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400 sbc horsepower stumped

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400 engine
21K views 56 replies 14 participants last post by  ericnova72 
#1 ·
I have just finished building a 406 sbc stock crank scat 5.7 7/16 cap screw rods speed pro flat top forged pistons 5 cc valve releifs RHS Pro Action aluminum heads 200 cc runners 72 cc chambers howards hydraulic roller cam,241 int-245ex duration @50 . 545 int 565 ex lift 110 lsa matching lifters crane roller rockers 1.5 ratio, rpm intake holley hp ultra 750 dp cfm carb msd streetfire hei.1 3/4 headman headers .
I had it dynoed on a dynatech roller dyno it showed 427 ft lbs of torque at4200 rpm and only 319 hp at 6000 rpm fuel ratio was perfect throughout the run timing was 34 degrees tried with and without vaccum cannister less torque withe the vaccum canister hooked up fuel pressure was steady at 6 psi i cant figure out why these rear wheel numbers were so low am I doing something wrong does she need more air,such as a team g intake maybe or more fuel or cfm any advice.After 1500 miles took her to the track ran a 12.98@ 105.72 mph in a 1980 Z28 with a 3:42 rear and a M21 4 speed and firestone radials was not to impressed but for a daily cruiser not bad i guess. It just seems there should be more power coming out of of her any advice would be helpfull I was thinking about porting the heads an go with a 2.08 intake valve and perhaps a beehive spring set up. Im stumped any help please would really be appreciated.
 
#35 ·
horsepower stumped

I definately want to keep the streetability and reliability aspect of the car,up untill now I've kept both although the cam is stretching it a bit my wife is still using it as a grocery getter,I quite sure the tremec with a 4.56 or 4.33 will make a world of difference.68* the 4.56 will give me a 3.10 final drive the 4.33 would give me a 2.95 final drive, I tgink I will port my RHS 200's and put in a 2.08 intake valve perhaps I'll switch springs from comp cams 987's to a beehive setup for less reciprocating mass and valvetrain stability. Thanks again everyone. As far as ignition wires go, again the taylors give me the best clearance issue on the plug side,perhaps i'll go with a different wire but taylor plug ends,i'll try a 1/2 inch phenolic spacer for some more air should I stick to a 4 hole to keep it dual plane or an open spacer, will it affect the air flow that much,anyone ever try it.
 
#36 ·
spacer

You wont need a spacer for a Vic Jr manifold.I only use a 3.50 gear. The tremec has I believe 2.78 1st gear.That gives me close to 10:1 first gear over all ratio with a 27 inch street tire it does 54 ish mph in first.just over 2k at 60 mph.I use a solid roller and it buzzes flawlessly over 7k.I put a 6k chip in the rev limiter now as I have too much power to traction ratio atm.
You will have the same problem with the better manifold.If you used a 4.1 rear gear that would give you 11.4 :1 over all first gear. What over all first gear do you think is best?
 
#37 ·
horsepower stumped

Its a stepin the right direction with a 4:33 rea end and a.68 overdrive I'll have a 2.93 final drive which is where I want to be on the highway with a 4:56 I'll have a 3.10 final drive again thats fine.
does anyone run dynomax ultraflo welded mufflers and if so how do they perform and sound, Thank you again everyone you have all been a great help
 
#38 ·
horsepower stumped

Well i hace freed up the cats and installed 3 inch maganaflow 4inch round bullets HOLY CRAP F Bird you were so right the machine breaths abd does not run out of breath, last night I put her through her pace and she kept pulling and pulling I took her to 7000 rpm with no hesitation although I know I have to keep her no more than 6500 rpm cant wait to put in the 5 speed with 4.10's i'll keep you posted, oh yeah if like flow and loud go wiyh bullets
 
#41 ·
horespower stumped

IN regards to timing i have 18 Gedgrees initial 36 total however i have my vaccum advance set to port vaccum and the timing raises to 53 degrees I have read in David Vizzards books that that is what a sbs with a large cam needs once were up to highway speeds,would port or full vaccum be better ,not only for mileage but for plug cleanliness and throtle response.
On the dyno though with no vaccum advance i picked up 27 ft-lbs more torque at the wheels,as well is it better to use nylon or plastis scews for the rotor and or weights so that there will be no spark jumping or arching,sometimes after 2 or 3 WOT runs,foe some reason it always happens at the track, I'll get a little hesitation regardless of the amount of time at WOT but if I let off momentarily everything rights itself back up,i've checked my fuel pressure and it does not drop at WOT under load it stays at 6 psi would jet extensionsand the right floats for clearance possibly help,my wires are brand new and tuked and taylored as far away from heat sources as possible with loom separators attached to the valve covers,I know some of you are not fans of taylor wires but they have the most clearance on the plug boot side of any 90 degree boot that i know of Ive melted MSD's and morosos and accel boots but the taylors seem to be doing fine.
 
#42 ·
horswpower stumped

Okay I regapped my plugs to .35 even though the gm manual for 1980 says .45 with HEI. .35 for points But I went with your advice,however I just changed my plug boots 2 weeks ago and when I took them off the plugs to regap them the plugs were clean on the tips and tan in colour but the porcelan part of the plug was covered with carbon should that not be the cleanest part of the plug since it is covered buy the boot..
as for thr the prevvious comment the 1st 2 runs were my best then
I ran into those studdering problems after the the car /fuel lines got hot, makes .sense
 
#43 ·
stumped

changed the cap & rotor also canged the #2 wire in side yhe old cap all the contacts had carbon and welding type marks but the #2 looks like it had been tig welded so far so good at 2500 i hammer it and she lights em up asfor the phase travel on hard deceleration i show 20 inches vaccum on 1/2 throttle or more vaccum goes to zero.
 
#44 ·
sapsZ28

any advantage to locking out the timing and if so how is it done,As well after changing the cap and rotor and trimming the wires with proper looms,new hei boots etc I now have a constant zipper type sound coming from my stereo when the engine is runing ,but not under batery power ,
 
#46 ·
sapsZ28

I did 1 3/4 headman headers 3 inch collector 3 inch xpipe,got rid of the H pipe, 3 inch 2 chamber flowmasters ended up not liking the magnaflows, also put in a 1/2 inch open phoenolic spacer breaths alot better and climbs the rpm ladder faster,I might have room for a 1 inch spacer that will be the next step,not alot of clearance under the Camaro but today i'll find out if it fits.
 
#48 ·
saps Z28

Thats why I went with RFI supresiion wires and plugs for 3000kms and 3-1/2 months no noise through the radio,which is a constant noise not the winding rpm type due to rfi suppression or bad grounds this sound is like listening to the distributor firing order throgh a specific sound wave.
This all happened after I changed my cap & rotor and put new hei boots on after custom cutting to length my existing wires , they were way to long from the factory,all parts wereexact as the ones I tossed ,MSD and TAYLOR,. and last I put on a 1/2 inch spacer last weekend and there was a significant difference the car could breath and wind up under load better,last night I switched it and put in a 1 inch spacer ,phoenolic open bore,I only moved the car to park it in the garage but I think I finally woke up the beast .just from pedal feel and sound.althugh i will eventually check it again do spacers in the 1 inch range need the carb rejetted due to the air volume change in the plennum vs before.

Thank YOU EVERYONE who has helped me along the way with my ride.
 
#49 ·
saps Z28

I changed the contact under the coil and it was all black with carbon on the spring as well the cap and rotor kit came with 2 contacts the [stock] one,and the Msd steel one which I used with dialetic grease,as for the traction issue no I have not adressed it yet, on a daily basis the cars tire will stay as is remember I use it city and hwy on a daily basis thats why I built it to drive it and enjoy it its my little time machine.ive made my tranny decision tremec 5 speed with a .68 overdrive and a 4.10 rear end ratio,i,ll check the ohm readings on the ignition system and let you know, Your right about the 1/2 inch spacer not a huge difference but there was a significant improvement with the 1 inch spacer,
 
#52 ·
sapsZ28

they are Taylor spiro pro's 8mm resisitor type Thanks for the ohm info I will do the redings and get back to you I am assuming the lower the reading the better.
As for the noise its not that winding radio noise its a static crackling sound on battery power there is no noise only when the car is running and its a very low frequency soundit goes through all four speakers but I'm not sure if it goes through the sub i have 2 separate amps I'll get back to you.Thanks again
 
#53 ·
sapsZ28

well I figured out why at times my motor stumbled and momentarily lost power then csme bsck to life I only had a 40 GPH freefflow fuel pump on it rated to 300hp I put a edelbrock performer rpm fuel pump on it which free flows 110 gph and holy crap the motor really came to life before it would pull to 6500 rpm but after 5000 rpm it would take its time now even with the 3:42 gear the car goes to 6500 rpm in a heartbeat ,what a bonehed move I pulled but when I make a mistake i admit it it runs so much better now,I also bypassed the regulator since the pump is preset for 6 psi which is what my ultra 750 calls for,Thanks agaim everyone for all your advice and input.
Now we start to save for a 5 speed.happy cruising everyone
 
#55 ·
sapsZ28

Hi F-Bird with the new pump and exhaust and a custom diff pinion snubber,22 degrees initial and 40 total I had a 1,91 60 ft 12,79et @110.68 mph I launched it at 3100rpm its getting better plus I drove it 340 KM round trip to cayuga and back next up is ported heads with a 2.08 int valve 5 and a 125 shot of spray over the winter Thanks for the advice. I know gears and tire when I fry my rears I will go with a drag radial BFG I still want streetability and some handling
And thank you for all your input.
Thank you all
 
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#57 ·
I totally agree with this...you need to really finish sorting out all the little things naturally aspirated first.

Don't even think about nitrous without an electric fuel pump.

"Bad things happen fast on nitrous" is an understatement for those who don't have all their ducks in a row first. It will happen faster than you can even begin to react to save the engine...literally "the blink of an eye".... and the engine is hurt.

Along with the fuel curve, the ignition timing has to be corrected for the nitrous use.
 
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