The Stovebolt Site Forums The Shop Area Engine Shop 235 carb to TBI swap

I have a 55 Chevrolet car with a 235 and three speed which I restored some time ago and I would like to swap to TBI and ditch the 1bbl carb. For better drivability.

I searched and couldn't find post on this on this site.

Now I have done several V-8 Gen III swap and think the TBI would be easy.

After searching the local pick and pull the 4.3L TBI unit looks to big to fit the 235 intake. I found a 2.5L motor that has a 1 barrel TB on it and is almost the same size as the 1bbl carb.

I should be able to use the 2.5l TB and a signal 454 TBI injector for the correct amount of fuel and burn a chip to control it all.

Right now I am in the planning an gettin parts stage. I was just looking to see if anyone has alreeady done this and if I could get a link to there posts.

Thanks
-Scott

I have not done this on a 235, but I have considered it. I leaned toward multiport instead of throttle body though. What do yo plan to use for a computer and ignition? Why the 454 injector?

Mulitport would be harder with the intake ports siamesed. Although you could use just there injectors. And batch fire them. But then you still have to worry about mounting them

I plan on using a standard GM 1227747 or 1228746 ECM and harness and sensors from a 92 astro van.
and tuning it to fire th single injector.

I have seen an HEI conversion for the 235 and paln on using it, so that should take care of the ignition control.


I figured using a 454 injector since the 235 is about half the size and the 454 injectors which there are two fire every other injector not both at the same time anyway. But I think a 350 singale injector would work as well. Just have to get things running and do some data logging. I know the 2.5L injector will be to small.

check out holley , they make tbi for small 6cyl jeeps use them

Hello BO185. HEI for a 235... interesting. Where can I get info? Grant.

I'm in the planning stages of a similar thing for a GMC 302. I would use the 4.3L TBI as-is but use a MegaSquirt system instead of a GM computer, you can tune it to your heart's content.

Hey 4onthefloor, what intake manifold would you use? My cousin who lives nearby has done this to an old MG. He praises the results and claims it to be easy and cheap. I've also heard of guys hiding the injectors in carb "shells" to make it look old school.
If my twin Rochesters don't play fair when I finish my motor, I'll probably do the megasquirt thing as well. It sure helps knowing someone who has done it He can also fab intakes.
I still have yet to see what it looks like close up but I'll see his MG soon.
Grant, I have HEI on my 235. I got it from Tom Langdons' Stovebolt Engine Co. The low speed driveability and low idle are amazing. More forgiving during warm up as well.

A 235 is about 3.8 liters isn't it? Did GM ever put a TBI on a Buick 3.8? That might provide some appropriately sized parts.

Have you looked into one of the two barrel or four barrel manifolds for the 235?

Since one of the problems with a single carb on an inline six is the difference in mixture between the center and outer cylinders, I'm suddenly wondering if you can tune the injector trigger to squirt more for the front and rear cylinders...

My thoughts about fuel injection usually center around putting a TPI on a big block. I've never gotten very far considering it for a Stovebolt.

On the Jimmy I'm either going to use the Howard Log manifold or an Offenhauser 4bbl manifold. The 302 doesn't have many options.

I may try it first with the stock 2bbl manifold just to see what the differance is. The engine has a Holley AA-1 (2 bbl 3-bolt flange) carb on it now with a 3" center dump exhaust manifold.

One thing they are retarded expensive! I figure for 300 bucks I can make it happen.

Actually a 4.3,5.0(305, and 5.7 (350) share the same TBI housing just bigger injectors I would think the 305 injectors would work good for a 302 GMC.

Actually, I measured the 4 cylinder 2.5L single TBI and it's about the same size as the 235 carb so it should be OK. Holley did make a single barrel TBI but discontnuied it it flows more than the 2.5L TBI and has a 2" bore.


I have seen them but I want to keep this kind of stealthy and stock looking. And those manifolds are expensive as well.

I think it would be OK since I should be able to get a little more out of the TBI. And the stove bolts aren't as bad as the ford inliners with their intake setup.

So may main problem now is were to put all the sensors namely the temp sensor.

It needs to be in direct flow of water so it will get a good reading. Plus, I need some were to put the Knock sensor. On the side of the block preferably.

Holley and Edelbrocks aftermarket systems are over $2,000! Thats way too much! They are good but I wish I knew of a cheaper system for my upcoming stovebolt. Have to check out the MegaSquirt system. Never heard of that one. I was quoted $2300 for the Edelbrock system at a spped shop near here. They used both but like the Edelbrock a little better. A matter of taste I would think. I am hoping to build a 292 or a 250 with a slightly higher lift over stock. Nothing wild. H.

The aftermarket kits (holley, painless, etc. are for those who have the money and can't or won't take the time to DIY.

And actually, MegaSquirt is the controller only, you will have to gather the remaining fuel system parts yourself ( injectors, sensors, fuel rails, fuel pump, etc.).

GM TBI systems are penitful and cheap at any pick and pull or even E-bay under 200 bucks for everything! And they can be mixed and matched to make what you want and tunning to support it. If you can handle the time it takes to gather the stuff and take out what you don't need from the harness they can be adapted to run any gas engine. I have seen one 250 that was fuel injected. It used a 4.3L system.

I've been away for a while, but came back today for quick visit and saw this. Search the archives, I covered this setup once already including part numbers. But here is the gist of it:
4 bbl intake manifold
4 bbl to tbi adapter
4.3 throttle body with stock injectors
747 ECM with stock harness (or painless harness if you have the money) and sensors
Use acomputer controlled distributor from a late model 250 6 cylinder, part number available in the archives
Good luck on the appropriate knock sensor, I used the one from the 4.3, worked ok
The big cost is the 4 bbl intake manifold.
Stock chip from an 87 5 speed 4.3 liter astrovan worked best for me.

This is a whole lot harder than hooking up a holley 2300 350 cfm carb with an HEI ignition and honestly wasn't any better for performance, but it sure was cool to show people.

Megaquirt will work, the above setup is easier.

BTW, use the 4.3 setup on a 250 and LOOKOUT. Its whole different animal. Throttle response like you cannot believe.

PM me with questions if you need to.

Chris

Another option for the controller is something I was introduced to when I was researching the parts I need to build the monster VW engine I want to put in my toy (Yes, I know "monster VW engine" sounds wrong, but we're talking a 3.5L turbo 4-banger that can turn 350+HP at the wheels).
It's by a company called Simple Digital Systems , thier basic system has everything you need short of the MAF & injectors, can run anything from a 1 cylender to 8, and is fully programible with a simple module that is part of the package (no computer needed). It's also designed to work with turbo setups if people wanna get silly like that. Pretty well rounded system for the coin.
Just a thought anyway.

As a newbie, I'm impressed with the responses, clean and helpful versus some of the other 'flamer" boards. Glad I fouund this site! Geez, and I thought I had thought of TBI 250 first. Been looking for 86-7 TBI truck, could drop a 250 in with factory mounts (like, the one in my 82) and hook up the TBI and have a good one. Thanks for the archive tip - I'll go look and get a parts list in hand.
Great site and great memebers!

Why spend that kind of money when a stock GM TBI system can be had for way cheaper than 1000 bucks.

If you can install that kit then you can put together a stock TBI setup as well

I searched the archives and all open forums using 250 tbi and all I found was the link to the diy-efi page. Did the archive get wiped or am I using wrong search criteria?

Maybe a tech article? that extra improvement in air/fuel is looking might good at $3.00/gal (not to mention the cold driveability - always a problem in my 67 biscayne)

Looks like a 250 would be an easier swap!

Yes, I saw the post, was hoping for details on the TBI to 4bbl adaptor and the computer controlled distributor (like, a part number). I was thinking I could take my stock divorced coil HEI and use the remote coil from a 4.3, just need to check out the compatibility between the signals (possibly put the 4.3 guts in the 250 shell?) . Looking at the above, it appears that if I could find an Astro with a popped 4.3 cheap I could get everything else needed.

I've seen knock sensors mounted to the metal portion of the motor mount ont early V-8 conversions. Unless you run too much static timing it doen't have to be very picky, just tell you when she start knockin. We tested them in the plant by hitting the block with a brass hammer!

For the temp sensor I was thinking drill and tap the neck at the thermostat. Seems like that would be a good spot to pick up the flow.

You can get four barrel adapter to TBI adapters from Holley for pretty cheap. Search there site. I think some 250's had a temp sensor threads case in . I seen one housing on E-bay four sale for like 12 bucks which looked like it would work. As for the disturber don't see why the guts would swap as long as you mod the cap. Some one else my know.

All right some parts!


I went to the local U-pull it this afternoon and scored a single barrel TB unit for $35 bucks it looks like it's been rebuilt as well. NOTE: the bore is 1'' 11/16
and I think, the 235 intake is almost the same, I need to mic it to be sure but I just put a tape on it and it was close to the same size.

first

second

Now I also found an ECM out of a 1992 Astro van, which they wanted $31 bucks for it, but I didn't get it. It's coded 16151111 AULN

third


But on another note the harness out of the Astro was $38 bucks complete. I didn't ask how much for the sensors. All there prices seemed high to me BTW.

But now I need to make an adapter!

Any one know if the Langdons Mini HEI for the 235 will work or be modified to work with the ESC?
Photo A


This is a 250 six HEI which can be modified to work on a 235 but is the large cap. Will it work with he ESC?

Photo B

I've been running a TBI setup on my 54 GMC with a 302 for about 5 years now. I took a complete 4.3 system from a 90 Astro Van and adapted it.I used a 4BBL manifold from Patrick's and made an adapter for the TB using a piece of 1/2" steel plate. I took the wiring harness apart and used only the wiring needed for the computer, TBI,ignition etc. The hardest part was modifying the 4.3 distrobutor to fit the 302. I already had an old style HEI, but needed the electronics for the TBI system. The old style HEIs are easy to modify to fit a 235, 261, or GMC 6. I know within reason that if you used one of them and used the 7 prong module from a 81-86 GM car with the computer controlled carb you could make it work if you knew how to hook up the wiring for the HEI to work with the TBI. I just haven't found that information. This would be a much easier way than modifying a V6 distributor.
There is a frame mounted fuel pump that will work with the TBI. I will have to find that information on brand and part number. It is listed as a replacement TBI pump.
I mounted the knock sensor in the water drain hole on the side of the block just like it was on the 4.3. I drilled and tapped an extra hole in the thermostat housing below the thermostat. All the sensors, wiring, plug-ins, distributor, are all original factory off the astro van. The only after market items I used were the fuel pump and an electronic speed sensor I ordered somewhere.
The only problem was that the 4.3 TB injectors were too small. I replaced the TB with one from a 350 and it has worder much better, however I still get a lean backfire occasionally. Still needs more apparently. On the whole, I am very satisfied with the system. The 4bbl manifold, the fenton dual manifolds,the fuel pump,the speed sensor, and various steel fuel lines etc. was the only money I spent. The whole astro van cost me nothing. I would have put the manifolds on sooner or later anyway so I cant really count their cost. All it takes is a lot of time, patience, and a good wiring diagram. Hope this helps. Joe Dial
P.S. I didn't notice a real difference in power or mileage between the 2BBL carb and the TBI, but the easy starting, the smoothness, and most of all, the cool factor is what counts.

FOund the earlier thread in the Hi-Perf forum. Use tbi as the seach words. Here's a link that is buried in the thread,
http://www.diy-efi.org/gmecm/
If I remember right, that plus the megasquirt link above got me looking for the 90-91 Astro/Safari donor.

Many thanks to all who posted above, this newbie appreciates it.

I have a book called GM TPI Fuel Injection Swappers Guide or something very similar. After reading this thread I went back and looked at it again. I must say that the port injection sure seems a more attractive approach on an inline six.

The lean condition backfires are probably in the front or rear cylinder (or both) and that would be completely eliminated by port mounted injectors.

Well, a 302 is closer to 5 liters than 4.3 so you are probably running a bit lean.

The reason I want to use a Megasquirt is that is completely tunable by just plugging a laptop into it. It is compatible with GM TBI units and HEI ignitions.

My reasoning for going with a programmable ECU is simple: Stock EFI systems are built & tuned to specific specs, engine displacement, projected & metered flow of air & fuel, injector duty cycle, cam profile/timing, & so on.
Unless you can get it on an analyzer & retune it, a junkyard EFI & ECU is not much of an improvement over a carb. Sure, cobbling a system together & using an ECU from another engine may work, people do it all the time, but will it be the best option for the engine, it's power, & overall efficiency?

Just my own worthless oppinion (as many of them are) but if someone was just gonna half a$$ it, spending the money to get a better intake with a 2bbl or dual 1bbl, & have the carburator/s tuned to the engine would make more sense. It will still scream, & with alot fewer little things waiting to crap out on you as you're passin through the intersection of BFE & you got a purty mouth.

Tuning it is no problem thats easy enough there this tuning software for them.

I think it will work better anyway for me! And I didn't post this idea to get your opinion about is EFI better than a carb. I know what I want and it my car, so plesae post YOUR OPINION else were not here!!! I would like to keep this thread for How-to swap to TBI not for you to bash it! If not, I'll report it to the moderators!

Thank you!

BO185, dude, you are waaaaaaay off on that line of thinking.
If I'm gonna bash something it will be blatantly obvious to everyone, if I wanna start something everyone will know it, so throttle back & reread the post. You may note there's some humor inserted here & there for that exact reason. As it stands you are more than welcome to ask the mods to have a peek if you feel I've commited some greivioous offense.

Back to the topic at hand though,...

You asked why spend the kind of money a custom ECU like the Megasquirt or SDS when you can use OEM form another vehicle, I answered YOUR qeustion with MY reasoning.
And since I'm more interested in the actual EFI swap subject than anything here's a lil more reasoning go along with the subject.
I'm all about using EFI, I put a system on the 350 in my '65 3/4 ton Chevy and loved it. I did a full conversion with a Holley Pro-Jection system running a 650cfm 2bbl TBI on top of a Eddelbrock Peformer intake. Custom stainless fuel lines, modified tank, all the bells & whistles, only thing I didn't have was a MAF & an O2 sensor. And man, it flat out screamed. Pulled hard from idle to WOT & was a breeze to tune at rest or on the fly with no computer needed. It even got better emissions than new cars, and with no smog equipment, I loved it.

My point in saying what I did is I have seen many people make junk-yard EFI systems work, but playing the devils advocate here, I have also seen just as many suffer from problem after problem because the ECU just doesn't work with the engine it's on. Can quickly tunr into a nickle & dime ya to death expereince.
EFI, especialy a closed loop system with full sensors is far superior to carbs, always will be, but only if it works. Is a tunable ECU a better way to go with mismatched parts? Of course, but I'm not saying it's the ONLY way, not by far.

Just what this topic to stay on track with questions or actual installs or help with parts.

BO185 -- Your response to FREQ2002 is offensive and out of line. He was offering an opinion and did not deserve to be flamed.

Calm yourself and accept the courteous input of others (doesn't mean you have to do what he says or even agree with it) or leave this web site.

Bad attitudes and flaming are not welcome here.

Thank you,
John

I don't think I FLAMED him! It could have been alot worse! I was trying to keep on topic but this won't go away. So I will!

Thanks but, No thanks!

Perception, how many wars has it started?...

The easiest way to keep things on topic is not to let a perception make one post things that are off topic.
I was on topic, just providing counterpoint & cautionary statements as well as options as asked for. Even kept it on topic after you sounded off about my post by posting more relavent information.

This isn't like many sites tho, I doubt you'll find one better for basic knowledge & help with your old bolt. I have yet to find a board with as many knowledgable people who dont discern between who's a FNG & who's an old hand in the network.

Another vintage vehicle site I was on, The H.A.M.B., there are numerous people who would refuse to talk to me or flame me simply coz my other car is a VW & I was insane enough to be proud of it on thier precious board. I simply dont care enough about the opinions of assinine people I will never meet, & wouldn't care if I did anyway, to allow myself to act like they do.

Simply put, I can say from my personal expereince in the short time being on the Stovebolt that dropping off over something silly like this would be a loss of a great resource. Your call tho,...
Dont sweat the little crap.
BTW, it's ALL little crap.
________________________________

BACK on topic tho, if anyone is still interested, I actualy DO have some helpfull points to put out there.
Scary thought, I know.

Distributor selction: For a dizzy, many of the modern ECU's for EFI use a hall effect sensor (magnet/coil/rotor/stator, no moving parts other than the dizzy shaft) to trigger the ignition, so you'll want to ensure what type of distributor trigger system the engine you get the ECU from was using & if it's compatable with other types.
Also need to see if the donor vehicle uses mechanical timing advance or electronic.
After that it's all about finding one compatible with the ECU & with similar dimensions to your stock item & get it machined to fit your engine.

Knock Sensors: Thanks to the ricers, there are a load of aftermarket Knock Sensors to be found, that may be more suited to custom/cobbled EFI than an OEM item refit to your engine. Afterall, if the calibration of the junkyard sensor is too low or too high for the application (If it even works at all).

Temp Sensor: As for locating the water temp sensor. I had this issue on my '65 when I installed the ProJection system. I managed to find a thermostat cover with a bung in it for just that purpose, drilled it out and the sensor screwed right in. Right there in the prime water temperature location & it cost me all of $5 at a yard.
Definate option if the dimensions are similar across the models like some of the GM V8's, I'm just not sure about the 6-bangers tho.

Oxygen Sensor: One thing I haven't seen mentioned is the O2 sensor, and in a modern system thats an essential feedback item for a closed loop EFI control system. Welding in a bung for the sensor is simple enough & you can get the bungs from many places, pretty sure Summit Racing sells them.
There is also an ideal position for it, too far down the pipe it wont heat up properly & give bad readings (this can be remidied by getting the self heating variety, but they aren't cheap!).

One of the previous posts mentioned the TBI unist that looked like stock carbs. Someone tossed together a super clean body that when assembled looks exactly like a 2bbl Rochester, perfect if one wants to keep it stock "looking". Take the top off & where the floats should be is a solid billet of metal and two TPI injectors, clean & stealthy as can be. just have to be creative in how you route the wiring.
Have seen them in the mags recently, if I can dig up the company website I'll post the link.

Thanks John for your reply to BO185. His responce to Freq2002 was the harshest thing I've ever come across on the Stovebolt page (even if as BO185 says, it could've been much worse). That is precisely why I love this forum and spend many hours reading it. It is (usually) always clean, encouraging, and always infomative. I look at other forums (I too have a VW Beetle)and am shocked at how people talk to each other, knock them and their ideas etc. Once again, thanks for the awesome work that all the moderators of this sight do. Kudos one and all.