400 chev

[jetboatnutnz]

hi ppl,
i just put a 750 holley d/per on my 400 s/b chev to try and get some more punch.

its stock apart from roller rockers,toquer 2 inlet with 1 inc spacer,new hei and headers.
i run it on 95 pump gas,
it was dynoed before i got it with a 600 v/s ,4900rpm@ 319 bhp.

i rekited this 750 and put 70s in the prim/and 80s in sec,(jets)
and a 6.5 p/v,
its a 4779-6 model with down legs,4corner idle,

can some one give me some ideas on setting this up for me motor? tha:juggle:

[Mr. P-Body]

If it still has the stock Chevrolet cam in it, you're not going to gain much no matter what else you do, short of an external power adder. I would be surprised if the bigger carb netted you more than 10 HP, but it might push the "peak" up about 400 RPM.

I would get a performance cam and go from there. If you tell me which head casting you have (last three digits of the casting number, in between the valve springs), I can make a good cam recommendation.

Jim

[jetboatnutnz]

HI Jim,
thanks.
ill shoot home and check the numbers out on heads,
just heep in mind i run this motor in a jetboat and the rpm range is from idle to 5000rpm max.most of the time it sitting a 4500rpm and the 500 or so left is just to hook a corner.
i use a 743 hamilton unit,witch will pump water best at 4500 rpm but will still work until 5200rpm,
i dont have to long befor next race so,pulling the motor down befor then is not realing ideal.
nathan.

[jetboatnutnz]

hi .
the head numbers are 8873493
block nubers are 330817.thx

[jetboatnutnz]

hi,me again,the speed shop in town here gave me a price on a street cam
info on the cam is: 444 lift,214 degre rpm is 1800-4800.
what do u think of that? its cost is $180 plus lifters $160.

[sleepy]

I use the Ultradyne 285-295 105 Lc cam for dirt track the power between 3000=6000 is awsome.

[RandyW]

Boats like to run rich due to the load, what impeller are you running and what clearance on the wear ring/housing?

[jetboatnutnz]

hi Randyw,
i dont know,ill try and get hold of my unit builder and ask him the pich of impallas and clearance of statter housing,
i would say it is set for 350 hp,as thats what i asked for,i got the nosel back off him when he rebuilt it. at 95 mls, but ive takin it down to 92 mls to get some more load/speed because the rpm range has changed form the 302 chev to the chev 400 s/b.
i did try it with the 4oo a month ago with the nosel at 88mls but it wouldent put any higher that 4100 rpm with the 600 v/s on it,
so now ive set it at 92mls nosel and fitted the 750 d/p ,and tryed removing a little more weight out of the boat.its a ali craft,16 ft mono hull,2 seated.
it did have a 265 hemi six with side draft delortos (48s) and worked like a e49 motor about 300 hp.,
it did 115 kms on the water,

[Mr. P-Body]

Maybe "3973493"? That's the only "493" that shows up in any of my books.

76 CC chamber, decent runners, 1.94 intakes. Not a bad head.

That price for a Chevy cam is OUTRAGEOUS! Flat-tappet, right? Awfully small for a roller.

In the boat, I would recommend Comp Xtreme Marine 12-240-4. Good for the compression ratio and a jet boat. RPM range (advertised) 1,600-5,800. 226/236 @ .050, .480/.489" lift, 112 LSA. Very good for an "A" impeller.

That should cost about $210, cam AND lifters. Be sure to put a high quality timing set in there at the same time. New valve springs wouldn't be a bad idea, either.

Jim

[jetboatnutnz]

hi guys, well the 400 s/b is in the speed shop now getting a birthday
we are fitting: 350/5.7 rods i beam (probe) with arp bolts.
balanced crank.
30 over keath black flat top pistons
a 6 ltr boat sump
cam and heads are still gona be the stock 493s but well clean them up.

[Mr. P-Body]

RED FLAG!!!

KB hyper-eutectic pistons are a very poor choice. The top ring must be gapped to the point of rediculousness (around .032" in this application). Speed Pro offers a much better h-e piston without the design flaw of the KB, and for less money. H616P is the part number.

Failure to follow the ring gapping instructions WILL result in catestrophic engine failure, in the form of popping the top off the piston at speed. This is not a "maybe".

Highly recommend you change the cam while you're in there! No need to do anything to the heads but make sure the valve job is fresh and the springs are good.

Jim