455 in olds delta 88

[Racincc85]

I like the idea of using a disc brake rear end. How would i go about modifying the proportioning valve to operate it properly?

[curtis73]

Its quite easy itself. As always, I recommend a full flush and bleed when doing this. There are two types of prop valves and the one is easy to modify in 10 minutes on the car. I think the other type has to come off, but its been so long that I have to re-confirm my info.

The prop valve on B-bodies has retained the same pressure bias for years; designed for disc/drum. Since drums in general take less pressure to provide the same braking, the fluid bias was about 90/10 which provided a braking power bias of about 70/30. When they did the rear disc brakes, they didn't modify the prop valve. So sending 90/10 fluid bias creates about a 90/10 brake bias which is not optimal. On our impala SSs, we pull a cap off the front of the valve, pull out a part, and reassemble the cap. Super simple and it totally fixes the issue.

If you find a car with the disc brake rear, pull the front spindles and brakes, too. 2 reasons: 1) Your current wheel bolt pattern is 5 on 4.75". The disc brake rear is 5 on 5". Getting the front stuff to match will make sure you have 5 on 5" all around the car. 2) The front brakes on rear disc cars are 12" rotors and have a slightly taller spindle (only about 1/4"). You would get the bolt pattern right, bigger brakes in front, and a touch better handling.

I'll have to do some more research before I tell you exactly what to do before you tear into that prop valve. If I don't get back to you on it, cruise over to either www.impalassforum.com or www.impalasuperstore.com and go to the forums and ask there. You'll get a few hundred responses.

[Racincc85]

thanks. Now all i have left to do is figure out what to do with the suspension and then i can go shopping for parts. I am assuming i will need very strong springs, but what brands should i look at for shocks?

Also, since the 403 has windowed main webs, whats the max RPM i could safely get out of it? I would be very happy with 6000 RPM

[curtis73]

Since you're not adding any "block" to it you probably won't need any different springs. The 403 should be within 3 or 4 pounds of the 307.

If you are keeping a stock ride and stock springs I would stick with a good Bilstein gas charged stock replacement. If you are going to make it a little lower and stiffer, I would suggest KYB adjustables. You can set them for stiffer or softer valving by turning a little knob. A set of stock Impala SS springs from a junkyard or swap meet would drop you about 2". Might be a nice compromise.

You'll be fine up to 6000 RPMs. Its not so much that they randomly break above that RPM, its just that they flex enough to cause tolerances to change. Sustained RPMs over 6000 may cause some damage leading to breakage. Depending on your cam, that 403 shouldn't need more than about 5800 to make most of its power.

You can make things a little stronger by using main studs instead of bolts, and for all-out stability, use Mondello's Main Girdle. It requires some machining and custom fitting, and probably not necessary in your application. The windowed main webs can take plenty of torque and pressure, just not the super-high RPMS, so you might want to focus on using good head flow and a smart cam to make your powerband in the 2000-5800 range.

[MagicRat]

All the Impala SS suspension pieces will fit. Also there are good aftermarket performance suspensions available for the Impala with better springs, sway bars and shocks.

[MagicRat]

Originally Posted by Racincc85

MagicRat- I considered the 455 and would love to use it but at the same time i want to keep the car streetable and get somewhat respectable fuel economy. I figured the 403 would be a good engine for a mix of perfromance and economy, if i gear the rear end right and get a torque converter with the right stall speed. With the 455 I'd have to yank the computer/emisson controls, and since it isn't identical externally to the 403 i would have trouble getting the A/C compressor mounted without modifying the lines. I figure that if i get a decent cam, headers, a performer RPM intake, and get a pair of heads with a smaller chambers to up the compression to around 9.5 ~10 :1 (as well as port and polish them) i figure i could get about 400`425 hp. ( what kind of 0-60 time could i get with this?)

The only thing i am concerned about now is whether the stock rear end of the delta will hold up to the extra power.

also magicrat, what were your 0-60 times with the 455 in your fleetwood?

I think it will be easier to reach your power goals with the 455.
You won't reach those power goals while retaining the stock 'computer'. The stock carb will not work well with a 400 and a more radical camshaft. The stock ignition is easy to retain, just use a 455 HEI distributor and plug in your stock wiring harness.
It would work with a stock 400, but that would only give you about 225-250hp or so.
Therefore, since you are changing your intake, cam, exhaust etc to get the power, make it easier for yourself and go for a 455.

Some 307 AC brackets will bolt right up to a 455. But if not, it would be easy to modify yours.

As for economy......this is the wrong project to build and still get good fuel mileage. 400 or 455, the tuning required to get 400 hp will really suck down the gas. That being said, though, a 400 will be cheaper to buy used, because the 455 is much more popular for performance use.

However, their 'popularity' proves my point. People build 455's instead of 400's because it's a better engine for performance. Go with the 455. It will cost the same to build, it will give you more power and it will be worth much more if you ever need to sell the engine.

As for my car....the 0-60 is about 6 seconds. It would be faster with lower gears, but I kept the stock 2:55 gears in the rear end and the stock low-stall converter, because I like low engine revs while cruising on the highway. (like at 130 mph all day out in Montana )

If I were to do this project again, I wouldn't use a full size car. I would put the 455 in an early 80's Cutlass, since its about 700 lbs lighter, and thus would be faster.

[Kriegar]

I did this swap in a '78 olds 98. Same frame specs.

No frame mods necessary-all under the hood.

1973 Olds 455 (station wagon)
Stock Q-jet (650 or 750cfm, I forget)
Stock 400th, HUGE torque converter

1978 Olds 98
Stock exhaust, cat emptied
A/C car-converted to R34
2.73 rear gears
KYB Shocks from PST
Polyurethane swaybar & endlinks from PST
trailer towing springs

Awesome all around road car, launch like a bulldozer, very logy motor spool-up. Top end out of this world

First mods:
Swapped Q-jet from '72 GP Model J-400ci: 850 cfm
Swapped torque converter from '72 GP 400TH (torched the tranny): A lot smaller, better launch, better motor spool-up
HEI ignition-swapped stock
Platinum plugs gapped @ .080
Accel Coil
Accel wires, custom
performance thermostat- 170 degrees
Double roller timing chain-set @ stock specs

I would have gone with ignition advance upgrades if I knew more about them, would have like an upgraded ECM module.

Change in launch power was tremendous. Acted a lot more like a performance setup.

Second mods:
200R4-B&M shift kit, B&M Trick Shift fluid
Transmission cooler-truck rated, routed through radiator, then cooler
Toggle-switch controlled lockup torque converter
Dual exhaust-Purple Horny mufflers

This gave me 3-6 inch flames from the tailpipes when dumping the secondaries (visible at night). Assumably, the secondaries were too rich. Launch was extreme for a car of this size and vintage, top end was extreme, and the car handled remarkably well for its' size. Mileage was approx. 21 mpg highway, which equalled out to approx. 483 miles cruising range, interstate @ 21 mpg. w/23 gal. tank
The car climbed hills well in overdrive (with lock-up) without bogging in the least (for testing only, not recommended on a regular basis), and ate other cars for lunch both red-light and highway.
This is a buildup I highly recommend for those who enjoy a POWERFUL full-sized car, and I was very pleased with it. I would further recommend 17 inch rims (as I now have on my '89 Cadillac Brougham), and certainly would want headers for the economy improvement alone. Would have also liked roller rockers.
At the time, I was lusting to have a Projection stand alone system, and a Cyberdine digital speedometer (in order to know the top end).
All of this goes to say that at the beginning, one starts with all of the basics up to snuff-Spark plugs, etc.
I later transferred this setup into a 1972 GP. 16 inch IROC rims, all else the same. GP was rated @ a little under 200lbs. heavier. Same 21 mpg. highway, with a lot of room to improve it. Biggest mistake? Not starting with a fresh rebuild-while getting the TV cable adjusted, the transmission hung up, and it spun a main bearing...end of project. But it was fun while it lasted!
Increased compression ratio would have been an immediate boost to power AND economy, as would have a cam upgrade, intake upgrade, etc. In all of this, I used the stock radiator for the OLDs A/C equipped 350 that came with the car. With out the change to a TH400, it is my understanding that a custom driveshaft would not have been necessary to do the 200-R4 swap

[curtis73]

Really good info, Kriegar... but in general its a no-no to revive old threads

Welcome aboard!