When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The beauty of the stock LTx and MR types of intakes is that they don't just work better at peak-power rpms, but they also have more power at rpms other than peak. So if we start talking about "power under the curve" the performance gap actually gets even bigger. If you spread the power curves across identical mph ranges, there will be no vehicle speed at which the TPI-equipped car makes as much power as an MR-equipped car. Knowing that power being produced at any given time is the determinant of acceleration, that means that an MR-equipped car geared to have the same mph range as a TPI-eqpuipped will accelerate harder at all vehicle speeds.
The miniram is a fantastic high flow intake with a low profile to fit under any hood. The only drawbacks of the Miniram is uneven airflow distribution, which the LTx has as well.
On LTx vehicles such as my '94, you have a cylinder trim to compensate for the fact that less air gets to the rear cylinders. If you are putting a Miniram on a batch fire car (that was TPI), you're going to always have slightly rich cylinders in the rear. Tis life.
The other problem with the miniram is it only has a single fuel crossover in the rear, and a quite small diameter at that. TPIS will modify the rails to provide a front crossover as well for an extra fee for those of us making a little more power then the average user.
Here is a snapshot of my miniram on my blown 412" SBC.
As far as gear ratios are concerned, it's always been a balance of strip vs street for me. On the miniram car I have a 3.42:1 rear end ratio. This is good for the street with my TH350 transmission. It makes tons of low end power, great for highway, etc.
However at the track, it's problematic. To cross the finish line in the 1/4 mile at 130mph I need to run a 24-25" tire to maintain target RPM. If I run a 26 or 28" tire I'm almost 1,000 RPM lower than peak.
What I should have done was ran a 4L80E transmission and a 3.73:1 rear end, but the more steep you go with the gear ratio the less strength you have in the ring gear/housing.
There is something wrong w/the forum. IDK who's affected by it, but it's more than just me. I know WVZR-1 has experienced this too...
I see the thread title in the list on the "C4 Tech/Performance" page, and I can see on that:
1. It's been responded to since I last viewed it b/c the title is in bold
2. Who the last poster is.
...since there is new comments, I want to view them, so I click on it and open the thread. But sometimes, the latest post(s?) aren't there -the don't show. All I can see are up to the last posts that I have already read. If *I* post, (and possibly if someone else posts too) then I can see the new posts previous to my most recent post.
This morning, I could see on the "tech/perf" page that you (Joe) had posted in this thread. I wanted to see what you said so I clicked on it, but your post #121 wasn't there (for me). StevenMack's post was the latest viewable post. I posted post 122....THEN I could view and read your post 121. Strangely enough, I didn't have to do that, to view your post 123. Wacky.
Last edited by Tom400CFI; Jan 4, 2017 at 09:57 AM.
The miniram is a fantastic high flow intake with a low profile to fit under any hood. The only drawbacks of the Miniram is uneven airflow distribution, which the LTx has as well.
On LTx vehicles such as my '94, you have a cylinder trim to compensate for the fact that less air gets to the rear cylinders. If you are putting a Miniram on a batch fire car (that was TPI), you're going to always have slightly rich cylinders in the rear. Tis life.
-- Joe
You are right on about the distribution issue with the miniram. Rear cylinders are always richer than the front.
The miniram is a fantastic high flow intake with a low profile to fit under any hood. The only drawbacks of the Miniram is uneven airflow distribution, which the LTx has as well.
This is an interesting point. Seems like a valid concern. The TPI does not exhibit the same problem? If not, is there any consensus on why it doesn't? Because the plenum portion has basically a similar layout: long skinny box with four runners near the front and four more near the back.
Also, I wonder if any attempts have been made to even out the airflow with porting slightly biased toward the rear runners? IOW, port them to slightly higher flow numbers on the bench so that on the engine they end up flowing the same.
This is an interesting point. Seems like a valid concern. The TPI does not exhibit the same problem? If not, is there any consensus on why it doesn't? Because the plenum portion has basically a similar layout: long skinny box with four runners near the front and four more near the back.
Also, I wonder if any attempts have been made to even out the airflow with porting slightly biased toward the rear runners? IOW, port them to slightly higher flow numbers on the bench so that on the engine they end up flowing the same.
I'm not aware of distribution issues with the TPI but the runner lengths may vary from cylinder to cylinder. I'm not sure really.
The correct fix for uneven air distribution is cylinder trims (sequential fuel injection). A lot of intakes have this issue. The miniram and LT1 just seem to have it a bit more pronounced.
Even singleplane intakes can have distribution issues depending on what you are using for a throttle body, hat, elbow, or even air cleaner.
This is an interesting point. Seems like a valid concern. The TPI does not exhibit the same problem? If not, is there any consensus on why it doesn't? Because the plenum portion has basically a similar layout: long skinny box with four runners near the front and four more near the back.
Also, I wonder if any attempts have been made to even out the airflow with porting slightly biased toward the rear runners? IOW, port them to slightly higher flow numbers on the bench so that on the engine they end up flowing the same.
I have posted the factory adjustments for the LT1 intake, i assume the TPI probably has some distribution errors but the factory batch fire system could not correct for the errors and they were probably small enough not to really matter. (FYI the 1992 and 1993 LT1 intakes also did not correct for the issue)
I have posted the factory adjustments for the LT1 intake, i assume the TPI probably has some distribution errors but the factory batch fire system could not correct for the errors and they were probably small enough not to really matter. (FYI the 1992 and 1993 LT1 intakes also did not correct for the issue)
That's interesting too! I looked at my factory settings from my 96 LT4 and they are different than yours. They still obviously are correcting for variances in runner flow, but overall the differences look a little smaller and not all in the same runners:
The tuner I went to awhile back said the problem with the Mini Ram was fuel reversion up into the the intake.They actually put a camera into the Mini Ram and saw the fuel collecting up into the back of the Mini Ram.
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Originally Posted by bjankuski
I have posted the factory adjustments for the LT1 intake, i assume the TPI probably has some distribution errors but the factory batch fire system could not correct for the errors and they were probably small enough not to really matter. (FYI the 1992 and 1993 LT1 intakes also did not correct for the issue)
I was also thinking ANY front-loading intake would have uneven distribution. It's been posted a lot here...and makes sense.
I'm surprised 94 and 95 could compensate for this issue. I would have thought it wouldn't happen until 96 when ODB2 became "active"? OTOH, I was aware the system was present in 94-95. Was the software active w/o the additional "sensor network"?
Also, in response to your post about my RA balance: How do you know the AMOUNT of material removed (shifted) is within reasonable comparison to the 400+ engines you referenced?
After reading a few articles on RA balancing, it looks a bit like a crapshoot in the sense that balancing machines (especially older ones) don't necessarily account for the distance -- from crank centerline/axis -- that the imbalance exists. And...shifting weight in/out affects rotational/centrifugal forces. At least my balancer was an IT guy before changing into his new profession. (So, that might presume he isn't dumb as a rock! LOL) Of course, it was his older, wiser partner that did the balance.
FWIW, I see the definition of balance (where a Scat9000 383 stroker crank needs 1pc of Mallory) isn't terribly definitive....meaning there are LOTS of sizes of heavy metal "sticks" which doesn't really define how much is needed to complete the balance.
I gotta say the amount removed doesn't look THAT far away from the size of the bolt-in weight on the damper. I wonder what that removable weight weighs? IIRC, on the back end, the 1pc RMS engines have a 30g weight...which SOUNDS a lot lighter than they look.
MMiller: I learned more about the forces in balancing and WHY the force exponentially increases with RPM. I'm starting to think my RA isn't really that much (if any) out-of-balance. When spinning it in the driveway, I can't describe it as worse with higher rpms. It seems like I need to shift focus more to what's probably a mild "miss-like" condition. Maybe a bad plug, plug wire, or injector? I also noticed my headlights dimming with reduced rpm. Maybe I have a bad regulator too? I also wouldn't be surprised if the ONE u-joint I never replaced (of the half/drive shaft array) is starting to weaken with age. On the road, that could add to the perception of imbalance...along with a possible orientation issue with the driveshaft itself. Lots to check on when we get out of this DEEP FREEZE!!!!
And now...back to your regularly scheduled TPI slam! LOL
I'm surprised 94 and 95 could compensate for this issue. I would have thought it wouldn't happen until 96 when ODB2 became "active"? OTOH, I was aware the system was present in 94-95. Was the software active w/o the additional "sensor network"?
As anesthes alluded to, the solution is to fire each injector separately and in proper time with its respective intake valve opening event. That's sequential port fuel injection. TPI didn't have that function, and fired all injectors at the same time (batch fire). I would actually expect batch fire to cause its own set of mixture problems even if the intake itself flowed perfectly equal in all runners, just because some injectors are firing at a closed valve.
But anyway, SFPI has been available for many years. In GM cars, it dates at least back to the 3.8L V6, including the famous turbo Regals. I'm not actually sure why they didn't include it in the TPI system. Probably and ECM that incorporates SPFI can adjust individual fuel trims. There would be no reason not to, since each injector is individually controlled anyway.
It's not related to OBD2 at all. OBD2 is really about more advanced self-diagnosis by the PCM, not more advanced performance parameters. The best example is comparing the 94/95 LT1 (OBD1) PCM to the 96 LT1/LT4 (OBD2): they have very similar tuning parameters but the OBD1 system doesn't have as many diagnostics.
I learned more about the forces in balancing and WHY the force exponentially increases with RPM. I'm starting to think my RA isn't really that much (if any) out-of-balance. When spinning it in the driveway, I can't describe it as worse with higher rpms. It seems like I need to shift focus more to what's probably a mild "miss-like" condition. Maybe a bad plug, plug wire, or injector?
I still doubt this is the issue, but it's easy enough to rule out so I would start by verifying proper exhaust temps in all the header primaries. You have to start eliminating possible causes.
They actually put a camera into the Mini Ram and saw the fuel collecting up into the back of the Mini Ram.
Originally Posted by GREGGPENN
I was also thinking ANY front-loading intake would have uneven distribution.
These posts helped me understand this phenomena better; I had always limited my thinking to air flow...there was some kind of air flow problem w/the LT1/miniram intake. Now I can see that it's the fuel movement, that is causing the problem. Fuel will "fog" back up into the plenum....especially at speeds where the cam and intake runner are inefficient. You can actually watch this happen on a highly tuned, individual carb/cylinder engine; go to WOT from idle, with the air box off and you get a "fog" of fuel out the mouths of the carbs.
This is probably less prevalent in a TPI b/c of the long distance from the injector to the plenum....before the fuel can make it all the way up and out of the runner on overlap, it's being sucked back down on intake. LT1 runner is so short, fuel shot into the runner/port will easily get pushed into the plenum during overlap.
The rear is exacerbated in the LT1, b/c of the velocity of air through the front of the plenum from the ~2.9L V4 in the rear, pulling air. The plenum needs to be way bigger, or the TB needs to be moved to fix the problem. Or it needs DI to get the fuel out of the manifold.
I cut apart one of my old MRII intakes to improve air distribution and also ran sequential fuel injection. It was "better", but never felt like it was adequate for the power levels that I was running.
Eventually left the MRII and moved on to the C4SP intake. Air flow and fuel trims seemed to be much better aligned with that set-up.
I would actually expect batch fire to cause its own set of mixture problems even if the intake itself flowed perfectly equal in all runners, just because some injectors are firing at a closed valve.
I've gone back and forth on that in a number of threads on the megasquirt forums, and on thirdgen.org - regarding which injection firing strategy works best. (alternating bank to bank, simultaneous, and number of injection events per cycle).
Stock TPI on both the '165 and '727 ECM do 1 injection per per revolution on both banks. (2 squirts per cycle).
I'm currently using alternating, so I'm firing twice per cycle as well, but only one bank at a time rather than both simultaneous. This allows for a larger pulse width at idle which makes it possible to run larger injectors.
The downside, is you are injecting a stupid amount of fuel on 1 side of the motor at a time. The theory is you are (hopefully) injecting onto the back of a closed valve, and when the valve opens the rush of air will atomize the fuel (with the aid of a hot valve).
Sequential would be better, but to be done properly you should also set your injector timing as your IVO will differ cam to cam.
A lot of engineering goes into the factory tune for a production vehicle. I'm sure a lot of tinkering was done between 94-96 to get it 'perfect'.
These posts helped me understand this phenomena better; I had always limited my thinking to air flow...there was some kind of air flow problem w/the LT1/miniram intake. Now I can see that it's the fuel movement, that is causing the problem. Fuel will "fog" back up into the plenum....especially at speeds where the cam and intake runner are inefficient. You can actually watch this happen on a highly tuned, individual carb/cylinder engine; go to WOT from idle, with the air box off and you get a "fog" of fuel out the mouths of the carbs.
This is probably less prevalent in a TPI b/c of the long distance from the injector to the plenum....before the fuel can make it all the way up and out of the runner on overlap, it's being sucked back down on intake. LT1 runner is so short, fuel shot into the runner/port will easily get pushed into the plenum during overlap.
The rear is exacerbated in the LT1, b/c of the velocity of air through the front of the plenum from the ~2.9L V4 in the rear, pulling air. The plenum needs to be way bigger, or the TB needs to be moved to fix the problem. Or it needs DI to get the fuel out of the manifold.
Right, and then things get very weird when you add boost.
I don't know if you remember any of my posts from about 10 years ago when I had the powerdyne on my other C4 with a miniram? I was constantly dealing with fueling issues cylinder to cylinder, to the point where if the plug was too cold they were fouling, if the plug was too hot the motor would ping under boost. I ended up switching it to a singleplane:
The kid that did the elbow for me did an awesome job on the radius - it was nearly even airflow into all cylinders, fit under the hood, etc.
The only real problem with the combo was the air cleaner hovering over the headers
Right, and then things get very weird when you add boost.
I don't know if you remember any of my posts from about 10 years ago when I had the powerdyne on my other C4 with a miniram? I was constantly dealing with fueling issues cylinder to cylinder, to the point where if the plug was too cold they were fouling, if the plug was too hot the motor would ping under boost. I ended up switching it to a singleplane:
The kid that did the elbow for me did an awesome job on the radius - it was nearly even airflow into all cylinders, fit under the hood, etc.
The only real problem with the combo was the air cleaner hovering over the headers
-- Joe
Very similar experience to mine with the MRII, then moving to the C4SP. Regarding the air filter over the header, I wound op placing a ~30* angle at the R series blower inlet and have a 12" long huge K&N that supplies air from over the valve cover area. It works well, and the only time I get elevated temps is if you were just idling for a long period of time. I used to have a temp probe mounted in the inlet side of the blower.
