Over the next 8 months I plan on building a 406 for my 92 GTA to install about this time next year. There are some requirements though. Mainly it needs to be CA Smog Legal.

Here is the list I have compiled so far:

Engine:

1. 400 High-Nickel 4-Bolt Block bored .030 (already have)
2. Ported Aluminum L98 Heads w/2" Intake and 1.56" Exhuast Valves
3. JE 10.2:1 Compression Pistons
4. Forged Eagle Crankshaft
5. Complete ARP Bolt Kit
6. Accel TPI Intake Manifold/SLP TPI Intake Runners/Ported Factory TPI Plenum (already have)
(Possible LT4 Intake & Fuel Rails, totally worked over but Definantly an SLP T-Ram if I can find one just to match my 'Hawk)
7. 28# or 30# Accel Fuel Injectors
8. 58mm Throttle Body w/Air Foil
9. LT4 "Hot" Cam w/1.6 Rockers
10. Custom PROM (done by me, I'm learning right now on my 305)

Exhaust:

1. SLP 1 5/8 Tri-Y Headers w/3" High-Flow Cat and 3" SLP Cat-Back Exhaust System & ZR1 Heated o2 Sensor (already have)

I figure I'll go with the heads I listed above because they are cheap, easily available, and smog legal. Same for the cam I listed. Does this all sound like it would work well? All suggestions welcomed. I am on a tight budget but as far as internals I will only use the best of the best. Also, what are the best rods to use?

Thanks!

 

Even though the Super Ram is a PITA to work on...I would consider going with that over a regular (although modified) TPI setup.

 

Technically speaking - that 400 could never be considered smog legal in CA according to the letter of the law. However, nobody will know it's a 400 so you can get away with it because all the emissions stuff will check out

Personally, I would go with SLP 1-3/4" headers instead of the 1-5/8". The 400s can flow lot of air. I would also go with AFR heads instead of the L98 castings (unless you know somebody who can work wonders with the L98s like LPE). Heads and Cam are where you make your power. Since you have to run a weak cam for fear of the CA emissions police coming down on you then you should run the best head you can afford. Why waste money on L98 castings? Save your money and buy a good part that can grow with you. The only choice is AFR since they have a CARB certified head. You'll need as much airflow as you can get given that you are going to put these on a 400. The LT4 manifold would never pass CA emissions inspection (it wouldn't bolt up to stock SBC heads in terms of port alignment anyhow). I'd go with a ported SuperRam setup due to it having CARB approval. The cam is far from emissions legal but you should be able to get away with it since 350s running that cam can pass IM240 emissions AOK.

Tim

 

First off...MAKE SURE and have the 4-bolt 400 block magged to check for cracks. The 4-bolt 400's are actually prone to stress cracks on the bottom end since there is so little "meat" left around the mains because of them having 4-bolt mains.

I'll agree with Traxion on the head choice. Why spend so much time and $$$ on the rest of the engine, to leave the heads as the DEFINITE weak link. Sure Lingenfelter has worked wonders with the alum L98 castings, but that's after ALOT of porting and flowbench work.

Personally, for the $$$, I'd go with a set of Pro Action Lightning Iron heads.....straight plug, 200cc intake runners, and 72cc chambers to help the 400 live on pump gas. Their out of the box numbers are right with the AFR's for ALOT less $$$$..under $800 for the heads I mentioned. Or go alum for another few hundred $$$.

I mean you're spending $$$ on quality crank ( forged, which is not a necessity on a street engine naturally aspirated ) and pistons, so why leave the rest of the combo hurting because of the heads.

As for the headers...I've seen some flywheel dyno tests, and on the average the bigger cubes small blocks ( 377, 383, 406 etc ) gained a few ( like 6-10 HP ) on the upper end and dropped a few ft/lbs of torque. Unless you can sell your current headers, and get these, I PERSONALLY don't think the bigger primary tube headers are worth the $$$.......I'd DEFINITELY upgrade the heads before I worried about the headers you have being the weak point.

As for induction, CA smog narrows your choices greatly. So keeping that in mind, if it were me , I'd go with a complete SuperRam setup ( proven BIG torque producer in the mid range where the 400 will LOVE it......) OR at least either port the crap out of the SLP runners or go with the large tube AS&M runners..but then with the $$$$ you're talking about, the SuperRam wins that hands down.

As for the heads being smog legal, that's the least of your worries, as the 400 isn't smog legal AT ALL In a third gen.....so if you're positive they won't run the casting #'s, then go for it......

BUT.....

If you don't want to take that chance, why not nab a 1 piece RMS roller 350 short block and build a 383? From all OUTWARD appearance, and as far as visual inspection for smog, it's only a 350, and that's legal for your car.

And a properly built 383 won't give up much at all to the 400, as you'll have MORE Than enough low end torque to turn the tires into molten blobs as it is.



HTH, and again, just my opinion.

 

You guys forgot the important part of his post, 'budget', like the one we are all on. That's why the L98 heads over the AFR's and using what he's got.

You don't need the forged crank, so you can save a little there.

With the 400, hot cam, and intake, you will be limited to 4000-4500 rpm. Don't buy the 58mm TB and save some money there, until a deal comes up you can't pass by.

Nothing wrong with using what you've got until you can trade up for better stuff.

 

Technically the block I have an original 2 bolt main but it has splayed main caps.

I want to get the best forged parts I can for the bottom end so in the future I can upgrade the top end and not have to worry about the end, I want it basically bullet proof.

I'm going to use the 1 5/8 Tri-Y's because that what I already have and I can simply bolt it on. I have a 3" exhaust from the collector back with a high flow cat and since I can't afford really good heads right now or a use a wild cam the 1 5/8 Tri-Y's should work just fine.

There is no way I can afford AFR's and I'm already going to be putting the Aluminum L98 heads I mentioned above on my current engine so that again would save me allot of $$ being able to use them on the 406. I know it will be pretty choked but the CA emissions are won't allow too much more anyway.

After I have the 406 in and tunned correctly I'll have it smogged and see how border line I am and how well tweaked I can get the tunning and then I will KNOW how much room I have to play with and based on that decide what heads and cam to eventually upgrade to.

Now, isn't it better to have an internally balanced 406 than and externally one? To build an internally balanced one all I need to do is have the entire reciprocating mass fully balanced and use a neutral flywheel and harmonic balancer right?

I'll more than likely use the same Accel TPI Intake Manifold/SLP TPI Intake Runners/Ported Factory TPI Plenum that I have on my current engine to start with so does the LT4 "Hot" cam sound like a good choice considering that and the heads I will be using?

 

Why go to the extra expense and hassle of a 400 cubic inch engine only to run the same times as a 350 cubic inch engine? The parts you have chosen are a poor mismatch for an engine of that size. Basically you'll have a slug.

With the 58cc chambers of those heads, you'll need pistons with a huge dish in them to get your compression ratio down to a reasonable level. That'll kill your combustion and flame rate for sure. Not to mention the 400 ci engine will want to draw lots of air, but the crappy long runner TPI intake and small runner size of the heads will really kill the power potential.

Trade the 400 block to someone who can really use it, and get a roller 350 block plus cash and come out ahead.

 

I'd keep the 400 block and use a scat steel crank, 5140 rods, trw pistons, and use what you've got. The heads, cam, and intake can all be swapped out later when the money gets better, do the basic short block first.

 

Since I first ran my 406 with stock 1970 heads and a stock TPI system (with an edelcrock baseplate to fit older style heads), I can tell you that it won't be so bad...granted, when I did that, I had (have) 1 5/8" headers and a free flowing exhaust plus a custom chip...but the torque was great.

I agree with 89gta383...make sure that the shortblock is done right (with forged pistons) and just so you know...it is externally balanced stock. I would have the rotating assembly balanced due to the aftermarket rods and crank.

 

88TPI406GTA,
I agree also, even when I had a completely stock tpi system on mine it would totally eat up most modded 350s. Is the cam you are running the comp cams 12-404-4? If so how does it idle with the 1.6 rockers as I am considering upgrading to them but want to maintain a good Idle.


92GTA
I think you are doing the right thing! invest in the strong bottom end first, as for the heads and intake, you can always swap them out at a later time if you are unhappy, (which I doubt you will be)!
Good luck,
Tony