Towing with a Turbo Gas engine?

[marttj]

I have never seen a gas engine have good tow ratings, but turbo diesels do well.

Why can't you tow with a turbo gas engine?

If I was to build a 454 Chevy and turbo it, it would be a beast for towing, but why isn't it done or why has it never been done?

My 301 Turbo Trans AM is no recommended to tow with, the Dodge/ChryCo turbo's were limited to 1000 lbs, the Dodge minivan turbo was 1000 lbs, but the 3.0L V6 was 2000-2500 lbs. Same trans. And many other turbo gas engines towing is discouraged.

 

[evelrod]

The only reason I can think of for not towing with a turbocharged 454 is fuel consumption.
As I see it, a properly set up SI engine (compression ratio, turbo, spark, cam timing, fuel injection, cooling, etc.)should do just fine. A lot of river rats around here tow with V-8 and V-10 engines. I guess if you can afford a $40+thousand truck and a $60,000 boat, you can handle 8 mpg!

I pulled race car trailers behind Ford, Chevy, and Dodge V-8's for 33 years before I bought my Dodge/Cummins. I don't recall too many major problems (Chevy wheel cyl. in'63, Ford tranny in '72 and Dodge radiator in '90). I will be towing my newest vintage Mini-Cooper behind my 454 powered motor home @ 6.5 mpg. I don't anticipate any problems except fuel cost.


Rod

 

[marttj]

I guess what I wonder is like my Turbo 301, it made 345 lb ft torque at 2800 rpm, with 3.08's that is right around 65 mph. Great towing range. BUT, they don't recommend towing at all, and if you do, 1000 lbs max. Granted, when I dropped in my 455, and towed 2500 lbs through the smokies, 70 mph UP the mountain was a cake walk. You would have to had told me there was a mountain. As for the lesser cars, they all were down to 50-60 mph at best, no one passed me going up, of course they were flying around me once we got to the top.
I suspect the reason towing with a turbo is bad is piston heat. I melted a piston in my 301 Turbo at 110 mph, heat related, it literally turned to liquid on the top side of it. Maybe just the pistons in a Diesel are tough enough to handle the higher heat of the boosted engine than a gas engine is.
I would think we would see lots of SB350 Turbos out there to replace the 454's to get better mileage and better power with a smaller turbo engine. If my 301 made 345 lb ft torque with those lousy heads, imagine what a EFI Turbo 350 would make. Easily smoking the 454 for about everything.
As for 6.5 mpg, I have been thinking of a 454 Suburban, the only one I have talked to about it said he gets 10-12 mpg no matter how he drives and no matter what he pulls. Sounds close? His was a TBI injected 94 Sub. 95 went Port EFI.
Tom

 

[evelrod]

Well , Tom, although piston strength may have played a part in your melt down, I suspect it had a lot to do with fuel mixture and/or ign. timing. I would definately check out the mixture and ign.curve on your setup before trying a maximum, high speed pull on that engine. Leaning the fuel mix out at the top end will surely destroy even the best engines. You usually don't here destructive detonation at high speed.
Most of the SUV's out here get anywhere from 8 to 15 mpg, but the higher figure is at a lower speed and no one drives at anything less than 70 mph around here. We have an overabundance of incompetantly driven wanna-be trucks on our roads and the usual roll-over-a-week.
My Dodge gets 19 to 21 mpg towing a 3500# trailer @ 55 to 60 mph. My son's later model Dodge gets even better mileage than that. Both have 4.10/1 gears and 235/85R 16 tires. The 454 in the 27 foot Silver Eagle is carburated and 6.5 mpg is about the best it will do with or without a trailer.



Rod

 

[GregLocock]

Manufacturers' towing restrictions on most cars are set by the strength of the transmission and driveline, and the brakes. In an auto the usual problem is hot oil, and the same in the diff. Most manufacturers have some sort of Alpine Pass (or equivalent) towing test for the brakes, which sets a maximum vehicle weight.

Cheers

Greg Locock



Cheers

Greg Locock

 

[marttj]

The question is why are they not any high towing rated Turbo Gas vehicles? i.e. the Dodge minivan SAME trans with a Turbo 4 2.5 L with more HP and torque than the 3.3L V6 has double or higher towing rating than the turbo. Why? Trans same, vehicle same, brakes same, more power, but less towing capacity. And towing is NOT recommeneded, but if you must it is a low 1000 lbs. But if you have the V6 towing is not a problem.

Why haven't the car manufacturers ever (yes, I know turbo's are not good for cold emissions, so they are on the way out)make a turbo or supercharged gas engine in a truck? A SB Chevy 350 Turbo/Supercharged will have more power and torque where you need it than a 454 non turbo, and get better mileage, but they don't do it, nor have they ever did it. Why don't you see ANY towing capacities on turbo gas engines?

Thomas Martin

 

[FireLover]

I don't know the answer to your questions, but I have a few ideas that may give some insight.

It seems there are two questions here... SI turbo vs. CI turbo, and SI turbo vs. SI naturally aspirated. Background on the first question is given in the threads, "CI vs SI" thread in this forum, and "why do diesel engines have more torque than gasoline engines" in the automotive engineers forum. As I am sure you are aware, towing large loads means operating on the full load curve for extended periods. Meaning you need torque, torque, torque. These threads explain the problems of detonation limiting SI engine operation at full load. These factors only worsen with turbocharging. CI engines on the other hand are ideally suited for turbocharging to increase torque, and can run there for extended periods. This is one reason why the trucking industry uses diesel engines and not gasoline.

On question #2... I would guess fuel economy is the cause as Rod mentions. Production gasoline cars are not made to run at full load for extended periods of time. At full load, gasoline engines (turbo or not) run rich. The reason being to cool the exhaust and keep from melting the catalyst. Tempertures in the combustion chamber may also be high enough to cause damage without this enrichment, especially with a turbo. In addition, towing means slower speeds with an undersized engine, reducing air flow for cooling, and further increases in coolant and catalyst temperatures. So running rich causes fuel economy to suffer significantly, and turbo charging would only make it worse by needing more enrichment, or other means to provide thermal protection at the cost of fuel economy.

Again, I don't know that these are the reasons, but it seems likely.

 

[marttj]

That may be it, increasing enrichment to protect cat converter may do more harm in emissions (even though WOT emissions are not 49-state tested), so they don't do it, and if you are under heavy load, the eng is running in boosted conditions, (14.7 psi boost is double the CID ingested by the engine), which a 350 is around 700 CID. That probably get worse mileage under boost.

But not under those conditions, it would be much better.

I guess there is tradoff's... Plus the additional heat may be not very tolerable by the engine, requiring internal mods like special high $$ pistons, monster radiators, etc to keep it cool, where the 454 is just plain cheaper....

 

[TheBlacksmith]

I think the answer is the turbo design. Most of the turbo diesels make well over 1 lb-ft of torque per cubic inch, and about 1/2 hp per cubic inch. On a diesel, since the induction system is only air, a turbo can actually provide some cooling by pushing large amounts of air through the cylinders. A turbo gas engine typically was used to give 4 cylinder economy and V-8 performance, with over 1 hp per cubic inch. In fact the Chrysler engine cited here had two hp ratings, ~ 150 for 10 seconds (long enough to pass or merge) than the computer pulled the power back to around 135 hp (to prevent engine damage). In summary, I think if the gas engine were properly designed (low static compression, good knock control, etc.) it would work well, but most production turbo gas engines were performance oriented and thus had load restrictions to prevent damage.

Blacksmith

 

[marttj]

My 301 Turbo made 345 lb ft torque at 2800 rpm (had start of boost by 1200 rpm), the 231 Buick GN V6 made 345 lb ft torque, making enough, Turbo ANYTHING makes GOBS!
I can't wait to turbo my lawnmower....
Honda OHC....

But at repeated blasts from 55 mph to 100+ mph, I finally literally melted down a piston. So performance, yes, reliabilty at that performance, not with cast pistons you don't!

Thomas Martin

 

[evelrod]

Tom, in referance to your lawnmower, you need to read the "Any car can be fast" thread in the Automotive Engineers forum. As well as some of the postings on turbocharging with forged pistons.

We all are nuts when it comes to cars and car related stuff, myself included. When I didn't have much money to play with, I hopped up my Briggs & Stratton lawn mower. Ran great, I left it in Colorado when we moved. I would like to have seen the look on the first person that fired it up!!(Brazed up and reground the cam by hand, DelOrto carb, milled head, tuned exhaust, etc.)



Rod

 

[marttj]

And I thought I was bad porting and the intake on my 3.5 hp Honda and running 0W30 synthetic oil!

Mine would go though tall grass at a very conservative engine speed and not stall, and redline was a very scary rpm! It screamed at the high end! I never have needed more than "3.5" hp in that one....

 

[TheBlacksmith]

Exactly. My point was not that turbo gas engines couldn't make torque, but that they made so much horsepower that they are pretty much stressed out and couldn't take the additional load of towing. I don't know too much about the turbo Trans Am, but the Buicks were making as much as 276-278 hp from a 231 (GNX), which is 1.25 hp per cubic inch. As for hot rodding anything, I grew up in the North and snowmobiles and their hop up parts used to be cheap! I used to spend my summers porting and polishing the piston ported 2 strokes until I could reach scary redline RPM and pass stock sleds with 100+ more cubic centimeters. Had my share of blown head gaskets, ventilated pistons and broken engine mounts to show for it too.

Blacksmith

 

[GregLocock]

I worked at Austin Rover when they were developing the A series turbo engine. I can't remember what the power output was, probably a bit shy of 1000 hp from 1.3 litres, but the first durability test was 100 hours at max power. Incidentally it passed first time.

Admittedly this is a fairly mild turbo installation, but I think that this suggests that the guts of a conventional SI engine CAN take high loads for long durations without a meltdown.

When we used to run engines in the conventional wisdom was that you'd blow them up at the high speed low load conditions, rather than high speed high load.





Cheers

Greg Locock

 

[GregLocock]

Ack. 100 hp, not 1000. Obviously! Cheers

Greg Locock

 

[evelrod]

Didn't the Dan Gurney-All American Racers Toyota effort for GTP make about 1000hp from 1.6 liters a few years back?

I am shooting for a bit over 150 hp from my 1380cc A+ Mini engine for the Cooper S with one 45 DCOE 9 Webber carb.




Rod

 

[TheBlacksmith]

Let us not forgot the 1960's (!) Ford "4 Cam" Indy V-8 engine. It was a rather large 151 CI (2.5 liters), but it made 750-850 hp in race trim (lasts at least 501 miles) and pushing 850-900 for 10 miles of qualifying. This was on methanol and nitro-methane and an Indy race car is a long ways from the 454 CI tow master truck that started this string, but there have been a lot of advances since the 60's, so the numbers being posted are believable. I still think you need to trim the hp a little if you're going to tow.

Blacksmith

 

[evelrod]

Blacksmith:
Check out the F-1 BMW and Ferrari engines. Half the size same power range, but at 18,500 rpm !!!!! and for 2 hours flat out . Amazing. I wish I could make it to the US Grand Prix at Indy next year. I worked two F-1 and one CART race at Long Beach, and F-1 is the race to see.

reminiscing----Rod

 

[TheBlacksmith]

Yeah, I wish I had the time to go- F1 is amazing. As I stated, the Ford 4 cam was in the 1960's, without electronics and fairly large displacement, but at a time when 1 hp per cube was big bragging rights on the street, they made 5 hp per cube. Even then F1 was turning 11,000 to 12,000 rpm and making 600+ from 1.5 liters, I did make it to the old Watkins Glen track in 1969. Note that the F1 cars used the engine to start moving, while the Indy cars of that era had to be pushed off the line due to no low end torque at all.

Blacksmith.

 

[GregLocock]

hasn't that got more to do with clutch design, and accepted practice, than the low end torque?

Cheers

Greg Locock