Prochraged LT4 Going to the Dyno... any bets
10-28-2018, 09:09 AM
#41
Race Director
ive ran 12 psi since 2011. That year, i had stock compression bc i hadnt yet switched to bigger cc afr heads.
the only problem i would get would be occasional knock activity under hard accel (which would ruin the pull due to spark retard but save the engine). I have a knock gage on the dash making real time monitoring easy.
Now, once i did detonate under boost bc my methanol system malfunctioned (i have since set up a pillar gage showing methanol pressure and fail safe to prevent motor from going into boostby stumbling injectors).
I was certain i did damage, but when i did compression check i was pleasantly surprised to see all was good.
the OP needs to go to the c5 forced induction site and ask questions (dont tell them you have a c4). Those guys run 12 psi all the time on stock bottom end with similar compression ratio
10-28-2018, 10:45 AM
#42
Melting Slicks
383.3hp/358.3tq 8PSI
not too bad. In discussion with the guys at the shop, and they are a Procharger shop, they feel the car has a very conservative tune. Suggested ditching the FMU and going to a larger single pump, injectors, cam, and headers to stay safe and get maximum results. They feel getting to 450whp would be doable on stock bottom end if it was done right and then not abused.
10-28-2018, 11:24 AM
#43
Racer
I agree with Dizwiz. I have a stock bottom end LT1 from a Z28 (with the exception of ARP fasteners) and it has 11.9:1 compression due to being decked for .035" quench. I have a 220/230 cam and a Vortech that makes 9-10 lbs boost along with water/meth injection and have never had a detonation event. The engine is in a much modified MGB roadster and it makes 470 rwhp and 479 rwtq. It has been running for 2 years now.
10-29-2018, 08:18 AM
#45
Race Director
You know better than to compare an LT1/4 with any LSx engine. They are totally different architecture. The bottom end of an LS is more akin to a BBC than a small block as far as "beefiness" is concerned.
Another observation is the 95-up LT engines have powdered metal connecting rods. PM rods have low tolerance to overloads from detonation. I'd be a little uncomfortable with forced induction on a PM rod assembly. But that's just my opinion based on experience with Syclone and Typhoon 4.3's at a stock 14.7 psi. (The 4.3 is basically a 5.7 V8 that's missing 2 cyls. The rod bearings are .1/8" narrower, but that's the main difference). We bust and blow stuff up all the time in these V6's, and bend rods from detonation. No one runs PM rods in SyTy. While dizwiz has been successful at 12psi with water injection, I don't feel the OP would be as likely to achieve the same success at 12psi in a PM rod LT4.
In the context of PM rods in LS engines, I was curious about the rod material in the LS7 and LS9. Quick research revealed: Titanium. So GM doesn't use PM rods in high BMEP (LS7) or forced induction (LS9) applications either.By participating in this thread, I learned something I did not know. Cool.
Another observation is the 95-up LT engines have powdered metal connecting rods. PM rods have low tolerance to overloads from detonation. I'd be a little uncomfortable with forced induction on a PM rod assembly. But that's just my opinion based on experience with Syclone and Typhoon 4.3's at a stock 14.7 psi. (The 4.3 is basically a 5.7 V8 that's missing 2 cyls. The rod bearings are .1/8" narrower, but that's the main difference). We bust and blow stuff up all the time in these V6's, and bend rods from detonation. No one runs PM rods in SyTy. While dizwiz has been successful at 12psi with water injection, I don't feel the OP would be as likely to achieve the same success at 12psi in a PM rod LT4.
In the context of PM rods in LS engines, I was curious about the rod material in the LS7 and LS9. Quick research revealed: Titanium. So GM doesn't use PM rods in high BMEP (LS7) or forced induction (LS9) applications either.By participating in this thread, I learned something I did not know. Cool.
You will learn a lot on that forum about tuning and methanol water injection that can be applied to your engine
now yes, the timing is totally different for an lsx motor vs ltx/sbc. I will give you that.
10-29-2018, 10:53 AM
#46
Team Owner
Pro Mechanic
Is there any documentation that shows a forged PM rod is any worse than I regular forged rod? I've read that they're about the same strength....
10-29-2018, 11:53 AM
#47
Drifting
Thread Starter
10-29-2018, 11:54 AM
#48
Drifting
What is up with the low mph? Is this a stick car? And were the pulls done in 3rd gear?
If so, I would think a 4th gear pull would show closer to 400 rwhp.
If so, I would think a 4th gear pull would show closer to 400 rwhp.
10-29-2018, 11:58 AM
#49
Team Owner
Pro Mechanic
Both materials are probably about the same in tensile and compressive strength when intact. It's what happens when they are stressed beyond their design strength, particularly in compression loading. Which is what detonation loading is.. In the FWC boats the PM rods explode from a hydrolock event, the forged rods bend but the engine continues to run. 4.6, 5.4, and the 6.5 V10 Fords, have ongoing, frequently discussed failures of their PM connecting rods. So no, I don't have documentation for PM rod strength, just anecdotal evidence.
10-29-2018, 12:01 PM
#50
Drifting
Thread Starter
You know better than to compare an LT1/4 with any LSx engine. They are totally different architecture. The bottom end of an LS is more akin to a BBC than a small block as far as "beefiness" is concerned.
Another observation is the 95-up LT engines have powdered metal connecting rods. PM rods have low tolerance to overloads from detonation. I'd be a little uncomfortable with forced induction on a PM rod assembly. But that's just my opinion based on experience with Syclone and Typhoon 4.3's at a stock 14.7 psi. (The 4.3 is basically a 5.7 V8 that's missing 2 cyls. The rod bearings are .1/8" narrower, but that's the main difference). We bust and blow stuff up all the time in these V6's, and bend rods from detonation. No one runs PM rods in SyTy. While dizwiz has been successful at 12psi with water injection, I don't feel the OP would be as likely to achieve the same success at 12psi in a PM rod LT4.
In the context of PM rods in LS engines, I was curious about the rod material in the LS7 and LS9. Quick research revealed: Titanium. So GM doesn't use PM rods in high BMEP (LS7) or forced induction (LS9) applications either.By participating in this thread, I learned something I did not know. Cool.
Another observation is the 95-up LT engines have powdered metal connecting rods. PM rods have low tolerance to overloads from detonation. I'd be a little uncomfortable with forced induction on a PM rod assembly. But that's just my opinion based on experience with Syclone and Typhoon 4.3's at a stock 14.7 psi. (The 4.3 is basically a 5.7 V8 that's missing 2 cyls. The rod bearings are .1/8" narrower, but that's the main difference). We bust and blow stuff up all the time in these V6's, and bend rods from detonation. No one runs PM rods in SyTy. While dizwiz has been successful at 12psi with water injection, I don't feel the OP would be as likely to achieve the same success at 12psi in a PM rod LT4.
In the context of PM rods in LS engines, I was curious about the rod material in the LS7 and LS9. Quick research revealed: Titanium. So GM doesn't use PM rods in high BMEP (LS7) or forced induction (LS9) applications either.By participating in this thread, I learned something I did not know. Cool.
I am very pleased with where the car is currently other than using a FMU. Sure the car gets an occasional WOT blast, but it will never see regular track use while I own it. Just not something I am interested in doing frequently. IMO the car could be as is for a very long time. However, I have no reason to believe the LT4 bottom end can't get to a reliable 450whp done right. I won't be doing it with additional boost. If I do anything from here a larger Fuel Pump, Injectors, and Cam will be the route. Might have the intake and heads polished up a bit to reduce restrictions going in. That way, at the same boost level I can get cooler (safer) air in and make more power with it.
Last edited by KyleF; 10-29-2018 at 12:02 PM.
10-29-2018, 12:03 PM
#51
Drifting
Thread Starter
10-29-2018, 12:41 PM
#52
Drifting
10-29-2018, 03:21 PM
#53
Drifting
Thread Starter
You should be pleased with where it is currently. It's reliable and probably plenty fun to drive.
I think you're going to be fine if you stay in the 8-ish psi range. My comments on the rods and things are regarding detonation over-stressing parts. There's more to it than "tuning". When boost goes up. particularly with stock N/A static compression ratios on pump gas, the likelihood of detonation increases exponentially. You are aware of this, so are looking at other areas for improvement other than boost. A conservative approach. Cool.
A comment was made above questioning exhaust restriction. This is frequently an area where big gains can be made. If exhaust back pressure is higher than chamber pressure when the piston nears TDC (it is moving very slowly at TDC), the incoming charge is diluted by back-flowing exhaust gas prior to the exhaust valve closing. In the turbocharged SyTy my last three builds have utilized camshaft profiles where intake duration exceeds exhaust duration, LSA is about 114-ish, and overlap is minimal. All the exact opposite to what is done in N.A. engines. While turbocharging is a little different than mechanical driven supercharging, I would think that significant gains are possible with a forced-induction specific camshaft.
As you make changes such as improved exhaust or camshaft profiles, if the charge dilution discussed above is reduced, the engine will be more prone to detonate because of the increased charge density. So tread lightly after changes to the exhaust until you establish that detonation is still under control.
Carry on.
I think you're going to be fine if you stay in the 8-ish psi range. My comments on the rods and things are regarding detonation over-stressing parts. There's more to it than "tuning". When boost goes up. particularly with stock N/A static compression ratios on pump gas, the likelihood of detonation increases exponentially. You are aware of this, so are looking at other areas for improvement other than boost. A conservative approach. Cool.
A comment was made above questioning exhaust restriction. This is frequently an area where big gains can be made. If exhaust back pressure is higher than chamber pressure when the piston nears TDC (it is moving very slowly at TDC), the incoming charge is diluted by back-flowing exhaust gas prior to the exhaust valve closing. In the turbocharged SyTy my last three builds have utilized camshaft profiles where intake duration exceeds exhaust duration, LSA is about 114-ish, and overlap is minimal. All the exact opposite to what is done in N.A. engines. While turbocharging is a little different than mechanical driven supercharging, I would think that significant gains are possible with a forced-induction specific camshaft.
As you make changes such as improved exhaust or camshaft profiles, if the charge dilution discussed above is reduced, the engine will be more prone to detonate because of the increased charge density. So tread lightly after changes to the exhaust until you establish that detonation is still under control.
Carry on.
10-29-2018, 04:47 PM
#54
Race Director
Both materials are probably about the same in tensile and compressive strength when intact. It's what happens when they are stressed beyond their design strength, particularly in compression loading. Which is what detonation loading is.. In the FWC boats the PM rods explode from a hydrolock event, the forged rods bend but the engine continues to run. 4.6, 5.4, and the 6.5 V10 Fords, have ongoing, frequently discussed failures of their PM connecting rods. So no, I don't have documentation for PM rod strength, just anecdotal evidence.
dizwiz: There is a myriad of differences other than "timing" that makes an LS stronger than a SBC. Crankshaft, bearing diameter and width, main saddle structure, head bolts that extend into the bearing girdle. All this stuff makes the LS STRONG. Take a look at the bottom end of one sometime. You'll understand why these engines hold up to the power levels and abuse they do, and make reliable power at levels unheard of in a small block. The first time I saw an LS1 crank at the machine shop, I at first thought it was a Big Block crank until I noticed the reluctor and figured it out. An LS crank is beefy.
dizwiz: There is a myriad of differences other than "timing" that makes an LS stronger than a SBC. Crankshaft, bearing diameter and width, main saddle structure, head bolts that extend into the bearing girdle. All this stuff makes the LS STRONG. Take a look at the bottom end of one sometime. You'll understand why these engines hold up to the power levels and abuse they do, and make reliable power at levels unheard of in a small block. The first time I saw an LS1 crank at the machine shop, I at first thought it was a Big Block crank until I noticed the reluctor and figured it out. An LS crank is beefy.
just hear me out for some of this.
lsx is wimpy aluminum. They get block/bore distort > 800 hp. Though i realize 800 hp is still plenty fun to play with. Now a heavy, iron truck motor 5.3 lsx is a different animal, but we are talking c5 corvette here.
i think i heard somewhere that there is only a net of 4 bolts around each cylinder vs an effective ‘5’ on the SBC -making SBC the better engine for boost.
The comments on the lsx crank are interesting. Ive never seen one. Is it forged? Or just tougher (ie. Eggheads designed it with CAD and finite element analysis)
Smokey Yunick always said an sbc cast crank is good to 600 hp - but data on failures above that is tough to come by. Also, what is the weight of the vehicle the crankshaft is propelling? Is it a comparatively lightweight corvette, or a pickup truck pulling a load uphill?
I would go splayed 4 bolt main, forged crank on sbc vs Lsx for ultimate strength.
also note: LSx head flow ‘magic’ hp (cathedral intake ports, more favorable valve angle) disappear once boost is added. If ive got to add 2 more psi boost to ‘beat’ the freer flowing heads of an LSx, then so be it.
as for resistance to detonation caused damage, there is no difference in the strength of pistons / ring lands which tend to be the weak link on both motors. Detonate on either one and you are at risk of breaking ring lands. Both motors are forged rods / hyperteutic pistons. again, nothing magicAl on lsx.
There is a huge history of stock lsx bottom ends supporting mega horsepower only because people now know how to do it right. That same know-how can be applied to the SBC. Except GM isnt building those anymore so you dont hear about them.
Todays Know-how (that didnt exist 25 yrs ago when SBC ruled ) Includes:
1. Big enough fuel pumps
2. People know how to tune
3. Methanol/water injection (not new, brought out again and applied )
The other wildcard we can play is sheet metal intakes. There are big gains to be made there by adding one of those.
The LSx biggest strength is not that its stronger, its that its lighter - and for a lightweight n/a road race engine that makes it better.
But for forced induction in my c4, ill take SBC (and my optispark. Lol. Which works great for me).
For ultimate strength and 2000 hp, yeah maybe an iron block lsx is better
Last edited by dizwiz24; 10-29-2018 at 07:17 PM.
10-30-2018, 05:29 PM
#55
Le Mans Master
I want to make a case for the SBC and forced induction vs LSx and forced induction.
just hear me out for some of this.
lsx is wimpy aluminum. They get block/bore distort > 800 hp. Though i realize 800 hp is still plenty fun to play with. Now a heavy, iron truck motor 5.3 lsx is a different animal, but we are talking c5 corvette here.
i think i heard somewhere that there is only a net of 4 bolts around each cylinder vs an effective ‘5’ on the SBC -making SBC the better engine for boost.
The comments on the lsx crank are interesting. Ive never seen one. Is it forged? Or just tougher (ie. Eggheads designed it with CAD and finite element analysis)
Smokey Yunick always said an sbc cast crank is good to 600 hp - but data on failures above that is tough to come by. Also, what is the weight of the vehicle the crankshaft is propelling? Is it a comparatively lightweight corvette, or a pickup truck pulling a load uphill?
I would go splayed 4 bolt main, forged crank on sbc vs Lsx for ultimate strength.
also note: LSx head flow ‘magic’ hp (cathedral intake ports, more favorable valve angle) disappear once boost is added. If ive got to add 2 more psi boost to ‘beat’ the freer flowing heads of an LSx, then so be it.
as for resistance to detonation caused damage, there is no difference in the strength of pistons / ring lands which tend to be the weak link on both motors. Detonate on either one and you are at risk of breaking ring lands. Both motors are forged rods / hyperteutic pistons. again, nothing magicAl on lsx.
There is a huge history of stock lsx bottom ends supporting mega horsepower only because people now know how to do it right. That same know-how can be applied to the SBC. Except GM isnt building those anymore so you dont hear about them.
Todays Know-how (that didnt exist 25 yrs ago when SBC ruled ) Includes:
1. Big enough fuel pumps
2. People know how to tune
3. Methanol/water injection (not new, brought out again and applied )
The other wildcard we can play is sheet metal intakes. There are big gains to be made there by adding one of those.
The LSx biggest strength is not that its stronger, its that its lighter - and for a lightweight n/a road race engine that makes it better.
But for forced induction in my c4, ill take SBC (and my optispark. Lol. Which works great for me).
For ultimate strength and 2000 hp, yeah maybe an iron block lsx is better
The crank main caps are cross bolted on an ls, They are literally, when torqued, Part of the architecture of the lower block pan rails. Take a SBC main, Push it down in the block so the top of the cap is level with the pan rails, then widen it so it touches and bolt it through the outside... There is absolutely no comparison on strength there...
Pistons and rods are a moot point, more or less equal.
No matter which one you use, you try putting down 800 horsepower on a stock bottom end, it won't last long at all. As often as people do it, they still blow up.
Cheap and fast won't last. You have to put some effort into it, a solid build up on either would be able to yield the same power... But A lot more would be spent getting the SBC trick parts that are already standard on an LS. The major thing a SBC has going for it still is that they are still a lot cheaper to build, aftermarket still eclipses the LS although it is catching up, and they are physically smaller.
10-30-2018, 07:11 PM
#56
Team Owner
Pro Mechanic
The crank main caps are cross bolted on an ls, They are literally, when torqued, Part of the architecture of the lower block pan rails. Take a SBC main, Push it down in the block so the top of the cap is level with the pan rails, then widen it so it touches and bolt it through the outside... There is absolutely no comparison on strength there...
with this. No comparison in architecture. Most LS cranks are cast, but they hold up to more power than a cast Gen I crank for a few reasons. I've read the most meaningful reason is that that block is stiffer, and thus it supports the crank better, reducing the strength requirement of the crank. IOW, you could make more power on the same crank in a Gen III block than you could in a Gen I/II block.
10-30-2018, 09:41 PM
#57
Melting Slicks
I can tell you my 383 didn't last long with the P600b on 8lbs. On the build sheet the CR is 11.5 but when I called and discussed it they said more like 11.8 Popped the head gasket between 3 and 5 one day and melted the head. Expensive mistake.
Last edited by Snakecharmer383; 10-30-2018 at 09:42 PM.
11-01-2018, 09:13 AM
#58
Drifting
Thread Starter
That is a beautiful engine though.