[chevyguy81]

Let me start off with this is the motor that was in the car when I bought it. I am just trying to figure out what I can do to improve the power. So with that said here is what I have:
402 BBC
Performer RPM intake
750 Vac secondary holley
Cam is a XE274 230/236 .552 .555
353049 heads <- have no idea what has been done to them
I also don't know what the compression ratio is.

Transmission is a th350 with a shift kit and a 2800 stall
10 bolt rear end with posi and from what I can tell a 2.56 rear gear? It is a little over 2 1/2 turns on the drive shaft with 1 full rotation of the wheel.

I have played with the timing and air/fuel and the car runs decent but it just lacks the power that I think it should have for being a big block. Besides ditching this motor to build a larger motor what would you change?

 

[VinceS427bb]

that 2.56 gear ratio will make most engines seem like no power...
what year/model are we working with??
rear axle with 3.07 to 3.55 gear would be much better for taking off,
but cruise rpm goes up about 200rpm each gear ratio step up...

 

[lg1969]

Change the rear between 3:55 to a 4:10 gears and remove the check ball in the secondary pod. How can expect to get any performance with those desert gears?

 

[sschevellefan]

Well without knowing the pistons you have, the 049 heads are going to drop the compression down quite a bit and then the 2.56 gears arent going to help much either.

Do you know what pistons were used? It`s possible that you can swap to some early closed chamber ovals to get the compression up but you need to know what pistons were used first. Then change the gears to 3.55-3.73 as already mentioned. Then optimize your timing and carb. Do you know what your ignition timing is?

 

[gnicholson]

The 049 heads have atleast 10 more cc's if not more in the chambers than the original closed chamber head.no compression coupled with the cam you have is a pretty good reason it doesn't run that well.closed chamber oval port heads or maybe something like the 100 cc edelbrocks would help.going lower in the gear to around 342 would help a bunch as well

 

[badrad]

Let me start off with this is the motor that was in the car when I bought it. I am just trying to figure out what I can do to improve the power. So with that said here is what I have:
402 BBC
Performer RPM intake
750 Vac secondary holley
Cam is a XE274 230/236 .552 .555
353049 heads <- have no idea what has been done to them
I also don't know what the compression ratio is.

Transmission is a th350 with a shift kit and a 2800 stall
10 bolt rear end with posi and from what I can tell a 2.56 rear gear? It is a little over 2 1/2 turns on the drive shaft with 1 full rotation of the wheel.

I have played with the timing and air/fuel and the car runs decent but it just lacks the power that I think it should have for being a big block. Besides ditching this motor to build a larger motor what would you change?

Looking at the list if the rebuild used the cheap rebuilder pistons you're probably below 8:1 compression and that cam will want about 10:1. 402's run hard but the need the compression for bottom end grunt. If you don't want to change the rear consider a 2004r trans swap, it is a bolt in but will need a new convertor.

 

[chevyguy81]

This is in a 72 chevelle. I'm not sure what pistons are in it. I went through all of the paper work he had with the car and came up with nothing. The timing is set at 21 initial 36 total all in by around 2500.

 

[Hollow65]

You got 1000mph gears. Get some deeper 3:42-3:73 if it's a cruiser. Also does it ping with that much initial timing?

 

[jeff swisher]

Even with 256 gears a strong engine will feel good once you get it going.
I have ran 229 gears and still spanked the newer WS6 TA with my old 350
Never came out of first.

But one issue that you really need to pay attention to is what has been stated.
Compression.

My last .030+ 396 got some 11:1 domed pistons and the 280H comp magnum cam.
210psi cranking pressure.
No issues running 36-38 total timing and 91 octane.
Iron heads that are ported and chambers polished and all sharp edges removed from combustion area.
Some worked over smaller chamber heads would really help.
Gears are nice but a weak running engine will still feel weak.
Ported heads are nice also..a simple bowl port and good valve job will get you 300cfm on the intake side on most old iron heads

I had a car with 370 gears and a 350 in it that ran 12.50's that was with uniroyal tiger paws.
Then i pulled the engine to build it stouter..I stuck in a bone stock 1978 350 in the mean time.

Wow what a putz!.. been so long since i felt what a stock engine felt like.. even the 370 gears did not make it worth a hoot.

That 274 cam will rev, you need some decent valve springs with it if you go to the upper 6000 rpm range.
same with the 280H with the heavy 2.19-1.88 valves i found 121psi seat pressure was not enough.. good for 6500 then valve float... could be it just does not like that comp cams spring.

Lot's of things to pay attention to , of course you may know this.

 

[chevyguy81]

Thanks for all of the info guys. I'm going to just get through this summer with it like it is and this winter start changing some things. At least I know now what to start with.

 

[MikeN]

IMHO, 2800 stall is a poor match for 2.56 gears. I would change one or the other.

 

[sschevellefan]

maybe consider picking up another bbc core to build while you continue driving this one.

 

[ddeennis]

Let me start off with this is the motor that was in the car when I bought it. I am just trying to figure out what I can do to improve the power. So with that said here is what I have:
402 BBC
Performer RPM intake
750 Vac secondary holley
Cam is a XE274 230/236 .552 .555
353049 heads <- have no idea what has been done to them
I also don't know what the compression ratio is.

Transmission is a th350 with a shift kit and a 2800 stall
10 bolt rear end with posi and from what I can tell a 2.56 rear gear? It is a little over 2 1/2 turns on the drive shaft with 1 full rotation of the wheel.

I have played with the timing and air/fuel and the car runs decent but it just lacks the power that I think it should have for being a big block. Besides ditching this motor to build a larger motor what would you change?

I was looking at some old posts about 10 years ago when i had about the same combo you have right now.

looking back I had a 396 10.2 to 1 motor with 2.41 gears th350 tranny and a delta cam 233/239@ .050" with .551" lift. it ran 14.47 @ 98 mph with 2.15 60 ft time in street trim.

with some work - intake, carb timing, rhoads lifters and such the car ran 13.50 @ 107 plus mph with ONLY 2.73 gears.

it appears I had about 180 psi cranking compression at best and worst was 170 psi after I installed the rhoads lifters to help with bottom end torque.

Maybe you could type in "ddeennis" in the search and read my posts from 2003 and 2004 which is detailed to what I did and shows times with changes how I got from 14.47 to 13.50 and gained almost 10 mph trap speed with no real big changes that involved pulling the engine. looked like i might have pulled my heads did some porting and installed shim gasket to boost compression more.

Might be some things there to help you out.

here are a few links to some of those posts back then.

http://www.chevelles.com/forums/showthread.php?t=24848&highlight=

http://www.chevelles.com/forums/showthread.php?t=18179&highlight=

http://www.chevelles.com/forums/showthread.php?t=17888&highlight=

http://www.chevelles.com/forums/showthread.php?t=21414&highlight=


Back in the early 90's my 396 had 7.7 to 1 compression( didn't know that then), 272 crane cam which I believe was
218 @ .050" with like .515" lift, had open chambered heads with rebuilder pistons and they was like .050" down the hole with .040" head gasket ( couple of years down the road I found this all out when my engine was going slower at the track trying to make it go faster with bigger cams, converter, gears, intake and carbs) but stil managed I believe 135 psi cranking compression and I had to push timing around 44-46 total for best results at the track. had cheap small tubed headers headers, stock low rise intake with 1" carb spacer and I think just a 600 cfm holley, stock th350 tranny and single spinner 2.56 rear end and that thing would spin that tire for well over a block long and I stomped anyone I raced back then- of course I knew how to take off without spinning my tire. I finally took that little 396 to the track and it ran 14.80 at 99 mph ( first pass) the best I did that night at the track was 14.40 pushing it hard of the line best i could without to much spinning with a 2.19 60 ft time at 99.xx mph, I was so trying to crack 100 mph, my shift point was 5500 rpms.

Not to shabby for a 3600 lbs camaro with a 396 and 2.56 gears.


maybe see what your cranking compression is, remove all the plugs and wire open the carb and throw a battery charger on and get the reading from each hole.

 

[kettbo]

I've played around with the 396s and 402s here.
You need the big dome "11:1" pistons with open chamber heads on a 396 or 402 to build enough compression. Small bore and small stroke is not great for swept volume.

look at this chart, see the CR fo engines with 119cc chambers
http://www.flatlanderracing.com/trwchevy396_427.html