Inliners International Forums General Discussion Hi Performance street compression?

I finely picked up a 250 to rebuild.
I cc'd the head last night and came up with an average of about 70.5 cc. The deck height of about .030, but still need to check if the head and deck are flat. Anyways thinking about using the silvolite 307 flat top pistons #1438, does anyone know how many cc's the 4 valve reliefs are? Hoping to get away with a .030 over bore on the block.
Crunching the numbers,
.030 over bore and no milling, 9.1 to 1

.030 over bore and milling .010 off the head and .010 off the block, 9.49 to 1

This does not include the 4 valve reliefs or any chamber work that will be done.

I want to run 87 octane in this motor,what compression should I be shooting for?

Thanks vince

Dear Vince;

Check with Larry aka "twisted six" as he will have all of that data & advice.

Good luck.

for a street motor, i would try and keep the comp 9.5 or below. you can get a cam ground from competition cams to build power in the 9-9.5 range. they do it very successfully with the v things. tom

The head volume of the 307 with the 4valve reliefs
is 4cc this is what silvolite is showing.
What other head work are you plaining on doing?
Stock, bigger valves? If you are thinking bigger valves You should unshroud it this will also give you some room to play with the CC numbers.
If you give me the casting numbers off that Head I mit be able to tell if it has been Cut before or not by the list of casting numbers i have with the stock CCs. To me it already sounds as if the head has milled at least once already. If your showing 70.5 cc average Head CCs are 72.38 TO 74.00 with a 194 head being 60.32 cc Being the smallest off all & up to again 72.80

I was thinking 2cc but 4cc is better.

The head is intergrated cast # 14015499 I'm thinking it has been milled, its definitly been rebuilt.
Not sure how much can be done to this head, but going to clean up and polish the chambers to start with.
Been thinking about the valves but not sure yet.Thinking maybe a little bigger intake might help it out a little.
Thinking about using crane cam #200511 max velocity.

thanks vince

what are the specs for the cam? if going to bigger vales consider only going to 1.90 for intake. less shrouding than a 1.94 valve. tom

Going to have to look for a different cam I think,looked up the spec's and it's recommending 7.75:1 to 8.75:1 compression. Would that be static or dynamic compression?
The reason I was thinking of using this cam is because it says cruising rpm 1600-2200 which would have worked out great with the overdrive.Then when I'm pulling my quad in drive I would have still been in the cruising rpm range.
The other cams I was thinking about was Comp Cams High Energy 252H or 260H but need to figure out the cruising rpms and compression recommendations.


thanks vince

Your deck height is too much (.030) , therefore giving you a bad quench.
If you run that much gap you could possibly get knock @ 9 to 9.5 -1 compression.
Try & mill your block down & get as close as you can get to .000 deck height.
I ran a positive deck height of .002 to .004.
I had 12-1 comprssion running 91 octane. Did not knock one bit.

What I am saying, you need to look closer at your quench. It will allow you to run more compression w/out knocking.
One more thing, polishing the chambers will not help you in power or basically anything else ( it's just for cosmetic purposes only)
You can deburr any sharp edges in the chambers & unshroud the valves ,(that will do more).
Larry has the right stuff to mod your cylinder head.
Another two cents.

Well as i read back you said you have the intergrated head. Well first off If you were thinking of a different Intake YOU can for get that Right along with any type of header OR dual exhaust. secondly. What i have will NEVER work with that head to start with.AND your pretty Much Stuck with the stock carb or a 2b IF your lucky.but surly nothing more.
So now I really have to ask what is this going in and what are your over all plains for it?
( I guess This Should have been the Very FIRST Question asked to you Before we even started all this)

Your right Larry I guess I should have said that from the start.Sorry about that.

Its for an '81 G10 short wheel base van.

Weighs about 4000#
700R4, not sure on stall yet
3:23 or 3:42 rearend
28" tires

I use it for cruising and long trips so fuel econemy is always a plus.Sometimes I pull my quad when I go hunting total 1300# so I'm thinking a little more compression and RV cam.I want to use 87 octane and it must pass smog.

Right now it has 350 trans and 3.08 rearend.

I drive it about 8000 miles or less a year.

thanks vince

You can always open up the chambers.
Sink the valves, use tulip shaped valves.
Notch the pistons,changing different head gaskets, all of these things to lower your compression.

It would still be advisable to get your deck clearance closer to .000 = zero deck.

The head on my Camaro now I believe is 82-84 cc's.Trying to remember???
This was for my supercharger.
Prior to this I had the 194 cyl head milled & got 50 something cc's, it's been a while.
So just by swaping heads & head gaskets, I went from 12 to 1 , down to 8.4 to 1 w/forged flat top 307 TRW pistons.

About the deck height,when I first measured I only measured the rear cylinder just to get an idea of what it was.Now that I went through and measured each cylinder I'm a bit confused.
clinder#
1= .011
2= .017
3= .021
4= .022
5= .026
6= .030

not sure why, but definetly interesting.Is it the crank, rods or pistons? I wouldn't think its the block but then again anything is possible.

thanks vince

Wow now thats a trip, I responded to Hank and when the post came back it was...

Mean buzzen half dozen
a.k.a. Hank

I love the new name Hank, very clever.

vince

When ever you get your new pistons, rods resized or different rods.
That is when you need to take your new measurements.
Just a guess, but,,,,I would say your block needs to be milled straight.Or angled milled straight.

Hummmm? How Much carbon is on the top of those pistons?? But Like Hank said Check it with the new stuff OR clean Up the old stuff. Then recheck
it all.That seems Liek a PRETTY Big jump from one to the other.

Ya I know this #'s aren't that important just thought it was interesting.

No carbon on pistons, cleaned them before I measured.

What about a bad align bore?

thanks vince

So what compression for the street?

Everyone I talk to says 10:1 or less for street, but they are guys that build those bent things.

thanks vince

i would say to aim for 9 to 1. no problem with gas that way. tom

well between 9-1 to 10-1 is fine for most. 9.5-1 should stil be fine for you. YOU really don't want to know what mine was Hehehe But this may???
give you a clue lol I started out with a 307@ 12-1 had it fly cut.225 to clear the valves WITH a 194 head AND Yes i was useing 87oct. cheap stuff BIGGEST issue was turning it off. Other that IT ran fine NO ping and NO Pitting in the pistons or the head. But to go back and guess at it now It was somewhere between 13.9-1 to 15-1 Is the best guess Even from glen Self and yes this was my Daily driver and I ran a average 16 city with it.
with 3:08 gears and a 4speed And No it did not like below 45mph The cam would take over and the car would start to Lope/Leep/launge how ever yu want to look at But it wasn't happy Unless i held 3rd gear.

"It was somewhere between 13.9-1 to 15-1"

What was your cranking compression?
When I had 12 to 1,,, my cranking compression was 220 psi. But I doubt I could run 87 octane gas.

Larry how in the world did that thing run on 87 octane without pinging?
Ya gotta love the lope/lunge.

There is some pinging pits in the head I'm going to have to smooth out.

thanks guys now I've got to get this head tested so I can start on it.

vince

G10-250
,
what cylinder hear are you going to start working on? The integral one?

Yes I gotta run what I brung.That's a joke,sorry.

Yes Hank I think I'm going to go with the intergrated less hassle that way from the man.

I'm still waiting for the guy to show me the other head with EGR.

thanks vince

How did it run. It ran fine 3:08 gears & the 4speed it ran 15.15s all day long. But the head gasket would Blow out after the 3rd pass. I have picture of the top of the Block when I toasted the gasket.So you can see the pistons are Just fine. More then what i could say about the Head because it put a .010 groove in it.
As to shuting it off That wasn't going to happen without loading teh clutch first. As for it starting, It was just Reach in and Bump the key it would fire right up. When I built it I thought?
It would have been like my Old Big Block with 12.5-1 It wouldn't have started BUT Boy was I wrong I didn't even Have the clutch linkage hooked up when i first started it. Talk about someone Crapping a stack Of Bricks when I went toshut if off. All I could do was Unhook the fuel line and Wait till it ran out of Fuel.Trust you me
I made dang sure the Clutch was hooked up after that.
And When I filled up with Race fuel It shut off Just fine after that. But To run back and fourth to work I just ran 87. and ran it this way for about 10yrs. Then all the car seen after that was Much BETTER gears and nothing But track time.

What was causing the groove in the head?

Did you run a idle speed solenoid or throttle position solenoid, what ever you want to call it.

I know some guys out here with big street compression have been using them with good results.

vince

When IT burned out the gasket It also Took a nice bite Out of the Head From the HEAT I was lucky that it didn't do the same to the Block.
The first time this happened I thought it was a header gasket. So i made a header gasket sandwhich
you could say. Two Mr gasket gaskets with Copper RVT in between them and as it Burned away the gasket(it left the RTV) I also seen it had a mark down the edge of the block(carbon) which then i could tell it was the head gasket NOT the header gasket as i first thought. SO in the time it took me to figure it out It had Burned a .010 groove into the head(this is what it took to clean the head back up)

Ok I see what your talking about.That must have drove you nuts trying to figure that one out.

That was just a good excuse to bump the compression a little,like you needed it.lol

vince

YEPPER LOL why not right I think it needed
Juuuusssssssst a Litttttttle more hahaha Hey the compression was just fine for that 583-607 Bump/Lump stick I had in it for 17 years.

But i got bored with it so My new motor is still pushing the 13-1 with a 690-680 bump/lump stick.
this should be yet more fun hehe and everything
now should be ready to rock & roll next season.
Because I don't think I'll be ready for our Nov.
Nostalgia event. Because I still have to weld up my New Valve cover finish my side covers and Rebuild the muncie,Headers yet. Hum where does the time go???????????????????????????????lol

Holly smokes, thats a whole lotta lift.Why did you lower the compression?

When you get that baby running you need to post the sound of it.So see we can hear it.I for one would love to hear what it sounds like.
I've never heard a inline run with that much cam in it before.

vince

One main reason for lowering the compression was I didn't feel like having to have the Block Or
the head O ringed. as for Posting some video I have some of the Old motor on my web site. So Not to worry I'll have more once i get the new one in and running. I always Video the runs So i can tell
what the car is doing.

Thanks Larry those videos were pretty cool. Can't wait to see the new one run this spring.