Syclone 1178
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JS Mfg.
Definitely difference in color and the SyTy mains that I had didn't have a part number on it compared to every other GM cap I've ever seen had a part number on it.

I don't know if any one year block is really better than another. People on here say to stay away from the late block which has the balance shaft as its supposedly not as "meaty" as the earlier blocks. Don't know myself unless I have them x rayed or sonic checked. The balance shaft blocks are more work if you get rid of the balance shaft as you have to plug the oil supply holes to the now gone balance shaft.

I've compared the stock rods, L35s, and SBC rods.. The stock ones are what Id call light duty on the big end. The L35s are slightly beefier . The beams looked the same to me. SBC rods are the wrong size on the big end and IMO once you have them machined to work you'll have as much $ in them if you just went out and bought Eagles.

Stock pistons are hyperutectic(sp?) which have a higher silicone content than forged which allows tighter piston to wall clearances to keep cold start noise to a minimum. Hypers wont tolerate much more detonation than reg cast pistons in my experience and we all know detonation is a huge problem with our application. I use TRW forged or J&Es myself. TRWs wrist pins are heavier than the J&Es and J&E seems to have a little better quality control than TRW. Both are durable and long lasting but J&Es are pricey.

Cranks are all the same for the TBI/syty stuff. All cast even fire. The general thinking here is the stocker is good for ~600hp if its prepped.

Budget build(my opinion)

Start with a syty block(gotta have those main caps IMO)
hot tanked
new cam bearings/freeze plugs
oil galley plugs "staked" in place or block peened around them
.030 over bore
ARP studs(2 bolt)
line bore checked and honed if needed
standard rod/main journal crank
chamfered oil holes(can be done at home)
removed casting parting line on crank(can be done at home)
Melling Z28 oil pump(standard volume with a higher pressure bypass spring)
Smoothed/chamfered oil galley in lower section of pump(done at home)
One piece oil pump drive(integral sleave)
Smoothed oil passage on rear main and chamfer(done at home)
TRW .030 pistons
L35 rods, checked. Resize only if needed
Balance rotating assembly.
Childs & Albert ZGS rings part# RS-4 4.035(pricey but worth every penny)
Double roller timing chain from Jegs/summit(part# escapes me right now)
stock cam(its a roller so it can be reused if journals are OK)

L35 heads, cleaned, new valve seals, valve job(3 angle), new guides if heads have high miles.
ARP Head bolts(6 point or 12 point doesn't matter)

Dirt cheap rebuild:

clean and reuse stock pistons with moly rings and stock rods(DIY)
hot tank block and new freeze plugs and cam bearings
block honed for new rings(DIY)
new main/rod bearings(DIY)
standard replacement timing chain(DIY)
same oil pump as above as its dirt cheap
disassemble heads and clean everything. Install new seals(DIY)
ARP main cap bolts if you can or reuse stockers if your really poor
Reuse stock head bolts

Crank scraper pulls oil off crank.

Motor Priming
The screwdriver method only primes half the engine. You need to simulate the dist housing, to get the other half, which I believe is the camshaft area.

I also just recently heard of a motor builder, REQUIRING his customers to prime the motor for I think it was 1hr, might have been 30 min. Granted not all at same time, but goal was to remove all AIR from system. He also wanted crank rotated 90 deg. after a few minutes of priming, until it had rotated the full 360deg.


During any motor rebuild it goes without saying that the upper and lower intake should get a good cleaning to remove any carbon/oil deposits that have accumulated over time. Most of the oily residue in the upper and lower intake can be attributed to the PCV system that pulls vapors from
the passenger side valve cover through the line connected to the throttle body.

GM makes a product called "top end cleaner" that allows you to eat away and burn off deposits in the upper/lower intake, valves, piston tops, and combustion chamber. The only drawback is that it produces a lot of white smoke out the exhaust when it's being burned.


The EGR system is designed to recirculate the exhaust gas from the heads into the upper intake to reduce emissions (?). The problem with this is that it dilutes the amount of oxygen in the upper intake and can cause a fair amount of heat soak in the upper intake. There are a number of ways
to get rid of this system.

EGR (Basic)

The easiest way to disable the EGR system is to have a chip burned that raises the EGR enable temp to a level that will never be reached by the stock system. This is useful if you live in an area that has emissions testing and the complete system needs to stay in place for the visual
inspection. Just remember to have it enabled during testing.

EGR (Intermediate)

If emissions testing is not a concern that you have, you can remove the EGR system and all associated vacuum lines (be sure to plug fittings where needed). You will need an EGR blockoff plate from GM, or have one made that will replace the EGR valve mounted to the passenger side of the upper intake next to the throttle body. You will also need to have a chip burned that raises the EGR enable temp to a level that will never be reached by the stock system.

This will still allow the exhaust gasses to make it's way from the head up to where the EGR port is, but will not allow the gasses to enter into the upper intake. This is better than having the EGR system, but not the top of the line.

EGR (Advanced)

If you are confident with machining, etc or have access to a decent shop, you can have the EGR hole in the lower intake plugged with a pipe plug to make sure that no exhaust gasses leave the lower intake at all. This is the best option.

Porting/Port Matching

If you have the ability and equipment to port your upper and lower intake you can do it yourself, or have it shipped off to a machine shop that knows what they are doing in this area. There is a difference between just grinding away material and correctly porting your intake. The theory is that you want to
get as much flow increase as possible while removing the least amount of material (?)

Porting/Port Matching (Basic)

From the factory there is a mismatch between the intake runners of the upper and lower intake. The basic porting would consist of matching the upper and lower intake runners to each other so that there is no "lip" between the two that could cause unnecessary turbulence in the air flow path. The professional
way to do this is mark the area with machinist die and scribe an outline of where to port to. You can also use the upper to lower intake gasket as an outline.

The same process can be used to port match the lower intake to the heads. Just be sure not to mess up the injector bungs that protrude into the lower intake runners.

Porting/Port Matching (Intermediate)

The next step would be to enlarge all of the openings and a portion of the runners (as much as physically possible) in an attempt to increase the amount of air that can travel through them. Again, caution should be taken not to hog out these areas simply to say that they are huge. Size is important, but not at the cost of airflow (?)

Porting/Port Matching (Advanced)

Without cutting into the intake itself, you can only port so far into the intake runners. The next step (which should be done by someone who knows what they're doing) is to physically modify the intake runners so that they flow more. This should probably be done with the aid of a flow bench to
make sure it's done properly. If I remember correctly, the #5 runner does not flow as much as the others and requires the most rework to get it to flow the same amount.

Remember that if the airflow limit is this early in the intake path, everything downstream (i.e.: heads and exhaust) will only be able to flow as much air (or less) than it does here.

The other area that may need welding in order to port effectively would be the lower intake runners where the injector bungs are located. There is only so much material that you can grind away before you have issues with the injector bungs that protrude into the runner itself.

Cooling (Advanced)

The main goal of cooling modifications as it relates to the lower intake are to evenly distribute the coolant to the front and back of the heads. The stock lower intake is cast with two coolant passages that run from the thermostat housing to the water jackets in the front of the heads.

In order to get even distribution to both the front and back of the heads, you can drill and tap two holes (one on each side of the lower intake) at the rear where the water passages are located in the heads. Two lines will need to be made to transfer water from the front of the intake to the rear where the new fittings are located.

Some owners have stated that it took longer for the engine to reach operating temperature when these lines were installed but I'm not sure if that drawback outweighs the benefit of having a more even coolant temperature in the heads.

Anyway, the reason for it is because of the wrist pin probs that GM had on the #4 piston on the 2.5 4 cylinder(AKA"Iron Duke 4 cyl). The water passage for the #4 cyl wasn't of the greatest design and that cylinder ran "hot" compared to the others. This caused wrist pin gulling issues from the heat/detonation and the engine would develop a "knock" from the wrist pin bore opening up. The only cure was to replace the piston/wrist pin and make absolutely sure the EGR system was working(bad EGR sys=light throttle detonation).

So... Figure that if there is going be a "hot spot" in the heads of the 4.3 its gonna be on the rear cylinders where the coolant is more "stagnant" than up front. If it happens to over cool the engine then its a heck of a lot easier to cap off the cross over than it is to add one once the engine is built.

Coatings (Advanced)

There are a number of companies that offer thermal coating of both the inside and outside of the intake (Swain Technologies comes to mind). While I don't have any data concerning the benefit of these coatings, if you have some money to burn it might be worth checking out. The main area to be concerned with would be the bottom of the lower intake. This area is exposed to the hot oil in the lifter valley that can splash up on to the lower intake thus heating it and the intake air going into the heads. Other than coating the lower intake one could use a custom made lifter valley tray that is designed to keep oil off of the lower intake instead of having it coated.

Head Bolts (Advanced)

The newer style Vortec heads (1996 and up?) do not have the same bolt pattern as the L35 or stock heads so the lower intake cannot be bolted to them in it's current configuration. There are several options in this area to get the newer style heads to work with the stock intake manifold, but I would not
consider them a Basic or Intermediate modification.

* Modify the lower intake

The unused bolt holes in the lower intake can be plugged (either welded or using some sort of pipe plug), and the correct bolt holes can be drilled.

* Modify the heads

The other option is to plug the bolt holes in the Vortec heads, then drill and tap them so that they have the same bolt pattern as the stock or L35 heads.

Matt H
Robert P
Les Y
Tony M
Jeff D
Nolan N
Jack O
Mark L
John W
9.89@137 10.26@13
10.29@137 10.71@126
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