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Old 07-14-2019, 10:08 AM
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350 target master upgrade

I purchased an older jet boat with a 350 Targetmaster engine , from research I found it has low grade heads , not much power, it has 127 lb even compression , donít know if thatís good, could someone tell me if itís worth putting better intake and upgraded cam in this motor to get a little extra hp ? Thanks for any info

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Old 07-14-2019, 11:00 AM
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It will help, but if it is worth it depends on what kind of power you are looking for.

The biggest problem with this engine is the crummy cylinder heads....changing those would help the most.

So what are you looking for power size??

This is the basic 190-260 HP type replacement engine for 70's/early 80's smogger engines, correct??
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Old 07-14-2019, 12:17 PM
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You need to determine just how much money you're willing to put into this engine against the cost of replacing it.

The TargetMaster was a low output SMOG replacement engine. It uses the '929' 300 horse 327 cam found in decades of 327 and 350 engines in power ratings rainging from well under 200 to 300 depending on the cylinder heads and induction system used. The short block under the heads being pretty common in terms of pistons, rods, and crank used. This cam is also found in 283's, 305's and 307's so it's been around a long time.

I guess we need to start by determining whether the bottom end is in good enough shape to justify the expense of a decent top end being put on top of it.

Assuming it is, really the first thing to be done is to replace the heads. The existing heads are horrible slow and incomplete burners of what ever gets into them, this is a chamber design issue not fixed by milling, polishing, larger valves, or anything else you can do. Add to that they are very low compression usually advertised as 8.5 but when you measure the chambers they constantly come up at 7.7 to 7.9. They don't even get to the minimum of the dynamic or compensated engineering base line compression of 8 to 1 when considering the consumed stroke on the compression cycle at the point the intake valve closes After Bottom Dead Center (ABDC). What this portends is that adding cam without correcting the heads does increase power but not nearly as much as you paid for in cost and time; and eats way more fuel doing it. So correcting the heads not only lets you get even far more power out of the cam you have but will show burning equal to better fuel consumption against what you currently get doing it.

The almost obligitory step at this point fot the last nearly 25 years has been to bolt on a set of GM L31 Vortec heads. These on the cam you have are an instant 50 horsepower injection that just gets better with bigger cams and better induction. However, the GM head requires a unique intake do to repositioning of the intake ports higher and greatly changing the bolt pattern to the heads.The GM casting is also quite thin and subject to severe cracking problems. The best bet is to go to the aftermarket where there are a ton of heads with equal or better performance characteristics that, also, take the standard pre 1987 intake bolt pattern and often are offered with that plus the Vortec bolt pattern so if you already have one or the other style either can be used. The aftermarket heads can be had in iron or aluminum, in 64 or 76 cc chambers but all in the Vortec/Recardo chamber, from modestly priced imports to outragiously priced domestic full up competition heads. There are so many people making and selling Chevy heads it makes your head spin with the choices.

So for power it's all in the heads, everything gets in line after that assuming the bottom end is worth building upon. Given the expenses and effort of doing a top end replacement, if the short block isn't worthy you're cash and time ahead to buy a better crate motor from the gitgo of which this is another sea of oppertunities from brand new GM or aftermarket or full up excellent remans.

Bogie
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Old 07-15-2019, 08:00 AM
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You need to estimate your budget first, and then look at upgrade/replacement alternatives.

If the bottom end of the engine is sound, the best upgrades would be new Vortec or aluminum aftermarket heads ($700-$900), new dual plane intake ($140), and a roller conversion cam ($700-$900) or an updated flat tappet cam ($200). And then you have to add in the additional cost for gaskets, labor, and other items you need to install these parts (maybe new carburetor, etc.). Those upgrades combined with headers should give you at least 325-350 HP, maybe more depending on the cam you choose.

Now that you have an estimate to upgrade, compare it to a new L31 Vortec long block ($2000) or an equivalent basic crate engine from ATK, Blueprint, etc. You will probably still need to buy a new intake, fuel pump and other accessories to go with the crate engine.

Bruce
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Old 07-15-2019, 11:02 PM
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Vortex heads

Thanks for all the info really appreciated, do Vortec heads use same manifolds as my Mexican heads , Iím hoping my water cooled manifolds on my jet boat will bolt on to the Vortex
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Old 07-16-2019, 07:30 AM
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GM iron Vortec heads have a different intake manifold bolt pattern than the old Targetmaster heads. You also want to watch out for TBI intakes and heads, which are also different than the intake for your Targetmaster. However, some aftermarket heads, like the Blueprint aluminum heads I used, can be used with either the old or new intake manifolds. The Blueprint heads are also drilled for both perimeter and center bolt valve covers.

With a better intake and an RV cam (duration in the range of about 213- 218 @ .050) you can get more power out of your engine, and its relatively cheap. However, beyond that you usually need to look at different heads. I don't know if there are any exceptions for a boat, since you run in a different RPM range. Poor heads and long duration cams usually suck for low end power, but you don't run much at low RPM in a boat. GM tried using a 222/222 cam in the 350/290 HP GM crate engine, but it was not a good match to the low compression heads.

Bruce

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Old 07-16-2019, 08:02 AM
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Thanks for all the info really appreciated, do Vortec heads use same manifolds as my Mexican heads , I’m hoping my water cooled manifolds on my jet boat will bolt on to the Vortex
They should be able to use the same exhaust manifolds. Bolt pattern is the same. You may want to match up ports on both heads and manifolds to a gasket to check port alignment and that there will be no steps in the interface that will impede flow, but I suspect they will be OK as-is. Good luck!
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Old 07-16-2019, 09:15 AM
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I have the "Goodwrench" 350 in my car. I installed ProMaxx 183 heads and roller rockers (1.6 intake and 1.5 exh) with .015 head gaskets and the car runs much better while still keeping the high vacuum and smooth idle I was looking for. I was not going for max power, just sick of the emphysema heads.

I think I am somewhere around 300 to 310 horses and it fits the car well.

Good luck.
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Old 07-16-2019, 10:33 AM
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Thanks for all the info really appreciated, do Vortec heads use same manifolds as my Mexican heads , I’m hoping my water cooled manifolds on my jet boat will bolt on to the Vortex
NO! They do not! Reread my earlier post.

The bolt patterns are completely different and the intake ports of the Vortec are taller and repositioned upwards. If you tried to modify these heads to this intake, which people try, this often results in leaks both along the top to atmosphere and/or along the bottom to the valley blowby. This doesn't always appear at assembly, but given the resultant thin gasket area that is clamped, the failure occurs in operation after a few heating and cooling cycles the engine starts sucking air or blowby into the ports as the gasket grip fails. The standard Chevy head uses 6 bolts that address the gasket surface at 90 degrees, a variation of these from 87 through 95 reangle the center plenum bolts to 72 degrees to the gasket surface. The Vortec head uses 4 bolts at 45 degrees to the gasket surface in a different location than the older pattern. Add to that the L31 Vortec head is a very thin casting with a bad reputation for cracks, in the junk yard the average chances of finding an uncracked head is 50/50 or less, so this is a widespread and well known problem. Other issues are to be found with limits to valve lift to about .45 inch without machining the upper guide shorter. They do not have cast in pushrod guides they use a self guiding rocker so you either have to make that change or convert them to hex headed studs with push rod guide plates. They also do not have any provision for exhaust crossover to heat the intake if you need that feature.

To make this work with the intake you have you need to go to the aftermarket. Most all aftermarket heads are cast thicker and do not exhibit the typical cracking problems of the GM made heads. They come set up for more valve lift well into the half inch plus range. They also come set up for hex base screw-in rocker studs and sheet metal push rod guides. They reposition and resize the intake port so is accepts either the standard or L31 Vortec intake and are drilled and tapped for either. These generally use the FelPro 1206 for standard bolt pattern or any L31 pattern gasket for those intakes. Aftermarket heads are available in aluminum or cast iron. Without doing a head deck operation on the block the cast iron is easier as they are just a swap, aluminum typically uses a thicker head gasket that compromises the Squish/Quence clearance to the high side of ideal, they can be used but boats and their constant heavy loading on the engine can become a detonation problem, it is workable but you need to pay careful attention to gasket selection.

If you need an exhaust crossover port at the intake, the selection becomes more limited. Engine Quest (EQ), Dart, and possibly some others do make a head that uses the L31 style combustion chamber along with conventional port locations and bolt patterns with or without an exhaust crossover.

Buying heads is not simple anymore, there are a lot of choices. This requires a fair amount of prior planning to understand your technical requirements and budget constraints against what the market place offers. It gets to be worth the effort as modern combustion chambers can add power as a larger cam does without the operating drawbacks of big cams. However, we are talking some pretty good money and some pretty good chances of getting the selection less than ideal if you go in without quite a bit of study to understand these issues.

There are a lot of guys that find their way here after they made decisions to buy parts that don't work together with the rest of the engine with heads being one of the more common trouble areas.

Bogie

Last edited by BogiesAnnex1; 07-16-2019 at 10:38 AM.
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Old 07-16-2019, 04:19 PM
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NO! They do not! Reread my earlier post.

The bolt patterns are completely different and the intake ports of the Vortec are taller and repositioned upwards. If you tried to modify these heads to this intake, which people try, this often results in leaks both along the top to atmosphere and/or along the bottom to the valley blowby. This doesn't always appear at assembly, but given the resultant thin gasket area that is clamped, the failure occurs in operation after a few heating and cooling cycles the engine starts sucking air or blowby into the ports as the gasket grip fails. The standard Chevy head uses 6 bolts that address the gasket surface at 90 degrees, a variation of these from 87 through 95 reangle the center plenum bolts to 72 degrees to the gasket surface. The Vortec head uses 4 bolts at 45 degrees to the gasket surface in a different location than the older pattern. Add to that the L31 Vortec head is a very thin casting with a bad reputation for cracks, in the junk yard the average chances of finding an uncracked head is 50/50 or less, so this is a widespread and well known problem. Other issues are to be found with limits to valve lift to about .45 inch without machining the upper guide shorter. They do not have cast in pushrod guides they use a self guiding rocker so you either have to make that change or convert them to hex headed studs with push rod guide plates. They also do not have any provision for exhaust crossover to heat the intake if you need that feature.

To make this work with the intake you have you need to go to the aftermarket. Most all aftermarket heads are cast thicker and do not exhibit the typical cracking problems of the GM made heads. They come set up for more valve lift well into the half inch plus range. They also come set up for hex base screw-in rocker studs and sheet metal push rod guides. They reposition and resize the intake port so is accepts either the standard or L31 Vortec intake and are drilled and tapped for either. These generally use the FelPro 1206 for standard bolt pattern or any L31 pattern gasket for those intakes. Aftermarket heads are available in aluminum or cast iron. Without doing a head deck operation on the block the cast iron is easier as they are just a swap, aluminum typically uses a thicker head gasket that compromises the Squish/Quence clearance to the high side of ideal, they can be used but boats and their constant heavy loading on the engine can become a detonation problem, it is workable but you need to pay careful attention to gasket selection.

If you need an exhaust crossover port at the intake, the selection becomes more limited. Engine Quest (EQ), Dart, and possibly some others do make a head that uses the L31 style combustion chamber along with conventional port locations and bolt patterns with or without an exhaust crossover.

Buying heads is not simple anymore, there are a lot of choices. This requires a fair amount of prior planning to understand your technical requirements and budget constraints against what the market place offers. It gets to be worth the effort as modern combustion chambers can add power as a larger cam does without the operating drawbacks of big cams. However, we are talking some pretty good money and some pretty good chances of getting the selection less than ideal if you go in without quite a bit of study to understand these issues.

There are a lot of guys that find their way here after they made decisions to buy parts that don't work together with the rest of the engine with heads being one of the more common trouble areas.

Bogie
Bogie, I think he is talking about boat exhaust manifolds.
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Old 07-16-2019, 05:20 PM
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The Promaxx heads setup for a FT cam are probably one of the cheapest, proven bolt on's that will let you use all of your current stuff (manifolds). You will probably need a different pushrod, but that's about it. Ought to pick one with a chamber 4-6ccs smaller than what you have now for a small bump in compression if you don't plan to re-work the bottom end. I wouldn't consider swapping in another FT cam - too much of a waste of money to not go roller. But a roller with new heads can really blow a budget.

As everyone has mentioned, comes down to your bottom end's health and your pocket book.
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Old 07-16-2019, 06:59 PM
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Bogie, I think he is talking about boat exhaust manifolds.

I ripped through that without even thinking about the exhaust side, mental agility is going to hell; next I'll be like my old man in his latter years stewing that the neighbor down the hill is after his jet engine secrets. When he did that I didn't catch where that was coming from either and said "dad your jet engine secrets are 50 years old, nobody cares about them anymore". I got a WTF look from him, like "kid your an idiot", I being around 63 at the time.



Bogie
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Old 07-16-2019, 11:34 PM
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You guys are a fountain of knowledge,thanx......so that being said ,if I go with Vortex heads , Edlebrock intake , that should give me about a 50 hp bump ? If you guys think that’ll work I’ll leave the cam alone
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Old 07-17-2019, 07:37 AM
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You guys are a fountain of knowledge,thanx......so that being said ,if I go with Vortex heads , Edlebrock intake , that should give me about a 50 hp bump ? If you guys think that’ll work I’ll leave the cam alone
Yes, you should get a serious bump in power over what you have now by going to Vortec Heads and an aftermarket intake.

Just make sure the bottom end is in tip top shape. I suggest a proper leak down test on a warm engine with a real leak down tester to evaluate the true condition of the rings and cylinders. If the bottom end needs any work (I would say more than 15% leakdown on a used engine - for reference my 383 is still 3-5% after 4 seasons - my older 350 taken out was 20-25% and still ran fine but was getting tired), IMHO you would be better to buy the complete BRAND NEW GM L31 Vortec engine as they are available for right at $2K. You even get a stock roller cam with it for cheap upgrade in future. Since this is brand new there is no core and you could sell your old running engine for maybe $500 or more to help defer the cost. Still would need an intake manifold, but result might be similar in cost to upgrading your current engine (don't forget you will still need pushrods and rocker arms in addition to the heads and intake). Lots of ways you can go depending on your pocketbook.

Not sure exactly what you would need to do to hook up your boat drive to the 1-piece rear main block. On cars it takes a different flex plate/flywheel as the balancing is different than on the 2-piece rear main seal blocks. You will want to research this if you decide to go this way.

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Old 07-17-2019, 12:20 PM
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Yes this will work and you should feel the difference. My preference would be an aftermarket head simply from a material strength standpoint. Thermal shocks crack the GM casting, it is an OK head otherwise in this regard. But it does not like to be overheated, a lot of that probably relates back to the significant problems with Dexcool filled cooling systems that were not well maintained. If you have confidence in your boat's cooling system the GM head should suffice.



The other aspect you will or can affect is the squish/quench clearance between piston and head deck. The conceded ideal clearance is .035 to .040 inch piston crown to squish/quench step of the head. This clearance has a lot of effect on detonation tolerance especially as compression ratio increases. Given you are going from a 76 cc chambered head to one of 64 cc's these will be an increase of a ratio or more. So watching this clearance becomes more critical so-as to avoid having to make other adjustments. These being running richer mixtures and/or decreasing the timing lead either of which increase fuel burn and decrease power. The Goodwrench uses the standard SBC piston to deck clearance of .020 to .025 inch which to get into the ideal range requires a gasket of .015 to .019 inch. GM typically uses a .028 gasket in marine engines which both lowers the compression ratio and widens the squish/quench. All things considered for marine engines this gasket insures a better seal on surfaces of less than ideal quality and across a wider range of temperature excursions. I'd wait on gasket selection till I have the existing heads off to see what is there already and what the block deck surface quality is. You also need to get the heads off to see what the deck clearance is as while .020-.025 is the engineering specification, in reality production can be different on what you can think of as reworked block resulting from production incident damage where a slightly damaged gasket surface is re-machined to some dimension less than the specification.


So you have to be ready to make compromises based upon discovered realities. Nothing new in this it is something a good shop does and you pay them for the time it takes. Many amateurs and crappy shops skip these details either from not knowing or as a cost cutting venture. If you get away with it all is fine, if you don't the fixes can be mighty expensive.


Bogie
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