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Performance from a mild 350. What is good enough?

sreidmx

sreidmx

Fortify Offroad
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Soo.. i have seemed to have reached a crossroads with my sbc and truck in its current config. I feel like there should be better low end torque but I feel that something is out of wack. I would say that I am a very competent mechanic and understand the holley carb and its functions very well. I have all the necessary tuning aids to verify that the engine is operating within normal parameters.

Ill lay out my expectations and scenario as to outline what the deal is.

I expect the engine in the truck to respond quickly. like TBI quick. I know there are compromises with carburetor trucks so that I understand. For what the engine is 355 ci flat top pistons, rv cam, rpm air gap, thorley headers, 700 holley dp, 4.10 gears th350 and 36inch tires.

Maybee my expectations are too high? I am not expecting the truck to blow the tires off from a stop light but I do expect a good running sbc to get off its but when I ask it.
Dont get me wrong it does run really really well and much better than it ever has in its life but it seems that this doesnt really way up until 2500-3000.. I kind of think its a symptom from the tires and gearing along with a tight converter.. (1300-1800) That is guess I havent actually tried to measure the stall. But in low the truck is an absolute ape, it will in 2wd low blow the tires off into 2nd gear on the pavement. and low will rev out to around 45mph so I feel if I can go that fast in low gear it must be gearing related.

my wife has a 92 tbi truck with 33s on 3.73 gears with a 700r4 and it gets out of the hole much harder then gives up the ghost 4krpm. My k5 is the opposite... the cam isnt very big, it makes 16 inches of idle vaccum for godsake.

I dont know but what are you all feeling like with your sbc? Does it need more cam and higher stall and lower gearing to get the grunt and broad spread of power? I had a smaller 600 cfm vaccum sec holley and that wasnt any better down low, heck the DP make the low end better and has much better response.. but still falls short of what I want. btw my AFR is on the rich side 11:1 idle to 3500 and 12:1 to 13:1 by 5krpm I know I can make jetting changes but that I dont think is worth 50 hp..
 
I'm married to 16.5's these days.. :doah:


want snot, gear, gear, gear... :pimp: :haha:
 
You know I was considering twin turbo very seriously and that may be the only way to get what I want.. Power wise..
 
Mutt is totally married to the 37 mil's.. and that's fine at $100 to 125 a piece.. :saweet: I'm actually looking to pick up 6 more baja's so I have em for down the road..


anyway, twin turbo stuff is fun.... and involved... :pimp:






I know LS schtuff is all the current rage :rolleyes:, but PLENTY of power to be made from oldschool rotating chit if wanted...

it's like buying a tried and true PS3 with a huge library of great, cheap games, as opposed to going with a new PS4 and an unknown, expensive library... :haha:
 
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I completely agree. Part of the reason I got the dp holley to move that direction. Boost is gooood
 
I run a 2500 hughes stall in the mostly stock 408 and it makes me happy when i step on the skinny on the street. 33s and 3.73s. 700r4.
 
IIRC just some 350 heads with steam holes drilled. Added roller tip rockers.

I spent $1200 on the entire engine rebuild. Summit 1103 cam, roller rockers, and freshened everything up.
 
Alright well your up a lot more cubes than me .. Maybee it's time for a cam and converter
 
700R-4 and 5.13's.

That'd give you 50% more torque to the ground.

TH350 and 4.10's multiplies engine torque 10.33:1 (2.52 x 4.10)
700R-4 and 5.13's multiplies engine torque 15.7:1 (3.06 x 5.13)

The deeper gearing would get your 355 into it's sweet spot in a flash.
 
Your calculation leaves tires out of the important equation. 4.10 with 31s accomplishes similar goals.
 
sreidmx said:
Your calculation leaves tires out of the important equation. 4.10 with 31s accomplishes similar goals.
Click to expand...

I was working with the assumption you were happy with tire size. You really want 31's? :confused:
 
No your assumption was correct and 5:13 is prob the best performance gear. But 700r4 has a really large jump from first to second and the th350 doesn't and is closer ratio, the th400 is even closer ratio.
 
You need more advance timing. These old engines need more time to burn the newer fuels. But, you need to be able to modify the curve. Warm your engine up and back off the vacuum advance. Using your timing light, dial in 2 degrees more advance. Turn the engine off, wait a few minutes until the engine heat soaks. Crank it. Repeat this process until you try to crank it and the starter struggles or it spits back through the intake. From this point, back your timing off by 2 degrees and that will be your initial timing.

If you have an MSD distributor you can easily change the total advance with a different stop bushing. There are suppliers of stop bushings bigger than MSDs 18* bushing too. I have a 10* bushing in my Suburban and 14* bushing in my Bronco.

No more stinky idle and MUCH more responsive.

Make sure you use only full vacuum, not ported for the advance. Cooler idle and better fuel economy at cruise.

My 86 Suburban is at 24* initial. Total 34*

My 74 Bronco is at 22* initial and could go more. Total 36*
 
That's my issue is I don't have a way to limit total advance and my vaccum canister only adds 5 degrees, I was going to get a can that pulls 12 and change the advance curve so it comes in faster like 2800-3200, but isn't there a way to grind on the center plate to limit mech advance?
 
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