morgsie

iTrader: (1)

I had an engine built a few years ago and got it checked out by a local machine shop last year. A few things were found that were less than ideal. In an attemp to save money the machine shop assembled the short block and I did the heads/top end. Engine is currently in the car and running, but needs to be tuned (TBI). The guy at the shop recommended I use some "standard" thickness head gaskets to keep my compression ratio "acceptable".

H345NP .030 pistons (4.030" bore, 5cc valve releifs, 1.560" compression distance)
Felpro Q17030 head gaskets (.039" thickness, 4.125" bore)
Vortec heads cc'd @ 64cc
Pistons are .020-.023" in the hole
Cam is a Comp Cams 07-466-8 (advanced 4*)

If I am doing my math correctly my current CR comes out to 9.9:1. Quench is .059-.062". With a .020" thick head gasket the quench would be in the .040" range but CR would be 10.38:1. Would this CR be to high for 91 octane? I am better off leaving the engine "as is" or is it worth it getting the quench to a more desireable range?

Thanks.

1gary

Said better than I can:

http://www.crankshaftcoalition.com/wiki/Quench


http://www.crankshaftcoalition.com/w...pression_ratio

morgsie

iTrader: (1)

Gary, I was hoping you'd chime in. With a .020" thick headgasket I worked my DCR out to 8.4:1. Not sure if calculated my valve timing correctly. On my cam card it shows valve timing @ .006". Intake closes @ 63* ABDC, then I added 4* because my cam has been advanced. So in total I used 67* in the calculator. Is this correct? I cannot find specs for valve timing @ .050". Also some calculators say to add 15*....?

I was planning on running 91 anyway (92 is very rare in Canada). Just would like some input before I go an tear the top end of my engine apart again. I should also make a decision before I get a tune as this will affect it.

Orr89RocZ

iTrader: (20)

To be honest i dont think you will see much difference between 9.9 and 10.38 to 1 comp, but should see some difference between .040 quench and .060. That said i would shoot for better quench but its gonna be hard to get it to live on pump gas.

Advancing cam closes valve sooner so do not add the deg, rather subtract it. This makes dcr worse.

You want to use .006" timing values, do not take .050 numbers and add 15-20 deg like some calcs say.

I would not install that cam at 109 intake centerline as specified on cam card. I would install straight up on a 113. That should delay intake closing and help dcr somewhat.

Run atleast 2 steps colder than stock rated spark plug. Run a cooler thermostat and try to keep engine temps cool as possible. May want it richer than you would commonly see to keep chamber temps alittle cooler.

Lastly back off timing and work your way up. Vortecs seem to like 30-32 deg at wot for most builds, sometimes typical 34-36. However on high dcr higher compression ratios, it may want 26-28. Definately want to watch timing levels and monitor spark knock. That all may help but no guarantee. May want to consider a bigger cam.

bjankuski

Shot for the .040 quench and use a 160 t-stat with fans coming on at 175 and off at 170. You should be fine on pump gas. The timing should be adjusted to give the most power without knock retard which is around 32 degrees with vortec heads.

1gary

IF your DCR is around 8.5,your good to go.Now I prefer to deck the block so it ends up using the thicker .039 head gasket for better sealing ability.The thinner gaskets do require surface finishes on the deck and heads to insure long term reliability.

morgsie

iTrader: (1)

I want to make sure I'm understanding this correctly. Installing a cam "straight up" means making the ICL the same as the LSA. My cam is considered to have ground-in advance correct? So, my cam was installed 4 degrees advanced on the timing gear, so 109 - 4 = 105 degrees? Which would mean if I would want to install it "straight up" I'd have to retard it 8 degrees on the timing gear. This of course is assuming the cam didn't need to be degreed, which could be why it is advanced 4 degrees...

I think I'm running R44LTS right now which are even hotter than what was in my L05... As far as thermostat I was told (by rbob) to run a 195* stat because of my TBI. Helps with fuel atomization, etc.

I was planning on setting up my timing on an eddy current dyno, I don't like the idea of relying on the knock sensor to find the limits of the head plus much more controlled environment. As for another cam what would you suggest? I realize if I bump my compression up a bit more I can prob run more duration correct?

The block was decked .007-.008". Machine shop didn't want to zero deck because they were worried about my compression. Hindsight should have done this research a year ago as I think they were just trying to hurry me out the door and take my money, which they did.

Orr89RocZ

iTrader: (20)

Yeah technically straight up using standard keyed timing set, that means dot to dot. That cam as do most shelf cams has advance ground in, so dot to dot actually is 109 intake centerline with 113 lsa. I am simply looking at icl. Install it retarded 4 deg from dot to dot should put it on a 113 intake centerline and delay intake closing to bleed off compression.

May help. Dyno tuning cruise will work great. I would seriously consider 2 steps colder than stock rated plug for this higher DCR build. Hotter is asking for trouble imo.

If you went bigger on cam i am not sure how tbi will handle it. I dont see many big cammed tbi builds so not sure how stable/smooth idle and part throttle performance will be. If multi port efi i would say no problem goin bigger on cam.

You are looking at next step up atleast, advertised 274-282 i would guess and intake closing around 68-72 deg? Should get dcr lower. Like a 280 xfi or 282hr 230/236 but that is a good bit of cam in a 350" motor. I tuned a 280 xfi and its definately a hot street cam, very driveable with good tune but does have alot of lope and makes higher rpm power. Not exactly what you need or want with tbi, yet compression kinda dictates the need for abit more cam.

morgsie

iTrader: (1)

So if I installed my cam "straight up" it would be @ the 109 ICL? Or is straight up when you set it so the ICL is same as the LSA degrees? Sorry I have seen people say two different things, just want to get my terminology right.

What is a good indicator of neededing to go to a colder plug? I thought going to a colder plug was mainly a forced induction thing. What about gap? Current ones are gapped @ .045".

This project was started almost 4 years ago with a 2.5 year break inbetween. I had the engine built by a guy that did a less than steller job. Then got it "checked out" last year and the new builder found a bunch of things not right. I should have just sold that started from scratch, but instead I got it rebuilt and as time goes on I realize that i should have spent more time on the details. Live and learn I guess? I think at this point I will just leave it as is and tune it on the dyno and at least enjoy it this summer. If I am not happy then maybe do something about it this coming winter.

Thanks for the help lads.

Orr89RocZ

iTrader: (20)

Alot of engine builders and cam guys I know say "straight up" means no advance in the cam. This means ICL is same as LSA. So your cam straight up would be 113 intake centerline, 113 lsa.

Generally for plugs, the higher the chamber pressures are, and with pressure the higher heat in the chamber, you want a colder plug to prevent preignition. Stock builds have a factory specified heat range. For me, I start with that and go colder depending on mods. Like a hot street build with better heads, cam, and mild comp increase, I may try one step colder. A aggressive build that is high compression or high on dynamic compression that may run into pump gas problems, I may try 2 steps colder. My 11 to 1 383 at 8.3 to 1 DCR did good with heat range 6, when a stock heat range is 4. Mild nitrous use on stock motor, 1-2 colder than stock could work. Nitrous on top of a more aggressive build, 2-3 colder. Same with mild Forced induction, 1-2 colder. Heavier forced induction on more aggressive builds, 3-4 colder. My turbo motor now is heat range 8, thats 4 colder. It may run ok on 7, i havent tried. Some race gas ultra high compression may run 9-10 heat range plugs.

You can tell by looking at the plugs and trying to find heat marks on the strap and such. Do some searches on the subject
http://www.wallaceracing.com/plug-reading-lm.html

Gap is usually ok between .035-.055. Depends, tuning for miles per gallon and lean mixes may need much wider gaps. Strong ignition systems may light off the charge with wide gaps too. Nitrous/forced induction run tight gaps.

So you can try the cam and a good colder plug to see what happens. Be easy with it. I'd put the cam in on a 113 ICL and see what happens. If it is not going to work, you can always sell that cam easily. Its a good cam and popular

camarito

I have 0.024 deck and use 0.015 head gaskets, 64cc heads, DCR at 8.3 and can run 87 octane if I keep the timing below 30*, and I don't feel much difference (if any) from the 93 octane and 34* but it takes aluminum heads, well tuned carb, 180* Tstat and a good cooling system, you keep the engine cool and a little on the rich side and you'll be good

1gary

I agree at this point it is a expensive lesson.Let it be and run it as is.Don't expect much.The Do-over if it where me would to find a L31 1996 to 2000 and build another over the next two yrs.If you apply what you learned from this one,maybe consider a set of aluminum heads with the correct chamber volume and that would give some lead-way of a addition 1 point(10.5) in SCR.

morgsie

iTrader: (1)

The engine made 375FWHP/420ft-lbs on the engine dyno with a carb and 91. This is why it ended up getting re-rebuilt, lower than expected oil pressure and went to drain the coolant out and the water jackets were PACKED with junk. With better bearing clearances and 1.6 rockers I would expect it to make a little more. The goal 4 years ago was 300RWHP. Hindsight, should have just got an LT1 and threw a cam in it, but I was given some bad advice by my boss at the time. Gary, since everything is setup already you are probably right about just building another gen I block. For a few hundred dollars I could buy some measuring tools and assembled/blue print it myself. The aluminum heads would be nice as I could prob run higher compression and pump gas. If I was to do it again I would have just got a newer LSx (5.3l or 6.0l) from the wrecker and called it a day.

1gary

My criticism of the LSx answer is it seems to me they tend in a N/A engine to lend themselves to more a HP engine than a low end torque engine.And dollar for dollar to buy after market parts for them seems pretty expensive.Price out a stroker 5.3 and a good set of heads and your will see what I mean.I looked at the aftermarket 5.3 427 block and heads and that was just mad money.Then guys want to turbo those with additional costs added on top.

It is for those reasons that I am suggesting another L31 1996 to 2000 engine.

Now you can trust in the fact my opinion isn't just old school talking.I'm am in a search all the time for new answers.In fact I wouldn't mind having a 5.3 or 6.0 in a engine stand around in the shop just to have one.But I think for now the dollars play out better for the L31's.

morgsie

iTrader: (1)

I finally got around to downloading Pat Kelly's DCR Calculator. If I was to install my cam "straight up" (no cam advance) and use a .018" thick head gasket my SCR would be 10.36:1 and DCR 8.38:1. What do you think? Would it be worth the day of work and a few bucks?

Orr89RocZ

iTrader: (20)

I would give it a shot. All else fails can you buy a few gallons race fuel to mix in the tank?

morgsie

iTrader: (1)

I was really hoping to run 91, but I could mix gas if need be. The combinatio I listed above is so border line with iron heads, I might just pull it off. I will have to run a 180* t-stat (currently running a 195*), have a HD 3 row rad but a stock water pump. Do you think it will be enough? What about running those flowcool "water pump discs" ? I also have coolant plumped through the intake under the TBI, I assume I will have to ditch that?

Orr89RocZ

iTrader: (20)

Could try some water wetter adder to try and reduce coolant temps. They say its good for a few degs. I used it but on my car i am working with a too small rad and or not enough airflow so it still seemed to run as hot as before. Good fans with shroud help. 180 tstat for sure and match cooling fan turn on/off temps and it should all go a long way in helping. Remember 2 steps colder than stock plugs and reduce timing for now and slowly work your way up.

Keep intake charge temps cool so bypass the coolant line to intake.

morgsie

iTrader: (1)

I must have made an error last night, with a .020" (compressed) headgasket and cam installed "straight up" my SCR would be 10.39:1 and the DCR would be 8.15:1. Current setup is: 9.91:1 SCR and 8.26 DCR.

Really on the fence on what to do here. For the price of headgaskets and a weekend of my time I could perhaps make things better? or just leave it alone? gah!

Orr89RocZ

iTrader: (20)

If its together now you can try it as is. I dont like the high quench height but 8.26 dcr if true should be doable. 8.15 isnt much of a difference but the quench can make a bigger difference

morgsie

iTrader: (1)

Ya I am going to just leave it as is. I will go 2 steps colder on the plugs as you suggested. I can get R42LTS locally, do you recommend another brand? I've always ran delco in GM stuff but that has been for stock stuff. You still think I should run a colder stat + bypass my intake cooling? Currently have a clutch fan but plan on getting a dual fan setup down the road. Will be building a cold air intake this weekend. 4" aluminum mandrel bends and a 9" amsoil cone filter behind the headlight. Going to build a box or devider behind the drivers headlight.

Orr89RocZ

iTrader: (20)

I would still do the bypass and tstat. Plug brand is fine. Some love champion, i have stuck with NGK, some like others. Whatever works best for you

1gary

I do for good reasons like the target of .040 and a DCR of 8.5.I will say I have seen guys squeak by with as high as DCR of 9.0.
Thing is the gas varies alot even with the same brand gas in different locations in the same town.The 8.5 does give you some wiggle room for that.And the reasons behind 8.5 is it is a very good performance DCR that does make a difference.

chas0218

We need to know a little more info. What cam and what is the duration at .50"? I run 11.5:1 compression on pump gas but I have a lot of duration.

1gary

The point is to find a value where your not trading off more than your gaining. NYS gas is high risk.Wide DCR's turn potential good performance engines into turds. So does ignition timing adjustments.Do-overs costs money.If your backed into a corner,aluminum heads might be the answer.Raise the SCR by one full point.

88FormulaKiller

iTrader: (8)

ummmm what????

5.3 from a pickn pull $80-$150, practically boost ready @ 10-15psi, cheap turbos run 150-300, custom make pipes and use flipped truck manifolds. Dollar for dollar dude? seriously? I'd leave LSx comments out, 5.3 Turbos pushing 400HP +++++++++ is the cheapest budget V8 engine you can do right now with someone with moderate welding skills. Even some LS car turbo hot sides work.

Johnny Blaze

iTrader: (15)

I'm in a similar situation. Assembling my engine now.

Same pistons, 64cc 083 heads, pistons .20 in the hole.

Looking at gaskets as well. I was thinking of going with the thinner to get better quench but am concerned if it will live on premium pump gas as well.

Orr89RocZ

iTrader: (20)

Then theres swap costs and wiring to make it work. It can add up but if you are handy diy-er you can certainly take the junkyard stuff far for cheaper. But build an lsx motor using aftermarket parts is not cheap lol

88FormulaKiller

iTrader: (8)

Orr i agree man, its not cheap, but its affordable. Send me a PM when you wanna go LSX and we can chat on the phone, ill hook you up with all the cheap LS parts you could want or need for a swap.

Orr89RocZ

iTrader: (20)

I am actually considering doing a forged 347 for my trans am but then again not sure. I dont want to get crazy with it. Probably stock crank but rod/piston deal. Was gonna boost it for now but also considering all motor for cam lope sound. I miss my all motor build. Oh well another time another place but if you have deals on things, i got tons of lsx friends

1gary

Johnny,
The .040 quench helps to prevent issues in pump gas.

Johnny Blaze

iTrader: (15)

Gary, thats what I was thinking/hoping.

My options are 10.29:1 with a .035" quench

or 9.73:1 with a .059" quench!

I figured higher compression with tighter quench would be the way to go.

Orr89RocZ

iTrader: (20)

Some researching among engine builders there seems to be a phenomenon where most consider .060-.100 or .060-.120" "quench" height as a detonation zone. Anywhere in this height can increase chance of detonation significantly. If you go above .100-.120, the engine returns to "normal" and it wont be as detonation prone. Not sure how or why that works or how true that is but alot of people seem to agree. Tight quench in the .03-.040 ranges seems to be most common.

Johnny Blaze

iTrader: (15)

Interesting.