Thread: first 496 build a running success

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had a 402 in the chevy and sum jerk who put it together neglected to put a retaining plate under the cam bolts which came loose, sent 2 with flat washers through the engine which seized the oil pump twisted the top off it and well you know the rest. on tear down found the 3rd bolt just about to go too. the thing turned out to be a way worn lucky dip engine anyway and with the cost of rebuilding i thought id take pats advice, just get a 454 block and make good use of the fully worked heads and brand new stroker crank id had sitting there for a few years and make a 496. i was paying for a rebore, pistons and balance either way and with the money i saved on not havn to get the old heads overhauld the price of the conrods didnt really come into it.
so i finally got the 496 together and going and it worked out real good, has gobs of mid range torque which was what i was hoping for, i thought the tall diff would give me harder traffic light launches as it wouldnt keep lacing off the mark but still get off it real quick holdin you pinned in the seat because of the big crank AND have plenty of top end, a goal which i achieved and works well. now i know theres been tons said about big block stroker builds on here already and have drooled over them all and now after havin a 496 im hooked but i was just wondering if any of you guys could run your experienced eyes over MY final choice of combo, let me know if its any good, give me some tuning and dissy curve advice or whatever, maybe give me an idea of the power id be getting (there arent any dynos where i live except one and the shop are notorious for blowing things up so i dont wanna go there) and tell me if theres any room for improvement. mainly exhaust size and carb bein a bit small and valve springs. here goes

66 impala, 295/50/15 rear tyres 26.6" tall, 9" diff with 3:1 gears, stage 2 shift kitted th400 with 2200 high stall converter, engine is 9.8-10:1 compression, needs 98 octane pump gas, 454 block 60 over with 4.25" crank, scat 6.385" rods, keith black flat tops, all balanced etc, hei dissy, heads are 3931063 casting planed a bit so a little under 100cc chambers, with severe duty 2.190" intake and 1.880" exhaust valves both with 3 angle grind, been cced, ported and flowed, roller rockers, edelbrock performer rpm intake, 750 holley vac sec carb,

valve springs were 110lbs at 1.9" and 270lbs at 1.4" before adding 45 thou shims under them at cam grinders advice

cam is flat tappet hydraulic comp 280 magnum recommended by www.kelford.co.nz (check them out) i know i shoulda gone roller and got heaps more power but i didnt fancy spendin the $1200-1500 to run roller at this stage and ran outa muny, just wanted the car going, yous can relate? haha

exhaust are 4 into 1 headers 1 7/8" primaries, 3 or 3.5" collectors about 12" long i think(not quite sure on collectors car aint with me at mo im on holiday) into a twin 2.5" system with no crossover or balance pipe and uv570 mufflers which are a straight through type

heads were flowed at 25" test pressure which they do on their benches here so may need converting if they gotta be at 28":

int: .100 .200 .300 .400 .500 .600 .700
69 141 202 244 270 288 297

eh: .100 .200 .300 .400 .500 .600 .700
65 122 149 172 191 206 217

said heads would support 600-650hp and i really couldnt do better for heads on the street up2 6000rpm unless i go alloy which id need if i was putting it on the strip because the bigger runners would make it breathe better up top but these would have better throttle response on street from the velocity of the smaller runners (were on a stock 2 bolt twin turbo 454 with 750hp and ft/lbs torque under 5000rpm with bugger all boost before i got them)

it idles rough at 1000rpm with around 14-15" vacuum

i want it to be a mid range torque meister and it is, it pulls like a schoolgirl but only until about 4800rpm when it starts to valve bounce, its running fine, it aint leaning up top or stumbling or anything, im just wondering do i need stiffer valve springs to get 5000rpm? will there be any more power up there? or is that all itl spin to with that big crank. comp test their big block cams on 454s (small blocks on 350s) and i know bigger strokes lower the rev range but would it lower it that much from the stated 2000-6000 to 1000-4800 like it is with only 1/4" increase?

would keepin this exhaust for the velocity, stiffer valve springs, a bigger carb-say 850 and some 3.25 gears improve performance? or is it about as good as itl get already and should i just leave it alone since its running good and im quite happy. any other info needed let me know, cheers guys, appreciate your input

well the 750 vac is ok but ? i would thing if you used more gear you going to just hit the wall faster as for the springs they seam like there ok but if your in valves float ? you need more spring but the more spring the better your chance of wiping your cam at low speed that why i run rollers cams . as for a small 4 1/4 crank engine i have them that go to 8000 rpm and bigger then that turning 7000+ so if it built right it can go there i see no need to be in that rpm on the street but i know someone that has you may want to back off the lifters if more then 1/4 turn

yea thats why i didnt go for more gear in the rear end, this trans shop i was asking here told me to go for 3.7 gears and 3000rpm stall, i didnt think thatd be a good idea being it only goes to 4800 haha, i know rollers the way to go just wanted to get the hang of how to do things and sorta cut my teeth first time round, it is a street engine so will never need high rpm turning. lifters have 3/4 turn preload, what affect would loosening them up as you recommend have?

Originally Posted by chopped66impala

yea thats why i didnt go for more gear in the rear end, this trans shop i was asking here told me to go for 3.7 gears and 3000rpm stall, i didnt think thatd be a good idea being it only goes to 4800 haha, i know rollers the way to go just wanted to get the hang of how to do things and sorta cut my teeth first time round, it is a street engine so will never need high rpm turning. lifters have 3/4 turn preload, what affect would loosening them up as you recommend have?

lifters can pump up and hold valve off seat there less of a chance of that at 1/4 turn i think the cam could be bigger for a 496

ahhh sweet. yea what sorta cam do you recken? another cam co here recomended this custom cam 230/260* at .050" and .540"/.560 lift on a 112 lobe, i went for the kelford one because they asked more questions about my whole combo, also what are the heads i got like as far as heads go in your opinion?

Originally Posted by chopped66impala

ahhh sweet. yea what sorta cam do you recken? another cam co here recomended this custom cam 230/260* at .050" and .540"/.560 lift on a 112 lobe, i went for the kelford one because they asked more questions about my whole combo, also what are the heads i got like as far as heads go in your opinion?

well i use rollers so i can give out numbers on them but a flat cam i would of went maybe soild flat cam if looking for more rpms i would of went up on dur and lift but you would need to be at 10.5 cr . BUT back your lash off some try that your running a short back tire at 26.? and if you have more rpms out of it you could go to 3.50 i would not go up more then that if it is not pull up on the stall in 1 st with your foot on the brake in gear i would not add more stall . i have no hot flat lifter cams numbers.other then whats in the cam books . i have not use one in any bbc in many years i would have to work out the numbers to the cam you have and go from there for a better cam. are you sure your not running out of fuel and what do you have for a intake were is you timming at how curve? are you running vac av ? them heads are the old bath tub 396 head ? did you open up the chambers for bigger valves i think them heads work just as good with the small ex valve in them i used them both ways if so they are ok there is better i may have used a open chamber head big o port like 781or 049

true. yea cams 280/280 at 50 and 520/520 lift on 110, maybe the 282s cam better, wee bit more duration and probly 40 thou more lift. yea thats why i was wondering about carb bein too small, not feeding it up top which could be the problem, still have the stock fuel pump and 3/8" fuel line which i should probably sort so its got more gettn to the carb when it needs it. not sure about dissy curve havnt had that seen to yet and still learning about that aspect, was on a strip 350 before i got it though if that would make a difference, timing is 8 btdc, yes vacuum advance, manifold edelbrock performer rpm, and yea about heads, thats them haha i have stock 3993820s from the 402 but couldnt have had the work done to them that these others have for the price i paid for them

so perhaps start by backing off the lifters then bigger fuel line etc so its got more fuel there then get dissy curve looked at?

a guy at rare spares had a small block impala here, he put a 402 in and said it leaned out up top when he stompd on the loud button but was ok if easing the way up there at part throttle, reckons he fixed it by goin to a bigger fuel line because they used 2 different sizes from factory for big and smallblocks, mine doesnt do that now below 4800 and didnt do it with my 402 when i mash the loud button though and its still the same size fuel line i had with my 283 but should i do this as a precautionary measure?

Originally Posted by chopped66impala

a guy at rare spares had a small block impala here, he put a 402 in and said it leaned out up top when he stompd on the loud button but was ok if easing the way up there at part throttle, reckons he fixed it by goin to a bigger fuel line because they used 2 different sizes from factory for big and smallblocks, mine doesnt do that now below 4800 and didnt do it with my 402 when i mash the loud button though and its still the same size fuel line i had with my 283 but should i do this as a precautionary measure?

i would run the timming all in at 2500 rpm and with the flat top try 36 try running 24 or a bit more in the dizzy rest on the crank use a 3/8 fule line and tank pick up try if a mechanical pump and a carter street /strip pump or some thing like that use a ultra lite fuel pump pushrod back off you rockers to 1/4 and try it

awesome! thanks man, ill try that out and let you know how i get on