1BadaGTA

I was wondering I've almost total built my motor to a 383 stroker but I'm seeing more and more cars with more than 500hp. So I was wondering if with my motor (specs are as follows: trickflow aluminum heads 72cc, hsr, shorty headers, aftermarket exhuast, comp cam 230/236 .540/.536 113lsa, flattop forged aluimum pistions, forged steel rods, cast crank, I had the motor balanced, decked, line bored, the whole nine yards. I think with my setup I'll have a 9.5-9.7 compression ratio) do you guys think I can still run a forced induction on the motor with that type of compression? I want to keep the car a streetable car so I want to be able to run pump gas would I be able to do that or no?

SpitotRs305

it is doable but probalby not worth the money... at this point but you could always swap your pistons for some forged +12cc or something probably more get your CR around 8.5/8.9... you will make more power with the S/c than the compression and keep the engine safe for pump gas

xpndbl3

iTrader: (5)

cast crank and boost? Aluminum pistons as well? Sounds like you made a nice N/A motor, hit it with some spray and call it good. That isn't a good build for a blower at all.

V8Astro Captain

iTrader: (1)

I'm running 5psi on a stock L05 short block (2 bolt main, cast crank and pistons) and haven't popped it yet. You just have to be careful during the tuning process.

xpndbl3

iTrader: (5)

5psi is barely putting boost into a motor. In my opinion not worth swapping everything over to only hit it with a tiny amount of boost.

84z28350

If hes only going to run a small blower like a 144, 5psi is about all it will be able to do!

But like V8astro said, if you have a GOOD tune and keep the boost moderate, then even stock blocks can hold up for quite a while.

Now if you just bolt the thing on, jump in the car and put the loud pedal to the floor, your liable to leave a trail of engine parts on the road behind you!



But... We are not talking about a stock motor that has a measly 8.5-9:1 CR. I think 9.5-9.7 is going to be pretty high for even moderate boost unless you want to run race fuel.

V8Astro Captain

iTrader: (1)

I want to avoid challenging your opinion, but until you drive a roots blown vehicle every day I don't think that's a statement one can make.

I added my blower to the 350 that I was running in my Impala. So I had a baseline feel for the engine N/A. 5 psi of boost into this engine makes it feel like I put a JATO rocket in the trunk. I have no time slips to report, but any type of blower putting down 4-5 psi is well worth it if you ask me.

If you are worried about 5-6 psi on 9.7:1 compression I'd recommend a water/meth injection system. That compression with a little boost and water would be a mean combo.

305q_ta86

iTrader: (1)

Remember to back the timing.. Oh, and perhaps an extra thick set of head gaskets?

KnightWarrior

I don't see why that motor couldn't handle 5 lbs of boost.
Weiand says that even stock cast pistons can handle it, as long as you stay away from detonation. Jet the carb fat, cool the sparkplugs and retard the timing. It should be fine!
But how fast do you need to go? Sounds like you have a pretty nice motor already!

xpndbl3

iTrader: (5)

the average small roots blower adds 100hp and maxes out at 500hp. While that is a nice kick in the pants I don't consider that a huge jump when vortec heads can make 430hp on the cheap and AFRs can easily make the same 500hp on a 383 build. Now if you're running a 6-71 or 8-71 that's fine but roots blowers are horribly inefficient and at higher boost level create a lot of heat compared to modern centrifugal blowers.

1BadaGTA

Well I heard that since I'm at a basically stock compression ratio I could get away with running a centrifugal supercharger on low boost. Since I have really good interals and a fully balanced motor I figured that the amount of power would let me keep up with all the other sick cars around here. I know that theres always someone faster, but I was shooting to be a force to be reckoned with. :P So then if I run a supercharger at low boost how much of an increase would I see in my hp #'s. I built the motor to have something around the 500 hp mark but I just know that I'll want more power later.

rob_m

I really hate to dredge up the old 'boost vs. compression' argument, and I question their low estimate of CR value, but I agree w/ this sentiment:

http://www.inductionmotorsports.com/tech.html#cr

Consider ESPECIALLY in your case, you have healty 383 STROKER good heads, cam, how are you going to be unhappy with the off-boost response?! The only reason to not drop compression and increase boost is absolutely lousy off-boost response. Drop the CR as much as you can, (if you haven't bought the piston's yet).

1BadaGTA

Well I've already got the motor together I'm just buttoning it up now and I just figured that just on a small amount of boost I'd have more power all the time, not like nitrous where you hit the button and when it runs out your screwed. So basically which way then would I get more power out of 1. Vortech Supercharger or 2. One big shot of nitrous. which one would I see more power from. And I can't change anything to lower the compression ratio anymore just so you guys know.

askulte

I'd just build it as is. 5 psi is pretty low boost, and will be fine. If you've got big plans down the road to up the boost, then I'd drop it depending on what your goal is. Keep an eye on your air:fuel and timing, and you'll be OK. I'm running 8.1 compression in the Z28tt, and off boost (under 2000 rpms) it's not as snappy as a stock engine with higher compression (but I can run pump gas at 15 psi if I want to!)

xpndbl3 - all pistons on modern (last 50 years) cars are made from aluminum alloy.

305q_ta86 - Thicker head gaskets will lower compression, but increase the guench gap. This will make the engine much more sensitive to detonation, and worse for forced induction. Try to keep the quench at .035-.040" to keep knocking under control.

Drac0nic

don't forget, it's ALUMINUM heads too which means a lower off boost DCR since the heads dissapate heat; I wouldn't think 5 PSI should be an issue on it, they say that AL heads effectively lower your compression about a full point compared to iron.

5678TA

N/A all the way!!!! lol would it be bad to run .065 quench on a 10.65:1 motor??

327???

yes

1BadaGTA

Well like I posted before the motor has somewhere between 9.5-1 through 9.7-1 but I built it so It'd be below 10-1.

5678TA

1BadaGTA, i'm just kiddin.. mid 9 compression is kinda high for boost but very doable..

327???, just wondering cause thats how its gonna be.. i wont be zero-decking because i dont want piston/valve clearance problems later on down the road when i go HUGE solid roller.. and i already have a large duration cam in there so detonation isnt a problem..

askulte

I don't think you'll find any engine builder that would recommend that. If you're building it with .065" quench, you're asking for trouble, IMHO. Have you figured out your piston to valve clearance so accurately that that extra .025" makes that much of a difference? I'd personally run a smaller rocker ratio to cut .025" on the valve lift and run the tight quench. You'll get a better burn (faster, more complete combustion, more efficient, better mileage, and less emmissions too, if you have to pass a test) and more power from the tighter quench than from an extra .025" valve lift. Besides, that big cam might not make cyl pressure at low rpms, but at high rpms, you still want to keep the optimal timing rather than getting forced to retard it. 2 degrees (29 to 31) was worth about 20 hp at 5000 rpm when I was last on the dyno, if I remember correctly...

5678TA

hmmm.. thats askulte.. i guess i'll have to show this to my dad and change his mind.. i personally was down for the zero deck but its the dad that didnt want to do it.. i already know i can run the same cam(306s) at a .040" quench cause i did it before using a steel shim gasket.. but whatever, i do like the idea of more power.. thanks

askulte

No problem - If you and your dad are planning on designing the next engine and spec'ing the parts, I'd suggest reading David Vizards 3 books on smallblock chevies (valvetrains, rotating assemblies, and heads). They get pretty intense, but it's great on explaining how to choose and why. $60 on books and a dozen hours reading (they're a great reference too) is cheaper than buying new headgaskets.

F-BIRD'88

You want to look into a Water/methanol injection system.
Injecting water under a high pressure spray mist into the motor during WOT/boost will allow more boost with less retard while using a high compression ratio and pump gas. The water turns to steam (vapourizes) and in doing so absorbs a lot of heat in the intake charge (like an intercooler) It also tempers the combustion process, eliminating excessive heat and supressing detonation while under boost. Needs a little dialing in to get the water delivery rate just right but is very effective. The best results come from a approx mix of 50/50 water and methanol. Some people use the BLUE winter formula windshield washer fluid.
www.aquamist.co.uk
http://www.kennedysdynotune.com/
http://www.snowperformance.net/
http://www.coolingmist.com/
http://en.wikipedia.org/wiki/Water_i..._%28engines%29

that should be enough links to keep ya out of trouble for a while. good luck...

5678TA

i actually have the max hp book.. but i havent seen it in years.. a next motor will not be for many many years to come.. my dad has purposed to rebuild the original motor we built but blew up.. see sig for a taste.. so we will have the current motor and the original 383 with a new set of rods, a crank and a few new pistons..

SpitotRs305

well does quench even matter when running a dished piston? or is it only for flat tops as the dish would greatly increase the quench right? thought i saw the in turbochargers H. MacInnes

327???

it depends on the dish, i believe that you can get reverse dome pistons. those would be my choice, compression allowing.

level

boosting isnt worth it if you're only aiming for 5lbs.
descent gains generally start around 8lbs.

no you want your compression between 8:5.1 (non intercooled) and 9:5.1 (intercooled) for a roots supercharger.

obviously theres some wiggle room here.
if you use a whipple you can get away with 9:5.1 non-intercooled but won't make the most out of the blower.

edit: non-reversed dished pistons will work the best.