topping out rear end head setup

ElCafreak · Posted: Mon Jun 23, 2008 4:20 pm Post subject: topping out rear end head setup

How's it goin Dudes? Here is my situation.
My STRONG 355 is hooked to a great 350 turbo trans. The cam head that sold me the engine years ago told me it has small block 400 heads. I just changed the rearend oil and re-checked the gear ratio. I had 41/15 on the gears. That makes it a 2.73. Does that sound right?
At the track the best I can run is about 15.6 @ 89 mph. Which isn't bad, but it seems to wind out quick about 3/4's of the way down the track.
Do I have to change both the heads and the rearend to gain that extra second or to hit the 100 mph target?
thnx Dug
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1BadElky · Posted: Mon Jun 23, 2008 4:31 pm Post subject:

your best best is probably an OD transmission. As far as heads, I know nothing about 400 heads, but a set of old Vortec heads will be much better, or you could use aluminum if you have the cash.

as far as gears, I'd think 2.73 are too numerically low for track use. I don't see how you're taching out, but I dont know much about 1320 racing.

i could see taching out with 3.73s though...
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464elky · Posted: Mon Jun 23, 2008 8:11 pm Post subject:

Maybe the kick down is maxed and it is still in second gear Question

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Snaggle To0th · Posted: Mon Jun 23, 2008 8:33 pm Post subject:

Sounds like a tranny problem to me. Are you driving it in Automatic mode or shifting it manually from 1-2-D? TRY shifting it from 1-2-3 and see if that changes your times. I had a problem with my tranny where it shifted into 2'nd too early, couldnt figure it out so i bypassed it by shifting it manually. On my stock 170hp engine with MINOR mods anda TH350w with a shift kit the elky ran a 16.32 in 120 degree weather 2 years ago. A 355 if it was built right should do better. And if its not a daily driver upgrade to 3.73's and that'll help you out on that TH350.

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ElCafreak · Posted: Tue Jun 24, 2008 9:19 am Post subject:

The engine was deffinately built right. It was bored 30 over with a better cam. It's an older block and the highly respected guy that did all the engine work told me that the block alone was worth $1,200 dollars. It was 300 hp right from the factory.
The carb is working ok, and it was shifting ok too. I should look for a posi rear and 350 heads.
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Steve81OR · Posted: Wed Jun 25, 2008 7:23 am Post subject:

Cylinder heads for a 350 and 400 are the same, as they are for all SBC's. Although the factory may have used different heads for each engine, I believe they are interchangable. I bought Vortec heads for my 355 last year and everything I read said I should see at least a 20 ~ 40 HP gain (compared to stock).

As far as rear axle gears go, the 2.73's (highway gears) were stock for my '81 and I am running very close to the same times you are. I haven't managed better than 14.9 in the ¼ mile because of the gears. I'll be installing either 3.43 or 3.73 gears later this year, should still be drivable on the street and give me a better time at the track. But I'll have to suck it up and pay for the extra gas.
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elcamino74guy · Posted: Wed Jun 25, 2008 8:06 am Post subject:

400 heads would be drilled for steam holes for the siamesed cylinders and are made to fit on a cylinder that is 4.125 instead of 4.000 for the 350.

They should bolt up but there's not much power potential over the 350 castings since they historically flowed pretty badly. Depending on the year of the motor the valves will be 1.94/1.60's with around a 76CC chamber. 350's had 1.94/1.50's and the flow is the same.

My guess is that the builder had a set on hand that he didn't have a purpose for and built them up for your motor. 882 castings are generally the "Heavy Duty" castings and have more material around the bolt holes.

As for the trap speeds, It's very possible that the 2.73 rear is not allowing you to get the motor spun up fast enough to get into it's ideal range for a 1/4 mile pull. You may not even be into it's peak torque or horsepower by the time you cross the line.

Vortec heads will mean a new intake and it'd be best to match the cam to the heads for the best flow. I know what it cost for the rear end for my 74. For about the same money you could do the engine mods.

Good luck with your project!

Happy

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ElCafreak · Posted: Wed Jun 25, 2008 5:23 pm Post subject:

I'll have to look around and see if I can find the cam specs. I'll look and see if I can see the head numbers too.
What is the difference between vortec heads and regular 350 heads? I'll start asking around about a good posi rear too. What numbers should I look for, to be both quick AND economical or sturdy?
Thanx for your reply Dudes!
the project never ends Cool

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1980 El Camino
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1982 Fiat Spider 2000
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1BadElky · Posted: Wed Jun 25, 2008 7:13 pm Post subject:

vortec heads have I think a 64cc chamber, and have big valves.

they will require a special intake if you run a carb. the intake mounts differently. edelbrock and others all offer this type intake.
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Formerly 86Conquista

Currently undergoing resto.
Planned:
-350/?/3.42
-ZQ8 wheels
-Disc Brakes
-More

elcamino74guy · Posted: Wed Jun 25, 2008 8:44 pm Post subject:

Yeah the Vortec Head ports don't match up to a stock Small block manifold. THere are a number of companies offering specific CAM grinds for Vortec heads. Crane, Edelbrock and Competition Cams have all offered specific grinds in the past. Start with the big boys first.
GM probably has still has cams available that would work as well.

Happy

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74 El Camino Classic - project car #1
96 Camaro - RIP, Traded 10-16-2007

2008 Mustang GT, It ain't a Chevy but at least it's American!

MarkZ28 · Posted: Fri Jun 27, 2008 1:05 am Post subject:

Ports on the Vortecs are the same but the angle of the head surface is different and theres less bolts to hold it on to the head and they are also at a different angle. The valves are still the 1.94/1.50 but the heads outlfow anything GM made stock up to about 4,500-5,000 rpm, until the LS1 came out. Combustion size is 64 cc so that will bring up your compression by one point of you had 76 cc heads before.
I have a 3.73 posi rear in my 83 and it smokes the tires off the line pretty easily and they are 275/60R15's. A 3.42-3.55 would probably be a better compromise, the 3.73 make the engine rev at 3 grand at 60 mph.

turboapache · Posted: Tue Jul 01, 2008 11:33 pm Post subject:

One of the best ways to wake up these cars is to use a 2400-2600 stall converter. if you have the overdrive trans you will love it with the lock up feathure as the eng ratio is one to one at the trans flywheel in lockup .
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