Roots blown LT1, need serious tuning help!

This is what I've got....... A lil Weiand 142 roots blower on 96 Trans Am bone stock LT1 with the exception of headers and true duals. I can not get this thing tuned to save my life! I'm only running 5 lbs of boost, i have a 2 bar MAP so I halved the timing tables, meaning 50 kpa is where it goes into boost so I adjusted the timing accordingly. I'm running about 6* below about 3000 rpm and a gradual max of 10* above 3000*. My first question is should this thing run on the stock motor with just 5 lbs and no more timing than that?

Here's the problem.......been working on the setup for 2 years and no matter what I do I get knock as soon as it goes into boost and it will pull every bit of my timing out and it just falls on it's face. It's just like clock work, see boost see knock. Every once in awhile it won't knock but that's very rare. It's has true duals so I can't hear if I'm getting knock or not. I've got WOT AFR set to a rich 10.5 and I've tried going up and down with that.

I'm getting some lean tip in so today I lowered the injector constant from 42lbs to 24 and it seemed to help with that but i still get knock.

I built an intercooler for it and got that installed last weekend. I'm not sure how well it's working because I believe my IAT is getting heat soaked because of the way I have it mounted in the intake manifold so I'm not sure how true the reading is. I'm either going to redo the IAT or get a thermocouple and stick it in the manifold in the airstream to get a good reading. I'm seeing 135* air temps just sitting there idling, that's why I think my IAT is heat soaking, I wouldn't think it should be that high just at idle, could be wrong tho.

I do not claim to be a tuner by any means so I need some major help. I've ran 102 octane in it, still got knock, I've ran 105 octane E85 in it, still got knock, even tried meth injection, still got knock. I don't know if it's real knock or not. I checked my exhaust out today and checked to see if it was banging around and found a couple spots where it was hitting so I fixed that and still get knock. I know roots blowers heat the air up alot more than centrifugals but damn it's only 5lbs. The blower itself gets a lil noisy when it gets warmed up so I've thought about trying to isolate it from the rest of the motor with a rubber gasket just to see if it's causing it but it seems like to me if it was a noisy blower causing it then I'd get knock all the time.

If anybody has any suggestions or wants to walk me thru tuning it then PLEASE feel free to post up. i'm about fed up with messing with this thing!!!!

10* at WOT??????? Way too low. I would expect to see somewhere around 32 to 36*. As far as knock is concerned, why don't you disconnect the KS and put a resistor of 100K ohms on the harness to ground. This will satisfy the PCM and will remove the KS as a possible source of retard.

While you have the KS unhooked, measure the resistance to ground to be sure it's between 93K and 107K. If it's higher, chances are it's not grounded to the block at the threads properly. If it's lower, the KS is shot.

With regard to the tune, why don't you either send your PCM to PCMFORLESS or at least contact them for suggestions. I would not have waited 2 years to take a different approach.

One last thing, I wouldn't run richer than about 12 to 1. Obviously 10 to 1 is a little too fat.

With regard to the tune, why don't you either send your PCM to PCMFORLESS or at least contact them for suggestions. I would not have waited 2 years to take a different approach.

He will do a base tune and email it to you if you can upload it yourself.......Probly worth looking into after 2 years

I didn't mean I've been tuning it for 2 years, I've been working on the whole setup for 2 years. I built the intake manifold myself, actually this is the second design I have on there now, plus I built the CAI, intercooler, fuel rails and everything else that goes with it.

Explain the purpose of the resistor, are you just wanting me to bypass the knock sensor?? Reason why I haven't turned the knock sensor off is because I'm afraid if I'm getting true knock then there goes the pistons. I did zero the knock tables out once just to see how it would run and it ran like a scalded dog but I wanna know for sure I'm not getting false knock. Seems like if it was false then I'd be getting knock all the time or just randomly, this is pretty much like clock work, soon as I see boost I see knock.

I talked to Alvin at pcmforless awhile back and he said he wouldn't touch it thru an email tune, he wanted it there at the shop, Ed Wright said the same thing. I can't do that.

Are you sure it isn't the mechanical noise of the Rootes blower that is causing the knock retard?

Isn't Alvin the one at pcmforless that does the "chipped" cars through 93?

I've thought about the blower being noisy and causing false knock so I'm gonna try to isolate it from the rest of the motor with a thick rubber gasket. But it seems like if it was a noisy blower then I would get knock all the time instead of just in boost.

I don't know what Alvin tunes but I do know he put a roots on his a few years ago and it ran fine from what I understand. That's why I wanted him to tune it. Wether or not he was stock or lowered the compression or what I don't know. You gotta remember this is a stock 10.5:1 motor plus a roots blower not a centrifugal. Roots blowers heat the air up quite a bit more plus they are full boost soon as you hit the throttle. That's why I'm having such a bad lean tip in issue, roots blowers need a huge pumpshot.

I've even had the timing as low as 5* in WOT and still got knock. I've had the AFR from 10 all the way to 12, no change. Yesterday I did drop the injector constant way down to try to help the lean tip in issue. It would go up to about 17:1 for a second when I gave it any throttle at all. It did help that issue, now it will only go up to about 15.5:1 and the car was more responsive in cruising throttle but now my WOT AFR is at 9 or below and I've taken out all fuel that I can in the PE tables. Only thing I can do is bring the injector constant back up and that will make my lean tip in issue worse again. I need a "pumpshot" setting like the 93's have. I emailed tunercat last night and asked them if it was possible to make a pumpshot table for the 94-95 obd1 cars (I did the obd1 conversion).

I'm wondering if this setup can even run with this much compression but then I read about a guy over on LS1tech that is running 18lbs on a 10:1 motor on pump gas, go figure.

Sounds like you have tunercat. Email me your current .bin file and let me take a look at it. Curious to see how you have it set up. Like stated above, sounds like you have your timing way too low for one. I know your seeing knock, but it doesn't sound like its timing related at this point. Also it's too rich. You should be shooting for around 11.5:1 to 12.0:1 with no meth injection (assuming your not using it at this point). With the .bin, shoot some specifics about your setup like throttle body, if TPS sensor, where is voltage set up at, size injectors, fuel pump, cam etc. Maybe i can throw some suggestions your way.

Ken R.

What's the address??

What mode is the car running in? sd or maf moder or what, i may have some ideas, but i'd want more specifics on the car before i say anything, its too easy to wax a stock piston if you do the wrong thing.

It's running in MAF mode with a 2 bar map. Basically all I've done is half the timing tables and take out a bunch of timing from 50 kpa up and then adjust the PE tables. I'm running OBD1 but didn't change out the knock sensor. I was told all you have to do is turn off code 43 and you don't have to change out anything. Also have the LT4 knock module.

As far as mods here they are........roots blower running 5 lbs, 42 lbs injectors, 52 mm TB, pacesetter LTs, true duals dumped, 2 bar MAP, MSD coil, autolite 104 plugs gapped at .045, fuel pressure is around 45 going up to about 52 in WOT.

The car runs very smooth at part throttle, no hiccups or backfires or anything but as soon as it sees boost I get knock no matter what. The only time the knock isn't quite as bad is up in the rpm range, like past 4000.

Just sent you an email rougedriver.

[QUOTE=NXSLT1;5022625]
That's why I'm having such a bad lean tip in issue, roots blowers need a huge pumpshot."

Not sure what to say about your knocking problem but to cure the lean tip in try lowering your injector size even more (quite a bit) - this will increase the actual size of your pump shot since there's no other way to adjust it (increasing it by telling PCM you have smaller injectors). YOu will run richer which can be resolved by running Speed Density and lowering your VE tables.

I had lean tip in bad with my 83lb injectors, during my 2 bar conversion I initially went to 40lb/hr which made it run the same as the 1 bar with 83lb/hr (Still had lean tip in) so I lowered it to 30lb/hr and all lean tip in went away. :D

It's worth a shot... good luck. I had to lean out the cranking fuel and all other fuel tables (no MAF) it wasnt much work but definately worth the hassle.

Yeah I tried that already and it did help with the lean tip in but then my WOT AFR was at 9 with all fuel pulled out of the PE table. I wasn't running SD tho. I'm thinking about trying SD tuning this week sometime.

Far as I know knock sensors are not compatible between obd1 and obd2, I soldered a resistor into my pcm when I did the conversion because I had a brand new obd2 style knock sensor in my block. That may be your problem with the knock retard. Or it could just be the sound of the blower messing with the knock sensor. When you say you cut the tables in half what sort of readings would you be seeing if you werent getting knock? ie whats your table look like.

do you have any logs of this thing cruising that you could post?

If you turn off code 43 then it doesn't matter what knock sensor you have. Yes the two different knock sensors read a different resistance but turning off the code will eliminate that problem. I ran it like that for quite awhile before I put the blower on it and wasn't getting knock. I did have to install the LT4 KM right after the header install because they were causing false knock.

What I mean by halving the timing tables is since I have a 2 bar map that means 50 kpa would be 1 atmosphere or 0 vacuum. Anything above 50 kpa would be boost so starting at 50 on the tables that's where I would start my timing for boost. It's starts out around 4* and goes up to maybe 6 or 8 on the first table then the upper rpm table it goes up to about 12.

Yesterday I had my dad rev the car up while I was under it so I could see if the exhaust was hitting anything and I noticed my driver side motor mount had ALOT of play in it. I don't know if it's banging metal to metal or not but if it is that could be another cause. The car sat for 8 or 10 months while I was building the intake and everything for it, I don't know if the motor mount deteriorated in that time or if it's been like that awhile. I'm still gonna isolate the blower like I said and I'd really like to run the duals on out the back of the car and quieten it down so maybe I can hear knock if it's actually happening but nobody around here will attempt to run it over the axle. Wish I had a bender!

I can send you the tune file if you have tunercat and also a log file if you want.

I've been thinking..........is it possible detonation could occur with 0* timing?? I don't see how it could since yer not starting the flame front til after the piston is headed back down. Then again I don't see how it has enough time to happen with 5*. The only thing left would be pre ignition from a hot spot but I don't see it being that either because I get knock from just revving it up sitting still just as soon as I start it up. What do yall think?

I will be fixing up a gasket for the blower when I get off work today and will post up the results later tonight.

Just so you know ford didnt use knock sensors on the 03-04 cobras because the blowers were to noisy. i would chuck it up to false knock spend the whole 200 bucks and let Alvin from PCMforless send you a tune before you are buying a new motor along with that tune.....

Have you compared 92 octane to 110 octane yet? That would tell you pretty quick if it's real knock. If it gets any better with 110 then you know what's up. If it doesnt change then you know what's up. Either way you know what's up.

This might sound stupid but... my dad worked for GM for awhile and one time he hooked the knock sensor wires to the tape deck and you could hear every noise the motor was making... pretty cool really... sounded just a like a really good microohone but all you heard was the mechanical noise not everything else like exhaust... kinda of strange to hear actually.

you could hook that up to a recorder or something while you make it knock then play it back and listed for spark knock. A video camera would work with the audio input ports. You'd be suprised how clear it is.

I remember reading the other day about the ford blower cars not having knock sensors, must be something to that. I'm not wasting $200 on a tune until I know if it's false knock or not.

The highest unleaded octane I can get around here is 102, I even ran E85 for awhile which is 105 octane and still got the same knock.

I may have discovered something just a few minutes ago.......I put the blower on with the thick gasket and teflon washers under the bolt heads and then turned the key on motor not running with datamaster running and took a wrench and pecked around on the blower and still got knock (I've done this in the past to see how sensitive everything is). So I doubled the gasket which is now about a 1/4" thick and it still showed knock, but I did have to tap it alot harder to get knock. Well I pulled the blower off and decided to tap around on the top of my intake, which I've never done before and the knock count started going crazy, I'm talking just barely tapping it. Obviously the top of the intake is suuuuuper sensitive, it's waaay more sensitive than the headers ever thought about being. You can actually hear it ring through out the entire motor, I may be on to something here folks. I've gotta figure out what to do to deaden the top of the intake, any suggestions??

Since the intake is essentially a holow tube... it makes sense tapping it would make alot of noise... interesting

Ford must have given up on trying to silence it.

The new Vette SS Blue Devil whatever is supercharged along with a bunch of GM FWD cars, but those blowers are silent...

Do you have an intercooler under the blower? I bet that helps give structure to the intake reducing ring and act as a muffler by removing the ring/sensitivity.

One way to reduce ringing on pipes/rods is by grabbing them with something soft... think about clamping it with something soft.. ha yea right..

Yeah I built an intercooler and it's actually bolted to the underside of the top of the intake. You would think that would help with the ringing but obviously it doesn't. Right now i'm stumped on what to use to dampen it. I thought about using some kind of rubber coating on the underside of the top, I dunno.

Just pulled the intake off and that aint what's ringing. Tapped on the heads and it rings just as bad without it on. It sounds like it resonates out thru the headers and they are what I'm hearing ringing. Wonder if there is any kind of dampening "donut" you could put on the headers or exhaust somewhere?? Anyway, I'm still gonna coat the intake and use a thick gasket under the blower and see what happens. I'm almost tempted to just turn the damn knock sensor off.

well if you have been working on this car for 2 years i dont see how a 200 dollar tune is a waste..... you dont know what knock is or what it feels like if you have the timing as low as you do and you still think its knocking. it has to be false knock, no timing along with the fact you have put in high octane fuel and it did the same thing. Put a custom proven tune in the car, put it on a dyno, touch up the mail order tune and enjoy the car

Thats my 2cents

good luck.

I'm pretty sure I know what knock is bud. You might like to waste $200 but I don't. No it doesn't have to be false knock but that's what I'm trying to find out. I can't hear the motor ping for the exhaust, pretty simple to understand. And I think I know what my car needs more than a tuner hundreds of miles away that hasn't spent countless hours fabbing everything piece by piece and has never sat in the drivers seat, but thanks anyway.

If I was you I would put the one bar map back in the car set the timing back to stock and then subtract 1.5 degrees per pound of boost in the 85-100KPA portion of the table from 2000-7200 turn the knock retard to a max of 4 and then drive the car. I would hope you are tuning this car with a wide band you need to get the A/F to 11.5-12.0

Cars can continue to run with the ignition off, that means no ignition what so ever. That's because heat and compression ignites fuel all by itself... the name that give that is dieseling.

The reason diesel engines make so much noise is because they spark knock on each power stroke. Weirdest thing about that is they dont even have an igntition system, they rely on detonation (as you learned above = spark knock).

A diesel engine ignites because of the heat of compression... in effect, equivalent to pre-ignition, or "ping" on a gasoline engine. Detonation (knock) is not the same as pre-ignition. They are two different problems. Detonation is caused by a second flame front developing AFTER the spark ignites the mixture.

Both will damage your engine.

How many roots blowers do you know of sittin under the stock hood of a 4th gen F body and under the unhacked cowl? .....So I basically have nothing to go on as far as tricks and shortcuts so that's why I'm here trying to get ideas. The one about cobra's not running knock sensors was great news for me actually, didn't know that til I posted up here then did a lil research on it. But you can bet yer ass Ford made damn sure it was false knock before they decided not to put knock sensors on them.

Second, about the roots blower...... look up adiabatic efficiency then you'll know what I'm talking about. Adiabatic effiency: occurring without gain or loss of heat. A roots blower at best is about 50-55% efficient, a centrifugal can be as much as 75-80% efficient. That's a whole lot less heat than this roots I'm running therefore you can run 9 lbs of boost on a stock LT1 where as I can't unless I intercool the hell out of it. I'd bet this roots blower is a helluva lot louder than that centrifugal you have too, not just the whine but mechanically speaking. Also, a roots blower is pretty much instant full boost as soon I open the throttle, it doesn't gradually build pressure like a centrifugal. So that means if I'm puttin along at let's say 2500 and nail it I've got 5-6 lbs of hot [edit] air being shoved into a 10.5:1 motor at a very low rpm and that's a really good recipe for detonation.

I really don't feel like burning up my pistons or hammering my rod bearings til they fall out .....

OK.... stop fighting like a bunch of little kids, or the whole thread is going to be deleted. Personal insults are not allowed, and "infractions" will be given if they continue. Get enough points, and your account will be closed.

Do not override the language filter - it is actually possible to communicate intelligently without using the F-word.

Wow something strange happened with my last post. Most of it is gone.

Switching back to a 1 bar will not solve anything with this spark knock problem. At least... last time I checked.

A 2 Bar tune is better than the 1 bar tune on any boosted app. Do not get rid of the 1 bar tune.

I switched to the 2 bar and speed density on my boosted LT1 and never tuned any other car before and it really works swell.

Golly, I read alot of people that havent tried it say it cant work though.

How about I go somewhere where I can defend myself from being insulted and not have half my post deleted or censored. Thank you to the ones that tried to help, adios.

If you took the time to read the earlier posts, BOTH the posts that insulted you, and your return insults were deleted. No one prevented you from defending yourself... I deleted the posts or post content that caused you to feel you needed to defend yourself.

If you are so sensitive that what I did to remove the inappropriate material posted by BOTH parties bothered you, you will probably be better off finding another site.

Wow something strange happened with my last post. Most of it is gone..

Most of it is gone because it was argumentative and insulting.