Looking at building my new motor. Was looking at 10.63 to 1 compression ratio. Wanted to know if that would be ok for street on pump gas or not. Have heard many different opinions. Please help.

Here is the setup:

97 4-bolt 350 with roller cam setup. (bored over 0.030) complete ARP bolt kit.
ARP studs and windage tray for the mains
Eagle 4340 forged, light-weight crankshaft 0.010 and large journal
Eagle ESP forged rods 5.7 H-beam with arp bolts
TRW forged pistons dome .100 ( 10.63 to 1 cr with 64cc heads )
LT4 GM Hot Cam
Edelbrock Victor Jr heads 64cc 2.08 and 1.60 valves Custom Dual Springs and Perfesionally CNC ported all the way through and ARP studed to the block.
Holley Stealth Ram Intake w/ afpr -- fully CNC ported and port match with heads
58mm Throttle Body
30lb fms injectors
Full MSD setup
Hooker SuperComp Headers
Underdrive pullies
Edelbrock aluminum high flow water pump

Let me know if you can help me or point me in the right direction. I'm looking to get the highest compression ratio and most HP Naturally Aspraited form my 355ci. Thanks
Aaron

 

Just curious, what made you decide to run domed pistons?

 

I am going to say you can use pump gas as long as its the high test...

 

and dont use head studs, they suck

 

I'm running head and main studs, studs provide a more accurate torque loading over head bolts. But, if you ever have to pull the heads off while the engine is in the car, then yes they can be a pain.

 

Its not even that factor that bothers me. No matter what kind of sealant is used, almost every engine I have seen with head studs eventually leak around the studs. Not saying every one, but most.

 

With domed pistons I don't know. With flat top pistons and say 10.5:1 compression and the proper quench dimension then I would say yes.

 

I going with dome pistons for the compression ratio. What is so bad about domed pistons? What do i need to look out for? And NO one has answered the main question? What is too much compression for the street or 93+ octane? And has anyone else had problems with head studs? I'm gonna be running a 250 shot of nitrous and thought that head studs were the only way to go when shooting a big shot of nitrous.

PLEASE HELP......thanks for any info

 

no that is definately not too much compression for that grade of fuel. Domed pistons dont allow the flame of combustion to propegate as well as a flat top.

 

so to get more power is it better to use flat top pistons vs domed?

 

I am one of the few on this board that run high compression (13-1).u should be ok with pump gas at 10.5-1 compression(lt1 and ls1 are around that compression ratio).Im thinking u might be a tad over 10.5-1 with those domed pistons.also id look into getting a bigger cam than lt4 hot cam.as for the 250 shot ,your going to need race gas.

 

Using flattops, is the best way to get the higher compression that you want. But many people go the domed route, it'll work too.

 

There really is no predetermined limit. Prolly around 10.5:1 you'll be ok at full timing advance. But it really comes down to the heat, heat is what causes detonation, not compression. If you ran no thermostat, I would imagine you could run quite a bit more compression. I've read that two identically built engines will detonate at different points. Flat top pistons are a good idea, combined with a small combustion chamber. But really your just gonna have to test it out and see, I would highly suggest investing in a detonation sensor that will detect it and retard as nessessary to keep you right on the edge of maximum compression and detonation, a great place to be if you can not go over the edge. It's just to bad you can't return engine parts when they don't work out. lol

 

ar, if you're going to all that work and expense, perhaps
you should think about a 383 stroker.

 

I run the same pistons w/ 64cc heads that have been milled and have no problem with pump gas. I'm not sure how much the heads were milled, but I'm guessing I'm probably closer to 11:1 and the best gas we can get in CA is 91 octane. Based on my experience with my combo you should have no problems with pump gas.

 

At what level of compression a engine will detonate on a certain octane of fuel is different on one engine to the next. But going with a domed piston is not a step in the right direction. (convoluted combustion chamber). Your 10.6:1 rated .100" dome pistons will be about .025" down in the bore at TDC on a stock block. This , combined with a typical .040" thick head gasket will create a quench clearance of .065" . This is too much for a motor that will be on the edge. Better to use flat top pistons and deck the block so they come right up to the top of the block. .040" clearance with the gasket is just right. This tight quench clearance will make the motor much more octane tolerant. and make the motor require less ignition timing to make full power.
(less timing= more octane tolerance)
You can easily mill those heads to get what ever cr your're looking for with a flat top piston and a smaller chamber.
If I were going to use Nitrous (especially a big shot) I would go easy on the cr. (the nitrous will make the power) tons more than an extra quarter of a compression ratio will give ya. But it won;t make power or last long if it's detonating.

A flat top piston with a "0 deck height" ( block decked) .+a 040" gasket. + 64cc heads will give you a 10.33:1 cr. Plenty enough.
forget the cylinder head studs. normal head bolts used on a straight block and heads will stand up to a big shot of NOS.
The head studs will not prevent a blown head gasket when the motor is built wrong. (domed pistons, exessive quench clearance. too much compression.)

 

u could only mill a head so much.in order to get high compression 355sbc u need to go with domed pistons.the only way i got 13-1 compression is with domed pistons(350 .060 over).my total advance is 36 degrees.



domed piston =high compression= more power

 

thats great you have 13:1, and what kind of gas do you run it on? Yes in order to get the compression that high, you will need the domes, but for a street driven car, it is stupid to be running that high.

 

ok....well i will buy the rest of the parts i need for the motor by friday. So what is my best option. What should i do. Should i bore it .030 , .040, or .060? Should i stay with stock stroke or do a 383? Give me some help with the crank, rods, and piston setup that i might should do, and if i should keep the same cam or change it (if i need to change it....which one should i change it to.). I'm just looking to make the most power i can n/a and still be able to drive it. I don't mind spending the cash.....I just only want to have to spend it once. ANY HELP with be greatly appreciated. For all the expert motor heads.....whats a great power combo for my intake and head setup?

 

You can always help the octane and timing issues by running water/alky injection.

 

you can't always hear detonation,10.3 iron or 11 aluminum unless you have a really long cam or vortec style combustion chambers,is 5-7 hp worth damage from detonation?
Eric

 

btw .035 - .040 quench volume will help power and reduce detonation!

 

ar,
what deck heigth will your block have, from factory, it is 9.025 inch?
Check your 'stroke-rod-compression heigth ' calculation.
Keep in mind, that going from 10 to one, to 11 to one, CR,
only gets you 4 percent more power (if that).
IMO, 10 to one CR, is fine.
What alloy is in those pistons?
IMO, don't overbore it, 4.030 would be max,
Be sure to get the quench distance correct,
about 0.040 inch, final.
Double check your stroke-rod-CH.
If your considering a 383 stroker, obviously, different pistons.

 

so again......anyone have a nice combination for me that i should buy? RODS...PISTONS...CAM?

 

ar, here is a possible combination...
...
eagle crank 4350375057LA, 3,75 s, 5.7 rod, 350 style journals,
srp piston 139628, -16 cc, 1.425 CH, 4.030
gasket .040
block milled .025, , to 9.000
quench .040
compression ratio 9.9 to one
rod 5.7

 

since i'm running a stealth ram setup and all my poer will be top end.......is it safer or better to run a 6.0 rod versus a 5.7 rod? I have heard that the 6in rod is better for top end motors but don't know if that information is true. Any help?

 

ar,
5.7 v 6.0 rod lenght, is a controversial subject.
My opinion, I don't think it makes that much difference.
.
In some design workups, the concern I had was,
6.0 tends to push toward pistons that have very
low compression heights, with the concern for the
ring lands being very thin, and possibly breaking.

 

I'm running vortec heads and .125 domed pistons for about 10.7:1 compression.

With 94 Octane sunoco I never had an timing problems as long as I kept my WOT timing within below 34*.

The motor leaked oil and had some metal run through it so it got remachined and rebuilt. Pistons looked good considering I changed the timing about 25 times with no success in finding where the engine wanted to be, I had my machine shop inspect them, they were fine, no wear on the tops. This time around, I'm not going to be "guessing" with my timing. I gave my distributor to my machine shop to put on their machine and dial in the timing curve for my engine specs. So this time, instead of me guessing where my timing curve is at it will just be a matter of setting initial timing and I'm done.

If there was any pinging I couldnt' hear happening, it didn't show on the pistons. This was with 2000 miles.

 

Reducing the ignition timing to avoid detonation is one method. But won't get you maximum performance.
Only touble is the motor may make more power at 36degBTDC with the right octane for your motor. You would have to try some 110octane gas and different timing settings to see if the motor can make more power.
There is a big difference between typical 91 octane fuel and Sunoco 94.

On my 12.65:1 ported 305 headed 350 never heard any detonation on 94 octane but it broke a ring land and destroyed the motor just the same.

 

Build two identical motors with the same compression ratio. One with a domed piston and one with a flat top piston with a smaller chamber and proper quench and see if that statement holds up.
Or save your money and just believe what every good race engine builder will tell ya. (the flat top motor is better
{even with a little less compression}

Aftermarket aluminum heads have very thick decks. You can mill them a lot.

 

what about the windage tray, or crank scraper? Anyone against those? Any opinions on those? Any info you guys can give me on any of the setup would help. I got a good deal on the heads i bought. They are the Edelbrock Victor Jr. 23* Heads perfessionally CNC ported. Trying to find info on them. Has anyone used them before? Is there a certian roller cam to use on them?

 

12.65:1? Wow...well I sent my pistons to the machine shop for inspection and cleaning and I was told everything looked fine. No signs of wear on skirts or piston tops.

I just got back from the machine shop and it appears the Accel distributor I've been running is junk. He put it on his machine and showed me, long story short, it isn't stable, the timing is jumping around, and the magnetic pickup wasn't doing it's job accurately.

 

AGAIN

"what about the windage tray, or crank scraper? Anyone against those? Any opinions on those? Any info you guys can give me on any of the setup would help. I got a good deal on the heads i bought. They are the Edelbrock Victor Jr. 23* Heads perfessionally CNC ported. Trying to find info on them. Has anyone used them before? Is there a certian roller cam to use on them?"

I'm gonna be using a MSD distributor.......hopefully i should have no problems on the distributor end.....

 

how much power would u gain using the flat top pistons instead of domed pistons???

i wonder why piston company make domed pistons for ,when u could buy a "aftermarket alumininum heads with very thick decks" and shave em to your desired high compression ratio.

i also wonder if prostock motors just use flat top pistons and shaved heads..........
i think im going to go to my engine builder and give him a piece of mind for equiping my shortblock with dome pistons.when the desired compression could of all been done flat top pistons.

flat top+small combustion chamer+( tight quench clearance will make the motor much more octane tolerant. and make the motor require less ignition timing to make full power)=(less timing= more octane tolerance)

for cam selection id call up a cam maker.........as theres is too many variable in your engine/chasis/drivertrain setup.

 

Daverr,
I like ur additude towards peoples opinions and not facts. They tend to make confusion. For the curious people, my drivetrain is;

Race built 700r4 ( everything upgraded...and customized)
2400-2700 stall converter
Borg warner 9 bolt with 3.70 gears

I think i have found a cam....opinion's PLEASE

Edelbrock Part # 2204
dur@.50 234/238
lift 1.5rr .539/.548
Lobe sep 112*
Intake Centerline 107*

---------COMMENTS PLEASE---------

I think this cam will provide better power with the heads and intake combo that i have. let me know....thanks

 

ANYBODY?

 

Well here is the final setup. The block is decked to 9.000" and bored to 4.030" and is completely blueprinted and balenced. Let me know what you guys think.

My FINAL setup;

97 4-bolt 350 with roller cam setup. (bored over 0.030) complete ARP bolt kit.
ARP studs and windage tray for the mains
Eagle 4340 forged, light-weight crankshaft 0.010 and large journal
Eagle ESP forged rods 5.7 H-beam with arp bolts
WISECO ProTrue pistons ( 10.3 to 1 cr with 64cc heads and a 9.000" deck )
Edelbrock hydraulic roller cam ( dur@.050 234/238 lift (1.6rr) .575/.585 lobe seperation 112* Intake centerline 107*)
CompCams Pro Magnum 1.6 roller rockers
Edelbrock Victor Jr heads 64cc 2.08 and 1.60 valves Custom Dual Springs and Perfesionally CNC ported all the way through and ARP studed to the block.
Holley Stealth Ram Intake w/ afpr -- fully CNC ported and port match with heads
58mm Throttle Body
30lb fms injectors
Full MSD setup
Hooker SuperComp Headers (shorties...want long tubes)
Underdrive pullies
Edelbrock aluminum high flow water pump
N.O.S. 200 shot (wet) setup w/ dual purge kit

PLEASE LET ME KNOW WHAT YOU GUYS THINK and what hp and tq you guys think that this combo might make.

 

domed=worse flame front propegation=less power
fuel mixture generally isn't as good
flame front isn't as good or as fast moving
less octane tolerance
not the greatest a/f burn either being fairly inefficient

and you can get close to 13:1 without domes I would think but you would have to use very small compression chambers

but whats teh point of running 13:1 compression unless you really have the cams and head to run that amount?

 

thats more of a bandaid fix if anything
also with water/alky injection if the car is to be driven on the street that can't be very fun
then with water/alky injection it causes the above problems of bad burn rates, inefficiency and such

 

350hp +/- 10 hp on motor alone.

 

[QUOTE]Originally posted by daverr
[B]how much power would u gain using the flat top pistons instead of domed pistons???

the ability not to need to run premium all the time as well as if maybe not much but a little power all things being equal

i wonder why piston company make domed pistons for ,when u could buy a "aftermarket alumininum heads with very thick decks" and shave em to your desired high compression ratio.
I wonder why companies make things like the tornado, and such? but no in all honesty a lot of times those products stick around prolly cause that is what has been around since the dawn car racing time when someoen wanted more power and didn't understand the science of how to make something work a little better and just saw the dome as more compression... no offence by this but if for no other reason because there are still ppl like you out there.




i think im going to go to my engine builder and give him a piece of mind for equiping my shortblock with dome pistons.when the desired compression could of all been done flat top pistons.
your loss. even if it might only be small still your loss but then agian that is kinda the joy of building motors..... tio each their own


flat top+small combustion chamer+( tight quench clearance will make the motor much more octane tolerant. and make the motor require less ignition timing to make full power)=(less timing= more octane tolerance)



if I missunderstood you please forgive me as I am VERY tired

 

crank scrapers are nice little things. what they do is help get the oil that gets sloshed around and kinda misted up that ends up fallign onto the crank and scrapes it to to help prevent rotational losses...

the windage tray on the other hand tries to prevent the oil that is sitting ni the tray from being sloshed around and then turned into mist by the rotating crank shaft

 

dear mr Daverr,
i think "350hp +/- 10 hp on motor alone." is a understatement. I had a machine shop and the guy perfessionally porting the heads and setting up the springs tell me that this would be a very nice motor. I'm wanting POSSIBLE REAL numbers....lol.......

 

I would guess 400-425. Maybe a little more if you had it tuned perfectly.

 

yeah your right i should install flat top pistons and mill the heads to the point the intake valve is gone .damn 23 degree cylinder heads making me run dome pistons.

ok fine dyno the motor when its done....youll have your answer.
i do recommend that u do dyno the motors ,tuning is alot easier.

 

I'm thinking more than 425 at the crank.

Built a similar setup with a buddy for his Malibu (using an older 350 block) and had fully ported and polished 186 heads with a .535/.530 solid lift cam with full 1.6 roller rockers, carb setup and it's close to 500 hp at the crank with it. This motor pulls a full bodied, full interior 1981 Malibu down the 1/8th in 8.3@82Mph with ET Streets on the car with 4.10 gears. We run 93 octane in it with a total timing of 42* but his compression is around 9.8-10:1 running .030 flattops with valve reliefs cut in the pistons, stock crank, stock rods as well.

This motor sees 6 grand regularly during his burnout and shifts at 5700.

And this is a street driven car.

 

[QUOTE]Originally posted by daverr
yeah your right i should install flat top pistons and mill the heads to the point the intake valve is gone .damn 23 degree cylinder heads making me run dome pistons.
I'm not trying to be a smart bum when I made that last post but eh I'm game I guess as long as it doesn't get out of hand and they start closign threads but taking your same idea maybe we should get rid of the flat top pistons and instead put 3" domes on their so the intake valve can't open and you get nice head to piston clearance issues.
but I have seen heads out there with small combustion chambers and again though do you erally need 13:1

 

the correct question would be do you really need more power??

 

can see your point
but to need high grade fuel and the chance of problems plus using a less efficient setup;....


just for note back in the day there was a 502 built that use 12.3:1 compression using 87 octane with no detonation


but they used good setup and flat or dished pistons with a VERY small head