350 pistons what would you use

[beakerztoyz]

hmm it's winter and with an unheated garage I'm kinda bored.... so i was thinkin now i have a monza and a sunbird both with smallblock chevy's the motor in the sunbird is a 2 bolt 350 block bored 30 over it has dish pistons, factory 76 cc heads, an L79 cam offenhouser intake and a 600 cfm edelbrock. this motor has maybe 20,000 km on it.

the other motor which is in a car i just aquired is a targetmaster smallblock which i assume is a 350 at this point, all i know about it is that it has an aluminum L82 manifold on it, and seems to need the timing tweaked or maybe some plugs and wires to run properly, but it does start.

so even with my limited budget I'm still thinking it would be nice if one of these cars was quick... I have a set of camel hump heads in the shop I could bolt on to 1 but they dont have hardened seats in them .... got me thinking maybe i should just order up some good {compression wise} slugs and make one of the cars into a cheap bracket racing type car. I've never built the bottom end of a motor so i just kinda knew they had flat tops and domed pistons.... I looked on Summit racing and there is like 9 billion choices 2 valve reliefs... 4 valve reliefs Holy Heck.

so ah what would ya use? why? how do you know how many valve reliefs you need? say at this point motor wont go past 7500 T.J.

[cjbiagi]

The reason pistons have 4 valve reliefs is so they can be used on either side of the block. I used TRW L2256 forged pistons which is a flat top with 4 reliefs. These replaced the dished pistons that were originally in the engine so it increased the compression ratio somewhat, from 8.5 to low 9's. This is with 76cc heads that were also milled down a bit which reduces the chamber size which also increase the compression ratio. I am not an engne expert by any means, but there is a difference between cast, forged and hypereutectic pistons. A google search will explain the differences, pro's and cons. Much will depend on your choice of heads and desired compression ratio, intended use and budget. Spinning it 7500rpm is going to require premium parts, from the bottom end to valve train components. 6000rpm is probably more realistic for general builds.

[beakerztoyz]

thanks Clyde, I'm not to concerned about revving to 7500 from what I've been told over the years the stock crank and rods are fine till about there, the weak link in the stock smallblock is the valve springs which start to float around 5500. The Camel hump head's are what they used to use on the corvette in about 70 ish and have 64 cc chambers and if needed will get good springs.

Thanks for the explanation on the 4 valve relief thing I had no idea what that was about.

[Monza Harry]

Well TJ as you have seen there are a WACK of pistons to choose from. This is for many reasons as there are pistons. 2 relief pistons can be used on either side as well but only if they aren't an offset variety, (that will increase piston dwell at TDC and BDC which is good for cylinder filling at high RPM's but come's at a low end cost. Forged tend to be noisier than cast and hypereutectic. Since you are thinking "Bracket Car" I would use forged as you will end up wanting more (NOS or Boost) and the forged is the way for that. If this is going to be street and sometimes "Bracket Car" than Hypereutectic is the plan (lighter than cast and stronger) holds their shape better over a wider temp. range and therefore better ring seal than forged, but while very strong if you are thinking of spray above the buck and a half mark (150HP) you need forged. But most of all listen to the guy who is going to "Warranty" it, if he says you need XXX and you want ZZZ he may not cover the problem that could come up when you are pushing it to the limit. I will try and find some links for you as my memory just isn't what it used to be. There is lots to be learned from some of these sites. And BTW Hypereutectic means that the Aluminum is "super saturated" with silicon (yes just like the brand new for '71 Vega block, Thank you Reynolds and General motors) Anything other than a flat top piston is a compromise for any wedge motor (Smokey Yunick) as this interferes with flame front travel (not the same for Hemi's) So for more compression you ideally need a smaller chamber draw your compromise from availability and finances. I hope this helps a little and others will chime in, weigh your options, do some reading and keep us posted Harry

[cjbiagi]

Flat top pistons and 64cc heads will give you a compression ratio of between 10.5 and 11 to 1. There are a lot of factors that go into the true compression ratio so these are just estimates. Deck height, actual head cc volume, head gasket thickness, whether the block and heads have been milled etc all enter into the final compression value. I don't really notice any piston noise from my TRW forged pistons, so much depends upon the actual clearances. Forged pistons do expand more than cast so clearances need to be set according to what type of pistons you use.

[beakerztoyz]

Thanks guys I appreciate the input, at this point in the spring i might end up with one or 2 of these cars being street legal, if its only 1 then I'm not sure how i would go about making the other car just a bracket race car (this is complicated by the fact that the nearest drag strip is 2 hrs away... i can get a trailer but have never raced b4) so this theoretical motor could go many ways as for warranty at this point i think i may get the machine work done and have my dad help me assemble the bottom end. He has built a bunch and i never have and i figure seein as how I will b 38 that this will be as good a time as any to get him to show me seein as how neither of us are getting any younger.

I was looking at some whole bottom end kits ( crank, rods and pistons) on jegs last night and they seemed to make it sound like with 64cc heads flattops would barely get to 10-1 comp w 64cc heads. Dunno if i will go that whole route though might just do pistons and rings so i was thinking if it was all motor maybe i should go with domed ones... but as Harry points out maybe i should use good flattops and then get nitrous later, course wouldn't nitrous mean that like w a turbo or a supercharger i should use a forged crank and good rods too?

am i correct in assuming that there is basically 3 levels here
cast=stock
hyperutectic = better than stock
forged = pretty darn bulletproof but might b overkill

[Smiley]

If the 2 bolt has an L79 cam in it and is in good shape that is the one I would build up.
the double hump heads on the 2 bolt 350 will raise the compression a point or so and improve the breathing, cheap since you have them.
If you really want more than 10:1 make it into a 383, 64cc heads on a 383 with flat tops will be 11:1.
Budget permitting I would use aluminum 2.02 heads with 64 cc chambers on a 383 or a 350 with forged flat top pistons, 2 or 4 notch valve reliefs
the Offy intake is prob a step up from the L82 intake.
If money and hood clearance are not a concern,Edelbrock Performer RPM Airgap is my favorite.

[beakerztoyz]

ya the block w the 2 bolt block is in good shape, it was rebuilt just before i got it and has maybe 20,000 km on it.... its 30 over, the only downside to it now is it has dish pistons. one of my friends thinks i should just stroke it.. i thought you needed to do complicated machine work for that and i dont really wanna get into it.

also wondering and i know it would need measuring but is it possible to change the pistons without reboring it ?

[anorexicvega]

ya the block w the 2 bolt block is in good shape, it was rebuilt just before i got it and has maybe 20,000 km on it.... its 30 over, the only downside to it now is it has dish pistons. one of my friends thinks i should just stroke it.. i thought you needed to do complicated machine work for that and i dont really wanna get into it.

also wondering and i know it would need measuring but is it possible to change the pistons without reboring it ?

Depends on who you ask, lol. Personally I would leave the shortblock as is. See if you can find a set of fresh vortec heads locally, use a steel shim headgasket and buy a vortec performer rpm and be done.

[beakerztoyz]

Depends on who you ask, lol. Personally I would leave the shortblock as is. See if you can find a set of fresh vortec heads locally, use a steel shim headgasket and buy a vortec performer rpm and be done.[/quote]

Andy Beaumont...... is that you? lol I have a friend who loves vortec motors......

honestly though my choices in this particular build would be use the camel humps on top of the existing dish pistons, or put better pistons in first or i suppose do nothing, it should be said there is nothing wrong with my existing motor it runs fine

[anorexicvega]

Depends on who you ask, lol. Personally I would leave the shortblock as is. See if you can find a set of fresh vortec heads locally, use a steel shim headgasket and buy a vortec performer rpm and be done.

Andy Beaumont...... is that you? lol I have a friend who loves vortec motors......

honestly though my choices in this particular build would be use the camel humps on top of the existing dish pistons, or put better pistons in first or i suppose do nothing, it should be said there is nothing wrong with my existing motor it runs fine[/quote]
No, lol, my names Jonathan. IMO the vortec motor is the best first gen style sbc made. The camel humps will require hardened seats if you plan to drive it much. the cost of the vortec heads/vortec intake with your existing shortblock will be cheaper and gain more performance and ecomony vs the hump heads/ exhisting pistons or new flat tops

[anorexicvega]

Depends on who you ask, lol. Personally I would leave the shortblock as is. See if you can find a set of fresh vortec heads locally, use a steel shim headgasket and buy a vortec performer rpm and be done.

Andy Beaumont...... is that you? lol I have a friend who loves vortec motors......

honestly though my choices in this particular build would be use the camel humps on top of the existing dish pistons, or put better pistons in first or i suppose do nothing, it should be said there is nothing wrong with my existing motor it runs fine[/quote]
decent power gains could be had with a performance valve job and bowl work on your existing heads, a performer rpm intake and modern hydraulic camshaft.

[beakerztoyz]

my intended use for this motor is more of a cheap bracket racing car so I am not concerned with the fact that it will need a lead additive, while I agree with you that vortecs were great motors and your setup would make sense Im really trying to use mostly parts i have kicking around

[Monza Harry]

TJ all the motor advice is all valid from their take on the engines (and all pretty sound advice), but you have stated that you have never done this before (the track) so I would seriously consider your original approach use what you have and get a feel for it with little or no out of pocket $$$. If you have a blast (I suspect you will) but there are some who don't find the rush in it (rare) but while learning why not use up what you have and have some fun with it? Then you could jump to the next level when you break or learn what you really want, it isn't always the way we think it will be. Your smog bottom end with double bumps (small valve 1.94/1.5) with a healthy cam in my nephews S10 was running in the high to mid 13's and he had a blast. If you have access to a dyno program you should run your combo you will find it is possible to get to 300 ponies with that set-up pretty affordably and that set-up shouldn't be too hard on parts but will still be triple (+/-) any Vega came with and double the most powerful Monza Then you could ramp up incrementally as parts start to wear. That way you don't dump a ton of cash in something that you may not like or decide it is just too rich for your blood so to speak, and a race car is in the top ten worst investments of all time (financially speaking, fun-wise that call will be all yours to figure out) So I think you could start with your "good" short block and your double humps, and a few well chosen other parts and Burn some Rubber! Harry

[beakerztoyz]

Thanks Harry, and thanks everyone else too for all the advice I totally agree all of you guys have great idea's and are accurate in your assesments. if I was designing new from the bottom up it would be diffrent. in some ways i guess i just dont wanna end up like a friend of mine who rebuilt a motor and then added some good heads and has kicked himself ever since for using dish pistons.

the more i research on this it seems like if you run better pistons you need better rods which means u should just buy a rotating kit which is way more than the 2 or 300 bucks i was thinking of spending on pistons. I might be wise just to take your advice and pretty much run for free this yr and decide after that where to go.