I have an 88 GTA with the 305 MAF TPI and 700R4 trans. I thought about modifying this engine, and decided against it for now since it has 130,000 on it and it's a 305, and I plan to have a 400 in the future.

Before you flame me, I KNOW that what I am proposing will not make maximum power. That's not the question. The question is, is it possible, and what do I have to change?

I want to put a 400 in my GTA and have it appear like the stock 305 TPI engine on the outside, until I have the money to modify it like I'd like to. I've searched through the posts for questions like this, and have found a few, but none had all the info I'm looking for.

I'd like to start by putting a 400 in my car which has only had the short-block rebuilt, with a nodular crank, 6-inch rods and the necessary forged or hypereutectic pistons. I don't want to have to mess with the block again after I put it in the car. My goal is to one day have a 400-450 hp car, fuel-injected and N/A. It probably will have the miniram intake put on it at that time.

Can I use my MAF set-up on the 400 at first? I'll have a new chip burned if it's cheaper than converting to SD.

Can I use my stock injectors if I'm not making more than 300-330 horsepower? I'll use larger ones if necessary.

Will the stock 400 heads accept the serpentine accessory setup that my 305 has on it now, or will I have to buy aftermarket heads to use the serpentine stuff? I'd like to have AFR 190's at some point, but not now.

Will I need to buy an aftermarket intake base, since some of the holes won't line up right, or can I modify the stock one?

As far as the cam goes, I plan on a mild one for now. I'll switch that for a more radical cam when I start changing things on the top end of the engine. What would be a good cam for this combination? I'm open to suggestions.

About the flexplate - will I have to change my starter to switch to a flexplate with a different number of teeth?

I assume I'll need a different damper as well?

I'll even keep the stock exhaust for now, if I can.

What am I forgetting here? Feel free to shoot holes in it, but don't just say that it won't work and then not give me any reasonable explanation.

Has anyone tried to do this before, or know personally someone who did? What was the result? I'm not saying that I am definitely going to do this, but humor me, if for the sake of discussion if for no other reason.

Joe

 

I don't have all the answers for you on this but man its getting hard to find 400's. With a 383 you would not have to jack with the steam holes,you could use the same rods you found in a core 350 and the pistons would be a little cheaper.I'm not trying to talk you out of a 400 and I would love to have one myself but they are becoming a semi rare find.with a mild cam your MAF and injectors with the proper fuel pressure will be fine.Enlongate the center holes and use angle spacers for the intake base.I THINK the accesory holes on the heads are the same, you will need a new 2 piece seal flexplate and 400 harmonic balancer.I would also have the rotating assembly balanced.

 

A 400 is externally the same as any other small block. The 400 heads should accept the 305 belt drive setup with no problems. The flex plate needs to be on designed for the 400 but with the same tooth count as your 305 so you can use your starter. The stock fuel injectors might work with the 400 as long as your power levels are not too high, if not you will have to change to larger injectors. The intake manifold will have to be modified by grinding on the center bolt holes for use on the 400 heads.

There is no reason that I can think of that would stop you from using a 400 in your car.

 

Hey, thanks for the quick replies! I looked through my Summit and Jeg's catalogs and couldn't come up with any flexplates that had 153 teeth and were externally balanced for the 400. Am I right in my understanding that our cars use the 153-tooth and the 400 comes with 168? Could I use a regular 400 flexplate and one of the starters that says it works with 153 and 168-tooth flexplates? Or does the 400 block have different starter mounting holes and so forth?

So you all think I could use my stock MAF setup? That's great!

Oh, and around here we don't have a shortage of 400's (yet). There were two advertised in the paper this week, and I know of a third by word of mouth.

Joe

 

Speaking from experience.... After everything I have spent on my 400, I would have been better off starting out with a 383 crate motor.

To answer as many questions as possible:

- nodular crank, 6" rods and forged pistons are expensive. I used the stock crank, 5.7" rods and hyper pistons.

- maf setup works, however, you WILL need new injectors. If you pump up your fuel pressure enough to feed a 400 with stock 19lb injectors, your fuel pump wont last long.

- you WILL need to burn a chip. You may get it to start with a 305 chip, but it will not run well.

- stock 400 heads SUCK. and No, they will not accept a serpentine setup without drilling some holes. I would not even bother using them (even temporarily). Wait till you can get some better ones before installing the 400. I found some used trick flow heads that had been used on a fellow racer's 400 and already had the steam holes drilled. I had them ported and polished before installing them. The heads will be your most expensive single piece of the puzzle, and rightly so, since that is where all your power will be made.

- Although you can use your stock base (after you port, port and more port), an aftermarket base & runners would be much better. I went with an edelbrock base and ported SLP runners and plenum.

- as far as a cam goes... A relatively wild 350 cam will be mild in a 400. I went middle of the road, and didnt come out too bad. I had to pass emissions, and while it would not pass without a CAT (mine was hollow), it did as soon as I put a new one on. I went with a Comp Cams retro roller cam (needs cam button and good timing chain cover), and Comp retro hydraulic roller rockers. Cam specs are: #12423-8 Comp Cams 276/282 (224/230 @ .050), 502/510, 110 LSA, Installed on 107* centerline.

- 400 flexplate is 168 tooth. Get yourself one of the new GM high torque mini starters, or go aftermarket.

- 400's have an 8" damper that is balanced differently..so yes, you will need one.

- stock exhaust you can use...but if you are going through all the trouble, why not put headers on? Fortunately, I already had my Edelbrock TES 1 5/8" headers...but if I had the money to switch...I would get some SLP 1 3/4".

Your stock cooling system will probably not cool the 400. Aftermarket waterpump (I used edelbrock victor series), and an oil/tranny cooler may be the way to go. I have an aftermarket heavy duty radiator, that is not doing the job. I am installing an oil cooler now, and if it does not bring the temps down where I want them, I will be investing in a Griffin radiator.

All of this together = more money spent than getting a crate motor. However, I could not seem to save up enough money for the crate motor all at once, so I did my 400 piece by piece over 2 years until I had it built.

More details about my engine build can be found on my website below. Hope this helps make up your mind.

 

Mike, this is exactly the sort of info I was looking for! Thanks a lot! I went to your website and spent some time checking out your mods; looks like you spent a lot of time beefing up the whole car. Most people don't do that, so I'm impressed.

If you had to do it all over again, what changes would you make?

Is the ported TPI setup you have flowing enough air, or is the engine choking?

What RPM range gives you your strongest power? At what RPM is the engine pretty much done?

Also, why did you delete the cold start injector? I'm not that familiar with GM products yet; were you just modernizing to the highest level you could, or are there problems with the cold start injector design?

For laughs, what kind of fuel mileage do you get on a trip? Not that I'm really concerned about it; just curious.

Are you using the NOS system that you had on your 305 with the 406, or did you remove it?

Thanks again,

Joe

 

Thanks for checking out my website.

If I had it to do again...I would have tried to save up for a ramjet 502. TPI is ok, but you just dont get the revs out of it.

I built this motor to run mid 12's, and it should...however I have a few things holding me back. The biggest restriction to lower ET's is my torque converter. I Need at least a 2300 stall converter. I am currently running a stock corvette lockup converter, and I cant launch at anything higher than 1100 rpm or I start creeping through the lights. I higher stall will allow me to launch at a higher rpm, and result in lower ET. Another improvement I can (and probably will when I have time) make is to fully siamese my SLP runners. I have gone about 2 inches in, and ported the heck out of the plenum, but I can take much more material out. That will move my HP range up a bit, and let me rev a little higher.

I have not dynoed the engine yet...but that is coming soon. Engine pulls strong all the way up to 5000, but I still shift at 4800 for best results. It will rev higher, but power levels off after 5000.

Cold start injector was deleted for several reasons.
1) 89 MAF TPI does not have a cold start injecter. EPROM programming uses a cold start enrichment program instead.
2) Cold start injector is just one more thing to go bad
3) removal of the CSI and it's associated wiring and plumbing cleans up the engine compartment just that much more.
4) I used the CSI fuel rail fitting to plumb my fuel pressure gauge.

I have not taken any trips yet, and I have yet to run a full tank of gas through this thing without racing it (its just too much fun). So I really cant give you an accurate estimate of mileage other than what my heavy foot has been getting (about 13mpg city). I am sure as I burn more chips, and dial my combination more, my mileage will increase.

The NOS system I was using did not go back in. I was just using it for kicks on the 305. You can not consistently bracket race NOS without some kind of computer control, and it is just too expensive to run all the time. I have not felt the need to put it on the 406 (yet). 150 hp shot of NOS would probably get me kicked me off the track, because I am sure it would put me into the 11's and I dont have a roll cage.

 

Mike, how's that cam in your 406? Enough to run power brakes at idle?

I was thinking of using one that was very similar to this in my 400 that I'm building, and I haven't seen any opinions on that cam in a 400 yet.

 

Vacuum is kind of low at idle, but it still works the power brakes. Where I have found it not to be sufficient, is operating the AFPR. At a low idle > 750rpm, vacuum is not high enough to close down the fuel pressure. So at idle, my fuel pressure is around 40....then when the revs come up a bit, the fuel pressure drops to 37, then starts to climb back up like normal as you get moving.

Just makes tuning a bit harder in the low throttle/idle range.

 

I BUILT WHAT YOU THINK YOU WANT TO START WITH. I DID PUT ON NEW HEADS, A MILD COMP CAM (HYDRAULIC), ROLLER TIPED ROCKERS, 5.7 RODS, SPEED PRO PISTONS, UPGRADED INJECTORS TO SVO 24# AT STOCK PRESSURE, AND FINISHED WITH SLP 1 3/4 HEADERS THRU A HI FLOW CAT INTO A DYNO MAX SUPER TURBO. I KEPT THE STOCK TPI SETUP, BUT CHOSE ALL MY PARTS BASED ON THE RPM RANGE I WANTED, AND THE AMOUNT OF AIR FLOW I NEEDED TO SUPPORT IT. I STILL HAVE THE STOCK CHIP (RUNNING A LITTLE RICH), AND GET JUST OVER 20 MPH HIWAY ON 300-400 MILE TRIPS ON THE FREEWAY. I AM USING THE STOCK TORQUE CONVERTER THRU A 700R4 WITH A SHIFT KIT IN IT. IT DOES JUST FINE FOR WHAT I WANT. I DON'T RACE, JUST A FUN STREET CAR. RELIABILITY IS GOOD, I DON'T POUND IT HARD OFF THE START AND HAVE ONLY BROKEN ONE TRANNY MOUNT IN THE FIRST 11 MONTHS. IF YOU THINK AHEAD, YOU CAN GET YOUR RODS AND PISTONS RIGHT, AND CHANGE THE HEADS AND STUFF LATER. BUT AS SOON AS YOU START TO PUSH THE RPM RANGE UP, THE BUCKS GO UP TOO. CHOSE YOU HEADS WISELY SO YOU DON'T HAVE TO BUY 2 PAIR. YOU COULD USE THE STOCK TPI TO START WITH, RUN A LOWER RPM RANGE, AND PUT ON THE BETTER INTAKE LATER AND PUSH THAT RPM AND POWER UP. THE HARDEST PART WAS GETTING A STARTER TO FIT. I LET THE SHOP SORT THAT OUT. I AM PRETTY SURE WE USED A STOCK 400 STARTER, AND JUST CHANGED THE FLEX PLATE TO ONE THAT HAD A DUAL BOLT PATTER SO THE 700R4 TORQUE CONVERTER WOULD BOLT UP.

 

Stock 400 flexplate accepts the 700r4 converter (just have to use the 2nd set of bolt holes).

Of course.... If you are just building a daily driver (like the POST ABOVE), that is a different ball of wax. Mine was built to race and street. If you are going to race, then disregard the POST ABOVE WITH THE CAPS LOCKS ON.