Old School SBC Help!

[pretentious_pontiac]

Alright so I bought my second Grand Prix awhile ago and always thought it just had a SBC 350 with some tasteful mods ( that's what I was told from the guy I bought it from but the guy who built it passed away).
But the other day I was letting it warm up and I was looking around and noticed the harmonic balancer is weighted, it has a groove on like 2/3rds of the damper. I did some research and seen that no 350s came externally balanced like that and that it would mean its a 400 crank. I checked the block code and it is a 350 from the 70s so does this mean this is actually a 383 Stroker? I know I can tell by taking the pan or heads off but I'm not looking at doing that much work yet. I'm just curious if there is another way to tell if I'm right or if what I have discovered is enough proof to assume that?

I'm still new to the older blocks like this please forgive me, I'm still in my 20s

 

[ELCAM]

Pull a plug, insert a plastic or wood dowel. Turn the crank by hand. Find the top and mark it, find the bottom and mark it. Measure between the marks.

 

[64nailhead]

That was a popular way to build/make a 383 if using 5.7 rods back in the day. Most every 383 kit you find now uses a 6" rod which can be internally balanced and use a normal 350 balancer and flexplate.

The shorter rod has some advantages and disadvantages. The disadvantage is it's stock and limited by that, probably a stock piston as well. The advantage is that the lower stroke to rod ratio adds some low speed/rpm grunt. Not enough to get excited about, but definitely some. I mean who wants to live at 6500 rpms anyway pfft 😉

No matter, I'd find it highly unlikely that it's a 350 with the balancer you're describing. The cubic inches are the winner!!!

The best of all stock block 383's is a roller block with 6" rods, Vortec heads, 1 5/8" long tubes and dual plane Eddy intake - again, back in the day of 1990 it was the hottest homegrown build going.

 

[pretentious_pontiac]

Pull a plug, insert a plastic or wood dowel. Turn the crank by hand. Find the top and mark it, find the bottom and mark it. Measure between the marks.

Oh that's a good idea actually. What length stroke am I looking for?

 

[pretentious_pontiac]

That was a popular way to build/make a 383 if using 5.7 rods back in the day. Most every 383 kit you find now uses a 6" rod which can be internally balanced and use a normal 350 balancer and flexplate.

The shorter rod has some advantages and disadvantages. The disadvantage is it's stock and limited by that, probably a stock piston as well. The advantage is that the lower stroke to rod ratio adds some low speed/rpm grunt. Not enough to get excited about, but definitely some. I mean who wants to live at 6500 rpms anyway pfft 😉

No matter, I'd find it highly unlikely that it's a 350 with the balancer you're describing. The cubic inches are the winner!!!

The best of all stock block 383's is a roller block with 6" rods, Vortec heads, 1 5/8" long tubes and dual plane Eddy intake - again, back in the day of 1990 it was the hottest homegrown build going.

I figured pulling the pan would show me the most its just such a pain to get those down. even with a lift. I'm not sure if it was bored out .30 over or not either. Would someone only put the crank with stock everything and make it what? a 355? I'm not the best at those numbers.

 

[ELCAM]

350 = 3.5" stroke.
400 = 3.75" stroke.

 

[pretentious_pontiac]

350 = 3.5" stroke.
400 = 3.75" stroke.

Awesome thank you! I will work on that in the morning.

 

[64nailhead]

It's tough to tell with the pan down IMO.

Personally, I'd not worry about it and run it until it doesn't lol. But if you want to know what it is, off with a head and start measuring stroke and bore. But what is the point really? If it runs properly, then leave it alone.

I'll throw this out there for the Anti LS Consortium, a properly built SBC either as a 355 or 383 if properly tuned will stomp most any LS. It takes some motor building effort to make 400-450hp, but it's not even remotely impossible. But it will take a good head and cam setup - and of course a tune. The nice part (cheaper than LS) is that it will drop right in without oil pan, motor mount issues, etc. And if you want more, then a turbo goes onto a SBC just the same as it goes onto an LS. Been there and done that - trust me - it works.

If you want a good read about going fast with a SBC, then find Ole Bob's 9C1 thread - a 355 that hauled some serious *ss and looked good doing it.

 

[melloelky]

just for the halibut😆 see if there's more than 3 freeze plugs per side.if there's three per side you've got a 4 bolt 400.if there's an outline for a second one in the middle of the block yet there's only two actual plugs per side it's a 2 bolt 400.

 

[64nailhead]

just for the halibut😆 see if there's more than 3 freeze plugs per side.if there's three per side you've got a 4 bolt 400.if there's an outline for a second one in the middle of the block yet there's only two actual plugs per side it's a 2 bolt 400.

I was thinking the same.