Hi All, ordered the LT1 head/motor modification book,"how to Build Max Performance Chevy LT1/LT4 Engines" whist it arrives does anyone have a idea about cleaning up the combustion chambers? I have a steady hand done this many times on Alfa Romeos, just don't want to do the wrong thing here, the heads are absolutely standard, never been skimmed, will need to now due to corrosion on both cylinder heads, busy port matching exhaust manifolds and inlet manifold, then wills tart the same on the heads, these heads already flow well, so just want to trim them up a little.

The combustion chambers measure form 54 to 55 cc, pretty good for a std manufactured product for 1994. I have added a calculation for increased volume for skiming the head 20' or 40'
There are a few areas I would like to work on,
Marked as 1 - flat side of both inlet and exhaust seats
Marked as 2 - deep side of vale and combustion chamber
Marked as 3 - above the spark plug

Somewhere to start?

Volume calculations

Volume measured 54 to 55 cc

Volume measured 54 to 55 cc

 

Well I can read you are fairly serious about this Mr. Dubai so I will try to help even though you are new to the forum. And I happen to have a '94 LT1 myself (in my Z28 though).

Well that's a lot of work and unless you are installing larger valves (like I did) I'm not so sure the heads needs a lot of unshrouding. Now I haven't found any good information on reshaping LT1 heads but David Vizard in his book "Max Performance Chevy Small Blocks on a Budget" he details a vortec head chamber modifications. The Votec head chambers are a near complete match except for the straight spark plug casting bosses. But these casting bosses is what he says need the most contouring. Removing all the sharp angles from this casting bosses will greatly enhance swirl in the combustion chambers. You want to lay back the the area along the spark plug boss in the intake side for unshrouding there.
For the rest of the chamber I would just clean it up with maybe sand paper rolls. Vizard says not much to be gained with further unshrouding. Installing larger valves is another story but you haven't mentioned that.

I have that book "how to Build Max Performance Chevy LT1/LT4 Engines" by Cottrell and he shows nothing on modifying stock LT1 heads. He provides a guide to aftermarket heads for the LT1.

As far as shaving the heads my machine shop intented to cut my heads 0.030" but stopped at a 0.010" cut because the intake valve is sticking into the chamber. I'll attach some pix for you.

new larger valves

intake outside chamber

close up

Hope this can help. Intake valve is 2.00" BTW.

 

thanks for the help Cardo0,

New to Corvettes, not to fast cars, but built a lot of Alfa's, In South Africa you need literally need to be a millionaire to have a corvette, we mortals worked on what we had, South Africa has the second number of Alfas after Italy, they don't rust in the land of sun! Work for a journey man, we built a 10 second Nova street rod in SA in the 90's No turbo, no nitro, for less than $10000, the biggest cost was a 4 bolt Chevy motor out of a ambulance from Australia, $800, plus delivery!

Yeh I see the, valves are close to the head surface, Definitely need them out to skim the head, It also need welding on 3 areas of the water jacket, did you have larger seat inserts done or did you manage with the standard seats?
STD valves are 49.3 so your 1.5 mm bigger, did you enlarge the exhaust as well? valves look nice, are they LT4 light weight valves? did you go with 1.6 ratio rockers?

 

Intake valves are 2.00". The exhaust valves were larger than stock and I think they are 1.55 but can't recall exactly. Pretty much the same size as the LT4 but they are stainless steel and not the light weight titanium valves the LT4 uses. But the shop put in some strong springs they said though I never got a part number from them. All I wanted was enough spring to hold the valves for a 0.525" lift cam. I'm not going over 6,000rpm I don't plan to so I don't need light valves and gorilla springs. I should mention the largest valves that will fit an LT1 head w/o replacing the valve seats are 2.00" intake and 1.56" exhaust and with a modest budget build I just wanted to squeeze the stock heads a little. Hind sight I should have kept the stock valves and gotten the chambers polished or at least smoothed up.

I found a very good cylinder head shop near the speedway here in Las Vegas and the owner has decades experience with the sbc and I really trust him. So I didn't want the runners ported for this build. All I wanted was the throat behind the seat reworked. It's kinda like pocket porting but more science required than just blending - but much easier than porting the runners. For around $800 and change I got new SS valves, better springs and the throats reworked. Shaved 0.010" also. Wish I had gott'n the chamber reworked but I didn't get it written down on the build sheet and it didn't happen. Man my chambers are as rough as 100 grit or 50 grit sand paper. That rough surface will load up with carbon from use. I may try to revisit the shop for this as the larger valves could need more unshrouding also. Have them rework the spark plug boss also and open the chambers as if your chart is correct the 0.010" cut gonna take away 6cc and leave me with a 49cc chamber. Whoow!

As for rockers for my build I haven't chosen the cam yet but if I go with the "Hot Cam" most likely I would use 1.6 rockers on the intakes and 1.5 rockers on the exhaust.

 

Ok with the valves, if i needed new then that would be a great idea, not much room in there for larger valves,Yeh stared the throats on mine, worked the bowl clean up, started on the bowls, will port match the intake and exhaust, the dremel tool I have wont do that will need a lone bit and die grinder, still looking for one less than $230 here, and a long bit to smooth the runners.The exhaust ports were way of, some areas 1.5 mm out with the valve seat,ground back the valve seat and left a 2.5 mm wide section at the minimum seat for exhaust in cylinder no.8, didn't looks cleaning up the bowls, 1 to 1.5 cc of material. most of the work was at the throat and bowl, one day to do 4 bowls and 8 valve throats!

the first bowl polished the most, took out the least, loss a cc in the clean up, will get that back in the skim

The blue areas I took a few mm out, the orange to blend.

the exhaust port had cast flash in 3 of the ports, this was form 3 to 6 mm thick! inlets were relatively clean

adjusting valve seat throat to match aluminium dimensions, this was the worst throat seat.After this with a sanding roll.

removing machining lip where possible, and gringin of inlet port to match the seat.

 

I like it, nice work. Man doing that with a dremel tool a job and a half! Only thing I would say is don't hold back on the spark plug boss. Lay it back all you want - until it looks like a tit if you want. Well with the angle plug you really only need to lay back one side as the exhaust side is already blended. But there's quite a corner on the intake side that blocks some swirl (I think).

Working the throat and and the bowls gonna give you plenty more flow. I wouldn't worry about the runners unless you see chunks or ridges in there.

 

Why is the spark plug aimed at the exhaust valve ?

 

Hi im not sure what you mean, thatch the standard head on the LT1, its form my 94 C4, are yours different? Im looking for photos of the bowl on other relatively std motors

 

Hi If you look at the calculations 10" is 0.25 of a mm and that relates to approx 1.352 cc, so half of the first calculation. sorry man, you can increase compression by overbore, or decked pistons

 

Okay I miss read the chart and failed to do the conversion to mm. So 0.010" = 0.254mm and your chart has 1mm = 10% reduction or 5.488cc. Then 5.488cc x 0.254 = 1.394cc.
Well that's not so bad. I just need to measure the chamber but it's on the wrong end of my list right now.

Thanks for the correction. I can use a shallower dish piston now. BTW have you shopped for pistons? Take a look at Silv-O-Lite #3437HC and #1489HC. I like the 3734 because the compression height is 0.020" higher and should put the piston crown close enough to the deck for good quench. Those are stock replacements but very reasonable prices. And I'd like to go 0.060" overbore if I can but I was worried the compression ratio would go to high. Now I have less compression worries. Thx.

 

So today bought a cheep die grinder and bit, what was locally available and started on the matching of the inlet ports to the inlet manifold, had to stop to teach the kids math's, home schooling and still were paying school fees

This is the start, 3/4 way down the runner there is a hump in the roof

90% of the porting is on the outside of the runners, and floor, clean up the inside casting marks and then finally as I come out ill make the exits clean and straight.

Standard vs porting, will not touch the roof of the port, touched once or twice with the bit, will put a tin shim in tomorrow when I carry on.

 

You might be interested in this porting video on a vortec head - very similar to a LT1 head: https://www.youtube.com/watch?v=d55U...ature=youtu.be