Minivans are Hard To Go Fast In / TBI Bottom Ends Cant Handle Turbocharging

[Vigo]

This vehicle had an older thread here that details what i wanted to do with it before i realized how far gone it was cosmetically: http://www.turbo-mopar.com/forums/sh...ic-1990-Carava

I've had a 1990 SWB Caravan for about 10 years now. It was my first 1st gen van and the one that got me in to them (i now have a nice 89 with an SRT4 engine as well). It started as a 5spd tbi van, but i converted it to turbo in '09 using the original 230k+ mile TBI bottom end. I've been involved with the K-car online community since Allpar was a mailing list, or in other words since BEFORE forums became a thing, and in that time i'd heard a lot about how anyone turbocharging a non-turbo car should upgrade to the turbo bottom end. I figured I was in a good position to prove that wrong, or at least vastly oversimplified.

After 09 I never put any more real street use on the van as i kept buying other projects, but i never let the idea of testing out the TBI bottom end go, either. Eventually i had it up to 16psi on the street during testing and took it to the track, but my clutch let go on the first launch (slicks) and i drove it back home slipping. Then i let it sit over a winter with straight water in the cooling system and cracked the block. It sat around a long time more but i still had a hard time letting go of wanting to prove that the TBI bottom end wasn't worthless.

Now, my theory all along has been that the TBI pistons aren't bad or weak, and that the lightweight rods are hardly ever a problem for anyone, AS LONG AS YOURE NOT DETONATING ON THEM. All of the 'non turbo pistons are bad' stuff is based on unfounded or untested assumptions, or on the experience of people who would have broken the stock turbo bottom end parts in the same situations anyway. It seems the main problem we have with creating fast cars in this community is getting what is already there to work correctly. Bottom end parts are hardly ever the thing holding a TM back.

And speaking of things that are hardly ever holding anyone back, what about turbos? We seem to have a habit in this community of upgrading turbos even though we were nowhere near the capabilities of the last one and end up with paper tigers that look mean on a sig line but are slower than what a maxed out stock turbo is capable of. People seem to go into denial about what the stock turbos are capable of so that they can happily just spend money and bolt on shiny stuff rather than do the legwork of debugging the actual problems holding them back.

And speaking of people letting themselves off the hook, I think the whole 'vans are hard to go fast in' thing is overblown. They're not that big, they're not that heavy, they're not that DIFFERENT from a regular k-car. Looking at my van vs what the fastest mitsu-turbo vans and mitsu-turbo vehicles in general have done, i don't see anything that sticks out. The fastest mitsu-turbo passes i know of are Shelgame's 100mph Daytona, Terry Ryan's 99mph Sundance, and then Terry Ryan's 13.9@97 in his van back when it was a stock classer, and Gus Mahon's 13.9@96-97 in Mean Mini and now this 96.77 mph pass in my van. We're talking 2mph and change off a svelte coupe's trap speed with the same turbo (daytona or sundance, take your pick). My van gained 19.5 mph from 1/8th to 1/4 mile. I really don't see what is so hard about this van body style at these relatively low speeds. Sure, maybe it becomes a much bigger issue when you're trying to trap 115, but almost noone is or ever has. The problem has always been people with low-power vans like mine not running anywhere near what they should.

So anyway, if you want to run 13s in a van, here's your basic recipe: Take a stock 2.5T1 Caravan with stock bottom end, stock head, stock cam, stock 1pc intake, stock exhaust mani, stock mitsu turbo, stock downpipe (open or cutout like mine), stock injectors, stock ecu, and add the following modifications:

• Add a cut-out raiser
• Add an intercooler
• Add a stronger clutch (hint: If you don't need this you don't need to upgrade anything else on the setup either because it isn't running correctly anyway)
• Finally, add slicks and hopefully the ability to do a better burnout than me.

That's it! You don't need 'mods' so much as you need to make the thing work correctly with what it already has. Although i have shown that if you want to downgrade the bottom end to non-turbo parts, you may do so if you wish.

[Vigo]

So this is the current setup on the van:

2.5L Common Block
Stock 782 head
Stock Cam
Stock 1pc Intake
Stock Exh Mani
Stock Mitsu Turbo
Stock 2.5" downpipe with cutout in place of the cat
Stock 2 bar map
Stock injectors
Stock ECU
Stock 3.85FD A523 trans
Stock clutch disc

What isn't stock:
TBI pistons/rods with .033/.036 ring gaps
TurboXS 2stg boost controlled triggered by an MSD rpm window switch at ~4200rpm.
Cam is retarded 6* via an old 5-way cam gear with 5 different keyways for various cam timing offsets.
Dual-core TII intercooler top-mounted over the transmission
Zener diode to defeat overboost.
Walbro 255 external inline with stock fuel pump.
Accufab AFPR at stock pressure.
4th Cyl cooling mod
Dual diaphragm clutch pressure plate

What doesn't exist on the vehicle:
Any BOV
A Wideband.



So a couple of interesting things there. When i built the engine using the TBI pistons, i wanted to play it very safe until i knew exactly how worried i needed to be based on what the knock sensor told me. My way of playing it safe was to limit boost until 4000+ rpm, and retard the cam to further limit cylinder pressures in the midrange. I retarded the cam 2 degrees at a time until the engine 'wanted' to be shifted at 5600+ rpm so that it would always land above 4000 and stay in the 'high boost' rpm range of the boost controller. I ended up at 6* of cam retard, and the effect is pretty dramatic. The engine gets shifted at the 6200 rev limiter in first and then around ~5800 in all later gears. This is with the crappy 1pc intake with no plenum volume and long skinny runners, and blowing through the tiny mitsu turbine housing. It starts and idles like normal, makes 20" of idle vacuum and has no drivability problems, just makes a lot less torque down low while actually wanting to be revved way past 5000 rpm.

I never thought that the 6* of cam retard would help the car make any power, but it sure doesn't STOP it from maxing out the tiny mitsu at ~230hp based on 3200 race weight and 96.7mph. And, it actually makes the car way more fun to drive, in my opinion.

As far as no wideband, one of the things i wanted to show with this van was that you didn't really need to spend money on anything aftermarket to get good performance out of a stock setup. I wanted to show that you could make a fast van with 1990s technology, the way Gus Mahon did. So all i've done is monitor the narrowband o2 and cylinder knock counts through an old scan tool. I defeated overboost with a zener diode. Everything else as far as engine management is untouched. I focused 100% on making sure it worked correctly and didn't break and focused about 0% on actually improving the performance of any hard parts.

[Pat]

No additional fuel?

[4 l-bodies]

Those are some mighty big ring gaps Adam. Probably needed without more fuel as Pat stated. Pump fuel or rocket fuel (lol). nice work!
Todd

[Vigo]

No additional fuel. Watching narrowband via scan tool it would max out at 0.92v or so at lower boost. I had a passenger watch the o2v during the first pass after turning the 2nd stage of boost control to 'all of it' and it was still sitting at 0.92v. 33Lb/hr injectors do calculate out to be able to do ~230hp @ 85% DC.

The big ring gaps were mostly because that was the smallest ring gap I could get that was consistent across all 4 without getting different rings, but after all my discussions with Ondonti about ring gaps I also looked at it as an opportunity to test how small the side effects of 'too big ring gaps' would be. Judging by the amount of oil being blown onto my intake manifold from the open valve cover port, i'd say whatever blowby is going through those gaps is not outside of the 'norm' of what I've seen from other high-miles 8v engines. Right now I don't see a serious downside.

[Reaper1]

Awesome work! This is a great way to show how things are a system and when you get the system to work right, you have a LOT of fun!

[Vigo]

So the next thing I want to do with the van is start running it on e85. It will be interesting to see if i can push it as hard on e85 as i have on race gas.

The van already has a basically all-new fuel system including a new tank, new Rock Auto in-tank pump, a Walbro 255 external inline pump (that i converted from an internal!), and new high pressure hose throughout. I didn't WANT an all-new fuel system, but i had so many problems with sediment from the tank restricting the pump strainer and even clogging injector filter baskets that i was forced to keep replacing parts until i was 100% certain that i had good fuel pressure at all times. I drove around with a fuel pressure gauge on the windshield for probably the first several weeks after i got it running to chase down intermittent fuel pressure problems.

If it had been cranked up to higher boost levels at that time, i would have broken it. I think a lot of people have broken pistons over uncertain fuel supply systems. You have to monitor your fuel pressure under max boost and high rpm to KNOW that it is correct. The best solution is an in-cab fuel pressure gauge if you're willing to spend the money. I have two in other cars, but not this one, yet.

So now that i have a perfectly clean tank, all new hose, and two fuel pumps, all i really need to start using E85 is larger injectors. Luckily there is pretty good availability around here, so i should be starting down this road soon!

[Vigo]

Video of 14.06 pass:

[Pat]

No additional fuel. Watching narrowband via scan tool it would max out at 0.92v or so at lower boost. I had a passenger watch the o2v during the first pass after turning the 2nd stage of boost control to 'all of it' and it was still sitting at 0.92v. 33Lb/hr injectors do calculate out to be able to do ~230hp @ 85% DC.

The big ring gaps were mostly because that was the smallest ring gap I could get that was consistent across all 4 without getting different rings, but after all my discussions with Ondonti about ring gaps I also looked at it as an opportunity to test how small the side effects of 'too big ring gaps' would be. Judging by the amount of oil being blown onto my intake manifold from the open valve cover port, i'd say whatever blowby is going through those gaps is not outside of the 'norm' of what I've seen from other high-miles 8v engines. Right now I don't see a serious downside.

I think it's great that it's as fast as it is, but I'm stunned it doesn't need more fuel.

Does the stock cal run the injectors at 85% duty cycle at the 14.7 psi of boost that it can see?

[contraption22]

The first time I ever compared what my wideband was reading to what my narrowband considered "rich", I understood why my pistons had started to melt.

[Vigo]

Does the stock cal run the injectors at 85% duty cycle at the 14.7 psi of boost that it can see?

I dont actually know that. I can see pulsewidth but not duty cycle on the scan tool.

The first time I ever compared what my wideband was reading to what my narrowband considered "rich", I understood why my pistons had started to melt.

I'm not actually recommending not having a wideband, but during this 'build' i was intentionally limiting myself to basically the worst of everything to show that what most builds are lacking is not better parts but just a lot of sorting work and diligence getting things to work correctly.

I do plan to put a wideband on it before i start running e85, but the fact remains i've been careful enough to run 16psi on 93 octane and 20psi+15* base timing on race gas with 'high compression' non-turbo pistons without breaking anything with no more technology than what was available when Mean Mini originally cracked 13s. Even though that was proven and me doing it over doesn't prove anything new (except TBI pistons), i still feel like it's important to demonstrate that these cars aren't magical monsters and that if it's been done it can always be done again.

Just like Gary Donovan running 12.8 in the nearly stock T2 CSX he built recently, which is old news compared to the 12.6 he ran in a t2 daytona back in the day except for the fact that hardly anyone ever does run those high 12s on stock stuff without upgrading a bunch of stuff that didn't need to be upgraded first, as if these performances arent teaching us anything. Or the fact of you and Jeff Mass running high 11s (at one point) in L-bodies with 'only' s60 and s70 turbos. Or Pat going 110mph in a stock turbo/full weight TIII car, or at the extreme end of these examples, running a 10-second pass on cast pistons! I feel like these are important factoids because they remove possible excuses from other people's builds and encourage people to focus on getting stuff working right instead of bolting on a 50 trim t3/t4 and still being slow because that was never their problem.

[Reaper1]

While I agree that there are a lot of people out there that throw parts at builds just to be disappointed due to a system that is far from optimal, I also think it's important to emphasis that the performance you are seeing *could* be better if upgraded parts were used that work more efficiently in the ranges you are running at.

Just as an example, simply going to a better turbo, keeping the boost the same (or even turning it down) would yield better overall performance and power because it would be operating more efficiently. Not only that, but the part will last longer.

So, I agree with you 100% that absolutely the stock parts are up to the task, and you are making a VERY important point...make sure all your ducks are in a row to get the best results. It's not to say bigger/better parts aren't needed...

[Vigo]

also think it's important to emphasis that the performance you are seeing *could* be better if upgraded parts were used that work more efficiently in the ranges you are running at.

Sure, but I built the van with the 'worst' parts intentionally to show that it wouldn't hold it back from running 'only' ~13.9 (or 14.0 if you're like me and do a 1.97 60'). It's not that I think people should never upgrade anything, it's that people who are struggling to get something to work the way they want it to are always tempted to think that throwing dollars at it and adding shiny parts is going to help when it almost never does.

I put a TON of boring, dredging work into this van trying to get solid reliable fuel pressure in it and making sure the system was sufficiently clear of the sediment that got pumped around from the nasty old tank. I changed out pretty much every part of the fuel system except for some of the hard lines. So tank, pumps, pump hanger, filter, hose, rail, injectors, FPR, tank gaskets, filler neck grommet, sending unit. It was a ton of work and annoyance but if i had turned the boost up and romped on it before the legwork was done, it would be broken right now.

[Vigo]

I'm stunned it doesn't need more fuel.

Does the stock cal run the injectors at 85% duty cycle at the 14.7 psi of boost that it can see?

This has got me curious now! According an online injector duty cycle calculator, at 6000 rpm 85% DC is equal to 17ms of injector pulsewidth. I can play around with that and try to figure it out.

Something harder to quantify is BSFC and whether the higher compression from my TBI pistons is reducing my fuel demands somewhat vs a stock turbo engine making the same power.

[jefo]

Do you get wheel hop when on street tires?

[RattFink]

I love this thread! I always loved reading The Dodge Garage for these reasons alone, amazing things can be done with these cars on stock parts. It seems like you don't see it as much anymore. I may see how far I can push my old Log Intake car....

[Vigo]

Do you get wheel hop when on street tires?

No, I don't. But I also have the two-step boost control limiting boost til 4000rpm and 6* of cam retard so it really only makes full power from 4000rpm up.

amazing things can be done with these cars on stock parts. It seems like you don't see it as much anymore. I may see how far I can push my old Log Intake car....

I am actually planning to build a Log setup in my 82 Lebaron for the same reasons! I don't think many people have fully explored how far it can go. Todd/4 l-bodies is one of the few I know of who has built a fast one and is still active here. There was a fast one in the works a while back that burned in a fire that was setting up to be pretty exciting.

[mopar-tech]

I'm not actually recommending not having a wideband, but during this 'build' i was intentionally limiting myself to basically the worst of everything to show that what most builds are lacking is not better parts but just a lot of sorting work and diligence getting things to work correctly.

This is a story as old as time and has been going on since the first speed shop opened.

The magic is always in "the tune" not in the collection of parts. Many a racer with an impressive list of parts has had his --- handed handed to him by an opponent with a much milder looking package but was dialed in.

I do plan to put a wideband on it before i start running e85, but the fact remains i've been careful enough to run 16psi on 93 octane and 20psi+15* base timing on race gas with 'high compression' non-turbo pistons without breaking anything with no more technology than what was available when Mean Mini originally cracked 13s.

I applaud what you are doing but the point of using "turbo spec parts" is so the package is around longer. If Chrysler could have gotten away with using lessor parts then they would have. Personally I like my work to be around for a long period of time.

If an experiment and you have plenty of TBI parts about then by all means have fun.

Just like Gary Donovan running 12.8 in the nearly stock T2 CSX he built recently, which is old news compared to the 12.6 he ran in a t2 daytona back in the day except for the fact that hardly anyone ever does run those high 12s on stock stuff without upgrading a bunch of stuff that didn't need to be upgraded first, as if these performances arent teaching us anything.

The CSX actually has the potential to go faster than the Daytona as it is lighter. The Daytona had many, many passes under its belt to get where it was; the CSX blasted into the 12's the first time I took a serious crack at it taking advantage of what I learned previous. I had the opportunity to make more passes at Cecil but declined. The car did what I wanted it to do (run a 12, a pair actually) so saw no further reason to flog the car further.

After months of hard work the 'good enough" light came on and it was time to sit back and enjoy the racing.

Gary

[Vigo]

When i started the turbo swap on this van, leaving the tbi bottom end was just a matter of convenience. I knew it would work 'well enough' for a stock swap but didn't know exactly how far it would hold. I cut up the TBI EGR pipe and put it into the pan as an oil return tube. After it had been together and i wasn't finding any problems with knock counts going up slightly past stock cutout on pump gas, it made me want to see how much farther they would go. I knew i wasnt going to find the limits of ANY parts at the 220-240hp the Mitsu would max out at, so i won't learn anything else along those lines until i upgrade the turbo. You could definitely say it's an experiment since with ~10 cars parked at my house (not counting the rest parked elsewhere) there will never be a day i 'need' this van to work.

But since i knew that the pistons would have no problem at these low power levels i actually think the cam timing is a more interesting experiment right now. I knew i probably wouldn't make MORE power by retarding the cam since my limiting factor is the turbo, but i was interested to see if it would hold it back. I was surprised that it didn't cause any real negatives that i could find and that it caused the engine to act so differently. With 6* of cam retard it idles fine, drives around fine, and even with the long-runner/small-plenum 1pc intake and 'highly restrictive' mitsu turbine section, it still feels fine going up to the rev limiter now. This is the first time i've ever driven a 2.5 that felt just fine bouncing off 6200rpm. I was more or less expecting that i couldn't make it make decent power at 5500-6000 rpm just by retarding the cam and leaving everything else alone, but my trap speed so far suggests it's making just as much overall power running through the 1/4 at 4000-6000 as it would have at 3500-5200 with stock cam timing.

[Rrider]

And @ much less torque on those internals because of the extra revs..