JohnTN

You have a cam that needs more compression, so you need new pistons.

Or, you have pistons (low compression) that need less cam, so you could go to a RV cam (204/214). I've never rebuilt an engine, but isn't a cam change a lot cheaper and less work than replacing pistons?

In either case, a numerically higher rear gear (3.42-3.90) will add a lot of pep and makes a really nice street driver when mated to an overdrive transmission (TH2004r or 700R4). The overdrive gear is 0.70 I think and will keep highway cruising rpms in the 1800-2200 range with the higher gear ratio.

My street rod has a stock 1971 Olds 350 with an RV cam, Street Demon 625 carb, 3.42 rear, and TH2004R transmission. The engine has 146K miles on it with the original pistons, rings, bearings, and heads -- never opened up. Lucky I guess to still be reliable with no engine noise, no smoke, no oil useage, and get 18-20 mpg.

Stock 4 bbl in 1971 was rated 180 hp I think (rated by today's standards). Maybe it is a little over 200 hp now with the minor improvements and dual exhaust. Its not a barn burner but will lay short dual strips of rubber with posi rear.

If you really want to do an engine rebuild, my choice would be the higher compression pistons, but you can have a peppy car with the stock pistons, RV cam, steeper rear gear, and overdrive transmission.

John

cljolley

I do like the idea of the 200-4R transmission, but what all is needed for a swap like that? How do you make the th350 crossmember work? Are there cross members you can purchase for such a swap?

cljolley

Well I will try what I can, if I cannot fix it I will have peace of mind knowing I did what I could before selling the carb.

MDchanic

You use the same crossmember, just move it rearward to the next set of holes.

You will need to change or modify your driveshaft and your forward emergency brake cables.

- Eric

olds 307 and 403

I am in the middle of a 2004R swap right now. As said above the cross member will work, just move it back and the drive shaft SHOULD also work. I have swapped back and forth between a TH250C and 2004R on my G body. The emergency brake cable will have to be changed to a TH400 cable and or creatively modified.

STLCRZY

...i measure a high mileage low comp. 455 (8:1) with nearly 160psi and very mild comp cam 260H
https://www.summitracing.com/int/par...ake/oldsmobile

Fun71

That is with a short duration factory camshaft. With the 214/224 cam, which has a later intake valve closing timing, the cylinder pressure would likely be less (this is why the engine has noticeably reduced low end power).

STLCRZY

Which brand converter you use ?

STLCRZY

..till now , for the street engines i only use the EDE´s (hey they work and they simply) – but I have massive problems with the EDE 600 & 750 carb in a fresh mild built 403 that won’t run (it idle too high and runs like **** ....thinking about to use the street avenger carb, what you thinking about ?

cljolley

Is the E-brake cable just a matter of it mounting differently? And is there not a definitive answer about the driveshaft? OPGI says the crossmember is the only necessary modification, although they do give pathetically vague description on all their product listings.
The 200-4R does sound like a very worthwhile swap for my build though.
Is there any advantage to sticking with my TH350?

oldcutlass

You can modify the cable routing by fabricating a shorter take up rod that hooks on the passenger side. Then use the adjuster for proper cable tension. I did this on mine when I converted to a T400.

cljolley

Does anyone want to talk me into a particular carburetor for this build? My buddy wants to buy my Eddy after I rebuild it. I like the Street Demon, but what makes it any better than a different option. How does one normally go about choosing a particular design?

JohnTN

And the OP states he has the 224/234 cam!

My stock 1971 (except for 204/214 cam) has cylinder pressures of 150-160 psi. Use 87 octane gas, HEI, 16 initial timing, 20 mechanical all in by 3000 rpm, 12 vacuum advance on manifold vac.

John

ELY442

Its a no name brand converter that I bought in eBay for $117. They are from Oregon Performance Transmission.

STLCRZY

--
Ask because change back mine to stock because extreme SLIP with TCI Saturday Night (2000rpm) conv.

JohnTN

When we street rodded our '39 Olds I wanted to stay old school and bought a remanufactured QJet off Ebay for the 350 engine. After I finally figured out which primary rods/jets were best for it, it gave me good service for about 10 years. But in 2015 it started leaking and flooding frequently. I never figured out what was wrong.

I then saw an ad for the Street Demon line that came out in 2012, owned by Holley. It has smaller primary throttle bores and then the larger "goggle" shaped secondary. Although not as "sophisticated" as the venerable QJet I bought the advertising that the smaller primaries provided crisp throttle response and good gas mileage like a QJet. Also it seemed to be a new simpler design. I also liked the sound of larger secondaries opening up, and online reviews on Amazon and Summit were overwhelmingly positive - this was a big influence on me.

It will mount on either a square bore or spread bore intake manifold. Some people have had issues with air cleaner clearance and throttle linkage interferrence with the EGR boss on some intakes. I did have a clearance problem between the throttle linkage and the EGR boss on my Edelbrock Performer intake manifold. Had to use a 1.25 inch spacer under the carb. I don't use EGR but didn't know better when I bought the intake with EGR.

After going to leaner primary rods and jets on the Street Demon (my engine is mild - near stock) I am happy with performance (improved a little over the QJet) and gas mileage (about same as QJet).

From what I gather, unless you have a high reving SB or a BB, you don't need more than a 600+ cfm carb.

John

JohnTN

You might check out a thread in early April about tuning a 1406 Edelbrock carb.

olds 307 and 403

The 625 cfm Street Demon should be enough and is at least a better starting point than the 750 out of the box.