I was wondering if anyone here has swapped a 400 in place of a 305 without going nuts on mods. Lets just say mild cam, no headers, some head work and a cat back system. Anyone know of what kind of power you might get from such a swap? Likely the 86 computer would need a new chip? Injectors ok or not? Thanks. I have access to a 400 if I want it, and its making me wonder a bit....

 

A 400 would need larger injectors, or at least a fuel pressure bump to keep from going lean with the stock injector size. The stock chip might run it depending on how radical everything is, but custom burn is the way to go to maximize your combination. I'm looking at a 400 for the future myself...

 

Actually...you would need at least 22 lb/hr injectors and a chip burnt to accomodate that change from your current 19 lb/hr. The key is to maximize the torque potential that the 400 is famous for. This would mean freeing up the exhaust before touching the heads...

If I understand you right, this would be a budget deal, so headers and a free flowing exhaust will help you not only with torque, but also MPG increase.

The stock TPI system would be enough of a limitation that your higher rpms (4500+) would be limited...no way around that.

 

I'm thinking that a TPI system is going to have serious issues with delivering the 30+% more air flow that the 400-inch will want. A stock TPI barely moves enough air to satisfy a 305 at 5,200 RPM. If you want the 400 to do anything but choke, you might want to consider a different path. The 400 will already make plenty of torque, so a torque-friendly system like the TPI is not only a theoretical overkill, but will probably not deliver the air required to make that torque and will be a complete waste of higher RPM potential of the larger engine.

Even the "best" aftermarket TPI parts aren't going to satisfy a 400-ish engine without boost.

I'm thinking the LT1 intake would be a much better starting point, and it can easily be ported to feed the big mouse.

 

Price wise...I thought that the Lt1 intake and the HSR were about equal with the customization required...

and yes, either would be good choices over the stock setup

 

On one of my 85s, I have done exactly what you are talking about and lets just say for the money spent on this particular experiment, there was almost NO way to make your car faster for less money. I had, (still have) what was a beautiful std bore/crank 400 shortblock that really needed nothing laying around. I rebuilt the bottom end with Speed Pro plasma moly rings, all new bearings, oil pump, Summit double true roller timing chain and a summit 214in. 224ex @.050 camshaft /lifter kit. part# SUM-k1103,(I believe). Since I didnt want this to have low compression, I put on a set of 86 305 TPI 416 casting heads, (after I ported the **** out of them and drilled the steam holes). Next, (after slotting the heads to accept them) I added 1.6 Elgin stamped steel intake rockers on the intake side and left 1.5 rockers on the exhaust to try to make up for the small 1.84 valves in the heads. That completed the longblock!
I then used a fully ported stock 305 TPI intake and injectors, added only an air foil and an adjustable fuel pressure regulator, the final setting I used was 50 PSI. I already had K&N filters, Gutted MAF and air box, I used the stock exhaust manifolds, Y-Pipe and my existing dynomax cat back.
This car Idled and drove Excellent with the stock 86 Computer and chip and flew through a very strict southern California emissions test.
As for how fast it was, Lets start out by first saying which some of the above posters may not be considering. The 86 is what seems to be the slowest TPI model year that ever came from the factory and leaves very much to be desired. I dont know what trans and rear you might have, but I used only a shift kitted 700R4 with a 3.23 strong posi rear. If you make these upgrades alone to your car it will feel EXTREMELY fast. This car pulled harder from idle to 4500 RPMs than I ever imagined, It was fast enough for my brother to not even consider trying to race me in his 91 Vette 6 speed, and he is usually up for anything, it makes my 88 GTA 350 seem like it is very slow, and finally It was fast enough for me deceide that I needed a whole new aftermarket performance suspension and brake set up to match its power.
I had put about 2300 miles on this particular set up and never had a any problems, and I drive my cars pretty to very hard. The only thing that I did not like is that it only got 10 miles per gallon.
Since I am never satified with my cars and am forever playing around with different combinations in them, this engine is out of the car again for some major modifications I am doing to it. (Aluminum 202 heads, bigger comp cam, complete Superram set up, bigger injectors, SLP 1 3/4 headers, bigger cat back, suspension mods and so on). I cant wait to see what it will be like pulling hard to over 4500 RPMS and having some serious handling to match it.
On any vehicle I build in the future for some serious power I will first get rid of the 305 or 350 and start with a 400 block reguardless of what I have to put in or on top of it.
Keep in mind, once the short block is complete you can always add the other desired bolt ons at a later time.
Good luck!

 

85,

1.84" valves over a 400? As soon as you solve that restriction, I'm thinking that you'll find the TPI pretty limiting. It sounds like you've got the basis for a real monster, and the new heads are really going to wake it up. Strictly based on the runner diameter of even AS&M runners, the 400 is going to be choked, never mind the length of th erunners and plenum restrictions. I think a $200 conversion of an LT1 intake would really be worth the investment.

 

Vader,
The combination that I listed above, there is no doubt in my mind that the 400 was choked by the heads, intake and stock exhaust, as most people above said it would be. This set up was very fast for what it was and I think it would have really surprised alot of people. I knew all along that I would be pulling it apart and throwing a new top end and exhaust on it. Like mentioned above it was really just an experiment. I think the engine was working pretty hard to take in air and get rid of it and that is what made the gas mileage horrible. After all my 454 Suburban 4x4 gets better than 10 mpg depending on how I drive it. I had also bought an LT1 intake as you mentioned and was going to experiment with that, but I had just went ahead and bought the Superram set up and will install it instead because that car is due for another smog test in November and I honestly dont want to deal with a Superram swap while the engine is in the car again.
The only real point I try to make to people that are thinking of changing out a 305, rebuilding a 350 or considering making theirs a 383, is if they are looking to make big power improvements to their cars, it seems that you cant go wrong by starting with more cubes first because you can always upgrade the heads, intake and exhaust (if need be) at a later time. Since all of these things, (unless you have the luxury of converting to a stealthram or LT1 intake an non emission headers), and have not to worry about smog and legal issues. End up being alot more money than the Shortblock itself. I know I just dumped another $2500.00+ for all the engine upgrades I had mentioned in my post above.
But of course, this is just my opinion!

 

talk to AZIROC on the boards,his names chris,hes gotta 406 in his 86 iroc,he runs around 10's with the nitrous. hes a real cool guy,if u got aim,him aim name is falcon978, he knows a lil about what he got done to his car.