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Okay guys I’ll try to make this as “short and sweet” as possible, but, simply stated (?) …. here is my problem.
I’m building a 396 LT1 stroker motor and I designed this motor to have a .038” quench, (block decked to 9.012” using a .026” compressed head gasket), specifically ….. so that it would run on 93 octane premium unleaded fuel.
The problem is that something got “lost in translation” at the machine shop and they square decked the block to 9.020” instead of the requested 9.012” deck height. Soooooooooo …. after thoroughly washing and painting the block, installing all the freeze plugs, oil galley plugs, cam bearings, main and rod bearings, crank, rods, pistons, rings and torqueing everything to final specs …….. I finally “discovered” this deck height/quench error.
Furthermore, to complicate the problem, I’ve already got the cam, heads, throttle body, etc., etc., etc. to finish this motor, so changing cams to bleed off dynamic compression might be a more expensive solution to this, than just dis-assembling the short block, and sending it back to the machine shop to correct the deck height error.
So here’s the $64,000 question ….. have any of you built an LT1 stroker motor running 12.8 static and 9.2 dynamic compression ratio with a relatively “loose” .046” quench …… and have it run okay during the Summer months on 93 octane fuel ………. WITHOUT pulling timing or having detonation issues???
TIA for any experience, comments and/or suggestions you may have had in building LT1 stroker motors like this.
Last edited by 97 6speed z; 12-13-2016 at 04:43 PM.
From all the research I did while putting mine together, it sounds like you are right on the comfortable edge with the 9.2 DCR. Is that calculated with the .046" quench or the .038"?
From all the research I did while putting mine together, it sounds like you are right on the comfortable edge with the 9.2 DCR. Is that calculated with the .046" quench or the .038"?
Mine ended up being 11.5 SCR and 8.5 DCR with the parts I ended up using and seems to run great so far.
Also where did you get your cam from? If you got it from Lloyd he is pretty good about telling you what will work and what will not.
Originally Posted by Nostang
I would not run pump gas on it with 9.2-1. I have 9.3-1 and a .033 quench on mine and I do not feel comfortable running pump 93.
Casey96SS, thanks for the thread link you sent along, great reading there, and ... that 9.2 DCR is calculated using the .046" quench value, (i.e. with the piston .020" in the hole), and yes, the cam I'll be using is an older Lloyd grind.
Nostang, what octane rating fuel do you run when not on the NOS, and just Summer street cruising? Also, have you ever tried running you engine on say 95 octane fuel?
Something else I thought of. Did you actually measure the CC's of your heads and pistons? My pistons were 1.5 CC more that what the advertised in the catalog.
I know the tightest quench is supposed to be best, but maybe your DCR would be getting too high if you had the block decked again.
A call or email to Lloyd would be where I would start.
Casey96SS, thanks for the thread link you sent along, great reading there, and ... that 9.2 DCR is calculated using the .046" quench value, (i.e. with the piston .020" in the hole), and yes, the cam I'll be using is an older Lloyd grind.
Nostang, what octane rating fuel do you run when not on the NOS, and just Summer street cruising? Also, have you ever tried running you engine on say 95 octane fuel?
I am running Sunoco 110 leaded for racing and cruising. I am running a solid roller cam with solid mounts so there are no knock sensors on my setup. I think I could safely get away with a mix of 110 and 93 pump fuel. From what I have been told, in order to run pump gas I would have to back off my timing and detune my setup for it to be safe on pump gas. I have drove around on pump gas 93 at low rpms (under 3k) and the car was fine with no detonation. However, I would not trust it at WOT and shifting at 7k+ rpms.
.......So here’s the $64,000 question ….. have any of you built an LT1 stroker motor running 12.8 static and 9.2 dynamic compression ratio with a relatively “loose” .046” quench …… and have it run okay during the Summer months on 93 octane fuel ………. WITHOUT pulling timing or having detonation issues???.......
I'm right about where you are (12.5:1 SCR and 9.2:1 DCR) in my '96 street/strip Impala......and it get pretty toasty in San Antonio in the summer. That having been said, my quench is just a shade over .030".
Still, you should be OK with a good dyno + road tune.
And if it'll ease your mind a bit.....get a second PCM and have it loaded with the same primary tune except with a bit of timing pulled.....you know.....for when it gets a bit toasty where you are.
Something else I thought of. Did you actually measure the CC's of your heads and pistons? My pistons were 1.5 CC more that what the advertised in the catalog.
I know the tightest quench is supposed to be best, but maybe your DCR would be getting too high if you had the block decked again.
A call or email to Lloyd would be where I would start.
Casey96SS, I did cc my AFR 210 heads, and they came in at 54.4cc's on an advertised 55.0 cc combustion chamber. I have not cc'd the valve reliefs on my flat top pistons though.
Originally Posted by KW Baraka
I'm right about where you are (12.5:1 SCR and 9.2:1 DCR) in my '96 street/strip Impala......and it get pretty toasty in San Antonio in the summer. That having been said, my quench is just a shade over .030".
Still, you should be OK with a good dyno + road tune.
And if it'll ease your mind a bit.....get a second PCM and have it loaded with the same primary tune except with a bit of timing pulled.....you know.....for when it gets a bit toasty where you are.
KW
KW, thanks for your input, and this may sound like a really dumb question, but ...... you're not running cast iron heads on that 398 Impala .... are you? You are running some sort of aluminum LT1 head on that Impala, right?
......KW, thanks for your input, and this may sound like a really dumb question, but ...... you're not running cast iron heads on that 398 Impala .... are you? You are running some sort of aluminum LT1 head on that Impala, right?.......
I'm running LT4 AFR-210 heads......aluminum.
You're not running a LT1 intake with your AFR-210 heads, are you?
You're not running a LT1 intake with your AFR-210 heads, are you?
KW
KW, I know this has been hotly debated on many LT1 forums, but, yes, before ordering my AFR 210's I spoke with the tech department at AFR, and ....... they assured me that their newest LT1 210's will work with the LT1 intake. It's only their older 210's that required the LT4 intake.
To throw a caution right back at you however ..... you did use the AFR specific intake manifold gasket with your LT4 intake, 210 head combo right???? Using any GM or OEM replacement LT4 intake gaskets, instead of the AFR gasket ....... will cause you more problems than using the LT1 intake will.
KW, I know this has been hotly debated on many LT1 forums, but, yes, before ordering my AFR 210's I spoke with the tech department at AFR, and ....... they assured me that their newest LT1 210's will work with the LT1 intake. It's only their older 210's that required the LT4 intake.......
LOL.......OK.
Bought mine in 1999......I guess I have the 'old' version!
Originally Posted by 97 6speed z
......To throw a caution right back at you however ..... you did use the AFR specific intake manifold gasket with your LT4 intake, 210 head combo right???? Using any GM or OEM replacement LT4 intake gaskets, instead of the AFR gasket ....... will cause you more problems than using the LT1 intake will.
I've been using aftermarket LT4 gaskets......with no issues.
Felpro makes a great SBC Race gasket with taller ports that works well for AFR heads, PN 1206.
My heads are very heavily ported so actually still ended up with the gasket slightly shrouding the ports, which I cleaned up with a dremel, but for most heads the port will be smaller then the gasket. The weird marks in the right side port are marks and shadows on the ceramic coating that only show up in that picture - in person it doesn't look like that (?).
KW, glad to hear your older (not old!) AFR 210's are working well with the LT4 intake and aftermarket intake gasket. If it ain't broke .......
Puck, thanks also for the tip on the Felpro 1206 intake gasket.
At this stage of assembly I'm going to cc the valve reliefs in my flat top pistons, double check all my compression numbers, and then decide what to do.
At this stage of assembly I'm going to cc the valve reliefs in my flat top pistons, double check all my compression numbers, and then decide what to do.
And the results are in!
"Engine A"
Bore: 4.030 Stroke: 3.875 Cylinder Head Volume:54.4
Effective Dome Volume: 5.8 Deck Clearance: .020Quench: .046
Compressed Gasket Thickness: .026 Number of Cylinders: 8
Compression Ratio: 12.61 : 1 Total Displacement (in.3) : 395.42
"Engine B"
Bore: 4.030 Stroke: 3.875 Cylinder Head Volume: 54.4
Effective Dome Volume: 5.8 Deck Clearance: .012Quench: .038
Compressed Gasket Thickness: .026 Number of Cylinders: 8
Compression Ratio: 12.9 : 1 Total Displacement (in.3) : 395.42
So what's the thinking here. What engine will be LESS prone to detonation on 93 octane premium unleaded fuel?
Hard question to answer without the total build, cam specs, and even altitude.
Based on what we have, I honestly think that "A" with the looser quench will resist detonating more then B due to the 12.6CR vs 12.9, but with the right cam and good tuning (lots of timing pulled, not ideal) either will work. Keep in mind people run over 11:1 with relatively large .050+ quench, and stock LT1 is ~10.4:1 with a massive .070 quench.
I would say 12.9 is definitely pushing it for pump gas, even with a tight quench. Most recommend staying 12.5 or under, which is what I aimed for.
Don't forget a cam with more overlap and a later IVC can handle more compression safely then a small cam with less overlap and higher cylinder pressure. Solid roller acts smaller then HR so add a few degrees duration to compare the two.
I would say combo A is less prone to detonation with pump 93. Have you asked Lloyd Elliot what his opinion is on which combo could get away with pump gas?
I was told by many folks that anything over 12-1 is pushing it for pump gas. You might get away with it if the tune is spot on but the variability in pump gas could mean some piston damage if you happen to get a bad batch. Secondly, you cannot always hear detonation so you could be damaging the pistons and not even realize it until you have a problem.
If I were going with a pure pump gas 93 N/A engine I would not go over 11.8-1 static just to give a safety window for gas and tuning. You can use a cam with lots of overlap and a late intake valve closing to bleed off compression but that only works at lower rpms. Once you get under load and at WOT the ramming effect of the cam design could cause issues with detonation. Gearing and weight also play a role in detonation. Anything you can do to reduce the load of the engine will help with detonation.
Engine B......as long as you have a properly spec'ed cam.
KW
This. What are the cam specs? Opening up the LCA and having a late IVC helps, so do taller gears and a good tune (not just power tuning).
Can you soften the head combustion chambers? That should give you some added volume to offset decking the block more no? Shortening the deck height by .008" should remove 1.7cc. Can't we add ~2cc by softening the heads on the LT1?
I have never seen an LT1 a hair shy of 13:1 on pump gas, no matter what the cam or quench. Even with a grind that has tons of overlap that is still a lot of compression for 93 and won't leave any safety margin for a bad tank of gas or the old watery **** you get on from the bottom of the station tank before they refill.
There was a guy running like 13.2:1, but used race gas.
12-13-2016, 04:38 PM
Effect Of Quench On Detonation Question 
