350 Questons

Hi Guys, have just found this forum in the last few days and have found tonnes of useful info.

I have a couple of engine specific questions related to my build. I am quite the novice when it comes to engine building but am very mechanically minded and have brought various sbc rebuilding books and dvds and am exciting about my first build.

So I recently purchased the following
Ready to be assembled, 4 bolt main block, bored 30tho with new flat top pistons, brand new scat steel crank, 305 ported heads which also came with a 600 holley carb, mallery dizzy starter, alternator, block hugger headers and a edlebrock performer intake.

Anyway I am undecided if I should use these heads I have read the pros and cons of 305 Heads and noted someone had said that the best 305 heads are 14014416. Mine are 14022601 58cc, 1.84-1.5, 7 bolt ex. So from what I can see only differ by 1cc chamber. And yes I know Vortec heads are far superior but they are harder to get here (New Zealand) and are really outside my budget as I am also rebuilding a whole car (72 Holden Kingswood HQ Wagon)

I understand that the 305 heads restrict top end power and that doesn't really bother me but I am quite keen to run a tunnel ram which is the opposite correct? And therefore may not go together well with the heads.

Also if I do use these heads I would be fitting 1.6 roller rockers, does anyone know what length push rods I would need? Without measuring them?

Thanks very much for your help in advance.


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The heads will work, the 601`s came on 305HO engines. However, if this is to be a daily driver, and since your engine specs are on the mild side, you don`t need a tunnel ram. Tunnel rams have a typical RPM range of 3000 to 9000 rpm, so as you see they are for racing high rpm low geared machines, not a typical street car which is lucky to see 6000 rpm for any longer than a few seconds.
You won`t need a different lenth pushrod unless the block and heads have been milled excessively. You didn`t mention what cam you intend to use. Since your using a mild 350 with 305 heads focus on the torque output the small valve heads with decent compression ratio will give you. If this is a flat tappet block and you want a lopey idle, use a comp cams magnum 268 cam. It`s designed to give you a lopey idle but still retain plenty of low end power. Make sure you use a set of headers and dual exhaust so the engine can breathe. stick on the performer and your 600 carb and you`ll have a fun to drive street machine with sensitive throttle response. You`ll need to run the highest octane pump gas you can get as the compression ratio will be high with flat top pistons and 58cc chamber heads. Make sure you clean the block before you build, make sure the bores are spotless. spray WD40 on a paper towel and wipe the bore, if you see gray on the towel, you`ll need to scrub the bores with a brush and a good cleaner. When you can wipe the bore without getting gray it`s clean.

The 305 heads on 350s was a popular thing back in the late 1970s and early 80s as an inexpensive way to get the compression up in an age of low compression open chamber heads or expensive aftermarket or rare earlier high comp heads. They actually work quite well when ported and fitted with larger valves intake 1.94 and exhaust 1.55.

1.6 rockers are not effective with these heads, the problem is that they hit max port flow pretty quickly even when ported, so adding lift is not as effective as it could be as the only improvement will be on the rise and close side of the lobe, at max lift the ports is doing the best they can, so adding lift at this point will have no consequence on filling the cylinder. This is a case for more duration on the cam which buys more time to fill the cylinder when the port is maxed out. If you look at head port flows from various flow bench tests you start to see this effect where many heads show a flop over in the rate of increased flow above .5 inch as a typical spot where this happens. So I'd caution against 1.6 rockers as they won't deliver all that much improvement in flow and on the undesirables side they increase the loading the cam lobes and the lifters see which in this age of declining high pressure additives in engine oil can lead to excessive wear of these parts.

Bogie

very much there is some great information there already.

DoubleVision
I am not after anything insanely quick but still want some balls there when I need it. The car will pretty much only be a Sunday driver. The only reason I wanted a tunnel ram was for the wank factor. I understand they aren't really suited for my application and a lot of people have suggested I stick with the intake and carb I have. Maybe I should just go that route, hmmm.

I hadn't mentioned a cam as that was going to be my next question, didn't want to over do it on my first post haha. How do I know if my block is a flat tappet block? Would a block number help? The reason I asked about the push rod's is my engine didn't come with any and I see 7.900 is a readily available length but from what you are saying I would be better to get some standard 7.800's

oldbogie
Thanks for your information. I will enquire at a local engine builders about replacing the valves. What rockers would you suggest for these heads? As they came on their own so I thought I may as well get some roller rockers.

Thanks again guys.

I'm throwing that out as food for thought as much as anything. Cams can be difficult to choose as the lift rate on many modern cams is right up there with what 1.6 rockers do. Roller tappets lets you get away with more.

A block number helps, doesn't necessarily mean it has a roller but tells you whether or not it's possible simple to do or not.

Bogie

has 3970010 on the block. Does that tell you much?

Cheers

you're always better off with 1.6 rockers and a milder cam lobe to get the lift you want. It leads to less wear and more valvetrain stability. I'd get the higher ratio rockers and then get a milder cam profile so its more durable yet just as powerful as a more agressive lobe with 1.5 ratio rockers.

I have come across some RHS 906 Vortec heads with
1.94" inlet
1.50" exhaust
64cc chamber
170cc inlet runner

Can get them for $400NZD's or $200USD's

Do you think I am better to buy these than spend money on my 305 heads? Since I imagine getting new bigger valves fitted and the rest of the head cleaned up will be a few hundred anyway.

Thanks heaps.

Anyone around with some advise on this? Don't want to miss out on these heads if its my best plan as they seem like a good deal to me.

Were using the RHS Vortec heads and they have worked very well.
The casting looks great and not cheap, they perform great and the vortec heads are identical to the factory casting.
When we got these heads we were surprised they were so heavy casted which was nice considering the factory casting is on the thin side.
You get a good head for the money. RHS is a side of Comp Cams, and Comp isn`t about to put there name on junk.
RHS bought out the pro top line company when they were having financial difficulties.

http://www.mortec.com/castnum.htm

this is a great site for looking up chevy casting numbers.

Are the RHS heads ready to bolt on or do they require the machining like stock vortec heads?
Sorry to thread jack but you have do have to machine stock vortec heads to accept a .470 lift cam, right.

The RHS/ProTopline's don't require machining. There an after market Vortec type head with thick decks & improved cooling passages.
Bare heads sold each, assmebled heads sold in pairs & each.>>
http://www.competitionproducts.com/...ts.asp?dept=693