High Performance m30 questions

[steve]

More specifially. Who would this group say has the most experience in building m30 engines. And could answer some specific questions about different configurations and the results they have. Like flywheel weight, intake size and cam charateristics.

I have had a couple of issues while doing some tuning work on the
engine. And this is a very non standard setup using throttle bodies and a integrated ignition and ecu. I need some answers to what can cause some of the symptons I'm having and if I need to be looking at certain areas of my configuration.

I'm trying to "refine" my engine setup. Which is pretty good the way it is but... I think certain things can still be better. I may have to be going into the motor again anyway because of an oil pressure issue that my gut tells me needs to be addressed. Even more so since having driving TJ's CSL that has the same oil pressure gauge and his seems to be running at least double the pressure of mine. I didnt see his dip below 40 psi. And mine is rarley above that. Just doesnt seem right.


I've been trying to tell myself it's okay. But I drove in the heat a while back while going to visit TJ and it was just to low. And I've got to much into it at this point to not go in and have a look.

 

[steve]

I meant to add..

I had the chance to drive TJ's CSL and he has the same oil pressure gauge. I noticed that his didnt seem to ever dip below 40 psi. While mine seems to rarley go above that. Just doesnt seem right.

 

[x_atlas0]

Everybody seems to know at least one or two tidbits of info about the M30 that nobody else does, so post up your questions and people will chip in when they know something.

Flywheel- is it rattling or making too much noise for you, if it lightened?

 

[steve]

Well, while tuning it we were having problems (most noticeable in 2nd gear) under hard acceleration up to 4 - 5000 rpm then trying to go even or neutral throttle it wants to buck around. We can solve that by taking away some fuel enrichment but that ends up having consequences elsewhere. We (tuner friend and me) are both convinced that it is a physical aspect of the engine causing the problem and not a tuning issue.

So the question is what it is. Or is it a combination of things. I’m running a light flywheel and I suspect maybe to light. I forget the actual weight but I think under 10 lbs.(Not sure of that maybe 10 – 12 range) Also I’m suspicious that the throttle bodies may be too large. They are 45’s and I have had similar experiences with 45 side drafts and switched to 40’s and drivability was much better. So I’m wondering if the same would apply here.

 

[AndyM]

What cam are you running? What displacement? Is your injection system set up for speed density or Alpha-N? Speed density doesn't do well with tons of cam overlap or the dramatic changes in manifold pressure when using throttle bodies without a plenum. Oversized throttle bodies probably won't help the situation.

On the oil pressure, it could be something as simple as a loose bolt in the oil spray bar on top of the head. If you have high miles, then perhaps the oil pump or worn bearings. Keep in mind its hard to say what's "normal" -- some engines will have higher oil pressure than others. If its in "spec" then I'd just run it if there's no other reason to tear into the motor. What weight oil are you running? That can make a difference - especially when hot.

 

[velocewest]

Steve, a few thoughts --

Flywheel -- 10 lbs is a little light, but I am not convinced it's the source of your bucking problem. As I understand it, the engine works OK while accelerating, but when you try to hold steady RPM you get bucking? A few questions -- what cam are you running? Are you running a trigger wheel for timing or a flywheel magnet or? I assume your ECU controls ignition timing?

ITB's -- re: your comment on 45 vs. 40 Webers -- regardless of body size, can you run smaller venturis? You can choke a 45 DCOE down to 28mm, the 40 DCOE only goes one size smaller to 26mm. If you're running DCOE-style TB's I think you can change venturis just like a carb. Overall, the bucking issue sounds like a combination of intake airflow and valve overlap or cam timing. Kind of a turbulence problem, as it were.

Oil pressure -- never reaching 40 psi for a relatively fresh engine is low, but -- is your gauge accurate? Is it mechanical or electric, and is your pickup in the same place as TJ's? Have you checked the pressure with another gauge to be sure? Definitely put that on the to-do before you start a tear down.

 

[steve]

It is running a trigger wheel for the pickup. It has a schrick 307 cam. The displacement comes out to 3.7 and change. If it’s setup for speed density or alpha-n? I’m not sure. I did not setup the parameters in the ecu.

I can tell you its running an electromotive tec3 along with their distributerless direct fire coil system. My friend did all the programming of the ecu on and off the dyno. I’m still a little green on that end of it.

I’m not sure if I can choke down the throttle bodies or not. I guess I can look at their website and find out unless anybody knows about Jenvey throttle bodies?

The oil pressure concerns me for several reasons. BTW the motor has less than 10K miles more like 7.

I supplied the crank to the engine builder along with bearings. The person that I got them from told me to not lose the bearings. As they were a set. I assume that the crank had been turned and the bearings were made to fit. I have never heard of this but that is what I was told. I thought that they just come 2 or 3 oversizes. Any thoughts there?

The engine builder lost the bearings. Then had a hard time coming up with replacements.

After complaining about low pressure and having done a track day he remove the oil pan and inspected them and said there had been some scoring on the main journals and he replaced them. He said this likely had happened due to much heat. (No oil cooler.) Regardless it was low before the track day.

Yes I have checked it with two different gauges. And because my engine idles high compared to a stock engine I would say it’s out of spec at about 13 – 15 psi at 1300 rpm. According to the Bentley Manuel.

 

[andrey]

If it’s setup for speed density or alpha-n? I’m not sure. I did not setup the parameters in the ecu.

"Alpha-N" means that your ECU just measures the throttle position (from the TPS), ie: how much you've pressed the gas pedal down, and then tries to guess the air mass from that.

"speed/density" means that the ECU measures manifold absolute pressure (MAP) and intake air temperature (density) and from that extrapolates the air mass.

You probably need to use "Alpha-N" because you don't have an intake plenum (the big log thing on L-jet and the big manifold on Motronic). There's probably not enough of a volume to get a good and stable pressure measurement so the speed/density stuff wouldn't work well. You could also use a MAF or hot-film sensor like new cars have (and I think the ECU supports those).

 

[corsachili]

As I mentioned, I wouldn't worry about lower than normal oil pressure unless it continued to descend while driving. If it holds steady at a given level I'd be less inclined to do anything about it UNTI something started to make noise. My oil pressure registers 60PSI+ while cruising on the freeway and it idles between 10-20 depending on ambient temperature. I have no idea how many miles are on the engine. I use Castrol 10W-30 dinosaur juice.

I drove Steve's car and I have to say, that car hauls some serious tookus. It's a really bitchin ride, and I thank Steve for letting me thrash it around my personal track here in the mountains. Personally I didn't noitce any flat spots in the power but then I was "short shifting" at 5500RPM. =)

 

[steve]

Hmmmph. If thats the case then I would say speed/density. Because I know I have MAP and TPS working together.

 

[steve]

Yes I agree TJ. But while I was coming home from your house I was watching it closely. And as I got into the city and hit the doom and gloom fog coming up the hill to Daly City (Long uphill on the freeway thats fun to put it in full throttle.) the tempature had dropped at least 30 degrees and had expected to see the pressure rise. I did not see it rise at all under full acceleration. In fact it almost looked to have gone down. Although I could not keep my eyes on it that long.

As far as the flat spots the only problem it has is coming on hard throttle from a low rpm. We can fix that by adding enrichment but them comes the bucking at higher rpm. But in reality the low rpm problem is easy to drive around and really no big deal.

The thing that eats me about it is that I know if we solved that little issue then I could tune it just a little better. But maybe it really never ends... Just part of the fun of playing around with it.

 

[velocewest]

So Andrey, considering the 307 cam and ITB's, do you agree with my theory of reversion causing the bucking? Seems like there could be enough of a pulse coming back out of the cylinder to interrupt the inward flow. A smaller venturi might increase the inward charge speed and overcome this. I seem to recall that M car engines don't like really long duration cams for this reason.

As to the crank/bearing issue -- seems like if your builder lost the matched bearings, he would step up and have the cam reground to match new o/s bearings. I'm not buying the story that one track day is going to get you scored bearings, oil coolor or no. Unless you had oil starvation or dirt in the engine I would not expect any unusual wear from a track day.

 

[andrey]

Tony -- yes, at least I suspect so. An easy way to be sure is to data log or 'scope the MAP signal (and/or another MAP signal) and see what it looks like. If the waveform shows the valves opening and closing, then he's in trouble

I remember having a conversation about this with Devinder, he pointed out the potential for speed/density trouble on the S38 engine with its ITBs. I've since noticed that speed/density cars (80's GM, etc) always have significantly large manifolds and all of the ITB cars I've seen use mass air flow (and in some race cars, Alpha-N). Also there are other issues, for example the MAP sensor is supposed to have little to no 'hose' length for the vacuum line (unlike what Megasquirt does with the board-mounted sensor) because the vacuum line can amplify the valve 'noise', so to speak.

Steve -- if your ECU supports (I think it does) using a mass air flow sensor (say, a GM or even Bosch/VDO/Siemens), perhaps you could try it? It will be a lot of recalibrating but it might be much more doable.

That said, please take anything I say on this topic with a grain of salt since I'm still learning and I have only experimented for x amount of time and (so far) only on my engine/manifold.

 

[AndyM]

Steve -- on your oil pressure issue, I just learned that there are three different gaskets that were used where the oil filter housing meets the block. You can see them in the attached image. Some of the later 3.5 blocks have a passage back to the crankcase for a pressure relief valve in the housing. The only way to tell is by looking at the block itself. If someone used the wrong gasket, you end up with an internal oil leak. Also, if you use the early style housing on a later block you need to plug the passage or it never develops full oil pressure. Carl Nelson at La Jolla Independent was explaining this to me yesterday and has the plug if you end up needing it. Mine ended up being the older style (my block is an '85), but I was happy to learn about the differences for future reference.

 

[shanon]

hi steve,

have you ever had your car tuned on a dyno? not just the motor.
maybe that could help sorting it out underload....?

-shanon

 

[steve]

Andy thats very interesting and to be honest I cant tell you for sure if its one way or the other. I do know that I'm going to have a good look at it and find out. Thanks.

Yes Shanon I've had it on the dyno a couple of different times. What I havent done since I've had the problem is put a good wide band sensor and gauge in and see what the a/f ratio is doing when the "bucking" happens. Thats going to be my next test.