Hi, I've got Mortec but I do not know where to get the ID for the number on the front pass side of the block tab. I bought a running engine out of a '73 p/u yesterday to build as a spare. It's a 4 bbl engine with a 3 on the tree stick which I thought was unusual. Got the complete engine including the a/c pump, p/s pump, alt, starter, bellhousing and all for $300, and he pulled it. :) Anyhow, the casting # is 3970010 which shows too many applications. The engine tab # is V1103TJB and the head #'s are (3) or (8) 998993. If anyone has a site to go to for the tab #'s, that would be cool. Gonna have the flywheel off tonight to check for the 010 which assures it's a 4 bolt main. Thanks guys.... :cheers:


[Modified by MasterDave, 7:32 AM 3/5/2002]

 

Dave -

Sounds like it's original to the truck - TJB is a '73-'74 Truck 350 4-barrel 160hp, and the heads were used for that and many other 1968-1976 applications; they have 1.72"/1.5" valves.


[Modified by JohnZ, 2:47 PM 3/5/2002]

 

Thank you JohnZ, good info. I'm only interested in the short block anyway and my instinct tells me that being in a truck and a 4 bbl, it should be a 4 bolt block. It only matters for braggin' anyway since I'm gonna limit to 400ish hp. Always nice to have a spare engine on a stand ready to go... :crazy:

 

JohnZ & MasterDave,

These heads (3998993) came with 1.94" intakes and 1.5" exhaust size (I have a set that measure exactly that). Most Chevy 350 engines had those size valves, but these can be hogged out to the 2.02/1.6 valve size by any good machinest. They are termed "intermediate performance heads" (as opposed to either "base" or "high performance") and have 76CC chambers (or thereabouts). The exhaust ports in particular were better than average during that time period. I would not toss out these heads, since thet are better than most.

Note that I have seen some people claim these heads as "lightweight" heads which were prone to cracking. From the set I have (and dating), I know that to be false, and the lightweight head problem did not surface until the 1975 and newer heads.

Of course, Chevy has a way of swapping things a bit and confusing the interchange manual people. Example: I have an original LT1 engine from a 74 Z-28 that came stock from Chevy with #333882 heads with 2.02 intakes and 1.6 exhausts and screw-in studs. According to every interchange manual I have seen, these heads were only produced in 1.94/1.5 configuration. Go figure!



[Modified by Plasticman, 11:04 PM 3/5/2002]

 

Thanks Platic, good info. I took the flywheel off last night and the 010 is there so it is a 4 bolt. :cool: I also removed the heads and all looks very nice in the heads. The pistons though look different than I've seen. First off there is absolutely no carbon on the tops, they look new actually. I'm going to remove them this week but maybe if I describe them someone can tell me what they may be. They have 4 valve reliefs and a very slight dish (maybe .05) around the top of the piston about 1/4" in from the edge. The strange thing to me is the taper of the pistons. From the top ring groove they taper in about 1/4" or so and this taper goes to the top of the piston, the distance of maybe 3/8"-1/2". There is an ever-so-slight lip on the top side of the cyl's, you almost cannot catch your fingernail on it. The engine is supposed to have 98K on it but I don't see how by looking at it. Thanks for your assistance :cheers: , hey we need stuff to talk about here in C2 right? :jester


[Modified by MasterDave, 8:09 AM 3/6/2002]

 

MasterDave,

I do have a picture of what you have described (as shown in the Chevrolet Small Block V-8 Interchange Manual dated 1989).

It lists this as a 1976 400 piston, 8:1 compression ratio with 76CC heads. It also shows similar pistons for 305 engines (one shown has the taper and the dish, but no valve reliefs, and the other shown has the taper and valve reliefs, but no dish), so I am sure Chevy made them for 350's as well. This book also states that 350 pistons (flat with dish) (depending upon p/number actually used) will produce either 8.5:1 or 8:1 with 76CC heads. The valve reliefs typically add 2-4CC to the chamber vol. (depending upon depth of reliefs). Most (if not all) 350 Chevy engines had at least 1.94" intakes which dictate valve reliefs.

As for the clean tops, evidently this motor was taken care of, and did not see excessive load, nor did it idle too long, used quality fuel and oil, and did not suffer from a defective carb or ignition, etc. The low amount of cylinder ridge is also indicative of good oil maintenance.

Good luck,

 

Thanks Plasticman, I was waiting for you to give me some input here. Apparentley these are cast pistons. What would you suggest the comp ratio would be w/64cc heads? I have the Sportsman II's. I'll check the bores carefully for sure and probably install hyperutectic pistons in the std bore. I'm not sure though if forged or hyper-u pistons can be installed in a stock bore. Do you know? Want to be at 10.1 CR if possible.

 

MasterDave,

Yes these would be cast pistons with steel inserts around the wrist pin area (standard for Chevy pistons).

If you used the same pistons, my calculator says that the Compression Ratio would rise a little over one point using 64CC heads vs. the 76CC versions you have now (that is if everything else stays constant, including deck hgt., and gasket thickness). Note that 76CC heads can vary anywhere from 72CC on up to 80CC depending upon what Chevy was trying to do with them (we all just lump them into either the 64CC bin or the 76CC bin, but there is a great range in actuality). Therefore, if you were planning on using the old heads, you must determine what is the true CC vol. Note also what type of head gasket is on now. Back then Chevy was starting the transition to composition gaskets (typically .039" thick), whereas previously they used a steel shim gasket which was around .024" thick or thereabouts).

Forged or Hyper-Eutectic pistons can be had in a great range of stock and overbores, so you are not limited there. But, if I was building up an engine with all the work and effort necessary to do it right, I would start with a bore cleanup and use a larger piston (typically most bores can be properly cleaned up with a .020" overbore - depending upon bore taper, and scratches), and most pistons can be had in stock, .020", .030". .040", and .060" sizes).

Hyper-eutectic pistons would be my first vote for a non-supercharged street engine, since they do not suffer from the thermal expansion problems that a forged piston has (forged pistons require greater clearances and are noisier during warm-up), but forged pistons are the champs when it comes to strength.

KB has a hyper-eutectic #KB-228 flat top, 5.7" rod length (with valve reliefs) that would come in at 10.2:1 CR (depending again on the all important deck hgt. and gasket thickness). My vote would be to get the quench hgt. down as low to .045" as possible (combination of deck hgt. and gasket thickness). Since most composition gaskets, which is what I recommend, (Fel-Pro is #1 in my book) are .039" compressed hgt., you would need a deck hgt. of .006". Note that you can't just deck an block until you trial assemble it with the bearings, crank, rods and pistons you are going to use to determine what the deck is now, and the machinist will remove "X" amount to get down to where you want it to be. KB does not list the actual piston CC subtraction / addition vol., so a call to them would be in order to finalize the actual comp. ratio (for the bore size you end up with, since this does go into the equation - greater bore size, the greater the CR).

I would also CC the Sportsman heads you have, since I have found their chambers to be inconsistant (one head I had varied from 64 to 67CC, while the other was 62 to 65CC so I had to cut the heads on an angle to correct the opposite angle they cut them at, and take off more from one than the other).

Also, I assume you are going to use a pretty stout cam for use with 10:1 CR and the Sportmans. Recommend that you discuss the cam selection with whatever cam manf. you plan on using (they all are very willing to give this advise over the phone, and maybe even E-mail). Just don't fall into the trap of using old 1960's tech., since todays cams are better in just about every way!

Good luck,

 

Plasticman:
As a related aside to MasterDave's post, I was wondering ... You made mention of "hogging out" the 1.94/1.5 heads to 2.02/1.60 valve size as a possible performance upgrade .. In my case too I'm planning on rebuilding my stock old double hump 1.94/1.5's and changing out the valves to stainless steel .. Now that you made the "hoggin' out" comment, well, the 'ol wheels and gears in my head started turning .. :D ... Since I will be changing out the valves anyway, would the stainless steel 2.02/1.6 valves work out in this application too .. ?.. The difference in size of those 1.94/1.5 and 2.02/1.6 valves seems so close, is there that much difference in performance .. ?..
mrg

 

Lotsa great info here Plasticman. I'm still absorbing it. I'm taking your advice and am going to do this block right. I have the Comp XE274H in my engine right now and while I like the power intensity I am very unhappy with the idle quality. Seems like the 110 lobe sep is causing big resonation in the muffs (I think :confused:). I did not have this problem with the Summit K1107 cam I used to have and will probably to back to it or maybe the K1106. This cam had the same idle speed but the lope of the engine/cam was much farther apart (if that makes any sense) and I had no ear popping resonance, at least that I remember. This is as big a cam as I would consider using for street use, any thoughts? Cam selection, while I am getting better educated, is still kind of a mystery. Oh yeah, one more thing bro, this (truck) engine did have the thin metal head gaskets on it.

 

If you decide to upgrade from 1.94 to 2.02 valves, you'll need to do some grinding or machining in the chamber to un-shroud the intake valve, as the factory did with original 2.02's; if you don't un-shroud the intakes with the upgrade, it will actually flow less than it did with the original 1.94's.

 

JohnZ, I'm not going to use these heads, the Sportsman II's I have will be going on them. They are 64cc w/2.02 & 1.60's already. These heads are gonna be sold to whomever wants 'em. They look/work fine with no oiling or burned valves at all. Thanks for the advice though, I do appreciate it.... :cheers:

 

MRG,

There is a small difference between 1.94/1.5 and the 2.02/1.6 valve sizes. If you were strictly racing, then it makes a big difference since every HP adds up to going faster. For the street where you see a much broader RPM band, I would stay with the 1.94/1.5 and do a good bowl porting and 3 angle job. Now if you started with 2.02/1.6 valve size, I would not go back to the smaller valves intentionaly - just depends on what you have and where you are going to use it (se below).

Note also that since we are all using unleaded fuel these days, Chevy started adding induction hardened seats on the 1971 heads and up. If you hog these out to 2.02/1.6, you lose that hardened seat. Most of the time low milage street engines will not see seat erosion with the softer seats, but for hard working engines it is a different matter, and yes I recommend the SS valves (only way to go), but use quality valves with a fine finish on the stems.

JohnZ is correct to a point on unshrouding the valves when hogging out the seats. It depends on which heads your modifing, since some versions were used interchangably with both valve sizes from Chevy. These do not need unshrouding, and if you do, you will knock the compression ratio downward. Best way to determine if unshrouding is needed is when the seats are cut larger, the machinist normally will cut the top angle with a larger perdetermined diameter stone or cutter that does both the top angle and unshrouding at one pass. This top angle is around 30 degrees and is not the actual seat cut, just a transition cut for the 3 angle job (as in 65-45-and 30 degrees - or thereabouts) with the middle angle (45) being the actual seat cut. Your double hump heads were built from Chevy with both valve sizes and should not need unshrouding. They were also before the induction hardened seats (before 1971), so you could open them up if you wanted, but don't expect a great amount of difference, but high RPM will be a little stronger, and the bottom end will suffer a small amount (no free lunch).

MasterDave,

Understand about resonance and it can be a problem! I am not a cam expert, and that's why I recommended talking directly with the cam manf. I have been doing heads / engines forever, but cams is always been a problem of trying to keep up with the lastest cam tech. and theory. I have found most cam manf. do a very good job for you if you describe exactly your engine parameters (heads & valve sizes/manifolds & or headers/carb./CR/etc.) and usage/goals. They have seen them all, and know what works best. It is not in their best interest to recommend a "dog", and they know the latest technology. Note that if you want the ultimate broadest torque band, go with a hyd. roller, but these get very pricey! Some people just love the sound of a solid lifter cam and a big lope. It just depends on what you want.

The steel shim gasket will increase the CR a small amout, and Chevy used them for many years (cheap and durable), but I recommend a quality Fel-Pro composition gasket for most rebuilds. They can be had with SS fire rings for up to low boost supercharged purposes (and won't rust if only water is used for cooling - not recommended, but most boat engines use raw water cooling and need to keep that in mind). Note that Chevy use to make a great SS shim gasket (about .020" thick), but have since discontinued it. As I said previously, if you used the stock pistons and heads, and now a composition gasket, the CR would decrease (since the stock gasket was a thinner shim gasket), but since you are going to a complete rebuild anyway with new pistons, etc., this does not matter.

Good luck guys,

 

Ok .... Well, I think I'll keep the valve size as is, after all .. I'm more concerned with low to midrange street performance than with any other parameter .. There was some discussion some weeks back about cam selection for the small block and the factory "151" as well as the Comp Cams XE 262 were mentioned as good choices for cam selection .. I'll go with one of these ...
MasterDave mentioned about resonance in the mufflers .. I take it to mean it's a kind of popping sound .. ? .. Does the 110 LSA Comp Cams grinds in most of their cams "enhance" this effect .. ? .. Just wonderin' .. :) ..
Thanks JohnZ and Plasticman for your replies ... There's nothing like experience to set the record straight .. :chevy
mrg

 

mrg, it's not the cam lope/pop that bugs me, it's the resonance or loud humm of the muffs. Makes my ears hurt, (it's not loud), I liken it to the feeling you get in an airplane just before your ears pop while rising/descending. I've replaced with different muffs 4 times since the cam change trying to get it gone. It's still there. The only time I do not hear it is when I uncap my side pipes. I may just have to leave the sides open, dunno that is VERY loud. I may do a cam swap AGAIN just to see. The XE274 is a 110 ls and the Summit K1107 is 114, maybe that has something to do with it. Too much stress here just thinking about this. :crazy:


[Modified by MasterDave, 6:18 AM 3/8/2002]

 

MasterDave ..
That sure is something that FOUR different sets of muffs had that same resonance problem ... ? .. I dunno, but I'm wondering if overly long duration cams might add to this effect, irrespective of the lsa . .. ?.. Just a thought ...
mrg

 

MasterDave, are you running side pipes?
I have had to overcome this problem on several cars,
It usually occurs at exactly your normal cruising speed. (Murphy's law)
I have cured this with several different methods, but am
curious if you are using those side pipes?


[Modified by 396 RAT, 9:31 AM 3/9/2002]

 

Thanks for all the info fellas, been off the net for the weekend. Plasticman: Disassembled the engine and the pistons #'s are 6271096 GM, so they look to be stock cast pistons (std). It is a 4 bolt but Mortec shows the crank #3932442 as cast, also (std). That's ok, cast is fine up to 500 hp I believe. mrg: Yeah, that's kinda my thoughts (cam lsa) on resonance, still confused though. 396Rat: The side pipes have two header-type 3 bolt flanges I installed that 'T' off of the exhaust at the first bend the pipe takes going to the rear. I put a 1/4" thick plate btwn the flanges. With the plates installed, the exhaust exits the rear thru the 2.5" pipes into the turbo muffs, like a stock system. When I remove the plates, the exhaust takes the path of least resistance and even though some exhaust goes out the back, most goes thru the side pipes. The sides are actually simply 2.5" straight pipes with some glas packing (8" total) wrapped around some resonator tip (at the flanges) mesh to kill some of the noise pain. The resonance complaint I have is at idle. At speed it's fine. With the sides 'open' I do not have the resonance problem at all, just a headache from the loudness. I may just leave them uncapped, at least it's hard to hear the wife complain about the noise. :lol: I've been checking Speed-0-Motive and man they have some prices for complete short blocks (383) (350) that are hard to beat. They are $500 cheaper than I can get a short block done around here, and I don't hafta do nuttin' but wait for it to show up. Gonna have to check some more local builders around here. Sorry for the long post, hope to hear from you fellas soon.