hey all..im not a super mechanic so i decided the smart thing to do would be to have my vortech supercharger professionally installed. heres the deal: after taking my 87 iroc 350 tpi (stock motor) to the shop..they installed the vortech supercharger and a accel superram set up which i purchased...upon completion of the installation, the shop took it to a tuner so he tune it..i got a call the next day about during the tuning session, he noticed an extreme amount of what he called "blow by" - stating there was alot of air that was escaping around the pistons inside the engine..he said this was taking place around 4-5 lbs of boost and he was afraid to push anymore boost out of it for fear of blowing the motor. he then stated that the only way to fix the "blow by" and be able to maximize my set up was to put forged pistons in the car and rebuild the bottom end. in a nutshell, this would cost me around $2500-3000. he told me without doing this, i would only get approximately 40% (power-wise) of what the system could make..if it wasnt for the "blow by"...he said i could take it as is..but i wouldnt be able to 'beat up on it' for fear of blowing the motor down the road...i need some help here guys...i dont know what to think. im not a professional mechanic, but more a big fan of irocs who wanted to make myself one badass daily driver..well now its turned into a nightmare and i need you guys to give me some ideas, help, pointers, etc. is this true? is it partially true? or am i being ripped off? is this "blow by" preventing me from full power? and do i really need a bottom end rebuild? or would just forged pistons solve the problem? if not...what WOULD solve this problem in your expertise/opinion?? any help here is greatly appreciated. my back is against the wall and i dont know what to do... thank you in advance.

ps-regarding the car itself, it is a 87 350 tpi iroc. stock motor. just headers/cat back exhaust.

 

I don't see why an engine rebuild is such a bad thing since you just dropped a truck load of $$$ on a supercharger and an aftermarket intake.

BUT what the guy said is possible. In fact if the engine has alot of miles on it I'd second that. The forged pistons really don't have anything to do with fixing your problem tho. The problem is the engine is worn out and it's not handling the extra stress being put on it. I would say that if/when you do the engine rebuild have the machine shop install forged pistons and setup the bottom end for boost.

I have a friend with a "car" with a 302 Windsor and the supercharger setup is supposed to make 14 lbs of boost. It only makes 10 lbs because the rest attributes to firing the oil dipstick out of the tube. He's pretty much in the same situation as you.

 

Take it to a mechanic that you trust and have them do a leakdown test, that will tell you what kind of shape the engine is in, and if something is loosing compression somewhere where it’s from (valves, rings, head gasket…).

Not that I suspect this in your case, but I have seen where a tuner washed down the rings by giving the engine too much fuel permanently ruining the ring seal on a brand new engine.

I’ve also done a blower install on an almost brand new car that I specifically noted to the owner that he had all the signs of excessive blow by during dissasembly (the biggest of which was the intake was full of oil) which had nothing to do with the blower.

I doubt it… my brother’s blown 302 has worn to the point where it makes it’s own smoke screen through the valve cover breathers (at night if you turn the headlights on with it running it’s like a fog coming out from under the hood in front of the car) and it hasn’t seen any loss in max boost and very little if any loss in ET.

 

i spoke with a mechanic who said that 'its a known fact' that when you supercharge a motor, you have to use forged pistons because flat-top pistons cant handle the compression. what do you guys think. still trying to get a heads up on whether or not im being ripped off. your input is very appreciated on the subject.

 

That mechanic is bs'ing you.

You can run boost on a stock motor. Your blow by issue has to do with how worn the motor is, and boost is leaking past the rings into the crankcase (i believe). You do not necessarily need forged pistons to run a FI set up. If you wanted to run higher boost down the road, it would be worth your while to rebuild the bottom end with forged low compression pistons. Otherwise, you can run 6-8#s on a stock motor (correct me if Im wrong).

 

 

Woah... I think you guys that know your stuff are sending mixed signals here.

The best part about cars is that they are very logical toys.

Problem you are having is in fact blow-by. Get a leak test on that thing as see if the motor holds compression. If it does, then tell the guy to go to hell and go to another shop. If it doens't hold, that means you rings are getting old, or head gasket. That kinda thing. Something that is supposed to hold in the compretion isn't doing its job.

Now in terms of the forged pistons thing... You don't need forged piston to run boost. You will need them if you want to up the psi someday and start to get reall wild.

In conclution, if you are going to get a rebuild to fix the blowby issue, you would be an idiot not to go with forged, I mean why not, the damn motor is in pieces then anyways....

That price for the re-build is about right. You are not getting ripped off and the guy isn't a doughbag. He is just withholding a bit of info to try and make more $. You could get a rebuild and put in stock pistons, but that would be stupid. I guess he is just not presenting stupid ideas to you. Consider that a good thing.

 

I would do some searches on the internet, and do some reading on basic 4 stroke combustion engine function. I think you would feel less nervous about any engine situation you may be faced with now and in the future.

To give a short answer on your question. Blow by and adding more boost does not directly correlate to a "blown" motor. If there is excessive air getting by the rings under boost, you will have a pressurized crank case(i.e. Oil Pan and adjoined passages). As long as fuel and air are not wiping the cylinder walls clean of lubrication and the strength of the crank, block, rods, pistons, and bearings are capable of the extra force being applied to them, the engine should be fine. What you will experience is an extremely messy engine if you do not come up with a system to capture the oil vapor and oil coming from the crank case vents.

Things that will kill your engine in short order, are lack of fuel or improper tuning. If detenation happens with the current materials in your short block, it is unlikely that they will be able to cope with the stress, same goes for a lean or rich miss fire.

 

before you do anything else, make sure the shop that installed the supercharged modified the PCV system in such a way that you dont get boost into the crankcase.

ive seen people "forget" about that, then think they have massive blowby....

other then that... do the compression/leakdown check.... and see what comes from that.

 

Heh… forged pistons to run boost. So what’s with all the blower kits designed to be bolted to stock engines? Getting back to my brother’s car, it’s been running for years and hundreds of dragstrip passes running some of the cheapest, Badger brand cast pistons without any issues.

Mixed signals… no.

If the guy is saying that you cannot run boost with cast or hypereutectic or flattop pistons then he’s full of it.

Like I already said, WRT to blowby have it checked by someone that you trust/is willing to sit down with you and make sure you understand what is going on, if he can’t explain it he probably doesn’t know or is full of it, just trying to get your $$$.

And again, like I already said, it is possible that they did something to cause the blowby, specifically in tuning the engine, but it’s just as likely that that was the condition that the engine was in, and boost is just making the blowby more of an issue (a little bit of blowby NA is usually not that noticeable, even quite a bit with a closed PCV system goes unnoticed till the stuff clogs the PCV and causes other problems. OTHO, with boost now that blowby gets a little extra pressure to help it cause problems and very quickly you start seeing oil leaks and oil in places that it’s not supposed to be. Unfortunately, proving that it happened when they were messing with it vs a preexisting condition is next to impossible unless they caused it and then did something dumb like left the same oil in it (even without oil analysis you’d probably smell gas in it).

 

Here's an easy question. How many miles does your engine have, and how was it driven for those miles?

(hint: if the answer is around 100,000, and the car has been romped on, you're going to need a rebuild before running a blower with lots of boost).

 

Yea, that will give us some idea, but it’s not 100%. I’ve owned small blocks pushing 200K miles with nothing wrong with them (no excessive blowby/leakdown) and one engine (as in OEM) that I worked on showed signs of pretty serious blowby (intake full of oil…) at <3K miles.

 

just a piece of knowledge;

forged pistons just refers to how they are made. They are very tough, so they withstand lots of detonation (lots being relative). They also grow a lot, (more thermal expansion), so they need to have more "slop" in the bore. They have more gap in the bores. I think this'll have MORE of a tendancy for blowby. Obviously since they are stronger (tougher), they will survive higher compression without instant failure.

Forged can be dished (low compression pistons), flat top, or pop up.
You said buddy said "get forged, not flat tops". Forged refers to how the piston is made, and flat-tops refer to what the....TOPs look like. So they're not mutually exclusive, you can have either, both, or half and half.

Other choices are dished hypereutectic, or dished cast pistons. (dished since you want lower compression ratio with your blower).

But either way, be DAMN SURE that your rings/cylinder walls are the problem, before dropping $3k on a rebuild. Like mentioned PCV could cause that symptoms, and you know that's a cheeeeper fix right there.

Blowby won't kill it either. If you're cripping the blower to less power output to keep blowby away, don't bother. Crank up the boost and have fun. Keep an eye on oil level though. When it dies, it dies