I swaped from a TPI setup to a converted LT1 intake.
I got "new" #24 injectors.
I just starting to tune part time crusing ( got BLMS pretty *** at 128 on my 9th bin ) and I noticed a strange pattern.
After a tuning session I took off all my plugs to read them.
I noticed that my "front" plugs ( cylinder 1,2,3,4 ) got less carbon build-up then my "rear" ( cylinder 5,6,7,8 ).
Just like the "rear" plugs runs richer then the "front" ones.

Just to eliminate bad injectors ( not that its likley to have 4 bad injetors, but anyway ) I swaped the "front" with the "rear". Made some runs, same thing..

That made me think that I got uneven AIR distribution in the plenum.
When I mounted the intake I took extra care to gasget match the intake with the heads, so nothing bad there. Oh and the heads are brand new, so no bad vavle seals either.
Also tried swaping spark cabels.
The car is NOT eating any oil, and no smoke on startup or on acceleration.

What do you think? I cant think of anything else then uneven air distribution.

( the diffrence on the plugs its not HUGE, but I can truly se the pattern )..


Cheers

 

Did you go a heat range different from oem?.

Slightly too cold or too hot of plug can do that. BTW, what brand are you using?, Champions, and NGKs can be problematic, as well as the platinum, and multi electrode jobies.

 

I'm running R45TS Ac Delco plugs, and i can't say i noticed that same kind of difference. All of them looked the same except for the one cylinder that i had not firing/partially firing (burnt plug wire).

 

I use stock AC delco plugs for my vette with alu heads..

 

Yes I also tought about missfire or partially firing plugs, but as all of my "rear" plugs look the same I dont think that could be it, I should surely notice if all of my rear plugs where missfire...
This is strange...

 

The PCV is on the throttle body right? What about the EGR, where does it come into the intake. Aren't there small pin-hole like holes in the LT1 intake for something like EGR or IAC, I'm drawing a blank. Would it be possible to get pictures of the plugs?

 

I the TB there is a "hose" that whent to my passengerside vavlecover, when the car whas stock.
But now on my passengerside vavle cover ( after market ) I use a breather. So I plugged that "hose" on the TB
Se pic of how I routed the lt1 intake and the driverside PVC vavle. Perhaps its wrong?

I use TF heads ( old style ) with no EGR ports in them. I pluged all the EGR ports on the lt1 intake.

I try to post pics soon.

But you can imagine, the "front plugs" got grayish-tan color, the "rear" got dry sooty deposit on it.

I get som pics up later..

cheers..

 

I'm pretty sure the one you plugged is the correct PCV location. Might even try it removing PCV all together.
http://shbox.com/1/pcv.jpg

 

ahh these intakes do have noticeable air distrobution issues.theres a few sugesstions i can make. make sure the tb is opening all the way. make sure the ducting to the tb is straight for a few inches before entering the tb. and make sure that your fuel rail cross over isnt cavatating. this could cuase fueling issues.

the other good fiz ive seen on box plenum manifolds is a monoblade tb. it slows the air down enough when it enters the tb for it to flow into the plenum and fill it well. this is why GM went monoblade for the ls1 and alot of there other long runner large plenum intakes.

 

Cavitation is highly improbable with the design of the Lt1 fuel rails. How could cavitation be effecting the first 2 and last 2 injectors in the direction of fuel flow?
The reasons GM went to monoblade for the ls1 or any of their other intakes aren't for the reasons you've given. Not to hijack this thread but the monoblade doesn't "slow the air down," and the 2 reasons GM went with the monoblade were purely packaging and economics. Why have 2 throttle plates, 2 bores machined, more passages machined, when it can all be done with half the effort/parts. Tolerances for 2 bores is tediously stupid when 1 packaged correctly saves that much times however many millions they've produced. The other reason for the monoblade was the design and packaging of the LS1 intake. If you look at the intake it'll make perfect sense. Those are the reasons, take it or leave it. Monoblade's have a performance benifit in some setups that stems from their efficiency.

 

I do got a sligt bend on the ducting just before it eneters the TB. Going to fix that.

Devil..

 

Hmmm. Have to look in to that. I do have vaccume from the hole I use.

Thanks....

 

your wrong about this. it was done to aviod cylinder filling issues inherint in the damn twin blade design. with the twin blade design you had extremly high velocity air streams two seperate streams with odd convergent angles. this created and air wash in the intake that also helped with the air distrobution issue. the short runner become a problem with larger cams and combined with the twin blades it gets even worse. go back to fluiddynamics 101.

also caitation is highly likely in the lt1 fuel raisl for 2 reasons. the transistions form the cross over tubes are drilled at 90* angle with no radious and the rals create a bad bleeding loop with air hiding in the corners. but unless youve built some high specific output lt1 engines that have cavitated i dont know if youve got the experience to speak from. last on we had odd fueling issues with the back to injectors. made new -6 cross overs and put the fitting in the ends of the rails problem solved. but it was a high rpm 355 running 7800rpm. so the chance of cavitation from injector wash in the rials was fiarly high considering the injector cyclcing speed. and no it wasnt a volume issue.

 

Not sure if this helps, but I have a converted LT1 intake on a 350ci. The two front plugs (1 and 2) always have more carbon on them than the others. I have the PCV tapped into the plenum under the throttle body. It is a fresh engine that doesn't burn oil or smoke at all.
I may try tapping into the rear as you have to see if that is what causes the plugs to run richer.

J

 

cool Perhaps we got something here let me know..

 

Plug the PCV and put a breather on LH side.

Offtopic: did you look at my bin? PM or email.....

/N.

 

A 75mm mono is ~1.2 sqin bigger than a 48mm twin.
Velocity wise, for equal area the velocity is the same. Simple physics. Pinning the mixture distribution solely on the mono design is misleading.
48mm twin= 5.61 in^2
52mm twin= 6.58 on^2
75mm = 6.85 in^2
58mm twin= 8.19 in^2
So a 58 twin should be better than a 75mm mono.

 

This is the same issue I hear from every LT1 tuner. The factory fixed this problem by having cylinder fuel trims. If you look at an LT1 bin in tunercat, each cyl will have a slightly different inj pw.

Go boosted on an LT1, this problem becomes even more noticeable.

Some people will jump up and down, turn red, and almost pass out arguing that this <b>doesn't happen</b>, and we're all lying. So then, what did GM attempt to fix by having a cyl-specific fuel trim (that is HIGHLY different from front to back).


-- Joe

 

Yup, the stock LT1's lean out the back cylinders during both idle and cruising. Typical of a small log intake. I bet this is his problem. I totally skiped over the whole conversion part of his thread so if the computer is a 165 or 730 then this could very well be the issue. Oh, and funstick, have you personally ever done any CFD work on intake designs or did you just pass FD 101 and think you know everything?

Well obviously somebody wasn't paying much attention in FD. Air wash, you've got to be kidding me. You think that comparing just mono-blade vs twin-blade that you have air distribution issues? That's weak, very weak. The velocity of the air passing through a bore(s) isn't dependant on the number of bores, area has more effect... or did you forget that part? Like Z69 pointed out, the velocity of air passing through a large twin bore is less than that of a small mono...
As for the air wash, you're so off base here it isn't even funny. If air wash was an issue in this case you would be proving that the FRONT cylinders are getting less air than the rears... but this is the opposite.
Let's now quickly cover "cavitation" so that people don't get all worried about it. First off, the degree of cavitation (introduction of air bubbles by MECHANICAL means) is inversally proportional to the pressure of the liquid. In other words, at high fuel pressures as in port injection, cavitation isn't easy. Now you say "air can hide in the corners" and that the specific output of the engine has something to do with the reasons for cavitation... get real. The engine isn't a part of this system so don't even drag that into this, you're talking about cavitation and I'm telling you that cavitation is highly improbably no matter how large the injectors are. "Injector wash", lol. I'm not going to touch that one. Injector cyclcing speed... then you say it wasn't a volume issue. That's a big hole you just dug for yourself. Volume is exactly what that was. The first rail was probably robbing all the pressure leaving the drivers side rail with less! That's what happens with large injectors all in series. Did you even bother to pull the plugs before jumping to conclusions derived from people with more money than smarts? The whole reason for running the 2 rails in parallel is for the reasons I just gave, not for "cavitation." Got proof, I'd like to see it.

 

jesus your ignorant. theres no point in explaining the obviously proven air distrobution issues with the twin blade design. . since apaernetly you now do this day in and out. i dont really care what your computational model suggets. its holy inaccurate. and yes i worked with fluent and did cfd work in an airflow lab for about 1yr full time working on problems like this for an aftermarket company. just becuase you refuse to belive it doesnt make it not happen. and yes stock lt1 rails do cavitate. its a flaw in the maching process.yes it can lean out the rear cylinder by airating the fuel in the back 4 cylinders . more likely though he's got issues with distrobution from the twin blade throttle body. and again since GM cructhed the problem with cylinder to cylinder fuel trim its also and intake manifold design issue. the problem may be more prnounced on log style plenums but thats becuase larger box plenums like the superam mask the problem with more volume for inlet cushion. go run it through an accurate CFDcad program like fluent and get back to me.

 

You need to go back to school and retake ALL your classes. Trying to say that the twin blade is the problem for the air distribution is just pure .
Also, you wanted me to get back to you after I've modeled some intake manifold designs... alread did. 3 years ago we were designing the most powerful restricted 600cc engine to ever grace the FSAE competition. With the intake me and 3 others helped design we modelled all our old log intakes to compare our new design using fluent. You might want to think before calling somebody out or you'll look like an idiot again.
Your cavitation in the fuel rail issue still has no proof and your "solution" wasn't fixing what you thought it was.
GM didn't crutch that design. Do you even know why they would design a small plenum volume intake? I find it funny that you're comparing your knowledge level from an aftermarket stand point to that of an engineers. You have absolutely no ground to stand on trying to say the LT1 injector trim was a crutch. A crutch for what? Do you know how much money GM saved going from the long tube TPI to the 1 piece LT1? So until you've gotten to their level I'd avoid jumping to conclusions.
The fuel trim is a direct result of the OVERALL design of a log style intake. THIS alone is the major reason for distribution issues, not a monoblade vs twin-blade. The air could come from a hundred straws all bunched together, it wouldn't matter, the distribution issue would be the same at WOT.
Of course large plenum volumes decrease the distribution problem! This is what I've been trying to point out to you but you're stuck on the fact that the twin blade is somehow a major cause. A simplified model of the problem is the large v8, the firing order, the shape of the intake, and the air intake vector, not that there are 2 of them. I'm never said that it doesn't contribute to the issue but it is by no means a major factor.

 

dude your an idiot. i siad this already but your so busy telling yourslef your right you missed what i said. i siad that the twin blade throttle body is alot of the problem with the LT1 intake. what part of this didnt you get. also its a problem on the stealth ram. but then again i mentioned this a few weeks ago to. where is your head ? and yes the TB is a major factor. the other 50% being the short runner allowing alot of reversion inside the manifold. but then again i knew this already becuase ive been tunning and building lt1 motors for just a while now.but a large monoblade fixs 80% of the issue on mildly modified cars.you fix the things you can. the monoblade fix enough of the problem to tune the rest of it out. and again get a job working somewhere in the highperformance engine industry and then come back here and talk trash. dont be an E ***.

 

And I'm telling you it isn't, lol. Again with the comparing a larger mono-blade to a smaller twin blade! Do you or don't you understand that your orignial decloration, " the other good fiz ive seen on box plenum manifolds is a monoblade tb. it slows the air down enough when it enters the tb for it to flow into the plenum and fill it well. this is why GM went monoblade for the ls1 and alot of there other long runner large plenum intakes." Is incorrect? You generalized your statement saying GM went to a monoblade for the LS1.... you're all over the place answering my questions with questions. Get real man and pop the ego before your head exploads.
Also, where did you come up with the %'s, unless you've actually done the calculations I'd avoid throughing out specific figures as fact. So please, for the sake of this thread don't go injecting nonsense into an otherwise good recommendation. I never would have called you out if not for the "GM went to a monoblade for the LS1." Prove it to me or sit down and shut up about it. Remember, I'm the one calling you out because I want to see your conflicting "proof." When (if) you ever come up with the proof of your claims I'll release contradition straight from the source. Then we'll see how that pans out.
Also, when you go back to fluid dynamics 101 you might want to take an English class or 10.
Why do I have to be in the high performance engine industry to get back to you? I'm talking trash about your knowledge on GM's inner workings, not your ability to design and tune an engine . I'd give you an ultimatum for some of my questions that you haven't answered but I don't think it necessary.

p.s.- I designed, built, and tuned the fastest FSAE engine. Won and hold the acceleration event record. Turned down a job at Wheel to Wheel because of location. So if you want to keep calling me out to get back to you, well hell, that's not too hard to do!

 

Ok I this topic is dead now...