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Old 03-10-2017, 06:44 PM   #1
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1975 Argosy 26
1975 26' Argosy 26
Placerville , California
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Advice on replace carb with TBI

Without spending thousands for a kit does anyone have advice on installing TBI on a 1975 454? Also how much improvement in performance and mileage?
Thanks in advance,
al
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Old 03-10-2017, 06:57 PM   #2
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2008 19' Bambi
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From what I have read there is not much to be gained by going to a throttle body injection over a carb. It may run a little cleaner and run better at altitude with compensation built in. Even returning to a small block would not buy much in MPG when towing. Your engine will produce good torque, and run on regular, so not bad the way it is.
I was considering a Fitech EFI for my 350 SBC, but I think I may go the LS engine route with modern Injection. Much money though! My 350 gets 10 mpg and stinks like H, and that's not towing!
Russ
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Old 03-11-2017, 07:04 AM   #3
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1974 20' Argosy 20
Richmond , Kentucky
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Al, there have been several motorhome owners who have converted their 454s to TBI, myself included. This subject has been talked about quite a lot and if you do a search using Goggle you'll get a lot of hits. Try this search link: tbi site:airforums.com

Here's a link to WayneG's TBI conversion.

Here's a thread I started where I asked the same question, 454 TBI yes no good bad idea.

Here's a thread I started when I was getting ready to install a new carbureted 454 in my chassis. Around post 75 is where I start discussing my TBI conversion.

And finally here's my thread where I discuss the TBI installation that I did. Around post 611 is where I really start getting into the TBI build.

Mileage improvements are probably minimal as Wayne indicates but performance, starting, dependability, and maintenance are definitely better with TBI. Also if you use the right PCM you get built in controls for the 4L80e transmission which I also installed.

The difference was night and day as far as starting and sound after I started my engine with the TBI installation. Since my Argosy rebuild is ongoing I have not yet had a chance to drive it with the TBI. Needless to say I'm looking forward to that opportunity!

You'll get a lot of advice from both sides of the debate. Personally I'm glad I took the time, effort and money to do it.

Brad
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Old 03-11-2017, 08:34 AM   #4
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1972 31' Sovereign
Silverton , Oregon
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Greetings,
My Dad installed a FiTech unit on a stroked 434 Ford 351m, and he is pretty thrilled with it, before he put it on morning start up was an exercise in careful control to keep it running, now he can reach in through the window and flick it on. He went with the their surge tank fuel pump system so he wouldn't need to fit a return to his fuel tank, and it's been working fine. he did read that some people have fuel heating issues during prolonged idling though.
for the price of the kit i'm really impressed with it. as far as fuel mileage goes, it's been hard to tell, there was a lot of upgrades that went on at the same time, but I can say that it maintains the A/F ratio you request really well, during cruising it's right at 14-14.5 which is where he set it.
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Old 03-11-2017, 10:34 AM   #5
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As Brad mentioned, You may not gain much in performance or MPG unless your carb is in really bad shape, but to me, the convenience of a TBI system is worth the money & effort.
I can go outside today, in 10 deg. weather, turn the key, NOT touch the throttle and it will turn over in 10 seconds or less. Before the TBI, I would be lucky to get it to turn over at all today.
Same thing with a hot day and stopping after driving hours at highway speeds and turning off the engine to refuel. When I had a carb, I would keep it running for a fuel stop to avoid vapor lock, now with TBI, no worries.

Just be sure you get a good kit from a reliable source. I had problems with mine in the beginning, but I had great tech support and I am happy with the end result. Other than the program chips, all my parts are GM or equivalent, so if something fails on the road, I can get parts almost anywhere.
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Old 03-11-2017, 07:43 PM   #6
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1975 26' Argosy 26
Vista , California
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I did mine so I could have a 4l80e overdrive. I was disappointed with the fuel economy, no big difference , I must have been running very lean before, I did like the improved starting and the lower rpm's. Much quieter on the highway. If I could do it over I would go with newer technology. When it comes to the fuel pump I found that an in tank pump is a better, I was getting vapor lock with the external one, when crossing the desert.
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Old 03-12-2017, 08:31 AM   #7
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Converting to TBI

The specs on the 454 including the cam, compression ratio, combustion chamber size and a few other things change from to year to year affecting the air/fuel ratio required for the engine to run properly and, most important, at the right temperature. A too lean mixture can cause extensive internal damage like burning a hole through a piston or a burned valve. Too rich will mostly cause poor economy. Now, with that said, to get one these TBI systems properly tuned for a specific engine is difficult unless you can find a tune-up shop that can measure all the parameters and burn a chip accordingly. Even then it may have to be done a couple of times to get it right. All of this can get very expensive!!! I have found that the carbureted engines actually can make more power and better economy than the TBI. The Vortec is a different story! When your engine was new it probably ran much better than it does now so if you can get everything back to new specs I believe you will be happy with it. The key is the carb. You should get a replacement/new, matching numbers one set to the exact specs as the one that came from the factory. In '75 there were probably a dozen or so Quadrajets used on the 454 for different applications.
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Old 03-12-2017, 08:43 AM   #8
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Getting the TBI tuned in my setup was not that difficult. If you have a laptop, you just buy a ALDL to USB diagnostic interface and there is free software.
I sent the data to the supplier of the kit and they burnt me a new ROM to improve performance

The entire install is here:
http://theouterlimits.ws/projects/ai...de_Page01.html
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Old 03-13-2017, 04:16 PM   #9
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Thanks to everyone. After reviewing all comments it looks like my carb is doing just fine.
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Old 03-14-2017, 08:49 PM   #10
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Al,
If your drive-ability is good that is probably your best bet. It is hard to pull mileage out of the 454 when pulling loads. My little C10 with 350 only nets 10mpg non towing. The truck weighs 4100. The carb starts and runs well, with excellent throttle response, but produces a lot of pollution, and requires a little extra cranking in vapor locking hot weather. I would expect a TBI would bring the mileage up a bit into the low teens when not towing, but not worth a lot of trouble.
In contrast, I took our new Silverado 1500 max tow 6.2L out to the desert last weekend for a break in drive. We averaged 24.4 MPG on 2 lane country roads! That is pretty impressive for a 420 HP engine in a 5700 pound truck. It had been averaging 17 in town traffic. All break in miles with no Airstream in tow. I'll have to check the accuracy of the in dash flow meter.
The newer engine management has gone way past what carburetors can do, but the cost is high. I am thinking of going to a LS small block in the C10, mainly just to clean it up and gain some mileage. GM performance parts has Plug and play engines with modern ECU's available for swapping in, or wrecking yard take outs are another option. I won't have a smog legal issue due to the advanced age of my truck.
Russ
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Old 03-15-2017, 07:25 AM   #11
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I did the TBI in 2004 on the 'Silver Bullet'. All GM parts w/custom wiring harness and PROM in a 'silver' CPU. Before was getting 4mpg, wouldn't pull any hill in cruise. One hill on I-35 south of OKC would downshift from 4th (545 Allison)to 1st and top it out at 20 mph w/my foot on the floor.
With the TBI it topped the same hill at 65 with cruise in 4th. and getting 7.5 mpg.
It more than paid $1700 cost in just gas savings along.
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