400 small block- ideas, advice?

Hey I've got a 400 sbc that I want to use. I haven't done a compression test on the motor, but it ran without a problem after I rebuilt the carb and updated with a new HEI distributor.

problem is- it's a '73-'74 impala/Monte Carlo motor with a whopping 150 HP!!!

Is there anything I can do with this?- basically just bolt-ons.
I think that the compression ratio on this bad boy is like 8:0 (or possibly a dreaded- 7.5:1)

I've considered adding a dual plane intake and a small cfm spread bore 4 bbl carb. (I'm still running the factory Rochester "2-Jet").....

 

not that your wanting to get into a bunch of money , but ... a nice 5.7 rod and new pistons , throw on a pair of vortec heads and a small torquey cam ...you'd have a ball.... if its running and not causing any issues ....drive it....heck a pair of vortec heads and a intake / carb swap would help it a ton....throw in the cam while your at it ....and it'd probably be a tire fryer..... brandon

 

You would see a huge difference by just changing out the cam, intake and carb. 73-74 was the beginning of the smog years and those three things are the biggest problems with power in those years.

 

Second that, if you don't want to spend a lot on it a good torque cam, 4 Bbl. intake and dual exhaust will really wake one up and if you decide to pop the heads off to freshen them up you can slip thinner head gaskets on it to bring the compression up. You can also go a little bigger on the cam than you would a 350 and a little tighter on the LSA, the old Comp Cams 268HE is a nice daily driver cam in a 400.

 

Nice--So, how can I understand how I'm affecting the compression ratio?
Just a thinner gasket will do? I would go 9.5:1 if I could.

......And aren't the 400's sensitive to milling heads/head gasket issues because of the steam p***ages??

 

Brandon is on the money! Remember the 150HP rating was "net" (hp @ the wheels with all accessories runing). The vortec heads are 64cc which will pick the compression up to 9.5/9.75:1. Use a Comp XE268 cam, the extra overlap will allow pumpgas no problem and the combustion chamber on the vortec's
only requires 32'-34' total timing. Use a performer or performer rpm and the
Q-jet (they are 750-800cfm depending on the one you have). This combo will make 400-450hp (@ the crankshaft) and 450-475ft lbs. depending on how sound the short block is. If you just change the cam us XE256 cam and headers and your looking @ 350hp and every bit of 400ft lbs. If you want the Q-jet or the HEI done send it to RPM (818)767-8839

 

one word NITROUS!!!!!!!!!!!

 

Some of the 70's heads don't have a lot of material and are prone to cracking, as long as you use 400 head gaskets, a thinner gasket would not be a problem. You'll need to verify your compression height, dish volume, combustion chamber volume, etc. to determine exactly where you're compresssion would be for different gasket thicknesses

If you want to spend a few more bucks it is hard to beat a pair of Vortecs, definitely the best bang for the buck. They will need to have the steam holes drilled in them but it's no big deal. The intake manifolds for them are a bit pricey but are beginning to show up on the used market.

 

I've got a 400 SBC that was built 12 years ago...made 500HP on the dyno, and runs on pump gas. Trick Flow heads, nice rump-rump cam, single plane with 750 Holley. MSD ignition. To this day still runs very strong...I've put a lot of miles on it, and can hardly regret the initial build. Never raced.
Good luck!

 

Thanks to everyone that chimed in with their expertise on this!

Looks like I've got some figurin' to do

 

I've looked, but never found a thin head gasket for a 400. If anyone has a part number, it would be appreciated.

 

I'm running a 400 in my Tbucket with just a set of blockhugger headers 7 3 dueces & it runs great & its fast, try it before you do anything to it,maybe you can just get away with a 4bbl & headers.
jimV

 

Crazy. It looks like the XE268 tops out at 5800- so figure knock it down 3-400 RPM for the larger 400 (??)- Wow. All that power under 5500 RPM. That is damn tempting..

 

I have a 400 that was rebuilt and I used a flat top with 4 valve reliefs. try to stay about 10 to 1 compression. Also remember if you install any other small block head you need the steam holes drilled. If not engine will run hot. I also have a set of trickflow heads with TPI fuel injection. I ran a best et of 13.3 with a 2.41 gear ratio. Have since taken car apart and did not put engine back in the vehicle. hope this helps.

 

I belive there is an edelbrock manifold that correct the cooling problems these motors are supposed to have toward the rear of the heads. I remember reading about this when I was looking to put a 400 into a chevette.

I seem to also remember reading that people believe the 4 bolt blocks are weaker than the 2 bolt ones. The 4 bolt block is supposed to also weigh about 15 lbs less than a 2 bolt block. I'm not sure how much of this stuff is true, but this is what I read.

 

ive got a 76 400 2 bolt in my 63 c-10 backed by a borg-warner 4 speed of unknown origin. I had a set of 67 327 heads decked and drilled then i put in a mild cam, a weiand stealth intake, ****** compe***ion headers, and a holley 600 cfm carb. the motors never been dynoed and i havent calculated the compression, but it smokes tires going into all 4 gears and leaves most of the ricers in the dust.

 

I have a short rod 400 built up with brodix head hydr. roller cam. My experience is that with the short stock rods and inherently bad stroke/rod ratio. The 400 doesnt really make alot of power upstairs, even with a 215cc head. The short rod 400 really shines on the low to midrange. THICK TORQUE! I whole heartly agree with the comp 268 and a nice dual plane like the air gap RPM. That new endurashine coating is the bomb! Slap in a 268, Top her off with the RPM and a Holley 4779 mech. 750 and let her EAT! If you are gonna pull the heads you might aswell rebuild the whole thing and that kinda kills the budget and the point, cheap power... thats how i see it.

 

OK-- what the heck does the relationship of the rod length to the stroke length have to do with making power??
just asking-- I would ***ume that it would have more to do with durability, but either way I don't understand what a longer rod does in a 400 sb except increase the CR(??) I don't get it.

 

Dont worry about drilling steam holes,plug the water pump byp*** hole in front p***enger side of block and youll be fine.I plug the steam holes in the block on all the 400's i get and plug the byp*** hole on the deck because it is located dangerously close to the bore, but in your situation it would be benificial to plug it under the pump in the block.Run good oil those 5.5 rods are tough on bores.

 

i built a 400 small block back in the early 80's it came out of a 73 impala, and had a 2 barrel when i got it.
i basically did a stock re-build on the bottom end, used the stock heads, a .488 lift, 292 duration cam, performer intake, 600 holley, small tube headers, and an hei.
i put it in a 71 chevelle, with a turbo 350 trans, stock converter and a shift kit. the rearend was a 12 bolt, and it had 3:08 gears in it. i bolted on a 125 h.p. nitrous powershot, and that was good for low 13.0 second p***es in the 1/4 mile on street tires with full exhaust. off the bottle the car would run mid-low 14's, which aint too shabby for a pretty much stock daily driver.

 

Dad had a suburban with a 400sbc. He put the engine together with 1.72 truck heads. What a pig. I built up a set of 441 open chamber heads with 2.02 and 1.6 valves, angle milled .060 combined with anouther .020 flat (comes out to 67cc), and put 1.6 rockers on the rv cam. It ran great. The 400 loves big heads. Look at the power and torque 396's put out back in the late 1960's. Heads and cam.... Flat top's with stock heads work out great.

For a mild performance engine stick with the stock 400 rods. If you go with longer rods you will need to buy special pistons, and balance the rotating ***embly. There are better places to stick the money that will make more power, like heads. (and you might need it for gas)
Jeff

 

the longer rod doesn't increase the compression....the pin is moved up in the piston ....think the longer rod helps out on the wear... a friend of mine has a 5.7 dish piston 406...small aluminum brodix heads...thinking they're a pair of old -8's, small 540 ish roller....went 12.00's in a stock body nova with 3.08 gears and a turbo 350...a little work and those motors really make some power.... for your application ....look for more low end power...that makes things fun... brandon

 

Here's the recipe for a torquey 325 horsepower for $300 (if ya shop around)-

Summit brand or wolverine cam, whatever you can get for under $100 with lifters. Due to low compression and large displacement, stick to 450 lift and around 224 duration at 050.

"Z28" springs or whatever your source is gonna call their cheapo set of $40 SBC springs that will handle up to 465 lift. (optional- for some drivers the engine-imposed rev limiter created by valve float is necessary. If you're that guy, keep the stockers. RPM will kill this mutha)

Cheap dual roller timing chain

High volume oil pump (you're making a lot of power for a worn lower end, so keep those bearings packed with oil. I've abused a lot of worn SBCs in mud trucks, this is KEY to longevity)

Used single plane intake like a torker. Try to stay away from the super tall ones like a victor jr unless you're bumping compression. Common advice is dual plane, but I've done a couple 400s like this and if power from 3500-5500 is important, use the single plane. There will still be plenty of torque even with this sacrifice.

Something to clean up the HEI signal. You're stuck with a 5500 redline for durability reasons, but stock HEIs still have issues starting at 4500. Use a performance module & pickup coil. Stock coil however should work fine at this RPM.

Good luck

 

I had a destroked 377. It was pretty fast, 86 monte ss with a th400/3.77 worn out posi, trapped over 112 in the 1/4, never hooked hard though.

Sportsman II heads, air gap, 750 edelbrock, KB forged pistins, cam was a Elgin regrind with 495/525 lift IIRC, I tried 6 different ones.

 

I've done a few of these now. It's true that the short rods will put side load wear in the bores - I started with the stock rods, went to 5.7s and now run 6 inchers...

 

This is great stuff, you guys. Thanks.

One last question-- ***uming that I'm keeping stock heads, is it better to use a dual pattern camshaft??

 

Unless you're rebuilding it, use what's cheap

Putting a performance cam & intake on a hundred thousand mile motor is like lighting a 3 year/30K mile fuse on the lower end.

good luck with the project

 

To start from the beginning, it depends on what you mean by "bolt-ons." If you are pulling the heads and have the cash, then go all out as being described... these guys are spilling some good combos and info. My biggest piece of advice is to make sure you are willilng to spend what you need to do it right.

Just remember, you can try some 1.6 or larger aluminum rockers, good intake and carb, and free-flowing exhaust without double-spending. Meaning you can still use those parts (if you buy quality) if and when you go for a cam and heads.

 

Damn, you're right. Thinnest I could find was .038"...........

 

I am building a short rod 400. Very simple mild motor.

400 block - 30 over
TRW forged pistons with a 12.5cc dish
Stock rods and crank,
462 heads with some mild bowl porting and a trick vavlejob, but 1.94/1.50 valves, 64 cc chambers
GM 350HO camshaft - 224@50, 112 lobe sep, .460 lift.
Stock mid 60's iron Q-jet intake and q-jet
Rams Horn exhaust manifolds

Should be just under 10:1 compression, and make anywhere from 325-350hp with big torque everywhere. Should work ok.