safe compression ratio sbc

Good morning everybody, I am currently building a sbc stroker engine. Could someone tell me what a realistic safe compression ratio would be to run on this engine? I will be using the boat for transportation to & from to work and will not have access to good quality fuel at all times. Thank you.

OK, that is a very fair question.

Please first understand that the average SBC Marine build includes the dreaded GM full dished pistons.
GM sends them out the door with these, and many rebuilders will send them out the door with these.
These are a very poor choice, to say the least, and in particular for the 377 or 383 stroker build.

These pistons cause this engine to be very prone to Marine Load Ignition Induced Detonation.
If you are running low grade fuel, the issue becomes even worse.

Take a few minutes and read this old thread beginning at post #7.

http://www.marineengine.com/boat-forum/showthread.php?394668-V6-to-V8-engine-swap

If this hyperlink does not work, go to the the bottom of the page to: "other gas inboard mfgs IO Sterndrive questions sub forum, and find the V-6 to V-8 engine swap thread. Begin reading at post #7

Warning: Be prepared to hear from the Nay-Sayers.
The Nay-Sayers are typically not up to speed on this build!


Good luck with your build!

Generally speaking, by keeping it as close to stock CR as possible, you'll have the best long term results. I'm sure that Rick will jump in here with all his confusing diatribe about quench and all that stuff.
Honestly if you are attempting to gain a bunch of horsepower by stroking the SBC, your results will probably disappoint you in the real world. Adding 30 cubic inches and upping the CR will gain you more at the high RPM range, where marine engines hate to be. Your actual use with it somewhere around 4-4500 cruising so the extra oomph you're hoping for won't be there. In addition, the higher CR will induce the possibility of preignition.
If the hope is for more speed, you need a big block and a different propeller.
tl,dr: Just buy a remanufactured long block and be done.
Also, rebuilding an engine yourself usually costs 30 percent more than buying a remanufactured engine (that has a warranty)

Again, the gains will be negligible and the expense quite significant. Maybe find a good running take out for a few hundy. That would be my first option.
However, it's all up to you what you want to do.
You're correct Rick, I'm not up to speed...I took the bypass route.

.......

o2batsea said:

Again, the gains will be negligible and the expense quite significant.
With as much respect as I can muster up, that is simply not true!
First off, the full dished piston gives the flame front a place to hide, of which leads to ignition induced Detonation,
whereas the Q/E piston eliminates this.

Secondly, with the Q/E build, the ignition advance can be increased, therefor placing the LPCP closer to where it needs to be for much better torque, better fuel burn, better fuel economy and so on.



A set of GM style Full Dished hypereutectic 383 build pistons will run approx $230 to $260.

A much preferred set of LCQ style hypereutectic 383 build pistons will run approx $340.
This piston works well with the Vortec cylinder head quench surface.
(if using the older cylinder heads, you'd go with a D dished piston deck)

That's a price difference of only $110 to $80.

The cylinder boring, cylinder honing, rod-to-piston assembly, deck height check, piston ring assembly, head gaskets, engine build/set up time is almost the same.
The builder will spend a bit more time calculating the compressed head gasket thickness in order to achieve the correct quench dimension.
Camshaft profile can also remain the same.



Maybe find a good running take out for a few hundy. That would be my first option.
We have no idea as to Retruntrip's budget. His budget may certainly allow for a better build.


However, it's all up to you what you want to do.
On that note, we certainly agree!

You're correct Rick, I'm not up to speed...I took the bypass route
Perhaps spend some time learning about the SBC Q/E build, rather than being a Nay-Sayer right out the gate.

Not that this gives me ultimate authority...... I've been messing with and building the SBC since the mid 60s.
I am no stranger to this engine!
In all of those years, I have NEVER build one using the GM Full Dished pistons, nor would I.
It's just simply WRONG!

Same with the 335 series Ford (5.0L or 5.8L Windsor), or with any Chrysler wedge head engine.

Click to expand...

o2batsea said:

Again, the gains will be negligible and the expense quite significant. Maybe find a good running take out for a few hundy. That would be my first option.
However, it's all up to you what you want to do.
You're correct Rick, I'm not up to speed...I took the bypass route.

Click to expand...

OMFG....................Here we go again and again and again and again.........................

Why not just answer the guys question instead of dumping PCKR's opinion over and over again!

OP, ""Could someone tell me what a realistic safe compression ratio would be to run on this engine? I will be using the boat for transportation to & from to work and will not have access to good quality fuel at all times. Thank you.""
I don't see anything in this question asking for an over rated opinion on how to build the Stroker engine.


So the correct answer is what is an acceptable compression ratio for the stroker with crap gas.

MY opinion would be 9.0:1 to 9.5:1 expect approximately 150-170 PSI You should be safe with crap low octane gas. Just make sure your cam is not to aggressive. Keep the cam torque peak at or under 5500rpm. Your timing may need to be adjusted based on several factors....including what ignition you are running

Typical build specs

• Horsepower: 345
• Torque: 445 lbs./ft.
• Block: Seasoned OE 4 Bolt Main 1pc Seal Roller Block P/S Dipstick
• Bore/Stroke: 4.040 x 3.750
• Displacement: 383 C.I.D.
• Pistons: Hypereutectic
• Piston Rings: Moly Rings
• Compression Ratio: 9.5:1 Compression**** Based on head design so 9.0:1 to 9.5:1
• Camshaft: Hydraulic Roller
• Camshaft Specifications: 210/215 @050 .462in/.470ex 114LSA

Thank you for your response. I am well aware of the quench effect pistons from reading your well informed previous posts and totally agree. My only engine rebuilding and assembly experience has been with CAT, Yanmar & Volvo marine diesels. For me, luckily because i work many hours on the water, my budget is not very much of an issue. I understand the mirroring effect inside the combustion chamber to be very important between cylinder head & piston profile. I know exactly how to calculate compression ratio's. I am not looking to build a high rpm engine for my boat. Horsepower is nice, but a low steady torque curve is more important to me. Durability & torque is my goal, without getting into detonation issues. I already have a mercruiser forged stroker crank and a good one piece rear main seal roller block. I have recently purchased brand new G.M. bowtie vortec heads. I have no problem buying good "I" bea.m rods & was considering some Mahle coated forged pistons. If you think the Htpereutectic pistons are good enough I could go that route also instead of spending extra money on forged lower end components. I just cant seem to find a safe number on the C/R ratio. There is too muched varied information out there. Of course I would like to get as much power as I can get, but I must keep it in a safe zone before detonation happens & my gas engine starts sounding like the noise i hear all day with the diesels I work on. I will deck the block and probably take a little off the head surface so i can use the steel composite head gaskets, unless you advise me otherwise. When I am at the point of valvetrain components I would really appreciate some help there too. I know I could run a higher lift cam with the bowtie heads but that isnt to necessary, I believe a stronger lobe separation angle would be more important to consider to prevent water reversion into the engine. Looking at the way Mercruiser designed the ex. manifolds it looks like that could possibly be a problem. I fyou could give me a safe C/R # I would appreciate it. Thanks again guys.

Wow, thank you! exactly what I was looking for!

Thanks Kghost. I live up in Mass. and it gets cold working on the water. I want to put a heater core up in the small cuddy cabin of my boat, does anybody know if the factory marine engine waterpump can push that type of volume and not effect engine cooling. I am currently designing a closed cooling system with a crank driven raw water punp to have more flow on the raw water side of the cooling, unless you guys think the mercruiser sterndrive pump is sufficient. I already have a pump & heat exchanger i removed from a big block with a Volvo Penta set up.

Once again..... the Nay-Sayers chime in.
Pay little to no attention to them! They know nothing of what they speak.

Returntrip said:

Thank you for your response.
You are very welcome.

I am well aware of the quench effect pistons from reading your well informed previous posts and totally agree.
If so, you are on your way to building a proper Marine SBC, be it a 5.7L.... or a 6.2L or a 6.3L stroker.

......my budget is not very much of an issue.
You won't even come close to damaging your budget with this build.

I understand the mirroring effect inside the combustion chamber to be very important between cylinder head & piston profile.
Yes! Very important!

I know exactly how to calculate compression ratio's.
Excellent.
You can also use one of the better on-line static compression ratio calculators.

I am not looking to build a high rpm engine for my boat.
Correct!

Horsepower is nice, but a low steady torque curve is more important to me.
The Q/E will allow you to set up the ignition system as to place the LPCP at the correct crankshaft angle..... of which is 12* to 14* ATDC.
That is what produces torque.

Durability & torque is my goal, without getting into detonation issues.
Absolutely correct!

I already have a mercruiser forged stroker crank and a good one piece rear main seal roller block.
Excellent start!

I have recently purchased brand new G.M. bowtie vortec heads.
Use a LCQ style piston of the correct dish volume, and you won't go wrong.

I have no problem buying good "I" beam rods & was considering some Mahle coated forged pistons.
As you know, the forged pistons will cost a bit more.

If you think the Htpereutectic pistons are good enough I could go that route also instead of spending extra money on forged lower end components.
That would also be an OK choice.

I just cant seem to find a safe number on the C/R ratio. There is too muched varied information out there.
Yes, and when you read what people like Jack have to say, it gets even more confusing.
According to his own words of several years ago, Jack doesn't build engines.
If you notice, he is one of the Nay-Sayers in your thread here, and he doesn't really understand the Q/E build.
If he did, he'd be in favor of it.

Of course I would like to get as much power as I can get, but I must keep it in a safe zone before detonation happens & my gas engine starts sounding like the noise i hear all day with the diesels I work on. I will deck the block and probably take a little off the head surface so i can use the steel composite head gaskets, unless you advise me otherwise.
First prep the block, crankshaft and fit the pistons. Then take your deck height dimension.

When I am at the point of valvetrain components I would really appreciate some help there too.
Best advice would be to contact a reputable camshaft company rep, and give him you build specs and intended usage.

I know I could run a higher lift cam with the bowtie heads but that isnt to necessary,
Correct!

I believe a stronger lobe separation angle would be more important to consider to prevent water reversion into the engine. Looking at the way Mercruiser designed the ex. manifolds it looks like that could possibly be a problem. If you could give me a safe C/R # I would appreciate it. Thanks again guys.
With a good quench dimension, and with the correct ignition TA at the correct RPM, you can easily stay in the neighborhood 9.5:1 or so.
Your call on that!

Click to expand...

RicardoMarine said:

Once again..... the Nay-Sayers chime in.
Pay little to no attention to them! They know nothing of what they speak.

Click to expand...

Really................Cant you simply keep away..........Who on earth wants to read your SH!T over and over again!

You are so pathetic it isn't funny anymore!

You are not en expert in fact you are as far from one as anyone who posts on this site. You certainly have no credibility on Small Block Chevy engine building not even for a lawn mower.

So stop with your ill advised "guidance".

You are the only one who believes...............

Thanks Rick, I would actually never buy an engine that was assembled by someone else unless i knew them or the shop very well. If its done wrong its on me,if its done wrong by somebody else that doubles the problem.

Returntrip said:

Thanks Kghost. I live up in Mass. and it gets cold working on the water. I want to put a heater core up in the small cuddy cabin of my boat, does anybody know if the factory marine engine waterpump can push that type of volume and not effect engine cooling. I am currently designing a closed cooling system with a crank driven raw water punp to have more flow on the raw water side of the cooling, unless you guys think the mercruiser sterndrive pump is sufficient. I already have a pump & heat exchanger i removed from a big block with a Volvo Penta set up.

Click to expand...

The Alpha (if that is what you have for an outdrive), The impeller is more than enough to use for a closed cooling system. It will supply more than enough cold water to an on engine heat exchanger. But a standard crank driven system will work also. My money is they would flow about the same +/- a few percent volume.

I would have to look but I believe if you were to plumb the HOT out of the cooling system before it goes through the on engine heat exchanger for a closed cooling system (which would have a 50/50 antifreeze mix), Then to a second heat exchanger at the area you are trying to warm up, That would be the hottest temp fluid. Then the output of the area heat exchanger would go back to the on engine heat exchanger. I dont think it is plausible to only have one heat exchanger as the on engine one will have a raw water supply so extending that raw water supply to the area you want to heat up may not be workable and reduce the heat you want to extract for your area. So having TWO may be needed.

Of course there is always a chance that if the distance and the cooling of the area heat exchanger is good enough you wouldnt need an on engine exchanger or the cold water supply, At least in the winter. You would need it in the summer! Maybe experiment with that. Like have a ball valve shut off or diverter design for summer/winter.



I also feel the engine circulating pump has enough to do the job as long as its not probably more that 15-20 feet to area heat exchanger input.

If you use a 160 degree thermostat then your output should be while under load ~170 ish degrees F so it would be similar to a 1960's 180 degree Thermostat heating system in a car, Just enough on most cold days..........

I would not expect sauna like conditions!

If you may want to discuss send me a message with your number

Thank you very much rick. About a month ago I posted some questions & felt I was posting ignorant questions due to the response from Mr. o2batsea. It actually disappointed me & kept me off this forum. I appreciate everybodys knowledge, input & opinion and try to decipher the best to my ability. I have been reading your posts & others to gain knowledge to better educate myself. Im in my late 50's and love to learn as much as i can every day. Keep up the great work, your input is very much of a great help to me and surely many others. Johnny V.

Good luck out there Johnny V!

Wow great input. Yes I would definitely be using an engine mounted heat exchanger. I would run possibly be running a heater hose outlet off the therm. housing possibly or somewhere else. Im not sure what type of intake manifold ill be running, but i remember back in the 80's some GMs had a 5/8" cooling system nipple on them? would run a 15 to 18' length like you said and get a automotive heater core and fabricate a box around it with a blower fan. Then obviously a return line. Unfortunately right now the boat has an Alpha drive but I came across a boat that sank with only 22 hours on a complete repower including Bravo1 x drive. I have all the parts except the drive unit itself. I will definitely send you my number but I dont know if i should post it publicly, Im not very good on computers & not sure how to private message?

Thanks Mr. o2batsea

I have to go now, but will get back on later. Maybe you could let me know how to PM my #

No worries there Johnny. I'm out of this thread. You all can chatter all u want about your project.

Returntrip said:

Wow great input. Yes I would definitely be using an engine mounted heat exchanger. I would run possibly be running a heater hose outlet off the therm. housing possibly or somewhere else. Im not sure what type of intake manifold ill be running, but i remember back in the 80's some GMs had a 5/8" cooling system nipple on them? would run a 15 to 18' length like you said and get a automotive heater core and fabricate a box around it with a blower fan. Then obviously a return line. Unfortunately right now the boat has an Alpha drive but I came across a boat that sank with only 22 hours on a complete repower including Bravo1 x drive. I have all the parts except the drive unit itself. I will definitely send you my number but I dont know if i should post it publicly, Im not very good on computers & not sure how to private message?

Click to expand...

Left click on KGHOST next to the picture on a post and a sub menu pops up and choose Private message

How can all this entertainment possibly be for free?

Returntrip, you appear to be a nice person who has joined this forum in hopes of receiving some good and serious advice regarding your proposed engine build.
I am sorry that you've had to wade through some of the disruptive crap that has been posted to your thread.
That is totally uncalled for!
It is disruptive and un-adult like, and serves no one!


By the way and FYI...... PM's (private messages) are great for; "here's my BBQ chicken recipe" or "do you know Bill H from your area?" or "here's my address for shipping that to me."
However, when the forum topic is taken to a PM, the rest of the on-lookers become exempt from learning what is being suggested.

I suppose that there will always one un-adult like member who will use PMs for rather negative and unconstructive purposes.
Too bad!

******************************************

Returntrip, pay close attention to this author's responses. Ask yourself; is this a person who I want to take advice from?

OMFG....................Here we go again and again and again and again.........................

Why not just answer the guys question instead of dumping PCKR's opinion over and over again!
Had this person read the thread that I linked Returntrip to, it would have become clear.

OP, ""Could someone tell me what a realistic safe compression ratio would be to run on this engine? I will be using the boat for transportation to & from to work and will not have access to good quality fuel at all times. Thank you.""
I don't see anything in this question asking for an over rated opinion on how to build the Stroker engine.


So the correct answer is what is an acceptable compression ratio for the stroker with crap gas.
That's right..... but there's more to it. Allow me to explain:

MY opinion would be 9.0:1 to 9.5:1 expect approximately 150-170 PSI You should be safe with crap low octane gas. Just make sure your cam is not to aggressive. Keep the cam torque peak at or under 5500rpm. Your timing may need to be adjusted based on several factors....including what ignition you are running.
Incorrect!
The ignition advance is going to be limited by the piston deck profile.
The quote below is for the GM/Merc build, of which incorporates the GM style Full Dished piston.

Typical build specs

• Horsepower: 345
• Torque: 445 lbs./ft.
• Block: Seasoned OE 4 Bolt Main 1pc Seal Roller Block P/S Dipstick
• Bore/Stroke: 4.040 x 3.750
• Displacement: 383 C.I.D.
• Pistons: Hypereutectic yes, but what piston deck profile? I can guarantee you that it will be the GM Full Dished profile.
• Piston Rings: Moly Rings
• Compression Ratio: 9.5:1 Compression**** Based on head design so 9.0:1 to 9.5:1
• Camshaft: Hydraulic Roller
• Camshaft Specifications: 210/215 @050 .462in/.470ex 114LSA and again, calculated using the GM Full Dished pistons.

Click to expand...

Then there is this non-adult like post:

kghost said:

Really................Cant you simply keep away..........Who on earth wants to read your SH!T over and over again!

You are so pathetic it isn't funny anymore!

You are not en expert in fact you are as far from one as anyone who posts on this site. You certainly have no credibility on Small Block Chevy engine building not even for a lawn mower.

So stop with your ill advised "guidance".

You are the only one who believes...............

Click to expand...

kghost said:

The Alpha (if that is what you have for an outdrive), The impeller is more than enough to use for a closed cooling system. It will supply more than enough cold water to an on engine heat exchanger.
But a standard crank driven system will work also. My money is they would flow about the same +/- a few percent volume.
The crankshaft pump would be preferred for the 6.3L build with a closed cooling system.
On the assumption that you do have the A drive, the A drive seawater pump must remain due to upper gear unit cooling.
The A drive seawater can simply be ported overboard.

I would have to look but I believe if you were to plumb the HOT out of the cooling system before it goes through the on engine heat exchanger for a closed cooling system (which would have a 50/50 antifreeze mix), Then to a second heat exchanger at the area you are trying to warm up, That would be the hottest temp fluid. Then the output of the area heat exchanger would go back to the on engine heat exchanger. I dont think it is plausible to only have one heat exchanger as the on engine one will have a raw water supply so extending that raw water supply to the area you want to heat up may not be workable and reduce the heat you want to extract for your area. So having TWO may be needed.

The correct method for plumbing in a cabin heater or water heater, from a Closed Cooling System, is as follows:

coolant supply = the coolant port in the intake manifold just upstream from the thermostat location.
This area is under mild positive pressure.

coolant return = the Stbd most port on the coolant circulating pump..... what many call a "water pump".
This area is under mild negative pressure.

The difference between the mild pressure and mild negative pressure creates balance.
No balance = no coolant flow to/from your Water Heater and/or your Cabin Heater.






I also feel the engine circulating pump has enough to do the job as long as its not probably more that 15-20 feet to area heat exchanger input.
If this is referring to a Cabin Heater, simply increase the ID of the hose.
Doing so will lesson any resistance.

If you use a 160 degree thermostat then your output should be while under load ~170 ish degrees F so it would be similar to a 1960's 180 degree Thermostat heating system in a car, Just enough on most cold days..........

I would not expect sauna like conditions!

If you may want to discuss send me a message with your number
Again, info that can be shared and would potentially benefit all members, is best when kept on the forum.

Why take it off forum, unless there is another agenda?

Click to expand...

timguy said:

How can all this entertainment possibly be for free?

Click to expand...

Good one, Tim!

Maybe we can start charging and toss the money into a fund.

Full dish pistons work and make the most power on crappy gas. One reason for the full dish is for water intrusion, a little room for the water.... Another is because not everyone on the planet who owns a Mercruiser marine engine has access to 93 octane fuel.

The Alpha drive water pump will be sufficient for a half FWC system.... This means the exhaust manifolds are not included.... If you want to include the manifolds you will need to upgrade to a crank driven pump.

As for the heater, water port feed off the circ pump and feed it back to the intake cross over... Done.

.......

Docksidemarineservices said:

Full dish pistons work and make the most power on crappy gas.
All due respect, I would have to completely disagree with that.
The full dished piston offers a place for the flame front to hide.
Perhaps read a few articles by Jeff Smith, Larry Carly, Eric Labore, Marlin Davis, Keith Black, Dennis Moore, etc.
You can also find some good information from the Chrysler Wedge Head enthusiasts.

In my opinion, the GM style Full Dished piston has no place in the SBC, and in particular, the Marine SBC.
It is a poor choice at best!

Why do GM and many rebuilders use it?
Simple...... they are very inexpensive, one p/n fits all 8 bores, the guy installing the connecting rods can be drunk or stoned, and the guy installing the pistons/rods into the cylinder block can also be drunk or stoned.
The ignition advance is then held back in order to help with Detonation issues, leaving torque and power on the table.

The GM bean counters won, and the GM engineers lost!

One reason for the full dish is for water intrusion, a little room for the water.... Another is because not everyone on the planet who owns a Mercruiser marine engine has access to 93 octane fuel.
Poor fuel quality is all the more reason for a Q/E build.

The Alpha drive water pump will be sufficient for a half FWC system.... This means the exhaust manifolds are not included.... If you want to include the manifolds you will need to upgrade to a crank driven pump.

As for the heater, water port feed off the circ pump and feed it back to the intake cross over... Done.
Chris, again, all due respect, it is just the opposite from what you just described.

The coolant supply will come from the intake manifold port (within the cross-over area), just upstream from the thermostat.
The coolant return will be directed to the starboard most port on the circulating pump. The upper port will also work, but the starboard port works best.

Click to expand...

.

The coolant supply will come from the intake manifold port (within the cross-over area), just upstream from the thermostat.
The coolant return will be directed to the starboard most port on the circulating pump. The upper port will also work, but the starboard port works best.

Bingo......hooked up lots of heaters in my life.....live in northern MN.

Rick.....great illustration on cooling system.....it is quite accurate.

This is an excellent article.....I dare you read through it. We built 14:1 355 Chevys for Wissota dirt track Super Stocks.....limited to a Holley 2 barrel....specific restrictions applied to porting. By angle milling camelbacks and using appropriate pistons, ....cherry picking my 350 Chev blocks for minimal core shift and positive cast compositions.....looking for 10 percent tin, 20 percent nickel. We were able to produce 402 horsepower with 400 pounds of torque in a reliable build lasting more than 1 full racing season. These were the most powerful Super Stocks Wissota ever saw. Brother, Frank destroyed the shop.....but the records were never broken.
Can automotive racing engines be compared and applied to boat power engineering? Arguable for sure.....but guess what? Who's idea was it to put a car engine into a boat in the first place?

https://www.hotrod.com/articles/0606em-understanding-compression-ratio/

So I posted the water movement backwards.... Who cares.... the heater doesn't.

Millions of dish piston marine engines in service with uncountable hours of service, a handful of guys don't like them and that makes them bad. Like I said, put 2 ounces or so of water in the cylinder of your flattop piston build with a 76cc chamber and watch the connecting rod kink.