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Discussion Starter · #1 ·
What's going on guys need u engine builders input. I bought a 355 bottom end from a guy. Came with .30 speed pro forged pistons, stock crank custom grind cam made by comp cams. The cam specs are
In . Exh
301/ 312
272/ 283
588/ 609 lift lobe speration 112
This build is going in a 85 C10 a street car not DD. Is this cam to much n what's a good choice set of heads to go with? Thanks in advance.
 

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you have what looks like a rebuilder short block not machined for aluminum heads so maybe a 300 hp stockish build and a camshaft that should be in a 600 hp hot engine that needs a big split duration cam or a split rocker system?????
 

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That cam will need minimum 12.5:1 static compression ratio. You could run it on the street if you use the proper fuel and have the parts that will hold up to the revs that the cam will need (4500 to 8500). The cam will make no power to speak of under 4500, so you'll need to use a minimum 5000 stall race converter and some pretty stiff gears in the differential, like maybe 4.56:1. You'll need 100+ octane racing gas or methanol or ethanol or E85 from the pump. We'll need the part number of your pistons to advise you on heads. For heads, I'd be thinkin' 235/245 cc intake runners. Built properly, this motor will cost a minimum of $12,000, starting with an aftermarket block. While you're building it, make plans to own a dependable bicycle, because you'll lose your driver's license shortly after you get the truck running.

Now, would you like to pull back a little and get yourself a streetable cam ?

P.S. We still need the part number of the pistons.

.
 

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Discussion Starter · #8 ·
Speed pro pistons L-2252A aka 7009p
Pump gas no racing fuel
Head choice vortec or bowtie. Chose cast iron because a catastrophic event like running hot n heads gone. Nice but afraid of aluminum.
After reading u guys comments about cam think I might pull cam and go smaller.
Reason for building this engine got bottom end and components for a great price from a guy.
New to this want all input. Thanks
 

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remember that the low price was for a reason??? Sounds like the short block was machined and assembled by a non high performance shop. Also sounds like minimum block machine work was done. When building "high performance" engines its easy to spend a "G" note or more just on PRECISION machining.Make sure piston to wall clearance is correct with your piston choice.

NOTE: Vortec heads are a good choice for engines up to 400 hp and a bit more with well matched parts.

Aluminum heads are used all through the automotive world including diesels so that is where the power is in modern times. Buy quality parts for a quality engine. Power out put is determined by budget,,,
 

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Discussion Starter · #10 ·
So I think my best bet will be is strap the cam n go smaller. Just want a good strong street engine ready to run when I need it to. After input might give aluminum heads a shot. Maybe u r right why I got the shortblock for a good price just wished the cam wasn't so big. Are the pistons choice decent. Again thanks.
 

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your block machining is also an issue. Please take the time to post what you need from an engine?
As the short block sits you cannot use aluminum heads
 

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OK, do you want the bad news or the bad news, 'cause there ain't any good news.
Your pistons have 11cc domes, so any static compression ratio that you make with them, regardless of heads, will be too high for running pump gas.

It is generally accepted in the hot rod community that using today's pump gas will limit a motor with cast iron heads to about 9.5:1 static compression ratio and a motor with aluminum heads to about 10.5:1 static compression ratio to prevent detonation.

Scenario 1. If you used iron heads with 76cc chambers (early 70's cast iron Chevy heads), the static compression ratio with a 0.028" gasket would be 10.55:1, too high for iron heads (which are limited to about 9.5:1 for use with pump gas). Squish/quench of such a build would be 0.053", outside the normally accepted 0.035" to 0.045" clearance for an effective squish/quench clearance. Using a shim steel gasket to get a better squish/quench (0.040" with a 0.015" steel shim gasket) to control detonation would put the static compression ratio even higher, at 10.82:1 SCR.

Scenario 2. Use aluminum heads to allow the use of pump gas with a higher static compression ratio. You would want to use a combustion chamber that is at least 76cc in order to control static compression ratio down to around 10.5:1. Brodix makes such a head at a cost of $1,143 each head assembled....
https://www.summitracing.com/parts/bro-1028100-1/overview/make/chevrolet
The problem with this scenario is that you still have a piston compression height of 0.025", so in order to engineer a good squish/quench, you'd have to use a steel shim gasket. Now, there are fellows on this board who see nothing wrong with this, but I would have to ask why all the aluminum head manufacturers specify a composite head gasket? A composite gasket is at least 0.028" thick and will result in a squish/quench of 0.053" when used with your 0.025" piston deck height. Would that work to stifle detonation? I don't know, but I would not build such a motor.

Scenario 3. Change pistons that use no dome so that you can use a more affordable aluminum head. A piston with a flat crown, -6 cc's of valve reliefs and 1.560" compression height would make a 10.27:1 SCR with a commonly available 64cc aluminum head, using a steel shim head gasket (which I would not use with aluminum heads). Instead, I would disassemble the short block, cut the block decks to 9.010" and use a 0.028" composition gasket to make a 10.32:1 static compression ratio with a 0.038" squish/quench. With this motor, I would use a set of Profiler 195 heads, Weiand 8150 intake manifold and mount a 750 vacuum secondaries carb.

Scenario 4. Disassemble the short block and cut the block decks so that you could use a composition gasket with the aluminum heads and engineer a good, tight squish of 0.040". . This would also square up the block so that the heads will sit properly on the block and the intake manifold would sit properly on the heads. Your block deck height currently is probably close to 9.025", so cutting it to 9.010" would allow the use of your domed pistons with a composition gasket thickness of 0.028", making a 0.038" squish/quench. This would yield an 11.56:1 static compression ratio that still might be made to work if you used enough cam to bleed off some of the cylinder pressure.
 

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Tech's scenario's are spot on. Depending on your budget, the cheapest way out is to swap the cam to something like an XE 268 or XE 274 and bolt on a set of Vortecs IMHO.

The best choice is to zero deck the block, grab a new set of aluminum heads and swap the cam, but this is not budget friendly.

p.s. - I'd check the bearing clearances at a minimum - plastigauge is darn cheap.
 

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your pistons are too far down in the block. With proper composite gasket the heads will be too far away from the piston at tdc
 

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lets make something of what you have? What is the engine require to do? Be realistic. I'm thinking a 375 hp street engine,,,
 

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Wrench Turner
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I'm thinking your best option would be to get rid of the current pistons & replace them with a flat top.The flat tops would lower the compression to a level that would be pump gas friendly & allow a cam that would be better suited to the use.It would also let you use an aftermarket,or,OEM head off the shelf rather than trying make a head work.Trying to grind & even out 8 chambers to enlarge them would be either pretty costly,or,very time consuming.The flat tops would also offer better performance characteristics than the domes.It would just be a better all around choice,unless this is gonna spend 90% of it's life at the track.The domed pistons are also likely to cause problems with any modern performance head that utilizes the Vortec type heart shaped chambers.
 

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Wrench Turner
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You may even come out better at the end of the day to trying to sell this to someone,especially you did get a really great deal, & then starting over from scratch with a more appropriate shortblock.This would let you know exactly what you have & exactly what you need to get where you're going & wanting to be.
 
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