Building a 383 Stroker

[John_S]

Re: Building a 383 Stroker

You can get already assembled iron vortec heads that can handle more cam. See:
http://sdparts.com/category/sdpc-vortec-cylinder-heads-and-head-kits Depending on what you need, the price is less than $1000 clip. If you are moving to higher flowing heads form iron vortec/alum etec, the small port bowtie vortecs (assembled) are close to your $1000 price. They are iron. Moving to a higher flowing head like AFR/bowtie vortec puts powerband up over 5K rpms. Costs will rise from the other components needed to reliably run at those rpms.

With a few exceptions, the builds on this forum are rather conservative. Since you are looking at more of a performance engine build now, you will find allot more examples on some of the performance boat forums. You will find allot of people running AFR heads on those sites.

 

[greg82255]

Re: Building a 383 Stroker

I drove up to the machine shop to drop off my flywheel today (they are balancing the rotating assembly) and talked with the owner for a while. He told me that for this engine there is really no need to go with anything more than vortec heads. He said depending on the cam, I can realistically make close to 400 hp with them.

He also has a set of vortec heads in his shop equipped with comp cams spring retainers and stainless valves that has been there for 3 years. He's calling the owner to see if I can buy them, and he will refinish them for me. Shouldn't be more than 7-800 including purchasing and reconditioning. He also has a matching Edelbrock performer intake (he suggested I used the performer and not the performer RPM) in the shop that he said I could buy as well.

John S, what other forums/sites talk more about performance builds? offshoreonly?

 

[John_S]

Re: Building a 383 Stroker

John S, what other forums/sites talk more about performance builds? offshoreonly?

I think between offshoreonly and speedwake you will find enough info. But if not, there are others. google is your friend.

I am surprised he suggested the performer, given the hp you want. Look at step 3:
http://www.hotrod.com/techarticles/engine/gm_ht383_crate_small_block_tune_up/viewall.html The stock GM is close to the performer.

Did you talk compession ratio and cam specs to make your desired goals?

 

[greg82255]

Re: Building a 383 Stroker

We did talk compression ratio. He said he likes to keep it at 9:1 for marine engines - he gave me a detailed explanation but mostly what I got out of it was that he doesn't want it to detonate when getting on plane.
So this article suggests that the RPM air gap intake will add some HP/torque with the 383. He may just be suggesting the performer because he has a used one in stock that he can blast and give me for a cheap price b/c he knows I'm sort of on a budget. I'll suggest the RPM air gap and show him the article to see what he says.

As for cam specs, we haven't talked much about that yet. He said that my block will not work with standard roller lifters, and that we should wait until everything else is done before we choose a cam. Ideally I will get a retro-fit roller cam and lifter kit, but once everything else is done, we will see what the budget allows. He says a roller cam gives a smooth idle and is easier around the docks, which won't kill the alpha drive when shifting. Might be harder to idle a flat tappet depending on the lift #s. Is there a range of specs that I should be looking for? .500+lift? I don't know much about how cam #s work.

 

[John_S]

Re: Building a 383 Stroker

I would think a RPM or RPM airgap is what you are looking for. They both provide about the same performance as the stock cast iron intake manifolds that came on the carbed 350 MAGs. (high-rise dual plane) The air gap provides heat seperation from the oil galley. Not sure that has allot of benefit in a boat. I could see the performer if you were dead set on keeping qjet, but performer wouldn't be the right match for a 375HP @ crank engine. To get your HP goal the cam lift will be over 0.500.

 

[greg82255]

Re: Building a 383 Stroker

I sent the machinist an email about the air gap intake - still waiting for a reply. I also showed him the heads that you suggested and he said those would work if I can't end up buying the vortecs in his shop. I've read several different posts dealing with cam lift/duration and overlap, and about how if one of those #s is too high (overlap maybe?) then it could suck water back into the cylinders at lower RPMs.. How exactly does that happen, and do the "marine" grinds eliminate that problem? I don't want to end up with a brand new motor full of water.

 

[joewithaboat]

Re: Building a 383 Stroker

I sent the machinist an email about the air gap intake - still waiting for a reply. I also showed him the heads that you suggested and he said those would work if I can't end up buying the vortecs in his shop. I've read several different posts dealing with cam lift/duration and overlap, and about how if one of those #s is too high (overlap maybe?) then it could suck water back into the cylinders at lower RPMs.. How exactly does that happen, and do the "marine" grinds eliminate that problem? I don't want to end up with a brand new motor full of water.

Reversion the exhuast pulses backwards a bit at low rpm, thats why they sound so good or choppy.
Its a big problem if you end up with it, hydrolock. Bigger cams require aftermarket exhaust that apply the water further away from the head. That is why people have suggested you use a proven marine grind for the cam.

 

[greg82255]

Re: Building a 383 Stroker

Agreed, big problem. But what actually causes reversion? Which one (or more than one) of the cam specs is responsible for creating reversion? And would either a dry joint, or an exhaust that doesn't mix water until right before the transom tips solve that problem?

 

[RogersJetboat454]

Re: Building a 383 Stroker

Agreed, big problem. But what actually causes reversion? Which one (or more than one) of the cam specs is responsible for creating reversion? And would either a dry joint, or an exhaust that doesn't mix water until right before the transom tips solve that problem?

Valve overlap with a close lobe separation angle (LSA) is what causes reversion. As I understand it, on a performance cam, they use a bit of valve overlap between the exhaust and intake strokes to take advantage of the exhaust scavenging. In other words the exhaust valve hang ever so slightly open during the very beginning of the intake stroke to allow the exhaust scavenging to help draw the intake charge into the cylinder. If the valve is held open fairly long, you will start to draw some of the exhaust back into the cylinder, which in your case would have water present.

Some older Chrysler vehicles eliminated the need for an EGR valve by using a cam like this, because they were pulling some of the burnt exhaust gases back into the cylinder to keep the combustion temp's down, and avoid issues with NOx. Newer vehicles with VVT do it about the same, and have allot more control over it. Purpose built turbo/supercharged engines usually have a cam with a lobe separation angle of 115? or better, since the forced induction negates the use of exhaust scavenging, and valve overlap would just allow some of the intake charge to be pushed out of the cylinder into the exhaust.

Thats how I understand it anyway.

 

[joewithaboat]

Re: Building a 383 Stroker

Im no cam designer so i wont try to be one or act like i can discribe this well enough. It occurs when both valves are open at the same time from either duration or LSA.

This below is copied and pasted from a different site and is pretty good. The thread started out talking about reversion and ended up talking about blower cams but....


Overlap is the length of time, expressed in crankshaft degrees (or area expressed in inch/degrees), that defines the period between the intake valve opening point BTDC and the exhaust valve closing point ATDC. The greater the seat duration is on the intake and exhaust lobes and/or the tighter the LSA, the greater the overlap will be in degrees. It is during this overlap period, when the intake, combustion, and exhaust areas are all exposed to one another, that the pressure differentials in the respective areas interact. In some instances if velocity and inertia are low (rpm) exhaust reversion occurs when cylinder pressure is < ambient at the exhaust area. Increasing the overlap can increase peak power, but only if the exhaust system is properly designed to scavenge the cylinder and the engine is operated in the suitable rpm range.
Forced induction changes those parameters. With the introduction of a pressurized intake charge upstream the need for inertial cylinder filling and exhaust scavenging is greatly reduced. As boost levels increase (to avoid over scavenging) overlap area is generally reduced in forced induction applications by increasing the LSA.
Overlap crossover is probably one of the most important cam events, but it is the least talked about. It?s the time during overlap when the intake and exhaust valves are off their seats at exactly the same amount of opening. (Example might be .080" for each valve lift at 4 degrees BTDC.) This 4 deg value is known as the cross over centerline. Knowing cross over centerline can be useful when making performance comparisons at specified RPM values. As a rule, crossover usually occurs plus or minus 5 degrees near TDC. Examining the point of crossover is your reference point as to the advanced or retarded position of the cam. If you need to advance or retard more than 4*, you have the wrong cam. The formula for calculating overlap can be found here: http://members.uia.net/pkelley2/Overlap.html
Hope this helps,
Bob__________________
MarineKinetics@rochester.rr.com
1.585.654.8583

 

[greg82255]

Re: Building a 383 Stroker

Alright, so it's the overlap that causes the problem, and not the lift #s. All the marine grinds I see on cpperformance have a lobe separation angle of 112 degrees. The machinist wants to wait to select the cam until everything else is done, so I guess I have some time to think about it. Not that I want to put one in, but would a dry joint exhaust system solve the reversion problem?

 

[joewithaboat]

Re: Building a 383 Stroker

Remeber i sugested you find wca_tim?
Look here im not sure if this is what he currently runs, he might have changed by now. Start at post # 39 and back track. Look at his pistons,c/r, cam, exhaust, nothing like being able to copy from someone who has already been there.

http://forums.iboats.com/showthread.php?t=437877&page=2

Also look for 45auto he is using vortecs.

 

[greg82255]

Re: Building a 383 Stroker

I actually sent him a PM asking for his help, but he hasn't replied. Looks like he hasn't been on Iboats for a while. I'll take a look at that thread now and look for 45auto as well. Thanks Joe

 

[joewithaboat]

Re: Building a 383 Stroker

Did you check out that Dennis Moore book yet?
EDITSorry this book appears to be out of print!

Also look here, same guy as before talking about cams. Mentions that black scorpion JohnS was talking about. post #15

http://www.offshoreonly.com/forums/...-street-engine-used-marine-application-2.html

 

[joewithaboat]

Re: Building a 383 Stroker

post #6 was the other guy with vortec and cam upgrade and #31 is tim again also saw JohnS in there

http://forums.iboats.com/showthread.php?t=395312&page=2

 

[greg82255]

Re: Building a 383 Stroker

Yea I've looked for Dennis Moore's book and I actually called Moore Performance and he said it was no longer available. I read the threads - thanks for the direction. It provides some really good cam and head info. I'll be sure to post the cam #s before I select it. Once I get the block back from the shop, I'll start a new thread and document the build step-by-step and list the parts that I used so anyone else that wants to do this can have a good idea where to start.

Can anything be done to vortec heads to increase their performance? Port work maybe?

 

[John_S]

Re: Building a 383 Stroker

Also, look at MKos1980 posts. He knows his stuff, and has a decent 350 build.


Cam recommendations from DM's book:

A modified 350, 383, or 409 with 9.0:1 compression or less:

Flat Bassed lifters:
Chevy cam: 24502426
Comp cams: XE 256 H 10
John's comments: neither of these look that remarkable


Roller Based:
Chevy cam: 24502586
Crane retrofit: 119631
HR-284-2S-12 IG

I think the crane will be closest to your HP goals.

There are additional recomendations for 383's with more than 9:1 compression, free flowing exhaust, large valves,

Roller:
Crane retrofit: 119641
HR-296-2S-12 IG
John's comment: thats allot of duration for a boat.

 

[John_S]

Re: Building a 383 Stroker

Can anything be done to vortec heads to increase their performance? Port work maybe?

From articles I've read, it easy to mess up porting vortecs outside of minor clean-up, if you don't know what you are doing. They can be fitted with larger valves, but you can then just get the small port bow tie vortecs, that come with larger valves.

 

[joewithaboat]

Re: Building a 383 Stroker

Also, look at MKos1980 posts. He knows his stuff, and has a decent 350 build.


Cam recommendations from DM's book:

A modified 350, 383, or 409 with 9.0:1 compression or less:

Flat Bassed lifters:
Chevy cam: 24502426
Comp cams: XE 256 H 10
John's comments: neither of these look that remarkable


Roller Based:
Chevy cam: 24502586
Crane retrofit: 119631
HR-284-2S-12 IG

I think the crane will be closest to your HP goals.

There are additional recomendations for 383's with more than 9:1 compression, free flowing exhaust, large valves,

Roller:
Crane retrofit: 119641
HR-296-2S-12 IG
John's comment: thats allot of duration for a boat.

I think I agree with everything John noted, but would add a comment that most of the time when folks give cam recomendations in a book they tend to be a little conservative. This is sometimes good. I have seen an awful lot of people put a LARGE cam in a motor and cheap out on all of the other stuff that they need to go with it.... result is a motor that sounds great but is a real dog. I have also seen lots of motors that sounded tame but ran extremely hard, made great average numbers, flat steady curves, & HAUL BUTT. I would suggest copying one of these other members that have already tried multiple combos. MKOS1980 has found good combo, i would not have expected it to make that much power. Everything must match real well. Remember Tim went down a full point in compression but went to a head that flowed more and gained 100 hp (12mph) WOW!

This is a great article that gives good examples of bad combinations not really adding up to a faster boat. In the end they shoot for way more motor than we are talking about but still a good read and the first part will work for you.
http://rlcboats.com/index.php?main_page=page&id=11

I would also skip the port work. Past just general clean up of flash and rough edges, maybe gasket match, Most people who claim to know how to port heads, Dont!
I hang out in a shop with a flow bench and have seen it first hand. Its always a good laugh to put other peoples work on the bench to check what they did. Porting is really an art.

Looking forward to following your build.

 

[greg82255]

Re: Building a 383 Stroker

I'll definitely loook into MKos1980's post. I'll see if I can find him and see the specs of the motor he is running. Looks like I'll skip the port work on the heads. As for the cam, I want to get a retro-fit roller but we'll see what the budget allows after I buy everything else. I'll take a look at those cams - maybe I'll even give Comp Cams or Crane a call and see what they recommend for a ~375 hp 383.

Joe, that article was really interesting. I'm surprised a stingray maxim hull could handle 100 mph without falling apart. I did notice a few things in that article that looked like they may help my build.

1. Is it true that a water crossover system instead of a circulation pump will increase power and keep the engine cooler?
2. They installed a bravo coupler and mated it to an alpha drive. Are the shaft/splines the same, and would it make sense to get a bravo coupler for 375 hp?
3. Exhaust. Seems like I need a good one. Those CMI headers look so cool... but are they worth the 2grand... At very least, I'll switch out the iron manifolds for some aluminum ones to get rid of some weight in the back. Anyone ever used these tail pipes? they claim to add 10hp. (http://www.cpperformance.com/p-1341...ce-mercury-manifolds-standard-dimensions.aspx)
4. I think the aluminum intake/exhaust, and crossover should remove about 80 or so pounds from the back of the boat. Will this make any noticeable difference?