Hey everyone, I have a 383 with a 10:1 CR cast internals not forged, Mini-Ram intake and afr 195 heads. Was thinking of putting a turbo on it but the cons of turboing a high compression engine seems like it would be a bad idea, so I turned my focus onto a supercharger. I don't know much about them, I don't even know if I could run one with a 10:1 or with the internals I have. If anyone could share some tips or just some basic knowledge that'd be great, I hope this is the right spot for this question.

 

Same deal. Without lowering the compression you can't put much forced induction into it. Either need to lower the static compression (change pistons) or lower the dynamic compression (BIG cam), or you aren't going to run much boost - 5 to 10 psi max on that much compression. It takes about 15-18psi to double the HP on an engine (theoretically, and usually practically also), so the ROI on a supercharger kit that's running such low pressure likely isn't there. Also cast pistons with NA ring gaps are prone to breaking if pushed too hard.

GD

 

Forgot to mention my cam, ZZ9 cam with cam lift int: .323
I'm not trying to double my power because thats a lot! lol It is my street/ weekend driver, just want some oof to sit me in my seat. What would be pushing too hard? For the pistons to break. Thank you for your help btw!

 

Pistons can live with good tune.

if you intercool you will be ok for a few psi and make alot more power.

a cast crank kinda worries me some and unknown rods. Does it have studded mains? 4 bolt mains?

nice thing about a blower is its more predictable and linear with rpm. Easier to tune for. However it does have extra stress on the crank nose driving the blower.

 

I think the rods are forged, I have no idea if it's a 4 bolt or not, it is an L98 block but heads, cam, intake and Rotating Assembly is different

 

Turbocharger or supercharger, you're still facing the same problems. I've 'heard of' a few guys running boost with compression ratio that high, but have never seen anyone actually doing it IRL and having the engine live for any length of time. The cast pistons are a problem (and if the pistons are cast, chances are so is the crank) but IMO the bigger issue is the tight ring gaps used in NA engines; that's a definite NO in boosted application.

Concerning the connecting rods, AFAIK, all small block rods are forged.

 

So I'd really have to go in with a new rotating assembly?

 

If you want it to live, yes.

Building a lot of horsepower is a game of attrition; leave any weak links in the chain (in this case, the 'chain' is the engine assembly), and they will become apparent---usually catastrophically.

 

I see, right now I'm making about 375WHP, Im not aiming for ridiculous numbers but anything more than that you're saying I need a better assembly kit

 

I would not build a boosted engine with cast pistons and a cast crank. I have found, through experience, that initially spending more $$$ on high-quality (read, strong) basic engine components is cheap insurance against having to do it all over again at some point down the road.

 

I really appreciate your input, so when with a high compression engine I could boost it but the internals need to be forged

 

It's not that simple - if you get it into detonation (easy with high compression) you will just pound the bearings out of it - regardless of forged or not. It's not a matter of only having stronger parts - if that were the case then we would all have 25 psi on our 11.5:1 forged engines.

It's simply a BAD IDEA to put a power adder on a cast crank, high compression engine. It will have a hard enough time being tuned without any forced induction. With forced induction you'll be fighting having too much timing, and not enough timing at the same time. Raise the timing and you hit detonation real quick, lower the timing and you increase combustion chamber temps and again invite detonation. It's a no-win scenario and that's why most forced induction builds target 8.5 to 9.

GD

 

Okay I think I get it now, I appreciate your help man

 

Forged, yes; high compression, no. As has already been stated, compression ratio must be lowered when considering turbocharging or supercharging. IMO, 10:1 is too high.

 

I ran an 11.5:1 motor with a small 142 weiand supercharger. It has forged pistons, crank, and rods,...also the ring gaps are opened up for power adder. Ran on 93 pump gas with 30 degrees total timing. Ran 7psi of boost, then 10 with a smaller pulley. Didnt break any records but sure was a lot of fun. Currently have that same engine in an S-10 doing a twin turbo build. With mild boost i wouldnt be concerned about the compression at all. The ring gap would be my first concern.

 

Do you have E85 where you live? I wouldn't be worried about the compression, I would be worried about rattling those cast pistons and like was said earlier the ring end gaps. Do you know if they are cheapie stock replacements or aftermarket cast pistons? Do you know what the end gaps are now?
I ran 10.5:1 compression, miniram, afr heads and vortech blower just like you and car ran fine, but I had the SRP 4032 forged pistons back then. Your tuning window will be smaller because of the pistons. I can tell you now that I went lean more then a few times before I figured out I needed more fuel pump and more injector before I got it right.

You could put a blower on your car if you keep these things in mind: 1. sneak up on the boost, 2. sneak up on the timing, 3. run good gas (93 with boostane or other 'real' octane booster or race gas or E85, 4. work on your tuning skills before you turn up the boost or timing. The good thing about a blower is that the blower pulley size limits your boost vs a turbo. Run something like the 7.8 lower on a vortech and 3.47 upper and that should be around 6 lbs. Then at 6lbs max you can dial in your fuel and timing to keep them in the safe zone.

Do a search for my old thread called Vortech T-trim in this same forced induction forum and you will see that I got lean (leaner than 12.5:1) more than once when testing and tuning.

As long as you don't do that (go lean) and keep some good gas in the tank you should be good with 6-8 lbs of boost. Put an intercooler on it for sure.

 

10:1 isnt as bad as it used to be. Compression got a bad name with boost due to shotty tuning and intercooling imo. New turbos these days are more efficient, ppl know what they are doing moreso now. Better tuning tools available and efi systems. Better coolers etc

blowers kinda same deal. Slap on a kit with fmu and no timing control it will have issues. A good centri kit and intercooler can really do good with proper fuel control and timing control.

i’ve run 24 psi on pump gas at 9:1. I’m at 12 psi at 10:1 on my bbc and it will take more no problem but at 1200 whp it doesnt need it. Theres situations it works well.

you most certainly can run low boost on 10:1. But tune has to be more forgiving when dealing with cast pistons. Or even hyper pistons. Like others said a bigger concern is the ring gaps.

stock bottom end lsx guys have cast stuff as well but the fast guys adjust their ring gaps. Alot of those motors are near 10:1

 

Bringin kind of a dated thread back vs startin new. How much can detonation be warded off on high compression using some race octane? Assuming full forged lower end, And how would you determine what octane to run? I know for me, e85 is non existant, but 100+ octane is pretty easily gotten

 

Race gas lets you do what ever you want to do. C16 is 118+ octane and burns slow, so you can use that for any compression with boost. 93 pump gas with boostane will get you 102 to 112 octane cheaper than race gas. 15 gallons of 93 plus 1 can of boostane is about 102 octane. You will have to sneak up on it with timing after you get the air fuel right, all combo's won't be the same.

 

My 10:1 358 In my old Corvette with a little powerdyne supercharger and no intercooler was pretty reliable for a street car.

I would not be concerned with a small centrifugal blower and a good intercooler.

-- Joe