Also interested in this build up. So should you run 6.125 rods or 6.25 rods? do you have to have special pistons or just normal 4.165" ones? Also where do you find a 3.25" crank? Just getting into all of this advanced stuff, sorry if i sound stupid!

thomas

 

3.25" crank is what is used in 307 and 327 engines.

 

Looking back, I think you should run a 4.125" bore and a 3.3" stroke...

there's all kinda stuff out there for a 4.125" bore, and it's plenty large to keep whatever heads unshrouded

Find out whether or not 18deg stuff is allowed... tho i can tell you either way what we think

-Phil

 

A little confused, my feeble mind..... If the idea is to have a large bore, why is a 4.125x 3.3 better than 4.155 x 3.25? If the reasoning is cost... the 3.25 stroke is a standard size... should be a tad cheaper, and at this point an extra $200 for custom pistons should be a non isse. OTOH I'm tinkin that a 3.3 crank is an oddity...

Or does it have something to do with an ideal median of some kind?

 

I PM'd you...

I'm wondering if its the GT1 we're thinking of... if so it's the ole 18deg trans-am stuff...

Depending on what your buddy wants to do, and what chassis he's running.. I can tell you what kinda shortblock to put together if you wanna be competitive.. but it all depends.

If you can run 13:1 with 5liters and not have a weight penalty vs. 9:1 with 5.7L, then eh.. it'll depend on the chassis where we go with that. Either one will make over 600hp.. just depends.

Check your PM


-Phil

EDIT: oh yeah.. gotta rulebook you can copy/fax/putonline? Ill dig around online tomorrow if i can for one. Its just sticking in my mind that you may be limited to the aforementioend choices even though you mentioned unlimited CR... and i wonder if yer limited to 8200rpm like trans-am...

 

http://www.quickfueltechnology.com/
See what these say people a call about the carb. Talk to Marvin or Marty. Ive seen some of their work and it impressive

 

If you're building up the engine similar to the Trans Am engines, the big dogs are putting out around 700 hp with a 310 cu. inch engine and SCCA mandated 8200 rpm redline. No one is running 18 degree heads anymore - all the Chevy guys have switched to the SB2's. There really isn't anything exotic about them, other than running top of the line parts. FWIW - The front runner chevy guys in TA have gone to the short deck blocks to get the Cg lower, even with the weight penalty the short deck blocks get (25 or 50 lbs, I believe). CRD builds many of the front runner engines, and it might be worth a quick phonecall to them. Another idea would be to get a surplus SB2 cup engine.

A.

 

Shortdeck huh... recognize this? D'oh.. thats a $5k block there vs. less than half that for a regular bowtie.. granted it'd be decked quite a bit anyway.

FWIW, I thought GT1 was going to start allowing the sb2 stuff in the relatively near future since theyre emulating trans-am.

ahhh dunno for sure

 

http://66.228.67.107/SkarodoM/heads/AuroraBowtie1.jpg

holy short deck batman

 

i wish it were mine

i'd sleep with it under my pillow

mmmmmmmmmmmm

 

that's a IRL 4.0L rather than a 5.1L Trans Am block.

Yeah they short deck block is nice but it's twice the price of a CNC preped bowtie.

BTW that's out of the budget, so is the SB2 heads. $5200 for good CNC ported SB2's that's $10,000+ on heads and block!

Bret

 

$5200 for gail pauly's CNC'd sb2's.. but thats BARE lol... by the time you drop $90 per valve.. have someone finish porting them by hand... etc. etc. etc... more $ than my car is worth in one set of heads. D'oh

 

D'oh is right!

 

Allright, I have new information on the rules for this build. The car with driver weighs 2,800 lbs which means we can run up to 355 inches without further penalty, which puts me back to the 4.155x3.25 setup. I think we're going with worked 23* heads for budgetary reasons, so that should help narrow things down.

So... thanks for the help all- especially Bret and Phil.

Where do we go from here in terms of heads, cam design, and CR?

 

Back to the first topic - best bore/stroke. Usually, the best breathing (most hp) bore/stroke combo is the largest bore you can possibly run. This will let you run much larger, unshrouded valves, which breathes much better, creating more hp The shorter stroke also lowers the forces on the rotating assembly, since the piston doesn't have to travel as far in the same time (lower acceleration). Less force needed to accelerate the piston = faster revving and more hp to the crank, instead of accelerating and decellerating the reciprocating assembly. Shorter stroke also lets you run a longer rod, for better rod/stroke ratios, more dwell at TDC, and slower max piston speed. Max piston speed determines how much air is needed at that instant to fill the cylinder. If max piston speed is less, the peak flow required will be less, which is more efficient. If you'd like to learn more about this and make your own decisions (rather than going off of us internet gearhead techies!) I'd strongly recommend getting all three of David Vizard's books on small block chevies - heads, rotating assembly, and valvetrain. It'll expand your mind (and bonus! You'll be better able to help your paying customer!)

Heads - If you can sacrifice budget on the rotating assembly to get the best heads you can afford - you'll make significantly more HP. It comes down to your budget (what is it?) and whether the customer wants to trade hp for reliability (i.e. how close to the edge do you want to push your parts). The 23 degree stuff can flow well, but the 18 degree will be much better. It's all down to the budget again. If you want to spin 8500 rpms, you'll need lightweight ($$$) components that will eat your budget. If that doesn't leave $ for great heads, your power will be down. What are folks paying for the Katech engines, and what kind of power do they make? The TransAm engines usually go for $15k for the bottom of the barrel to around $50k for the top dogs, from what I've heard in the paddock. CR - run the highest you're allowed with the octane rating fuel available. Going past 13:1, the returns start diminishing. If you're building it to GT1 specs, get a copy of the GCR's. SCCA can overnight a copy to you. You *need* to get a copy, if you want to know what you can do on the engine.

Cam - it depends on everything else, but mostly on max rpm, bore/stroke, and head design. It's going to be a solid roller, but depending if you've got the budget for titanium valves, rebuilds every 500 miles, etc, will determing on how aggressive the cam lobes can be.

Get Vizards books. It will help you understand all of this, instead of just taking other peoples words for it. Maybe it's just me, but I like to know the *why* of it, and can't just take someones word. I'm sure you're on a time schedule, and can get most of the info you need quickly by asking here, but it's all explained in much more detail in the books. There are others that are helpfull too, but aren't as easy to understand as Vizards. Enough rambling from me HTH!

Andris