383 240z Posted March 9, 2003 Share Posted March 9, 2003 I have a 350 SBC with low compression pistons. I put a piston at TDC a measured the volume at 25.5cc. The highest part of the piston is .030 down in the bore. and the smallest chamber heads I have read 64.5cc. The gasket is 9.1cc (I got that from the Fel-Pro catalouge) my math says that makes it a 8.21:1 CR. is it possiable to make any power with this? the other variables are 3000lbs car weight 700r4 w/stock stall, 4.11:1 rear with 205/50/15 tires. I have small tube headers with mufflers an Edelbrock rpm intake and a 750 holley with vac 2ndrys. I hope you dont tell me I NEED new pistons as it will take a while to save up for them Keith Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted March 10, 2003 Share Posted March 10, 2003 If your on a real tight budget buy some hypertectic pistons. I believe they can be had for around 100 to 125. Check ebay maybe some used trw heavy forged pistons can be had cheap. Mike Quote Link to comment Share on other sites More sharing options...
Mike C Posted March 10, 2003 Share Posted March 10, 2003 You said you were going to buy a cam also, right? Norhtern Auto Parts has their 350 chevy high perf kit with hyper pistons, all gaskets, rings, bearings, oil pump, timing set AND your choice of Crane Energizer for $299. Buy David Vizard's book "Building SBC on a budget" from http://www.motorbooks.com. Way more information in two evenings readings than you can get from a 100 questions on a message board... Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted March 10, 2003 Share Posted March 10, 2003 read. it will help, first thing to do is buy these FIVE books, it will be the best money you ever spent, read them, and you will be miles ahead of the average guy. HOW TO BUILD THE SMALL BLOCK CHEVEROLET by LARRY ATHERTON&LARRY SCHREIB . HOW TO BUILD MAX PERFORMANCE CHEVY SMALL BLOCKS ON A BUDGET by DAVID VIZARD . JOHN LINGENFELTER on modifying small-block chevy engines how to build & modify CHEVROLET small-block V-8 CAMSHAFTS & VALVTRAINS BY DAVID VIZARD SMOKEY YUNICK,S POWER SECRETS http://www.sa-motorsports.com/blockdiy/blkdiy.htm http://www.hardblok.com/info.html http://www.findarticles.com/cf_0/m1...Bchamber+design http://www.speedomotive.com/building%20tips.htm http://www.se-r.net/engine/block_prep.html http://racerhelp.com/article_racing-10.html Quote Link to comment Share on other sites More sharing options...
383 240z Posted March 10, 2003 Author Share Posted March 10, 2003 I have those books I've read them each several times. Just from them I have gained a TON of knowledge in thery But in practice I have very little knowledge plus it is pretty hard for me to put down a couple hundred dollars and hope I got it right The first motor I built was a HUGE disapointment. since then I've read just about every book I could find. Now I'm just more than a bit gun-shy plus the wife is starting to see what this car is costing us. my company just went to forced direct deposit! I sent crane cams an info sheet (after your recomendation) I just hope I can get this all to work I'll read the links you sent after work on mon. Keith Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted March 10, 2003 Share Posted March 10, 2003 Dont be gun shy: experience doesnt come cheap-that is why experienced labor cost so much....they to (the experienced ones) made their mistakes. The difference from an experienced craftsman and a wannabe is that the craftsman learns from their mistakes. Keep learning; not until you know it all, which no one on this board does, will you no longer have to worry about making mistakes. As long as we breathe we will be making mistakes: the trick is to minimize the cost of your mistakes. I bet the next time you buy an engine you will ask a few more questions about the pistons....(lesson learned-unfortunately the hard way). Sorry about the dissapointment in finding out your SCR wasnt what you thought it was. I can only imagine what a sour taste that has left in your mouth. Keep on the lookout for pistons-If you have everything you need, except the correct pistons...work, watch, and wait and when you least expect it the right pistons will show up. Call all the speed shops in your area and ask them if they have any set of pistons for your engine-you'ld be surprised what a speed shop will have on their shelves in their back closets at any one given day. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted March 10, 2003 Share Posted March 10, 2003 Ok I get lots of questions on how to build a good street engine and how to find and match the correct parts, now Im going to be refering to your average hot street combos built on a budget with easily available parts. first the math (1)youll be limited to about 1.2 hp per cid on engine size (2) YOULL BE LIMITER to about 6400rpm with HYDROLIC flat tappet cams and about 7500rpm with SOLID LIFTER flat tappet cams (3)piston speeds that exceed 4000fpm usually lead to trouble (4)dynamic compression ratios of over about 8.3:1-8.5:1 with aluminum heads or about 7.8:1-8:1 with iron heads can cause detonation problems, but keep in mind only the dynamic compression matters not the static, because the engine only sees the dynamic cpr.try to get your dynamic compression as high as you can while still getting a cam wild enought to easily reach the rpm levels you need to to make good hp. (5) theres little to no possiable benefit to useing a cam that makes power above 6000rpm if your transmission ALWAYS shifts at 5300rpm and your geared so that youll be running 130mph before getting in high gear http://cochise.uia.net/pkelley2/ (5)the formula for matching POTENTIAL HP to INTAKE PORT FLOW is (.257 x port flow at max cam lift x 8(3 of CYLINDERs)= POTENTIAL hp (6) look closely at the duration used for each MATCHING rpm range. ALSO KEEP IN MIND THE DCR AND OVERLAP MUST MATCH look here these are the valve timeing overlap ranges that are most likely to work correctly trucks/good mileage towing 10-35 degs overlap daily driven low rpm performance 30-55degs overlap hot street performance 50-75 degs overlap oval track racing 70-95degs overlap dragster/comp eliminator engines 90-115 degs overlap but all engines will need the correct matching dcr for those overlap figures to correctly scavage the cylinders in the rpm ranges that apply to each engines use range OK now lets follow the rules and build an engine suitable for the average street strip car and lets set the goals at pushing a 3400 lb car to 12.5 seconds in the 1/4 mile with a 3.08 rear gear, and TH350 (JUST TO SCREW THINGS UP BECAUSE USEING A 4.11 RATIO MAKES THINGS TO EASY) 26.5" tires and an auto transmission to simulate an average late 70s car. well the first thing we are going to need to know is how much hp /tq will we need useing this quick guide http://users.erols.com/srweiss/calchpm.htm http://www.prestage.com/carmath/calc_ETMPH.asp http://users.erols.com/srweiss/calcrpm.htm we find that we need about 375 rear wheel hp or 469 flywheel hp to easily run very low 12s those 3.08 rear gears and 26.5" tires we will only be spinning about 4900rpm in the lights so well need an engine with lots of mid range tq, the 469 flywheel hp says we will require heads that flow at least about 230-240 cfm at about .48-.499 lift if we figure that we must build a hydrolic cammed torque monster that has very high intake port speeds for good volumetric efficiency in the mid rpm ranges to get the tq curve correct for those crappy 3.08 rear gears, the cam rpm chart shows we will need a cam in the 230@.050 duration range with about a 50-75 degree overlap and we need about 390-406 cid mimimum to get 469hp, REMEMBER WE ARE ONLY SPINNING 4900rpm in the lights so an engine that makes most of its hp at far higher rpms is a waste, that combined with the low rpm range would make a 383-406 the first choices here. http://www.prestage.com/carmath/calc_gears.asp]http://www.prestage.com/carmath/calc_gears.asp so what we wind up with is a 406 with a 10.5:1 static compression, a comp cams #12-246-3 cam with 190cc AFR heads as the smallest port heads that flow enough air at that low duration http://users.erols.com/srweiss/calchpaf.htm http://www.compcams.com/information/search/CamDetails.asp?PartNumber=12-246-3 http://www.compcams.com/information/search/CamDetails.asp?PartNumber=12-246-3 open headers 1 5/8" full length,at the track, an 850 carb and a dual plane intake. a 3000rpm stall speed, shifts at about 5500rpm now theres other combos and ways of getting there but you get the idea about how the parts should all be working towards the goal and within the restrictions , drop a cam like the crane cams #114681 and your hp goes up but above the rpm range that you ideally need it in altho the results are still good, a 3.73-4.11 rear gear would make the change to the solid lifter crane cam a far better choice Quote Link to comment Share on other sites More sharing options...
pparaska Posted March 10, 2003 Share Posted March 10, 2003 Hmm. 406, 10.5:1 compression, AFR 190 heads, 3.7:1 ratio, 26" tire, and a 114681 Crane cam. Sounds very familiar . Would AFR 195 heads have any advantage over the AFR 190s for the higher rpm (due to the 3.7:1 gears)? Also, how much do the bars in the graph at: shift to the left if any, when your talking about a 406? I imagine this graph was made up to cover the typical 350 engine. Oh, and note that the Comp 12-246-3 (XE274H) has 60 degrees of overlap, and the Crane 114681 has the same 60 degrees. The Crane cam has .518/.526 lift versus the Comp's .487/.490. Much more area under the curve. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted March 10, 2003 Share Posted March 10, 2003 pparaska THE RPM LEVELS EFFECTIVE RANGE DROPS ABOUT 500-700RPM WHEN CHANGING FROM A 350 TO A 406 DISPLACEMENT THERES LITTLE CHANGE IN FLOW SWAPPING FROM THE 190CC-TO-195CC HEADS CERTAINLY NOT ENOUGHT TO WORRY ABOUT. Quote Link to comment Share on other sites More sharing options...
pparaska Posted March 10, 2003 Share Posted March 10, 2003 Thanks Grumpyvette! Quote Link to comment Share on other sites More sharing options...
383 240z Posted March 11, 2003 Author Share Posted March 11, 2003 Ok I've read the links and your latest post and It is starting to make sense to me I'll be posting a decision soon thank you for helping me with this. I did a bunch more math and I relized that what I need is not what I THOUGHT I needed. Keith Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted March 11, 2003 Share Posted March 11, 2003 Thanks Grumpy. Another bookmark added to the homework list. Quote Link to comment Share on other sites More sharing options...
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