my 307 dilemma (warning, not a chevy truck lol)

[etizz]

Hey guys I'm new here and I hate to threadjack as well but I'm not sure where else to put this so if you could at least read it I'd really appreciate it.
I got a couple questions on a build i've been working on since
early spring last year. To sum it up i put a 307 sbc out of my dad's 73 nova
into my 85 rx7 and i've been driving it around for awhile but i feel like i
picked the wrong parts to put on it when i built it. heres what i have.

307 sbc, stock bottom end rebuilt, 882 casting 76cc heads refreshed and milled .010,
edelbrock performer rpm dual plane intake, holley 600, summit k1104 cam
(.465 lift int/exh 282/282 duration), shorty headers,
hei distributor with msd streetfire ignition, r45ts ac delco plugs gapped at .040
Behind it is a T5 5speed from a camaro and a ford 9 inch 3.55 gears.

heres my dilemma. as you can already see this was a bad combo to begin with lol. I've learned the hard way realizing that this car didn't have too much power given the horrible compression ratio. I got advice to get some 416 casting 305 heads with 58cc chambers to bump my compression up to about 9.5 to 1, so i found some from a guy for 40 bucks and had koi's machine shop inspect and redo the heads with a .006 mill for flatness and a valvejob with new springs n everything.

so the story goes i rip the old heads off the car and put these 416's on and i could not get the car to start no matter what the valve tightness was or the ignition timing was either i tried everything. i did a compression check and here are the results...
cyl
1 - 70
3- 120
5-115
7-120
2- 120
4- 120
6 -110
8- 90

those numbers seemed awfully low to me i just rebuilt the bottom end not even 10k miles ago(keep in mind i did however not bore it even .10 over and used same size rings. might be the issue) anyways it wouldn't even wanna start it would just crank and crank.

do i need to rebuild the bottom end again?

i checked the valves for leakage and had no luck finding anything wrong with the heads, not cracked, not anything that i can tell nor my dad could either. do i need special rockers or something? im clueless at this point.
since then i put the 76cc's back on and it started right up again and i drove it for awhile before finding another car to daily while i figure out whats going on with this.

so heres what i've been considering. i have an 020 casting block which apparently from what i've heard are better for boring out to a 4" bore ? can someone confirm that?
which would give me more options as far as pistons n rings availability and more power obviously.

i would really like to retry these 416 heads after that and see if the results are any different otherwise im just gonna spend my money on a gen 3 vortec motor with fuel injection cuz i give up with this engine lol

any advice would be greatly appreciated. Thanks!

[w3lfd]

You might get better results posting in the engine forum over at hotrodders.com.

There is really no reason those heads shouldn't work. I am running 416 heads on my stock bore 307. If you want to check out the info it is here:
http://www.67-72chevytrucks.com/vboa...d.php?t=434462

Your compression numbers indicate a serious issue with something. May be that your cam timing is off, or the shop that did your heads are clueless.

Did you do a leakdown test on all the cylinders? I am assuming you used new head gaskets when you swapped heads?

And on the questions of boring it out, that won't fix the problem you are having.

[swb85]

Agreed that you need to do a leakdown test to find out where the compression loss is.

[etizz]

Thanks for moving this for me. the cam timing is correct. And my dad said they probably screwed up too but the shop that did the 416 heads also did my 882 heads and any machine work my dad had done in the recent past. I used new head gaskets each time I swapped heads, made sure the surfaces were clean etc. I have not done a leakdown test , I cant say I've done one before
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[w3lfd]

Some links with info on leakdown testing:

http://www.aa1car.com/library/leakdown.htm

http://chevyhighperformance.automoti...nts/index.html

[SSC's76]

It sounds like you may have a few things going on here. I think on cyl 1 you may have the valves to tight and your bleeding off cyl pressure. The other is you do not have correct timing or any spark. If you have spark put the engine on TDC and see where the rotor is pointing. If it points on #1 or 6# on the cap then flip it 180* see what you get.

[Ticker]

Originally Posted by etizz

i just rebuilt the bottom end not even 10k miles ago [b[(keep in mind i did however not bore it even .10 over and used same size rings[/b]. might be the issue)

so heres what i've been considering. i have an 020 casting block which apparently from what i've heard are better for boring out to a 4" bore ? can someone confirm that?

i would really like to retry these 416 heads after that and see if the results are any different otherwise im just gonna spend my money on a gen 3 vortec motor with fuel injection cuz i give up with this engine lol

If you put in new rings and didn't bore/hone then it wasn't a rebuild - and that would explain those compression numbers. The leak-down test is the right way to proceed, but I expect the results to show that it's all going past the rings.

I can't think of any stock block that could be bored .125...but if you want to spend the money on a sonic test that will give you the answer for sure. You could go .030 over and use a 350 or stroker crank to pick up some CID...but honestly at that point I'd just start over.

The heads aren't going to make a difference - increasing static CR isn't going to help the massive blowby that is causing the low compression test numbers. BUT, the head swap shouldn't have made the engine stop running - so I suspect timing and valve adjustment and I'd check those in that order.

Do the math on an LS engine swap - it's a great swap but not a cheap or a "bolt-in" swap.

[cableguy0]

Your cheapest easiest most bang for the buck would be to just start over with a 350 block and work from there. As Ticker said if you didnt bore/hone the block you didnt rebuild anything and probably did more harm than good. The rings will never seat right and the cylinders that are showing almost decent compression you just got lucky.If you want to keep the 307 just send it to the machine shop Bore it .030 and call it good. BUt keep in mind its going to cost more to do that than it would to just find a 350 block and rebuild it.Have you pulled the lifters out to check and make sure they arent worn? A wiped cam will cause the same issues.Did you do proper break in on the cam? Are you using a zinc supplement in the oil?

[etizz]

Originally Posted by cableguy0

Your cheapest easiest most bang for the buck would be to just start over with a 350 block and work from there. As Ticker said if you didnt bore/hone the block you didnt rebuild anything and probably did more harm than good. The rings will never seat right and the cylinders that are showing almost decent compression you just got lucky.If you want to keep the 307 just send it to the machine shop Bore it .030 and call it good. BUt keep in mind its going to cost more to do that than it would to just find a 350 block and rebuild it.Have you pulled the lifters out to check and make sure they arent worn? A wiped cam will cause the same issues.Did you do proper break in on the cam? Are you using a zinc supplement in the oil?

i did hone the cylinders but i didn't bore them. I've been having trouble finding a 350 block locally for a decent price to work with. The cam is aftermarket from summit as are the lifters and there was no signs of wear i broke it in properly. i used stp oil treatment which supposedly has zinc in it for flat tappet cams.

i borrowed a leakdown tester from work and got myself an air compressor so im gonna figure out whats going on with that tonight.

thanks so far for the help

[etizz]

well after testing cylinder one having 70% pressure leak out of the valve covers at tdc i'd say that would be rings would it not? i think its safe to assume they're all ring related lol geezzzzzzzzz i have to say though for being a pretty much worn out 307 this thing had no problem lighting the tires up in 1st gear, i'm interested to see a healthy maybe 327 in this thing do some work.