74 NovaMan's 1979 Chevy Truck - LS Swap - 5/6 Drop

[74NovaMan]

LS motors are a different animal - the same cubic inch compared to a gen 1 can live with much higher CR.... on swill, a gen 1 could run 10:1 with careful tuning. Yet the LS you can play at 11:1 without a fear. As with any motor, though, what a motor will tolerate requires a solid knowledge of the parameters (air flow, cam duration and timing, and how the fuel is put in - efi/port, etc).... the common rule back in gen 1 days was 7 or 8:1 compression on a boosted application, now? 9-10 is considered just fine.

heads..... https://www.lsenginediy.com/ultimate...r-heads-guide/
there's the numbers for each and every LS head.....the 317/243/799 all flow basically the same with the difference being the combustion chamber size

and if you don't want to read down to see the flow works on the 5.3 head (despite the smaller valve)... here's this - say you send off any of those heads to a lingenfelter or such.... the same CNC program is used to port them, to me that speaks volumes about how similar they are (and how some trolls want you to believe their version is 'the best')....

Good insight as always. Thanks again. The reading I've done so far backs up your statement above. The more I look into the different heads, the more it appears that there is very little difference at the power levels I'm contemplating (given i have this cam in hand: https://www.summitracing.com/parts/nal-12638427) and that the combustion chamber size is probably the most critical detail.

[74NovaMan]

I run 11 - 1 on the street in the wagon but not on 87 octane.
I run 9.7 -1 on the street in the truck but not on 87 octane (it has cast iron heads).
What is the truck's main purpose - you looking to kick some ass or are you going the thumper cam and flowmaster route?
Those other heads sound like a good choice for a forced induction build so if that is probable then you might consider the best combination for the future.

How much ignition lead do those LS engines like?

The trucks main purpose is summer daily driver. Before the rebuild rabbit hole I was planning in stabbing a moderately hotter cam in it and hoped for 400 hp with cam, intake, headers and tuning. The 87 octane requirement is self imposed because I believe that it will be easy enough to tune for that with the flexibility of the fuel and ignition controls. Mostly I'm tired of the ever increasing cost of premium gas over 87.

Now that I'm spending more with the rebuild, I'm looking to maximize the potential I guess. I should probably focus on building a sound 350-400 horse motor with the flexibility to turbo it later.

[Deaf Bob]

Fuel rating... 350 small block, headers, intake, cam, big coil drives fine empty on regular fuel, but with loads, I find it likes premium better.. Lugs better, pulls better..empty less downshifting as well.. I might be running too much timing..

[Russell]

I have not been paying attention what was the reason for the rebuild? Is it getting boost, or maybe some day?

Go with the small chamber heads.

https://youtu.be/gJCT5RvPCwM

[SuperBuickGuy]

I see how you are! Making me do my own research!

Seriously, I very much appreciate your input on all of this stuff even if I end up going another direction.

I'm not much into, when I don't know, googling then acting like a solid resource... If I know, I'll tell you, if I don't I won't (unless you're my wife and you ask the same thing twice... then I'll give you the same advice I give here which is "under any circumstance do not follow my second bit of advice - even if it were possible")

Here is an interesting article on stock head choices that would seem to indicate that the 706 head is a better choice when all else is equal (on an NA motor).

http://www.superchevy.com/how-to/eng...nder-head-test

Question for the gallery: Is a compression ratio of 10.9 too much for 87 octane for this motor? Is 9.7 a better target? It appears to me that the tuning available with the fuel injection and ignition that too high a compression ratio (as long as its not crazy) is less of a concern.

LS motors are a different animal - the same cubic inch compared to a gen 1 can live with much higher CR.... on swill, a gen 1 could run 10:1 with careful tuning. Yet the LS you can play at 11:1 without a fear. As with any motor, though, what a motor will tolerate requires a solid knowledge of the parameters (air flow, cam duration and timing, and how the fuel is put in - efi/port, etc).... the common rule back in gen 1 days was 7 or 8:1 compression on a boosted application, now? 9-10 is considered just fine.

heads..... https://www.lsenginediy.com/ultimate...r-heads-guide/
there's the numbers for each and every LS head.....the 317/243/799 all flow basically the same with the difference being the combustion chamber size

and if you don't want to read down to see the flow works on the 5.3 head (despite the smaller valve)... here's this - say you send off any of those heads to a lingenfelter or such.... the same CNC program is used to port them, to me that speaks volumes about how similar they are (and how some trolls want you to believe their version is 'the best')....

[cstmwgn]

I run 11 - 1 on the street in the wagon but not on 87 octane.
I run 9.7 -1 on the street in the truck but not on 87 octane (it has cast iron heads).
What is the truck's main purpose - you looking to kick some ass or are you going the thumper cam and flowmaster route?
Those other heads sound like a good choice for a forced induction build so if that is probable then you might consider the best combination for the future.

How much ignition lead do those LS engines like?

[74NovaMan]

Here is an interesting article on stock head choices that would seem to indicate that the 706 head is a better choice when all else is equal (on an NA motor).

http://www.superchevy.com/how-to/eng...nder-head-test

Question for the gallery: Is a compression ratio of 10.9 too much for 87 octane for this motor? Is 9.7 a better target? It appears to me that the tuning available with the fuel injection and ignition that too high a compression ratio (as long as its not crazy) is less of a concern.

[74NovaMan]

The block checked out very well. I am going to go with the .005 over pistons and hone the cylinders to fit likely under $100 (vs $480 for boring oversize). My piston choices are 7cc dish: https://www.summitracing.com/parts/sum-2999273785-7 or 2cc dome: https://www.summitracing.com/parts/sum-2999273785-2

If I use the 706 heads that I have (pressure tested good) my compression ratio is either 9.7 or 10.9 respectively.

I have a line on 317 heads from a 2008 6.0L that were removed at under 10,000 miles from new that I can get for cheap. These would be ready to run but the chamber size is 71cc (vs 61cc for the 706 heads) Compression ratio for this head is either 8.7 or 9.6 respectively. This is according to the chart from Summit:

[74NovaMan]

whatever Google tells me...

I see how you are! Making me do my own research!

Seriously, I very much appreciate your input on all of this stuff even if I end up going another direction.

[SuperBuickGuy]

Thanks for the note on ring gap. I probably would have missed that. What are you planning for your gaps?

The new rods come with ARP bolts.

whatever Google tells me...

[74NovaMan]

if you do forced induction, remember to increase the gap on your rings..... that would really bite to spend all that money then hang a ring and break a land....

oh yeah, and buy the ARP bolts

Thanks for the note on ring gap. I probably would have missed that. What are you planning for your gaps?

The new rods come with ARP bolts.

[SuperBuickGuy]

if you do forced induction, remember to increase the gap on your rings..... that would really bite to spend all that money then hang a ring and break a land....

oh yeah, and buy the ARP bolts

[74NovaMan]

like most anything, replace the rod bolts with ARP and it will be fine. If you're planning on more then 600 hp, then rods are important.... at least that seems to be the prevailing theory. If you're not planning more then 6500 rpm, you don't even need to change the bolts.

I did not heed your earlier advice/warning and went down the rabbit hole yesterday "researching" the rod/rod bolt issue. Here is my logic (FWIW):

Given that the pistons need replacing I have it broken down to 2 options.

Option 1:
Stock style oversize piston to work with my original rods are $290: https://www.summitracing.com/parts/s...make/chevrolet
These require boring the cylinders: $480
ARP rod bolts: $97
Total: $867

Option 2:
Forged pistons in either .005 over (for a hone) or .030 over (bore) $500 https://www.summitracing.com/parts/s...make/chevrolet
Boring the cylinders (worst case assumption) $480
New Rods $440 https://www.summitracing.com/parts/s...2521/overview/
Total (worst case): $1,420

The cost difference is $553. Seeing as I'm rapidly approaching $3,000 why stop short on doing it right the first time. It also sets me up nicely for forced induction or nitrous (which may never happen). If I only needed rings, I'd just slap it together and call it a day.

[74NovaMan]

I like the Scat H-beam rods in my Fords - no clue if there is any issues with them in an LS engine. As to the bore - IF (IIIIIFFFFFFF) the bores are round and straight - then honing them to size probably will be OK. If the skirts are worn, I would suspect that there could be some wear in the cylinders as well. Honing does not always square up everything and remove the taper. What does the machine shop charge to hone ($150 - $200)?

Since we are spending your money, I would put a stroker kit in it while it is apart. As someone once said - there is no replacement for displacement!

The machinist said that he would be checking the block today. If there is any question, I'll just bore it at this point. I already have the stock crank polished and ready to go, but I did consider a stroker kit for a few minutes.

[SuperBuickGuy]

like most anything, replace the rod bolts with ARP and it will be fine. If you're planning on more then 600 hp, then rods are important.... at least that seems to be the prevailing theory. If you're not planning more then 6500 rpm, you don't even need to change the bolts.