. I have some ideas I want to try.



Mike -

It's more than just a drag car. It's a toy.

I've considered using an iron eagle and little chief combo., but have not made that decision. I am emotionally attached to the idea of working with the existing block, which is really well seasoned.


BTW, I chose the X-Trim because it has the highest adiabatic efficiency of their entire line. 79%

Highlander

They ys-trim has 78... i dont think there is any noticeable difference between them in that respect...

engineermike

So is mine. . . But there's no dis-advantage to building a proper combination and bolting on a set of ET Streets or slicks to see what it'll do.

Mike

rskrause

I agree. While a "mismatch" can be made to work I can't see deliberately creating one. OTOH, you need to think clearly about your goals in order to select the right combo. What might be a "mismatch" for some purposes will not be for others. Let's say you have a killer set of heads that don't stall until .700 but are building a street motor. You want to keep lift to .550 for valve spring longevity. That's a "mismatch" in a sense, but it suits your purposes.

As far as the specific combo suggested, it's not easy to analyze. But it will have huge bottom end, so I think the reasoning on that score is out of whack. If it makes 750hp at 6,000rpm it's going to have >500ft.lbs of torque by 2,500rpm. Also, a blower that big is definitely not needed for 750hp.

Rich Krause

LameRandomName

Well sure, I'm going to bolt on some slicks and see what it'll do.... for sure.

On the subject of the HP goal; as I've said, that's a wild-*** guess.

I don't really have a HP goal, I am more interested in exploring an idea.


Does anyone have a desktop dyno they can run this through?
Just for shˇts & giggles.

LameRandomName

OK, if nobody has a desktop dyno, perhaps someone has thoughts on a proper cam for something like this?

Heads oversized for engine, blower oversized for heads. 7000rpm limit

If you want to make that work, what do you do with the cam?

Jerm93z28

well, since you'll have a grossly oversized blower, and oversized heads, why not make the camshaft grossly UNDERSIZED?
like maybe 200/205 duration....

and then you could run an oversized 5,000 stall converter

and undersized 2.23 gears


undersized 2" single exhaust.....



it sounds to me like you want to build this thing regardless of what anybody says. like a few have already suggested, there really isnt much of a point to it, other than wasting time, money, and a GOOD performing car.
if you just want it to hook, i say look elsewhere. make the power you want to make, then make it stick by working the suspension or even pulling timing during launch or whatever.
if you do build it tho, good luck and all, i just think you would be happier with the stuff others suggested.
jeremy