cutlassefi

Thought I'd post this.
Been at the dyno all weekend. Did a 403 (it was given to me as a basket case) and a 455, both with iron heads, both with RPM intakes.
There have been numerous posts here asking if it's ok to use big block heads on a 403 without a loss of tq etc. Typically Joe P has stated "why not"? "Olds used those heads on a 400 big block so it only makes sense".
Well, as usual he's correct. I'll post the dyno sheet but here are the build specs;

.039 over 403, KB 6cc piston, .020 in the hole
N crank
4 main halo
Stock rods
C heads, 2.07/1.68 with just a clean up but no bowl work
221/228@.050 on a 112, in at 107 Custom Lunati Hyd Roller
5/16 one piece restricted pushrods
HS 1.6 rockers
9.0:1
QF 750 Slayer
Performer RPM intake matched to the heads
Accel HEI 30* Timing
1 3/4 Flowtech headers
Melling HV pump with purple spring

451hp@5600/512tq@3600. Run on 91 octane pump gas.

It pulled and revved great all the way thru. Stopped at 30* only because it made more power than I thought it would and it had stock rods.

Thanks Guys.

RetroRanger

Wow good numbers

joe_padavano

Holy tire smoke, Batman! Very nice. About the only thing I would have done differently would have been a forged 330 crank.

83hurstguy

Pretty impressive. How'd the 455 compare? Seems to always be trash talking between the 403 and 455 fan club...

svnt442

This is more why you hear about people trashing 403's. Granted this was most likely WAY overpowered to cause this type of failure.

http://www.jsmachineoldsmobile.com/403CARNAGE.html

oldsmobiledave

No aftermarket rods? I thought you did not use stock rods on your builds?

Regardless that is a great build. Congrats. Perfect engine for the 77-79 F body cars and the plethora of G body cars. Imagine a 79 HO or an 80 442 with that engine in place of the stock 350 yet everything bolts up as it should.

TripDeuces

For what's in it that's pretty impressive, good job.

cutlassefi

Thanks Trip.
Here's the dyno sheet.
Dave- you're right I don't use stock rods. But this was on a bit of a budget because the guy got screwed to begin with. Plus imo the sb rod is stronger than the bb rod, to a point.
I'll post the 455 dyno sheet over in the big block section.

olds 307 and 403

I am willing to bet that 403 made more torque considering the peak was at the start of the graph at 3400 rpm! Very nice, I will be getting you to do a custom cam for my 424ci 403 based motor down the road. Only a 4 main Halo as well, hopefully it holds up with that serious twist.

ELY442

Just for curious, what jets and air bleeds did you have?

GEARMAN69

Very Nice results ! LIKE

olds 307 and 403

Just curious Mark, what is the cam lift on this motor?

cutlassefi

I believe .542. Jets were 76/84 I believe. Didn't change any air bleeds so whatever the carb came with was fine.
By the way, look at the oil pressure. Std pan, restricted pushrods. That's all you need at this level. Although you'd probably pick up a few more hp with a deep pan not filled all the way.

Fun71

I think I would need a new gauge that went 20 psi higher than what I currently have.

cutlassefi

Lol! I use 20W-50 high zinc in everything to start with. Sometimes I change it to something lighter, sometimes I don't, depends on the clearances in the engine being dynoed.
This one could go 10W-30 in the winter, 10W-40 in the summer. Probably pick up a few hp in the process.

Oldcoyote

This is VERY interesting! Thanks for posting.
Curious why you chose 112 vs say, 110.

cutlassefi

He wanted good street manners. The 112 will help that. But it also depends on the lobes being used for both the intake and exhaust. Lift was .542/.536 with 1.6 rockers.

Mr Nick

If this build had aftermarket rods and retained the stock crank, what RPM would you comfortably pull it to?

cutlassefi

It's really not the rpm per se. It's where it makes power and how much. It also had stock rod bolts. That whole scenario just doesn't give me that warm fuzzy feeling.

marcar1993

Wow that's impressive!

Oldcoyote

This was obviously quite successful. Of the iron heads, which do you now prefer for the 403, big block heads or 350 small block? Or is it too soon to say.
Thanks

Pete403

Thanks Mark, from basket case to beast. I appreciate all the time, work and extra miles you went to make this right knowing I got screwed the first time around. I am glad I was introduced to you and you were able to fit this into your schedule and help me out. Much more HP/TQ than you originally told me and I know it was done right this time. People cannot say enough good things about you on this site and I agree.
Thanks again,
Pete

quaddriver

holy crap.

I mean like wow.

I would have never believed it. it did this without the bottom end becoming a semi attached rotating mass of junk?

how much would one of these cost? it would be a nice fit in a 78 regency...be able to bark with the base hemi chargers....

question... .039 over? why such an odd size or a misprint?

joe_padavano

You can buy this particular motor for a very reasonable price.

https://classicoldsmobile.com/forums...ile-403-a.html

olds 307 and 403

The .024 and .039" oversize are due matching up with 460 Ford ring sizes.