smallport to bigport swap

[72chevyman]

Hi I am new to the forum but i have been searching around for quite some time now. My girlfriend is the proud owner of a 1990 toyota corolla gt-s smallport 4age 5speed. The current motor spun a bearing back in december and we had lots of fun getting a new motor.... first motor we received was a 4afe . then they wanted to replace that motor which had "83k" with one with 140k for the same price. we then purchased one from a junkyard database my father recommended (he has 30 years in parts sales so i trust advise) and received a bigport 4age from an 87 fx16 corolla. I then called them and asked where the intake manifold was because i knew that the intake runners were different sizes. They assured me that aside from that it would work. Spent a lot of time cleanin her up... new paint cam seals gaskets (minus the headgasket) water pump timing belt and tensioner kit. I have been searching around on this swap and have struck out. I have most of the bigport accessories but half of it was never sent so i assumed that everything else would swap over. Just wanted to hear from some people with experience to see what i really got myself into. guess what im wondering is will it run on smallport computer? i read that the distributor will drop in, what about injectors and fuel rail? any ideas of how to mount the knock sensor? anyone sell egr block off plate? thats all i can think of. any help is greatly appreciated. im in a bit of a crunch for time at this point because she goes back to college monday and i start my new job and we only have one daily driver at this point. Basically this motor will hopefully just be temporary. we have plans to build a 4agte out of the other one. sorry for rambling on. just have a lot of unanswered questions and im trying to explain the task at hand as best i can. thanks in advance, Bobby

[gotzoom?]

Man, bummer on the engine problems. Depending on how much more work you're willing to do, I guess I have more bad news for you.

The large port engine has a feature called TVIS that is a set of butterflies that block off one of the two runners that lead to each intake port in order to increase low end torque. At higher rpms, the butterfies open and you use both runners. Guess what controls that. It's the ECU. Since the ECU controls it, that means you also need the wiring to go between the ECU and the TVIS control module. I suppose you could run without an ecu controlled TVIS, but the butterflies are normally closed, so you'd need to jig something up to force them to stay open, or just remove them from the TVIS plate entirely. You'll have much less lowend torque without it functioning, though. 4A blocks are 4A blocks, so you do have a threaded hole for the knock sensor to mount to in the same location as the smallport. The oil pressure sending unit and other stuff that attaches to the block will all be there. Basically, you need to run all fwd accessories or all rwd accessories in order to get things to line up properly. It's super easy to make an egr block off plate. Just get a 1" wide strip of 1/8" aluminum, cut off a 2" piece and drill two holes in it to they align with the bolt holes on the manifold. Put a thin layer of RTV on all edges and bolt it in place. Your fwd injectors will physically connect to the head and fuel rail, and as long as you use your existing ecu, no other mods are required. If you end up using a largeport ecu, you'll run rich with those injectors. I hope that helps.

As an aside, you can probably get a smallport head for under $150.

[yoshimitsuspeed]

The bung for the knock sensor should be there but on older blocks they weren't drilled and tapped. You can drill and tap the bung making sure not to go too deep, or you can try to find another unused hole in a similar location. I am running the sensor to my ECU in the stock location and another in a tapped hole right next to it for my knock light. This is on a BT block though so I can't be sure either are tapped on a LP block. Even if it's just close or even bolted to the upper half of the block just about any where I would say it's OK on this build. You are running a lower compression motor that will be very unlikely to knock.
I would just safety wire the TVIS open. I did that on my turbo running on the GZE ECU for years. You can gut it or do other things but it sounds like quick and dirty is the way to go for you right now.
Make sure you run the SP injectors or you will end up running lean. You will need the LP fuel rail though.

[ga_goosh]

anyone sell egr block off plate?

KSD engineering sells egr block off plates http://www.ksdengineering.com/KSDEngineering-EGR-Blockoff-Plate-w-Gasket-_p_59.html

also i have a complete uncut ae92 large port wiring harness if your interested I also have a FWD large port complete intake manifold and tvis plate too.

[oldeskewltoy]

My girlfriend is the proud owner of a 1990 toyota corolla gt-s smallport 4age 5speed.

The current motor spun a bearing back in december

received a bigport 4age from an 87 fx16 corolla.

I then called them and asked where the intake manifold was because i knew that the intake runners were different sizes. They assured me that aside from that it would work.

I have been searching around on this swap and have struck out. I have most of the bigport accessories but half of it was never sent so i assumed that everything else would swap over. Just wanted to hear from some people with experience to see what i really got myself into.

guess what im wondering is will it run on smallport computer? i read that the distributor will drop in, what about injectors and fuel rail?

any ideas of how to mount the knock sensor?

It likely will run, but not well. The smallport electronics have no provision for operating TVIS. Also, you will need an intake manifold, with a gutted TVIS. Fuel rails are NOT interchangable - good news here is your smallport rail is gold compared to a largeport rail

concerning cooling plumbing, I'd make sure you use as much of her sensors as you can... I'm sure her computer will operate the largeport better using all the sensors it is familiar with.

Fianlly, you will be down on power... not a lot, but a bit... largeport is about 8 to 10 hp less then a smallport

[Crownvicman289]

Some guys on the MR2 forums were sticking smallport intakes on bigport heads. Not ideal, but I do believe it'll work. Your biggest hurdle is the knock sensor. Is the original smallport head junk? If not, you could slap that on a newer 4AFE bottom end as some had knock sensor provisions.

[yoshimitsuspeed]

Some guys on the MR2 forums were sticking smallport intakes on bigport heads.

It will not work as a direct bolt on. The couple people who I saw do it used JBweld to fill in the gaps on the flange. Too ghetto for my taste. With the intake flanges I am selling now one could weld one of those onto a SP mani and have it bolt onto the LP. Not worth that kind of effort for the temp fix this guy wants though. Just slap the TVIS mani on the LP head safety wire the TVIS open and call it a day.
I do agree with you though. If the SP head is still good slap it on the healthy bottom end. Assuming it's worth the time and effort to swap heads.