Every thing I read about these motors have said along the lines of the long runner lenght being the problem.I want more than 4800 rpm. I have built 7500 rpm Tunnel ram motors that have long runner lenght .My guess is the cams has to have as little overlap as possible to still manage the ECU and related components.Can someone that really knows clear this up for me?TPIS could not give me the answers I wanted on the phone and they run some pretty big cams with their Mini Ram but would not clear up any idle issue questions I had.Ed wright told me any thing over 220@0.050 was difficult to manage idle wise.As you can tell I am new to the TPI but there has to be a way!Please don,t come back with torque is what you need on the street.I am tired of excessive low end power.I want a 383 ci with Kawasaki type power! He He!

 

What do you mean by long runner length...TPI air path is nearly 2 feet!

It's the combo of long runners and small runner diameter which provides the tunning pulses to build low end torque and also causes high rpm torque roll off.

The TPIS mini-ram is a compromize between the short runners of a LT-1 and the long runners of an L98. Combine this with the Big-mouth base and a 58mm TB and your 383 should sing a high note with no loss of low end torque over a 350, though it won't gain much low end either (their test 383 built peak HP at 6,500rpm).

Get a copy of TPIS "Insider Hints" to see some interesting dyno data on both intakes and cams.

 

My TPI motor revs pretty strong all the way up to 4500 rpms ! ;)

Vic

 

I might not be reading this right.. but the Miniram replaces.. the Base/runners/plenum with its one piece design

 

The TPI stops making power past 4500-4700rpm because it runs out of air. The TPI setup cannot provide the volumes of air that are need for high rpm breathin. This is because of the long runner tract, small diameter runners, and the small diam. base. The TPIS or Accel base will help with higher rpm breathing. The TPIS/Accell base with the siamessed runners (slp sells these) will get you more power and air at higher rpms. There is are several CF member who take their ZF Tpi's to 6000rpm, it will go there, but won't make any power.

You have to open up the top end as much as possible, wheather it be through the use of runners, Minirams, Superram, TPIS base....etc. The TPI cam is not the problem either, mind you a bigger cam is needed to feed the motor at higher rpms.

Good Luck...

P.S The reason your tunnal ram motor make more power and hit 7500rpm is because the "tunnels" in the intake are much much larger that the runners in the tpi base. The tunnel ram is long, but flows....

 

basically because GM screwed up and put a 305 intake on a 350, knowing that it wouldnt work right.

 

89Bowtie,
The reason the Tunnel Ram spins up is because it shares a mini plenum with the other cylinders to pull from but the runners neck down to a common port size on a given motor as it enters the head.Not to mention the 270 degrees of duration @0.050

But something is still missing.
When you take a pair of say 781 BB Chevy castings and install 2.19 intake valves"forget the exhaust for the moment" and bowl blend to the new valve seat cut the power comes from the original sized intake port to the new and larger area where the mixture enters the combustion chamber.In other words small to large in a very short distance = velocity.So I am now thinking the TPI with a 58mm throttle body has all the air needed for any 350ci motor. The TPI manifold is large where the runners bolt on and then necks down to where it meets the head alot like a Tunnel Ram but without the mixture being present and available like an open plenum carbed motor.It is a Individual Runner system.
It seems like if the fuel was injected into the plenum although it would stand a good chance of deatomizing because of the lenght it "mixture" would have to travel the motors would run up a bit more.Maybe leave the injectors where they are at at induce extra fuel using a spray bar behind the throttle body that is computer calibrated at wide open throttle and backing off the stock injector timing .
I would be interested in seeing a back to back test using a Super Ram Plenum with stock runners then a test using a ported stock plenum.
I am not trying to be a know it all by this post it is just 2+2 does not = 4 here on these TPI motors.The set up of them contradicts how the Tunnel Ram came about.Someone that knows please enlighten me!

 

First and foremost...Im a not pro on engine dynamic....so I am open to correction.

You bring up an interesting point velocity. The fact that the 350 is sucking air throw small ports is what created the velocity and helps generate the torque by having low rpm velocity. The TPI creates velocity by a sucking specific volume of air from a large area into a smaller area. Basically from the open plenum (the large area) into and down the runner into the base (the smaller area)

The tunnel ram is pretty much the same idea of a TPI, individual runners to some extent, with a common plenum. However, the tunnel ram has more appropriatly sized runners, they are not restriction. Fact of the matter is that the TPI runner tract is too small to deliver adaquete air supply. Hence creating the a restricting effect and increasing the velocity and increasing the torque on the bottom end and through the power band.

Look at a Nascar engine...the ports are HUGE. They have lower intake velocities because of the larger ports and runner tract. Which means that there is less restriction and that gives them high RPM breathing ability and less bottem end torque.

A good example are the SLP siamessed runners. They open up the runner area, decreasing the breathing restriction and helping to produce HP and upper rpm breathing ability. They do that and work good at that. But, the loss of the velocity from the open runners decreases the engine torque. Just goes to show the pricipal behind hp&torque with relation to intake velocity.

Placing a 58mm t-body on stock TPI has shown to actually decrease output. It decreases the velocity. One might think then....Less restriction, more high RPM ability....Does'n't work that way. Because the restriction is the runners and the base not the t-body. A good example is the Gm 502EFI motor uses a 48mm t-body. The intake system is designed well enough so that they didn't have to add a bigger t-body to let it breath.

Also, about the head example that you mentioned....
"small to large in a very short distance = velocity."

That acutally decreases veloctiy becuase the air has more space to fill up in the tunnel. That is why thing seem to be contradicting eachother...

 

"That acutally decreases veloctiy becuase the air has more space to fill up in the tunnel. That is why thing seem to be contradicting eachother..."

I agree to a point but the engine I used for example has extreme piston speed which would unleash a whole other topic.It is a mixture not air and it is already there waiting to get pulled in and that 4.250 bore with that kind of piston speed can certainly do that but again we are only talking the 1/2 inch distance and not a small block.Maybe I am wrong but please don't take it that I am arguing.

I spoke with a company that does chassis dyno, computer chips and computer burning only.They agreed the TPI individual style runner and it's lenght along with having to run a relatively small cam is the problem.Run a big cam that would make power at 6k verses a smaller cam that peaks at 4.8k it could mean that the smaller cammed motor would be 30hp ahead because the larger can will not get enough air to get to the needed rpm.The big cam motors just fill up the ports and hit the brick wall.Sound good or run good kinda deal.The short runners would be the ticket and I am not interested in the Mini Ram that will still make only X amount of power for the money spent.We have 2 L98's in the family.Soon to have just one because with all the other toys we have and 330 rw horspower is not enough a carbed motor is in my future.I have decided since custom chip companies delete the egr I will make a sheetmetal plenum and lower it to the lowest possible level in part by removing the egr valve and fabricate new runners "boxed"to the shortest possible length and see if it helps my son's IROC.It should.
.If reversion becomes an issue I can go in and put anti reversion dams in the runners.It should not take more than a few weeks part time to get this done and will be way less expensive than a Super Ram.
For what it is worth they also told me the best rear wheel hp they have been seeing out of TPI motors is the crate ZZ4 with 52mm TB,ported stock plenum and Accel base.They told me of a 427 w/Super Ram that made like 9hp more but had 520 + torque.

 

like 65z01 said above, the TPI is almost 2 ft from plenum to valve, and the tunnel ram is no where near that long. The other thing, is the cross sectional area of the TPI runner is very small, as it was designed for a 305 (also mentioned above). Velocity is good to a point, but once you get over a certain point (about 1/2 mach), the resistive forces overcome the airs attempt to travel faster. SO when you try to fill a big area (like a 383) from a small, long runner, you are asking the air to travel too quickly to feed it at higher rpms. Then you also have to consider the harmonics created within the runner. The longer runner resonates at a much lower rpm than a shorter runner, which is one reason you get great low end torque. The harmonics are actually forcing air into the cyl (like a virtual supercharger), but that effect is long gone in the upper rpm range, where shorter runner are better tuned. They don't call it "tuned port" for nothing.

Mountian, if you are going to go through all the trouble to fab a sheet metal intake, why not just modify your favorate carb intake to accept FI.


[Modified by ralph, 4:27 PM 12/14/2001]

 

I'm not tech savy enough to get in this conversation, but if you think you're limited by tpi, check my sig. I can turn over 6500 rpm's but peak h.p. is lower so why bother. :blueangel:

 

"I'm not tech savy enough to get in this conversation, but if you think you're limited by tpi, check my sig. I can turn over 6500 rpm's but peak h.p. is lower so why bother."

But I see you are using the Mini Ram.I did not want to go that far and was looking for another way to get respectable power at 5800 or so.I also see no reason for a car that makes max power at say 4800rpm and shift it at 6200.A guy will go slower in the 1/4 mile that way
That horsepower you have in your sig,was that from a chassis dyno? Or a Dyno 2000?

edited to add my Son has Mustangs to deal deal with around here!

[Modified by mountainmotor, 4:56 PM 12/14/2001]


[Modified by mountainmotor, 4:58 PM 12/14/2001]

 

You can fill that 383 better with large tube runners or maybe siamesed runners along with some port matchig. But I think you will not realize the full potential with TPI, not if you want it to build good hp up around 6k rpm. Again, "Insider Hints" has some great data for you.

For the best ET you would shift somewhat beyond peak HP. The object is to maximize the area under the HP/RPM curve between shifts. So it depends on the shape of that curve. Once you get a dyno pull and some time slips you can use a software package like Drag2000 to determine optimum TC stall and shift points. Of course you can just use time slips to figure out optimum shifting.

 

Everyone blames the TPI more than they should. True, a few things need to be done to wake upi the intake system, and you can do it with a few hours worth of grinder time on the base/plenum/runners.

It is MY OPINION ( and opinions are like you know whats...everyone has one, lol ) that the CAM and ECM ARE the biggest limiting factors of L98 RPM's.

The cam has like 204/206 duration ( cough...choke...cough get a real cam...cough ) and the ECM has timing problems above 3500 RPM so you have to retard the hell out of timing just to run without detonation...which kills all around power.

 

"Mountian, if you are going to go through all the trouble to fab a sheet metal intake, why not just modify your favorate carb intake to accept FI."
Ralph,
It is because I am computer dumb!Whatever I do must be GM computer oriented and tuned by the guys at Fast Chip which is about an hour away.

What does everyone think about an Accel base,ported stock plenum and huge boxed sheetmetal runners and just be done with it!No kidding.I am loosing sleep over this He He!I have a disease!

 

I thought about sheet metal runner boxes once...but it looks like clearence of injectors and rails will stop that.

I say just siamese the intake base, use large runners and siamese the runner entries. You shouldn't need any other intake mods.

 

You are probably right.But I am afraid of running into reversion problems with a siamesed base.One of the problems I have is that I have not had the oppurtunity to actually see a AZ Speed and Marine or a set of SLP's runners for examination so to speak.If the Super Ram was not such a pain to work on I would go that way.
Could anyone post a pic of AZ and SLP runners?

 

I've had my super ram breathing at 6300 RPM before. Usually I shift it at 5800. If this is the range you're looking for, go for a super ram. My desktop dyno #'s are 420 hp@5500 and 479tq@3500. Obviously I still have to iron a few things out, cuz the MD 250 gave me different #'s.

 

Thanks for all the replies.A forum member has emailed me in detail about the going on's in a TPI motor while running.GM did know what they were doing that is for certain.They just did not leave room for playing around.

 

A stock TPI will rev to 6500 , it just doesn't make any power past 4800. :cry


[Modified by BiZ, 4:23 PM 12/16/2001]