rebuilding a 351w

[wrecking-crew]

i have a few questions about rebuilding an engine(mine and a 350 block)
1)what type of piston would be best? cast alum, hyperwhaterver alum or forged?
2)which type of piston wold be better? flat top or dish type?
3) what bore should i go? 20, 30, 40 or 60?

and this may be going into a ranger and im even keeping the 3 spd on it.

the reason im asking is so i can price it

this is a competition me and my friend are having, who can build a better motor. he is rebuilding a 350 and im reboing a 351 to see how much power we get after and the best 1/4mile time

 

[AllanD]

Boring an engine any more than absolutely necissary than
necissary to clean up the bore is asking for trouble.

Hypereutectics primary virtue is that they have a very low
coefficient of expansion so that it is possible to fit them
much more tightly to the bores.

this is great for emissions
Not great for high performance or durability.

Forged pistons are the best for durability, but they also have
the highest coefficient of expansion, so when you set themup
in a block they require a great deal of skirt clearance.
This has some unfortunate side effects...

Anyone here ho has actually owned an old REAL muscle car engine
that was built with forged pistons knows what I'm about to talk about

Like the old 289HiPo engines, the noise those pistons would makes on a cold engine start has to be heard to be believed...
You actually had to strain to hear the noise of the solid lifter valvetrain over the ominous sounding piston slap until the pistons warmed up and actually tightened themselves in the bores via thermal expansion.

Cast pistons? well they are simply cheap.

AD

 

[mentalbreakdown00]

Well this will really depend, what is your hp and tq goal. Power adders or no, what rear end gear, and what trans. Will it be completely track or a street strip or daily driver. Answer these and i'll gladly help you.

 

[feellnfroggy]

Its gonna depend on what budget you two setup as well. One can easily spend more money and make mroe power where is the limit. Also, even if you too set a budget YOU will have to be insanely wise, because the 350 block is the cheapest motor onthe planet to build next to an X-mods.

1)what type of piston would be best? cast alum, hyperwhaterver alum or forged?
2)which type of piston wold be better? flat top or dish type?
3) what bore should i go? 20, 30, 40 or 60?

1. get forged, the piston head design will decide some of your compresion levels be smart.

2.flat top if your going n/a is what I would do. With valve reliefs so you can tighten the stroke.
3. If you bore it I would ABSOLUTELY NOT go over .030, I would do the .030 over and stroke it (longer connecting rods.) It means the piston travels downward farther, collects more air/fuel and travels up tighter and has a greater compression.(n/a) I wouldnt neccessarily do this if your getting forced induction, unless you got mad bank.

The most important aspect isnt so much what equipment you buy thouhg. It utilizing what you have wisely. Have the heads port and polished. (factory heads should be fine) have them decked which will remove unlevel inconsistencies, as well as mildly increas compression. have the block decked as well. Dont go cheap on gaskets unless your only gonna run it once. Cams are a big issue, REsearchResearchResearch. Call compcams and give them the engine specs you plan to run, they will guide you to the correct cam, or you can build the engine around the cam they suggest however you wanna do it. Anytime you make a mod like porting the heads, also make sure the machine shop can flowbench it if possible. (is flowbench he right words? flwotest)

Sorry about the punctuation, its been a bad night.

 

[mentalbreakdown00]

umm longer rods is not stroking an engine. Longer rods give a greater leverage to the crank, also they cause longer dwell times at bottom dead center and top dead center.....

 

[mentalbreakdown00]

On a second note, if you are going budget build stock rods are just fine, so is the crank, unless you have the buget for a stroker kit. But with the rods you want to weigh the big and small ends and the total rod and get them within a gram or so of each other after grinding the casting marks off. Also you want to do the same weighing on the pistons.... just let me know what I asked and we can get you through this with spending the money where it really counts... also carb or efi?

 

[feellnfroggy]

umm longer rods is not stroking an engine. Longer rods give a greater leverage to the crank, also they cause longer dwell times at bottom dead center and top dead center.....

Your right, my bad, My brain has been foolfartin around on me all day, I meant crankshaft not rods. Sorry.

 

[mentalbreakdown00]

hehe on a third note, if I was building a budget 351 here would be where I spent money. ALL engine fasteners, highest quality gaskets, a very good harmonic dampner, very good set of rings, (street, some strip N/A engine) hyperutectic pistons, slightly larger valves (after they cut the seats for the valves would do my own port and polish), cam and valvetrain, and depending on carb or efi the intake selction would come into play.

 

[feellnfroggy]

hehe on a third note, if I was building a budget 351 here would be where I spent money. ALL engine fasteners, highest quality gaskets, a very good harmonic dampner, very good set of rings, (street, some strip N/A engine) hyperutectic pistons, slightly larger valves (after they cut the seats for the valves would do my own port and polish), cam and valvetrain, and depending on carb or efi the intake selction would come into play.

You know now that you lay it out htat way, I can agree more. its very well balanced and solid which would help it make use of every last horsepower without alot of waste. The only thing is I wouldnt do my own port and polish, but thats cuz Ive never done one and dont wanna lose a competition becuase I over ported my system..Efi can be tuned to alot tighter perameters than can carbed and make much nice power curves. But carb'd is oh so much cheaper.


On a sid enote, invest in a sneaky pete nitrous system, one of the tiny little bottles that you can hide in a fender and run lines into the intake.(dry shot) or not.

 

[Will]

If I were building any engine I would spend my money on a set of aftermarket heads.

You want to hear what's sexy or what works? Rebuild it with cast pistons--use the stock ones if the bores are okay. Just use good parts and do a careful job. To need forged pistons you need a lot more thump than you are going to get with a mild cam and the stock heads. Be realistic and don't waste your money on things you'll never notice.

You want to go fast, throw away the factory heads. If you break something in the bottom end, which I doubt you will, then address that need.

 

[mentalbreakdown00]

I would suggest aftermarket heads too, but don't know the buget. Stock heads can only support around the 300-330 hp range, but re-using pistons during a re build is a no no to me. It's not rebuilt if you are re-using high wear parts. Also you may not notice a hair line crack that only shows up when heated, and then pop when you hammer on it. Thermal cycling comes into play with pistons in a biiig way. And nothing of what I suggested is the sexy way of doing things.

 

[wrecking-crew]

im trying to get the most power you could get with the engine n/a and carbed. i dont know what rear gearing ill be using. but ill have a 4bbl goin on it. the engine is complrtly stock as of now.
i dont even know my budget. im doing this after xmas 2010.

 

[mentalbreakdown00]

Well first you need to know what your budget will be so you can do this in an organized matter with the best foundation parts you can afford. For example if a good set of heads aren't in the budget then re work the stockers, but build the bottom end to take it for later... you should sit down and figure out exactly how much you can spend and sometimes you can buy a short block built the way you want it and blue printed cheaper than you can get the machining and all done.......

 

[Will]

The pistons aren't high wear parts. If the bore is in good shape it's a waste of money to just machine it for the hell of it. If the bore isn't good, then you have to replace them obviously but you don't need high-dollar pistons at all. Stock pistons can take as much abuse as you can give it using stock heads. It's better to spend the money on something that will give you more horsepower.

How much are you planning to spend on this? Does the 350 guy have the same budget?

The carbed 351HO that was in 1987 pickups made 190hp @ 3800 (factory advertised net) and 295ft# @ 2600. That's pretty good BMEP right there--113psi. If you change the cam for one that would pull to 5,000rpm without killing too much air pumping efficiency that would get you 250hp. I think that's a reasonable expectation. I would find an aluminum intake and a 600cfm Carter AFB off of Ebay and that's all I would do to the engine--I would use the iron manifolds and dual exhaust if headers were'nt chep to come by. You aren't going to win this off the engine alone and it will take a lot more money to get a little bit more power.

I would spend my money on the truck. This engine in a 3,000# truck should run about 14.5seconds and 100mph. Only if the truck is set up for it. It ony need to be able to go 100mph too, so any gearing that would let it go faster will take away chunks of the torque curve that would be better suited to accelerating it. To that end I would gear the truck to go 100mph at 5,500rpm with 4.10s and some 26" tall street slicks. You don't need to tell your 350 opponent what you are doing. And then you need to get the truck to hook up so maybe some drag shocks up front so it will lift easily and some preloaded slapper bars and a Lockrite in the rear axle. Move the battery to the tailgate and cut weight where you can. At that power/weight level, every 100# removed is the same as adding 10hp.

 

[mentalbreakdown00]

Will, hate to argue with you, but I ran extensive dyno tests for a few years in my younger days for high dollar companies like speed pro and wiesco. They found that cast and hyperuetectic pistons are really susceptable to heat cycling wear. With hyper pistons being nothing more than cast ones with a bit of silica added to help reduce the expansion of them. I never suggested he need to bore it yet. HE may find that when he tears it down it may not need a bore, but yet may be able to check and he has the ability to use a stock sized piston in the hole, but hone it to the proper clearance. What I am suggesting he do is build a rock solid bottom end first, then later on when he has the money for better heads, he can just slap em on without the worry for it, let's say i'm suggesting a solid bottom end first. It's not like I don't do this everyday......