I have found a 1986 Z28 305ci 5 speed, that I should be taking delivery of next week.

One of the first items on the agenda is doing something about the pitiful 165hp engine. I am not after massive power, just a nice (and reliable) street car.

Here is the plan:
*Wiseco pistons
*Aftermarket I Beam 5.7" rods - unsure of brand yet
*New camshaft - 222deg @ 0.050" (273deg Adv Duration), .470" lift (with 1.5 ratio rockers), 110deg lobe sep.
*Edelbrock Victor Jr manifold
*Holley 650 or 750cfm carb
*Ported heads

Some of the details are yet to be sorted, but I think this should give me what I am after, but these engines (i.e. older carby engines) are a bit foreign to me.

What sort of power would this combo give? I am looking for around 300hp. Will the stock gearbox and diff be ok with this power?

 

First, scrap the idea of the Victor Jr. Second, that cam is gonna want you to replace the stock 3.23:1 rear gears with at least 3.73:1. Third, you don't need Wiseco pistons or aftermarket rods. Your proposed combo is very mismatched. The cam should pull past 5500, maybe to 6000 if your porting is really good. SpeedPro H534 hypereutectic flat-tops will be fine on stock rods with ARP bolts. Then choose an intake manifold more like the Weiand AirStrike. Why are you planning on keeping the 305 anyway? 305s aren't worth fancy rods and pistons.
And for a 300 hp 305, your stock trans and rear are okay. You'll want to add a limited slip differential with your new 3.73:1 gears.

 

Thanks Atilla. I will be sticking with the 305 because it will be alot cheaper and easier to rebuild the engine than to get a crate engine and do a swap.

I have used that same cam in a previous car and it works quite well, it will work with a stock diff ratio, but shorter gearing will certainly be an advantage. But I was planning on going with 3.73 gears and LSD anyway, so that is fine.

I didn't realise that SpeedPro made pistons for the 305, I could only find Wiseco who has the correct bore size. If SpeedPro make a piston in a 3.74" bore, then that will work fine. As for rods, I wasn't sure how good the stock rods were and for the sake of a couple hundred $$ a set of aftermarkets is probably worth it.

The Edelbrock manifold no good? That is interesting, alot of people swear by them, but as I said, these engines are foreign to me.

Food for thought, thanks again.

 

he didnt say it was a bad manifold just that it was mismatched for your combination.

basically you want something geared for a lower rpm range. the most optimal manifold would be a performer rpm airgap i think.

as for rods hes right factory rods are fine as long as you put good bolts in them. if you want replacing them surely wont hurt you though.

dont go any bigger than the holeey 650 dp though.

also after porting those heads i would install 1.94 sized intake valves, have a 3 angle valve job done and then have them back cut the valve as well.

that should make for a 325hp motor or so...

i'd probably reccomend a xe262h comp cam though

 

Ok, new shopping list...

SpeedPro Hyp. Flat Top Pistons
ARP Rob Bolts (using stock rods)
Edelbrock Performer RPM Air Gap manifold
New cam
Holley 650cfm carby
Ported heads
3.73 gears with LSD

Cool, you don't find much for these engines on Australian websites, and I didn't check the US sites so my original shopping list was composed of what I could find. Now that I know what to look for I can get the Australian suppliers to get the right parts for me.

Hopefully this should make a nice street car - my old car was a Holden Commodore LS1, 6 speed making about 520hp and ran 11s on street tyres (in a car that weights 1700kg or 3750lbs), so the Camaro has some big shoes to fill...

 

I would do the 1.94" valves before the porting.

 

Can anyone tell me what the standard head chamber volume is for the 305 heads?

And also the deck height (volume between the top of the piston and top of the cylinder deck)?

I am trying to work out compression ratios for different types of pistons.

I understand that the 86 has flat top pistons already with 9.5:1 comp - so I am guessing an aftermarket flat top piston will yield the same result.

 

After minimal resurfacing, the heads should be around 57cc. You can mill them to 52cc easy. Beyond that you create problems. If you don't have the block decked, the pistons should end up about .024-.027" down. For 305 heads on a 305 block, I'd pay for zero-decking and use FelPro composite head gaskets specifically for your 305. They do exist.

 

Thanks Atilla. Just doing the basic maths on that - something seems amiss.

Cylinder volume = PI*(Bore/2)^2*Stroke = 3.14159*1.87^2*3.48 = 38.23ci,
covert to cc - 38.23*(2.54^3) = 626.48cc

So 626.48cc cylinder, 57cc head, 8cc gasket, 4.5cc deck = 696cc total volume. With 69cc compressed volume.

696/69 = 10.08:1 compression - that doesn't sound right.

And if you milled down to 52cc and deck the block you have 686.5cc total volume, and 60cc compressed volume.

686/60 = 11.43:1 compression

Something doesn't sound right there. Is there is a dish or relief in the top of the piston that needs to be taken into account - or anything else I am missing?

 

Your math is off. at standard bore and stroke, your swept volume is 625.253 cc. Now, the other. If you don't deck the block, and you do use a steelshim gasket, your deck volume is 4.312 cc, the steelshim is 3.2 cc, the piston is 5cc, and the head is 57cc. That all adds up to 69.512. so, 625.253 plus 69.512 = 694.765. 694.765 divided by 69.512 = 9.995:1 Perfect. If you instead zero-deck the block and use the composite gasket, you're still around 9.9:1. excellent.

 

Looks like I got an extra 2cc from somewhere, but 10.08 was close. I thought that the stock engine only had 9.3:1 comp?

 

GM has never been all that accurate in their advertised compression ratio. Some later LB9s were advertised as 9.3:1, while the L69s were advertised as 9.5:1. But as an example of their optimism, consider that the 290 horse 350 crate is not 8.5:1, it is just under 8.0:1, while the LO3, advertised as 9.1:1, was really 8.8:1.

 

So Chev have actually underrated the compression, where it is actually around 10:1?

Do you know if the Edelbrock Performer Air Gap manifolds with a Holley 650 carb will fit under the stock bonnet?

On the Edelbrock website it says that it won't fit under the bonnet of a Corvette, but doesn't say anything about Camaros.

The car only has 138000kms on it, so the bottom end should be ok for the time being, I was thinking of just doing a cam, manifold and carby swap to bump the power up until I have the time and budget to rebuild the engine completely.