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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: OldsFan on August 28, 2020, 05:34:09 pm

Title: Cam Swap in the 305
Post by: OldsFan on August 28, 2020, 05:34:09 pm
I use my C10 (1985, 305, th350c, corp 10 bolt) primarily as a parts hauler for other projects, but I want to eventually do an LS swap on it (maybe an LQ4 with a carb for starters, know a buddy who did that in a big body Olds - very solid).  Now's not the time for that though - maybe in a year or two.

In the meantime, I was thinking though, maybe I could wake my 305 up a little just with some freshening.  Something mild - no need to break the bank for something like this.  I've even got an Edelbrock dual plane kicking around somewhere that I can even add to it.

Parts notes:
- Stock heads with press-in 3/8 studs, etc. and it won't ever seen north of 5K rpm.
- Reasonable cam (max lift around .425-.450).
- Stock-replacement, single springs (maybe 100lb at the seat and well under 300 at max lift)
- Fresh flat tappet lifters, new 1.5 roller tip rockers, maybe new pushrods just to round things out.


We all know the problems with zddp and flat tappets and so on, but assuming I wanted to do a mild swap like this, what are the best ways to protect it? 

Thanks ahead of time...
Title: Re: Cam Swap in the 305
Post by: Stewart G Griffin on September 07, 2020, 12:24:39 pm
Well, the other thing is you could consider switching to a roller cam and then you don't have to worry about all that other stuff.


If not, i feel that if you're keeping the stock springs or close to it, then maybe you don't need to worry about zddp?

When i had the 350 and 305 (both with flat lifters-----i have since joined the 21st century with the 4.3 which has rollers) i ran Redline synthetic 10W-30 which has adequate zddp JUST TO BE SAFE ABOUT IT;   i figured the price difference was about the same as if i used conventional----and would have to change it twice as often.   Even though i still feel that with stock valve spring pressures you might not even have to worry about the zddp factor?
Title: Re: Cam Swap in the 305
Post by: OldsFan on September 08, 2020, 11:46:45 am
Someday, I hope to join the 21st Century, too....  :D

In the meantime it's been a lot of years since I swapped a flat tappet cam. I want to replace the 305 - let's face it, it is just not ideal for what I want eventually.  So I figured this is a great opportunity to either:
   a) See if I can still do it and if I can run it for another year or two with the 305.
   b) Give me a solid reason to do the engine swap sooner rather than later.  ;D

But seriously - I'd like to get "a" to happen if at all possible and to give me time to decide what engine, drivetrain, setup I want for the later engine swap.

The other reason I am thinking of doing this is that I got a mild Summit cam and lifter kit for free. Add a timing chain and some valve springs, gaskets, etc. and I should be able to do this.
Title: Re: Cam Swap in the 305
Post by: Stewart G Griffin on September 08, 2020, 07:36:15 pm
i think you can get good use out of the 305 for another year or two.   If i hadn't melted my 305, i would probably still be running it.

How mild is the cam?   Depending on how mild it is, you may be able to keep the stock valve springs is what i'm trying to get at?
Title: Re: Cam Swap in the 305
Post by: OldsFan on September 09, 2020, 11:31:12 am
Well, I got the package out and the cam card is in there, everything is brand new and soaked in some kind of (anti-rust?) oil. It is a Summit cam, has new lifters with it. Cam is part number 1102:

Duration at 050: 204 int./214 exh
Max valve lift (w/ 1.5 rockers): 0.421 int./0.444 exh
LSA: 112 degrees


The stock cam and springs in my 305 are just worn out, certainly the 35 year old originals. I bet that just swapping for a new stock cam and springs would be an improvement.

Summit recommends this spring set: https://www.summitracing.com/parts/sum-174001
Those are definitely in the budget but have an open pressure of 273-297 lbs... Is that enough to yank the rocker studs out?
Title: Re: Cam Swap in the 305
Post by: Stewart G Griffin on September 16, 2020, 08:05:19 pm
i was hoping others could chime in here as i don't know jack about valvetrain/heads etc.   i've done one cam change EVER---on a 283 (and kept the same springs....)

273-279lbs open MAY be too much and MIGHT pull the studs out.   Then go with screw in studs, but is that worth it for a 305 head....?

204/214 @.050 is still kinda tame even for a 305 AND you said you weren't going above 5000rpm, so again i question if we need such stiff springs?

Just my opinion, but my approach is when it comes to valve springs i only like to use as much as necessary---i just gut feel/think the engine runs smoother and less strain on the valvetrain.   The opposing view is that when one spring compresses on a sbc, another spring is expanding so it equals out.

Title: Re: Cam Swap in the 305
Post by: TexasRed on September 17, 2020, 12:43:47 pm
I'm not convinced that ZDDP is the saviour of flat tappet lifters. I've smoked them and a cam or two even with ZDDP oils. I think you're better of choosing something from the 540rat's oil blog that has high shear psi numbers.

A 305 doesn't like a bunch of lift. It's going to be even worse if you have the stock (2.73 or maybe you're lucky 3.08) rear end in it. The edelbrock intake would probably just add another issue, the carb getting hot from the heat radiating off the aluminum intake.

Have you done a compression test of at least cylinder number 1? What makes you think the cam is worn out? Or the springs?

It may just need a tuneup. Should be able to get the module checked out at the parts store and if it's bad, replace the COIL with it (stock coil). May be able to swap in a 4 pin module as replacement to disengage the ESC part. The coil cannot be checked reliably with an ohm meter when it's cold. I haven't found a parts store that has a tester. You may even have a problem finding a parts store that can check the module.

There's a performance setup for the ignition too, like locking how many degrees you'll get from the vacuum advance, using a slightly quicker spring on the mechanical advance.
Title: Re: Cam Swap in the 305
Post by: Stewart G Griffin on September 27, 2020, 09:42:13 am
Hope this video helps:
https://www.youtube.com/watch?v=xILCJc2o_L8

Also,what carb you got?
Title: Re: Cam Swap in the 305
Post by: OldsFan on October 03, 2020, 11:16:57 pm
Quote from: Stewart G Griffin on September 27, 2020, 09:42:13 am
Hope this video helps:
https://www.youtube.com/watch?v=xILCJc2o_L8

Also,what carb you got?

I am running the original Quadrajet (17085226) which I rebuilt a couple years back.  When I did the rebuild, I added a small spacer to help prevent heat soak issues and to be honest, it runs really well.

I talked to a few friends and a machine shop that I trust and they all said I should be ok up to about 300 lbs open pressure and Summit gave me the line that these are aimed at stock components and mild cams. Still, I like your idea of running the original springs if they check out ok. Thinking I'll check the pressures on them and if they aren't terrible, just keeping them - at a minimum for the break-in of the cam.

And yeah, the cam is mild... But it is reasonably close to the stock spec that I found for an LE9 from 85. I definitely want to replace the lifters and timing set, so I just figured the cam swap couldn't be a bad idea.
Title: Re: Cam Swap in the 305
Post by: Stewart G Griffin on October 10, 2020, 12:18:02 pm
The other thing is:  My uncle was a BOP tech for a while and he suggested to slightly drill out the secondary jets---only a little.  i don't like the idea of drilling, instead just buying the next size larger---but i'm not sure if the secondary jets on a q-jet CAN be replaced, thus that's why he suggested drilling?   i think the rational behind this is many (most?) 305 carbs were jetted lean for emissions?

You might also consider richening the primary jets, slightly.