how much boost can a ssei handle
 

how much boost will a stock 93 ssei ecm be able do understand? does it know how to handle an infinate amount or is it limited to a specific amount.

It is not how much the ecm or pcm or anything like that can handle. But much you can safely flow without KR (knock retard). Things must be done to your motor before cranking up the boost is safe.



Ed

If its too much it will retard the timing. You will see the term KR around a lot. That stands for knock retard. KR is a bad thing that is caused by adding too much boost causing predetonation. The PCM will sence this via the knock sensors and retard the timing to prevent engine damage. In order to run more boost you MUST have "supporting mods". For you to drop a pully size; intake, colder plugs, and a high flow cat are almost a must to prevent KR.

i have a cooling system for it and a/f mix computer to keep the detonation down. if there was no knock problem how much could it handle?

The limitation would probably be the heads hold down force. I know that is a problem with the Turbo Buick engine when they increase boost to 25 psi they blow out head gaskets. The sudden rush of coolant into the engine is not a good thing. :roll:

You would probably be safe to around 20 psi. Go ahead and try, then let us know. :twisted:

i was thinking around 18 to 20 psi. so the ecm will still be able to manage the engine at 20 psi is what i am getting at?

I know I'm running the stock PCM/ECM and it def. doesn't like 14+ lbs of boost. Not exactly sure how much peak boost is because it dumps it before it can get their.

what do you mean it dumps it?

How's he going to get 20 psi? the smallest pulley available is a 1.9" and that'd only get him about 15-16 psi, and that's enough to pretty much put him even with a non-sc'ed bonneville performance wise.
16 psi is alot of boost from an M62, especially from a GEN I and he'd probably see around 15* KR, thus his computer would be pulling all the advance timing it can give, which would translate into the engine practically stalling.
That is unless he has the supporting mods. With a CAI, colder plugs, full exhaust, cam, ported heads, ported Exhaust mani's, water injection, race fuel, and a pcm programmed for such mods he might be safe, but from what we've seen here on BC it'd take more than anyone has pulled from their wallet for a SI 3800, save maybe DR. J.

For the record, without my Jet Stage two chip, i was seeing 20 degrees WITH 2.2 on my 93...
that was in the winter as well..

The bypass would open untill it got less then 14-15 lbs. and then close once it saw that. Not eh safest thing in the world but you can bypass it and it will not dump boost. Safest thing is to get a custom PCM.

Don't think that you will be able to run nearly that much boost. Most Bonne's have a hard time running 12 lbs. without KR.

ZCRX, the M62 and M90 both reach a point (especially the Gen2 M62 you have) where the boost charge is so hot you lose efficiency. You may have a higher pressure, but it's so hot that you lose power. Your cooling might help, but at the same time, the M62 also has an efficiency limit.

You cannot get that much boost out of it. It's just not physically possible. I'm running a Gen3 top end on my 93 now, with an insanely small 2.2" pulley, but I've done alot of other prep work to the top end of the engine to get there. I may very well be beyond the point of good power returns. I have to characterize my water injection effects first, but may still end up moving back up in pulley size. As an point of comparison for you, I can produce the same boost as you if your car was running a 2.2", and my car was running a 2.5", but now I'm running a 2.2" as well. Make sense?

Your stock PCM will dump boost at a predetermined point based on lots of different conditions. It can be bypassed, but that is a very dangerous game to play. You have to allow the engine to protect itself, particularly when you understand the unique dangers to a forced induction engine under high boost.

If you want over 12psi of boost and you want it to work efficiently, you can't use a Roots blower. You need a centrifugal supercharger or a Turbo.

so what options are there for making the ecm tolerate 20 psi?i was looking at the bypass vallve a couple months ago and i think it looked like it was just operated by a vaccume diaphram. how does the ecm control the bypass valve?

www.gmtuners.com or www.sinisterperformance.com (they are one and the same), but you're not getting 20 psi out of an M62 even if you run the belt on the input shaft itself. You'll have a host of other problems you cannot overcome. And if you want to run that high of a boost pressure, remember that PRESSURE isn't the key. FLOW is the key. How are you going to efficiently get that flow through the manifold, into the heads, and out the ass?

Not going to happen without a bigger blower. A bigger blower would require so much custom machine work you could buy a Corvette for the same price.

Since you are stuck with the M62 I will reiterate what has been said above. To get more boost you need to spin the blower faster. When you spin the blower faster you need to improve flow through the engine to avoid KR and other bad things. (BOOM)
When you improve flow boost goes down. (Boost is air stacked up in the intake.)

A good example is my M45'd VW. When I went with a ported head, ported and port matched intake, header and high flow cat I lost nearly 2psi of boost but gained 30+ hp.

You can stuff all the air in the world into the manifold but if it doesn't go into the cylinders and out the exhaust you will gain nothing.

:stupid:

Boost pressure isn't doing anything for you. It's reserve. If you don't use it, you gain nothing. When you make flow improvements to the top end of the engine, you WANT to see your boost pressure in the manifold drop. That means you're USING it, not just storing it.

None...the ECM has a 2 bar MAP sensor table, it cannot understand higher pressures.

Cheers,

Well, in the Series I, the PCM has no clue how much pressure there is. The MAP is for the gauge only.

Correct, the MAP is only for the boost indication (to the gauge). However, there are other conditions that can be met in the PCM that will dump boost via the BCS.

so what does the sensor on the bypass valve do and how does it work? i tried to find it on a diagram but i'm not sure what it is called. could you mechanicly change the bypass pressure by adding resistance to the diaphram? i would just test it but i don't have my meter here.

What blower are you going to be using?

There is no sensor on the bypass valve. That's the boost control solonoid. The valve itself doesn't care about pressure. It doesn't control the AMOUNT of boost you get. It controls HOW MUCH AND WHEN you get your boost POTENTIAL. You can't trick those devices into giving you MORE boost. It doesn't work that way.

LittleBlackBird, he's talking about an M62 here. Gen2.

Seems like a motor itching to go by-by.

That's what I'm thinking. Or someone is filling someone's head with dreams of sugarplums and un-realities.

that wouldn't be to trick the engine. that would be to make the bypass hold closed untill a higher psi is reached.

The bypass won't release because of pressure. It's not like a blow-off valve.

Most of us know that playing around with disabling the boost control solenoid, that you are playing with risking terminal engine damage.
Most of us are using aftermarcket PCM's that have programming changes to optimize the control of this safety feature to allow slightly higher pressures.

I admit that I once used this technique before I replaced my computer. :oops:
It's simple to do. If you do a search on the topic it should explain everything.
I don't recommend it. :nono:

it is not like i have only 1 car and engine. i have two l67's setting on engine stands and i know where i could get 1 or 2 more. i'm just trying to perform and brainstorm. trial and error is the only mothod that has ever worked for me. just like to know as much as i can before a trial turns into an error. how does the boost control solenoid work?

It's told by an electrical signal via the PCM to either turn vacuum on or off to the BCS.

Rather than trial and error on this one, I suggest you learn from our knowledge and mistakes. Don't mess with the BCA or BCS.

In addition, you can't get 20psi out of a roots blower, and most of what you're talking about in this topic is going to require EXTENSIVE work to that engine and trans to support it.

I just want to make this as clear as possible, as it sounds like you're ready to move on some of these ideas.

i am still far from moving on anything.

how would i go about stopping the bypass from dumping untill 22 psi?

Again, the PCM will never know how much boost you have. The only reason the PCM will dump is if:
Knock
It thinks too much air is passing the MAF (maybe, I haven't confirmed this yet)
While shifting


You CANNOT program anything or tweak anything to make the wastegate hold till a certain pressure level, because it simply doesn't know what pressure is present.

High IAT temps (I recall something about this)
Lean fuel condition
Fuel cutoff RPM is reached
High trans temp

22psi? With what? The magic super-duper amazing boost producer? You CANNOT make an M62 produce that much boost. BARELY half that. Even if you could, you would produce so much heat that you'd melt a piston and destroy your engine.

We're not busting on you here, but we need to make sure you understand this. I suspect someone is filling your noggin with fantasies and misinformation.

John Wikoff (above) and I are perhaps the two most knowledgable Series 1 L67 guru's on this Forum.

If you want 22 psi of boost, go TURBO, with a bigass intercooler and a custom PCM. Beef up the entire bottom end and the transmission. When you're done spending that $15,000, we want video.

You need to quit talking about boost pressure and start thinking about how to increase FLOW through the top end, so you will see a DECREASE in boost pressure. That means you're actually using it and getting the best out of it.

Don't fall prey to the ricer-mentality of 'more boost!'. This isn't a Turbo 4-banger rice-bomb.

I don't think 92/93 monitor tranny temp, do they?

You won't be able to work 22 psi into your tune. You could, maybe work the side effects of 22 psi into your tune. But like Bill said, keeping that air charge cool is A MUST for that much pressure. You'd need a tiny spark plug gap, lower the compression ratio (is using 5 layers of head gasket an option? :lol: ), and maybe one of those bigass newer roots type blowers.

92/93 trannies have a thermister that switches states at a pre-set temp. When that switch is made, you go into limp/boost dump.

That is something I didn't know.

The PCM doesn't know (92/93) WHAT temp the trans is, but the PCM does know that it has reached a 'critical' temp. I saw the thermistor personally during my trans rebuild on the Zilla.

This was also discussed recently in Sandrock's swap topic in 92-99. Don and I went through the 92, 93, and 95 FSM's to determine the difference a couple weeks ago.

Well, a big old school 6-71 should get your boost that high but would look odd sticking up through the hood; not to mention the custom fabrication to get it on the engine.

Many people look at the pro racers and see the astronomical boost levels and think "that is what I need". The pro racers are running high boost pressures because they have rules restricting engine displacement, throttle diameter, etc... They use the high boost as a way around the restrictions. A turbo WRC car has a big intercooler and water injection to keep intake temps under control. Top fuel dragsters only need to run for 5 seconds and are rebuilt between rounds.

Hourly rebuilds and intercoolers big enough for a semi-truck are not practical for the street. Carefully ported heads, manifolds and a good exhaust are. (less expensive too)

If we think about how fast we can flow air through the engine instead of how hard we can slam it in we will get better results and longer engine life. (and ricers in the mirror)

Would the rotors of an M62 even be able to withstand the RPM it'd take to produce that much boost? Or more importantly, would they be able to expand enough from the heat and still have clearance between themselves and the case? Would the bearings hold? Maybe he's thinking of using just the L67 longblock and... a Whipple 2.3L or a Lysholm 2300AX?

A screw type supercharger would be more compact than an x-71 but would still require very expensive fabrication work to mount it to the engine.

The Eaton rotor groups are tested to 20000rpm The ~14000rpm design limit is based on diminishing returns from heat. (The added heat hurts you as much or more than the added air helps.)

As far as not flying appart is concerned, I don't know if Eaton or Magnuson have tested beyond 20000rpm. The test speed is far enough past the rated speed to make it point less to go higher, unless they just like destroying stuff.