Getting ready to finish up my 355 build. Here is the info,


355 SBC
Hyperutectic pistons flat top with 4 valve releif

Heads areCast Iron 083 castings 64 cc chambers. Chambers polished.

Quench is .035" if I run a thin head gasket.

Static compression with thin gasket comes out to 10.23:1 Custom Tuned ECM

Engine will be fed by a TPI Mass Air Flow system.

Cam is a Comp Hyd. Roller part number 08-501-8

212 intake 218 exhaust @.050"


Will this combo be happy with 92 octane?

If I put a thicker head gasket on it will drop my compression to about 9.73:1 but quench will jump to .059"

Thoughts?

 

I say it will be good. Keep it cool with a 180 tstat.
DON'T run the thick gasket!

 

It will need less timing so be conservative on that. Cam could be tad larger but i say it should run. Maybe try a heat range 6 plug or so, ngk or equal. Keep it coool as said

 

ECM is tuned to turn fans on sooner, will run a 180.

Tried to keep cam timing mild for milage. Comp actually wanted me to go smaller, with the 500-8.

Base timing table is a stick vette with some timing pulled out for the iron heads.
Running a t-5.

Thanks everyone.

 

Orr89RocZ, NGK 6 would that be equivilent to AC R42ts?

 

I would just be careful on the timing, vettes are know to be aggressive since they had aluminum heads with an inefficient chamber.
I would consider a 305 manual table as a quick guide.

Stock L98 with bolt ons on 93 oct will start showing knock retard at 36 deg at wot. Even some hits at 35 from what i remember. Yours may be ok there it may want 30-32.

You will have to experiment. Cruise light load rpms may want mid lower 30's instead of higher 30's. i know vettes run low 40-42 deg in some spots. Thats way to much

 

it should, just dont' get too carried away with timing.

I had a 383 with dart iron eagles heads & holley projection 4Di which ran perfect on 93 octane on the dyno and the street.

10.0:1 compression. max timing was 36 degrees never had issue with detonation

At the track I ran 93, 93 cut with 100 unleaded, and even staight 100.
Never any issue but the the car ran it's best 1/4 with 50/50 mix of 93 and 100, (call it 97 octane)

So I would say for street use 92 should be OK just read the plugs and listen for knocking if you have knock sensor, then no worries..

 

^ it's a tpi engine, so yes it has a knock sensor.

 

So use the 'vette timing table, the knock sensor should take care of the rest if there is an issue.

Still read the plugs to be safe and at the track you can always cut it with some 100 unleaded.

 

Thanks for the advice.

It will be my daily driver so I'm more concerned with low rpm cruise, and knock under load.
T-5 will limit full blown track use.

 

I would be careful. Knock sensor will remove timing as needed, up to 10-20 deg depending on bin settings but i wouldnt leave timing so high that knock sensor is constantly pulling timing. Back it off til it stops

 

My concern was that the loss of timing would negate much of the power gain of the higher compression ratio.
However, the only way to lower compression at this point would be the thicker gasket, which would kill my quench, and thus also require less timing.

I got parts thinking a 9.5:1 compression ratio, but speed pro under rates their pistons it seems.

 

0.035 quench is pretty tight, I would get a custom gasket to get it to 0.040 and it all be good compression and all, a few extra bucks are sometimes worth allot.

 

Where would I get custom gaskets?

 

what gaskets thickness will give you 0.035 quench?
there are a bunch of different size production gaskets out there but http://www.cometic.com/ makes any gasket size you need

 

your compression ratio is not the problem your quench is, you need to check valve to piston clearance with that tight quench, you know metal expands with heat

 

.015" gasket.
Pistons are .020" in the hole.

 

Don't let anyone talk you out of that .035" quench clearance. With typical bore clearance for hyper pistons, it's perfect. And it works in your favor as insurance against detonation. Keeping it tight results in better mixture motion, faster burn and less ignition advance required for best power.

 

Fel Pro used to make a steel shim gasket that was 'rubber' coated at .019 as I recall but I don't know if they still do - if not look up the Mr Gasket 1130G - I belive it's right at .019 or .020 and it was about the same design (coated steel shim)

 

Don't worry I won't.
The Internet has made .040" a magical number but my machinist all say you can run as tight as .020" with steel rods.

I haven't been able to find a .019" gasket, but I'll look some more, thanks for the leads.

 

Although the Internet doesn't believe car magazines, ironic I know, but the latest issue of HOT ROD has a story on the topic of quench,

"A good rule of thumb is that you can run as little as 0.038 to 0.043 inch with steel connecting rods. Steel rod street engines that don't see the far side of 6,000 rpm may even be able to shave this to as close as 0.032 inch."

"Don't run more than 0.060 inch quench even if you have a need to run a low compression ratio."

 

I've never tuned a small block that didn't like 40-46° advance at cruising speeds.

Even my 10.5:1 vortec like 42° at cruise and 4° more in lean cruise.

 

.030" on an EFI motor if the tune is in check.

Unless the rods are rubber and you think they will stretch.

-- Joe

 

Agreed. Light cruise and such is often 18:1 afr. You're not lighting that off with less than 40 degrees.

Manual tunes are way different than auto though.

-- Joe

 

Not at highway cruise speeds with the converter locked. The Auto and Manual act the same at light throttle above 45-50 mph.

 

Perhaps that's true. I've always had lockup disabled unless WOT on the few auto cars I've owned.

-- Joe

 

I guess you may not have tuned any efi setups on stock knock systems? I am not sure but my afr 195 heads never tolerated more than 36-38 deg. Knock sensor picked up something
My rhs castings take more timing however, but still dont seem to want north of 40. Difference in chamber pressures at low rpms from a large head with slower gas velocity vs a fast port head with a fast burn chamber like afr's.

The old non eliminator afr 190's and 113 vette heads love 40-42 deg.

I havent targeted any leaner than 15:1. Any leaner and car had no ***** on mild throttle transitions

 

The trouble I found with some of the stock knock code, like $58 for example was lots of false knock. A lot of people get all bent out of shape when they get knock counts in the log, but don't actually hear it. Before we had knock sensors we tuned our stuff by ear.

But anyway, we were talking more about lean cruise, decel, etc.

Keep in mind, with an electronic dizzy 45* might arc to the previous cylinder.


-- Joe

 

Yeah my decel has higher timing but i usually tune that to give me desired engine braking effect. It may take more but i may not want it to have it lol

Code59 seemed to be alittle sensitive on knock but i never wanted to try ignoring it with boost lol

I still noticed the same thing on my stock L98 and then the maf 383 on afr 195's. it was very efficient head at cruise. It was strange because it ran 38-39 deg at wot with no knock counts however it did not make peak power or trq with that setting. It wanted 34.

Cruise remained 36 mostly, some lighter loads nearer 38 but mostly locked out at 36. I guess i could have forced more but car was happy imo

 

That's not strange at all. Very typical with factors like: a good chamber, higher compression, low coolant temp, and good fuel.

 

For all the high comp AFR headed combos i have seen it does seem alittle odd to run that high and not have an issue imo but like said it didnt make best power there. I dropped down to 34 and it raised torque by 15 lbft and hp few ponies

 

Well yeah, 38-39 degrees with high CR and PUMP gas would NOT be typical
I run a 12.0:1 LT1 with flattops and .035" quench and it makes best power at 29 deg in the LT1 timing tables, even though it will tolerate more without knock. I know actual timing is something more than 29, but I don't care about the true number, as long as it's right

 

Maybe it is efi but i have also seen carb cars run more timing than efi with same or similar combos. Especially ls1's where most efi cam setups only run 26-29 deg however carb guys are giving them 30-36 like old school motors lol. Fuel delivery may have some influence on how the mixture burns and the resulting timing required. Interesting topic but in the end, give it want runs best, dont be concerned on the number.

It just been my experience most higher comp higher dynamic comp builds that are considered borderline pump gas compatible require less timing to reduce chamber heat and pressure, along with other tricks like plug heat range tuning and cooling the motor well

 

One thing that even many tuners don't know or acknowledge is that GM programming for many years now (including the LT1/4 and LSx platforms) adds timing to the base table values when under PE conditions. Some editing programs in certain year platforms let you see and modify this, but often they do not. This is what I was alluding to in my previous post about actual timing being more than indicated in the program tables.
So when you hear of LSx setups wanting only 26-29 degrees with the GM PCM, they may see they're running more than that if they verified it with a light.
But........like you said, Who cares! ...give it what it wants

 

That i dont know in lsx world but all the 80's tpi cars i tuned i always delete any timing adders and work from the main table. I will leave coolant temp vs timing but modify stock settings accordingly. Again engine will let you know whats best based on testing

 

Just to clarify, I was not talking about WOT advance, I was talking about part-throttle. The cast iron vortecs on the engine in my signature, running 10.5:1 compression still liked 42-46* advance at 3,000 rpm cruise speeds. My wide open throttle timing was 16* just above idle, 20-24 from 2,500-4,500, 28-30 from 4,500-5,500 and 32* at and above 6,000.

My bone stock express van with the 5.7 vortec would run 42-44* of timing going down the highway under the right conditions, egr on, cooler weather, etc.

 

I doubt they are running more than 26-29* of timing wtih the LSx setups at WOT. My modern Hemi with dual plugs liked 26* of timing until it was over 5,500 then only 28* above that. My Titan likes 28-32* of timing, although it was running over 37* stock at 10.4:1 air/fuel ratio.

 

Bring it back from the dead. This engine ended up going in a pick up truck, where I have put over 30,000 miles on it running 89 octane, with zero issues.

 

Good to know