I'm trying to put together the most powerful engine i can. I plan on using a chevy 400 small block with steel forged crank, high rpm cam shaft, roller rockers, heat treated push rods, 4 gear timing, edelbrock intake with dual 500 cfm carbs, old remachined 305 heads. Will the 400 block handle 1000 cfm? How big of an imporvement would i get from aftermarket performance heads? do i need aftermarket connecting rods? do i need an aftermarket fuel pump? With a setup as previously described, how much HP do you think that i will have? Is there anything else i could do for more HP? Am i even on the right track? Should i use a completely different engine block? Thanks for your time. -Ted

 

Ted, welcome to the board, first off. Second, slow down. Let's get at what you're really trying to accomplish. Race motors don't use dual carbs anymore. That's nostalgia/street rod stuff nowadays. Also, the 400 is difficult to make rev extremely high. It can do it with expensive parts (REALLY expensive) but below 6000-6500 is where it makes great bang/buck. And lastly, good flowing cylinder heads are ALWAYS the key to making big power on any motor so those reworked 305 castings will choke the snot out of a big 'ol 400 (not to mention send compression to the moon)- you want aftermarket heads to make big power on a 400.

So, what is the goal and the application for this motor? What's it going in? What is the vehicle's intended use (drag, autocross, etc.)? What is it's weight? Those questions will define a few basic parameters so that I and others here can steer you in the right directionm which is what we want to do. We were all new to this stuff once, too.

A Viper-killer motor can be built for under $3500, but you've got to choose the combination carefully. The more accurate information you give the easier our task will be.

 

Well, to clear things up, im looking to build a street engine for a Z28 between the years of 75-81. I got all of my ideas from JEGS and from my cousin who restores cars.

I'm not sure if this is too much to ask, but what i would really love is for you to help me make a list of which parts/components you would recommend so that i could learn a little bit more. Under $4000 would be great. If you feel that your engine is the best combination there is, please tell me what you've got!


Block - if not a 400, what then? SB/BB? 305/350/454? WHat are the most successful and not necessarily most common blocks used for a z28 prior to 81?

Heads - aluminum, steel, what sized valves, springs? Can you suggest some specific heads for the block you recommended? what is a good size for compression chambers?

Intake manifold - if not dual carbs, what then? edelbrock performance?

Carbeurator - Holley, edelbrock? How many cfm for which block? How many cfm is too many cfm?

Do i need aftermarket connecting rods? what type?

What timing setup?

Pistons - forged? flathead? any specific pistons you'd recommend

What type of crank?

Cam - I'm looking for a cam with lopey idle, made for street/drag. Should i get mechanical/hydraulic/roller lifters? recommendation?

Springs - how do you match springs with the cam?

Valves - what is the benefit of aftermarket valves

Roller rockers - 1:5 or 1:55 or 1:6 ratio? aluminum?



Thanks a ton for taking the time to read, and especially if you took the time to answer!

-Ted

 

Everyone's got their own preferred combination. I'm sure may will put in their opinions as well.

Here's mine....

I like nitrous motors. Why? Well, you can build a street engine you can drive anywhere, anytime, get decent mileage and generally feel good about driving without having to zoom the RPMs to the moon just to pull away from a stop light. In other words, strong, but not high strung like a strip car engine.

Then I lay a simple 125-150 horse plate nitrous shot to it and put a Viper in the rearview. Fun, cheap, reliable, cost effective. If this whole scenario isn't for you, then no need to read any further because that's what the following motor is....

BTW- I NEVER feel I have the ultimate combo. I always can build it better than what I got at the moment.

A 400 cube motor is a great starting point. A little more to build, but cheap for all the power you'll make over a little 350. Finding a good starting block that isn't used up is the main probnlem. Many mail order houses carry them, may local shops can build you one. I build my own, but you probably will want to buy at least the short block pre-assembled and build up from there if it's your first motor. If you can buy local I highly recommend you do. If you have to take it back you know where to take it back because you know where it come from (to quote AJ Foyt). LOTS of guys make the mistake of buying a dirt cheap motor on-line and then get frustrated and ripped off when it blows up or has problems- they can't send it back and if they can it's a big PITA to do so (remove motor, pay to ship it back across country). Work with people you know and trust if possible. If you don't read another word of this post at least read and believe that.

Now, as for the hardware, you want a 400 block, 2-bolt (not 4- they're actually weaker). You don't want any overbore beyond .040-over. The bottom end you can use a stock cast crank, no problem. Rod length is a matter of great debate but since we aren't going over about 6000-6200 and keeping an eye on cost with this motor you can use the stock shortie 5.56" 400-style rods. Make sure you upgrade the rod bolts to ARP WaveLocs. Accept no subsitute. Good rod bolts will make a big difference in bottom end longevity especially if you get a little "greedy" with the revs from time to time. Do you need aftermarket rods? In a word, no. For high RPMs, maybe, but for mild RPMs and under 500 HP, no. Pistons.... "flattops" will be just fine. Hypereutectics like the Keith Black units will work just fine and are cheap but if you're the nervous type you'll want to go with forged units which many are available (but for more money). This will bring your compression to about 10.2:1. This is acceptable but high for pump gas. If you use aluminum heads- no problem. If you plan on using cast iron head then you might want to consider using dished pistons with about 12cc of dish to bring compression down to about 9.5:1. See about the heads, below, too. This is a ~$2000 short block. BARELY more than a stock rebuild.

On the cam you can ask around. I suggest you call Crane and Comp Cams for their recommendations but I'll throw the Comp Cams XE 274 in as a good starting point. Flat tappet, hydraulic lifters, cheap, makes big power, requires no "exotic" valve springs. Very streetable. Don't go crazy on the cam. Unless you're going racing you don't need a roller cam. For this motor you don't even need a mechanical cam, although using one would make a bit more power, at the expense of having to do valve adjustments periodically and live with the valvetrain noise. It'll work OK with a stock trans converter (assuming auto transmission), but an upgrade to a 2200-2500 stall will benefit performance.

Heads...... real important. Expect to spend at least 1/3 to 1/2 of your budget on heads. There are a LOT of good ones for small block Chevys. Forget reworked stock castings. Anything aftermarket will crush them. I happen to have good success with Dart Iron Eagles (cast iron) or Pro 1's (aluminum). If you can swing the extra cost of aluminum I'd go for it. If not, you will make just as much power with cast iron, it's just your engine will weigh about 50lbs more. If you buy assembled units the springs they come with are compatible with the XE724 cam. If you buy them bare and assemble them yourself you can save a few bucks and just install the valve springs that are recommended for use with the XE274. You're looking for the versions with 72cc chambers (to arrive at the compression I figured when choosing pistons, above) and 200cc intake runners. Figure about $900 for a complete set of cast iron heads, $1100 for aluminum, assuming you don't assemble your own and save a few bucks.

Intake. Performer RPM or Victor Jr. intake. Can't go wrong with either, really. They both kick butt. I'd probably go with the RPM for a little more streetability, the Vic Jr. for a little more high RPM HP.

Carb. 750 CFM vacuum secondary. Holley, Edlebrock or Quadrajet will work just fine, but expect to do some tuning on them to get best performance. No carb will bolt right on and instantly be optimized, despite what Demon and other "tuner" carb manufacturers wll tell you.

Ignition. Simple GM HEI distributor will work fine. You can buy a new high performance replacement from Summit for $150. They work great. They also come with a pretty good ignition curve already dialed in. You can buy a junkyard HEI and build it up, but you have to know what you're doing with them to do so.

Exhaust. 1 5/8" or 1 3/4" headers with 3" collectors going into 2 1/2" duals through flowmaster 2 chambers or similar mufflers.

This combo will make an HONEST 1 HP/CI on the motor alone on pump gas when the tuning is dialed in. THrow a simple 125HP plate shot on it ($400) and you're over 500 REAL HP. Now if you add up the numbers you'll probably soon see that with the carb, ignition, and various odds-n-ends I'm probably pushing more like $4000-4500 for this engine with nitrous, including a lot of screw-it-together-yourself work. True. You'll have to do some work yourself if you want a killer motor for cheap. But you can sell off your old engine in various pieces for at least $500, which will bring you back down a lot closer to the $3500 I promised. And this is all stuff you can buy out of a catalog. No "mystery machine work" or unobtainable pieces or junkyard scavenging. Buy it, bolt it, run it. As for the manual assembly.... well.... read up or find a new friend who knows his way around a motor! Expereince counts for a lot when building stuff on the cheap.

 

Thanks

That all helps a ton. I will likely follow a lot of your suggestions.

-Ted

 

After re-reading your suggestions again, i have a couple of question. I don't understand how a 4 block main would be weaker rather then stronger.

Also, are you telling me that a stock distributor off of some old engine won't work as well? what will and aftermarket distributor do to increase my performance?

When you say that i'll only need aftermarket rods if I plan on revving high, what kind of RPMs are considered high?

Also, i was told that if i planned on doing any aftermarket upgrades that i should definately get a steel forged crank. Would i be running a risk using a cast crank?

Another question is, if i find a 400 engine that has been recently rebuilt and bored out to 0.030, and it only has 100, or say 3000 miles on it since it was bored out, can i just use it as it is if i plan on rebuilding it?

I looked into SB chevy dart eagle heads, but their are about 20 different selections and i was pretty lost. Also, if i get bare heads and want to assemble them on my own, how do i pick out the valves and the springs? can i call the manufacturer of the cam i buy and ask for their recommondations? i looked into the comp xtreme cams and they said that it was extremely important to match the valve springs, valve locks, retainers, lifters, rockers, rods, and "other related components." What are valve locks and retainers?

Another question i have is about the cam. I want a cam with a lopey idle, but also one that i can use for regular driving. my question is, if i got the most extreme drag cam their was, how would it affect my everyday driving? is the only thing that it affects the idle?

carbeurator - you suggested a 750 cmf. would the engine handle/would it be ok to use a carb with more cfm?

Again, thanks so much for all your expertise, im learning a ton.

-Ted

 

Check out the heads from these guys:

http://www.procylinderheads.com/

The flow numbers on the 180 cc heads compare nicely to much more expensive heads, even 200cc heads.

This place sells a complete 180 iron set for $675!:

http://enginekits.com/

Summit wants over $800 for them.

72cc w/flat tops are a good combination on a 400. I used Keith Blacks on my 400 and broke 2 of them. So I would recommend paying a little extra for forged, especially if you are considering a power adder.

 

I'll try them one at a time.....

WHy is the 2-bolt stronger? It's a quirk of the 400 block. They used 4 bolt mains on some but made the webbing the bolts screw into thinner and weaker, prone to cracking. This usually isn't the case on most motors, but on the 400 it is.

Old HEI distributors from a junkyard car will work just fine, if recurved and updated for performance use. For info on how to do this check out an article I wrote about doing just that over on thirdgen.org. It's titled something like "Tuning HEI distributors for performance" or something like that. It's just I figured I'd throw in a good source for a new unit in case you weren't into rebuilding junkyard stuff like I am. Ditto the carb- obviously, you can buy a used Holley for next to nothing but in what condition???

Revving "high" on a long-stroke 400 engine I would say is anything over about 6000. Spending extended time over that level, not a quick rev or two running like during drag racing. Below that stock rods will work fine if upgraded with better bolts. All stock SBC rods are forged and very strong right from the factory unlike some other manufacturers engines.

I've pushed cast cranks a LONG LONG way without ever breaking one. Nitroused 400s, nitroused 383s (400 crank in a 350 block) and my current supercharged 383 all had cast cheap-o stock replacement cranks, never any trouble in tens of thousands of miles. Racing, towing my boat, driving around town. Hard miles. It's high RPMs that stresses a crank mainly, not high torque. This engine buildup is for moderate RPMs, high torque.

If you can find a recently rebuild 400 you can definitely use it, if it's got pistons in it that are similar to what I described. You have to watch out for your compression ratio with a 400. Even with the large 72cc or 76cc combustion chamber heads you can still send compression to the moon if you have a slightly domed piston or they zero-decked the block. Be always aware of your true compression ratio- it's one of the key factors in specing out a motor for performance. I have a compression ratio calculator spreadsheet so you can make your own calculations- email me if you want it.

Assembling your own heads is not difficult, but it would take a long time to tell you everything you need to look out for. The main thing is to get a set of springs designed for the cam (they are available as a kit from the cam manufacturer). Then when you install them you need to pay careful attention to the spring's installed height (there will be a spec for this)- the distance between the spring pocket and the bottom of the retainer with the valve closed. You need to get this pretty close. But fully assembled heads from Dart already come with springs that are very close in spec to those recommended for use with the XE 274. You'd be looking for a set of heads with 72cc chambers, 200cc intake runners, straight plugs, and either 1.25" single or 1.43" single springs. Either will work. Retainers, locks, etc are not that critical on a moderate RPM motor. They'll tell you everything has to be matched like a Swiss watch. Not true. That's why many people use pre-assembled heads because they come complete and are usually matched plenty good for a street motor.

The cam I suggested will have a lice thumpy idle to it @ about 800. In gear it might have some strong lope with a stock converter, but probably not much with a looser performance converter that puts less load on the motor at idle speeds. Drag race cams are not for the street. Not only will the car be miserable to drive around town due to the lack of low RPM torque but it'll get bad gas mileage, foul out plugs regularly, require a high stall converter (think about revving to 3500 every time you want to pull away from a stoplight) and also break valvetrain components from time to time since they are designed for a short race, not thousands of miles of street driving. Happiness is a mild cam. Not that you want to go too mild but the XE 274 has about 40 more degrees of duration than a stock cam and almost 2 tenths more lift- it's no granny cam! But you can still drive it every day.

The 750 is a good, commonly available carb for not a lot of money. It's also the largest available with vacuum secondaries (except the Quadrajet which can be had up to 800 CFM) which helps drivability quite a bit. You can go larger but when you get up above 850 you're talking about some very expensive carbs that are only available in "double pumper" configuration which arguably does not have as good a drivability and is definitely more complicated to tune for best performance.

 

Thanks again. Im writing down everything you tell me.

Just a couple more short questions.

I looked real hard for your article on rebuilding a stock HEI distributor and i couldn't find it.

Also, I'd love to take a look at your compression spread sheet.

Do I have to worry about emissions if i get a z28 before 1981?

I was very interested in the XE274 cam but i ended up looking more into crane cams becuase they've got such a great web site and they post all the other necessary valve train components for each cam. What do you think about a crane PowerMax cam and what type of "basic rpm range" should i be looking for?

Again, thanks a ton. Everything that you've told me is invaluable.

-Ted