Vortec Bandit

Also, who's making off the shelf forged pistons for this motor. I am using 6.7 inch H-beams but need a .030 - .060piston with a 1.350 pin height and a deep valve relief.

Raylar

IT sounds like the head shop did a good job for you. They saved the heads and increased the valve size at the same time.
just have them cut down the OD of your valves and take what you can get. A good day in boat world. I don't think the HP3
heads had an exhaust valve that big. I would expect that they also opened up the exhaust port and trimed the hump going
to the valve guide?

If so, the heads would look something like these:
(ported, unpolished intake)
[ATTACH=CONFIG]508232[/ATTACH]

(ported, unpolished exhaust)
[ATTACH=CONFIG]508233[/ATTACH]

Larry Hofer

Vortec Bandit

As you said they are cutting the dia. Of the valves to 1.83-1.84.

Raylar

also as a note to VORTECBANDIT ,i have in stock,forged pistons for the.990 wrist pin and 1.340 and 1.350 compression heigth.
Without sonic checking the block, i would be cautious about going .060 over bore. I have had customers find blocks without core shift and go .060 but you should check first. This is a thin wall casting block.
Larry Hofer

Vortec Bandit

Larry, what's the weight on your .030 pistons and will the relief accept a 2.25 int.valve at .621 lift?

Raylar

Vortec: don't know the exact weight of the forged piston. They work well with our H beam robs and internal balanced rotating assembly. The engine shop takes care of the engine balancing. i wouldn't just plug them in and go. If i had a gram scale ,i would
weigh one for you, but i don't.The valve notch is plenty big.In the .700 area. Final answer is to always clay the piston to confirm to
your self that you wont break your engine.
Larry Hofer

Rage

Dart answers to my inquiry:

1.) Head bolts on the spec sheet does not make mention of the "two studs" used instead of stock GM head bolts that you mentioned to me. Please clarify. I have also read that head bolts for these heads must be obtained from you (ie implying that the stock GM head bolts do not work)? Please advise what head bolts must be used with your heads.

If you are using a DART block you would use standard Mark IV head bolts along with four longer bolts used where the head dowel pins are.

If you are using a stock GM 8.1L block you would do the same. Use stock GM bolts along with the longer bolts for the dowel pin holes.

Dart keeps these longer bolts in stock.

2.) Intake valve diameter says "2.190" or 2.250"". Does that mean that the Dart heads can be ordered with either valve size for the same price?

Depending on our inventory, if we have heads on the shelf already valve jobbed for a 2.190” valve then there will be an additional cost to re machine them for the 2.250” valve. If we have un machined castings on the shelf when you place your order then there would not be any additional cost.

4.) Can your heads be ordered with valve stem guides machined for 3/8" dia valve stems instead of 11/32" dia. for the same price?

This cylinder head is available for a 11/32” valve stem only.

5.) Can your heads be ordered with valve rocker arm stud holes machined with 3/8" threads instead of M10 threads for the same price?

We do not offer this as an option.

6.) Not related to the printed spec sheet.....with the stock heads it is very difficult to fit the HP3 race engine roller rocker valve train under the stock GM valve covers do to the polyloc nuts interfering with the underside of the valve cover such that it could only be barely installed by using low profile nuts on the exhaust studs. Is there ANY DIFFERENCE in the distance of the machined valve cover gasket surface to the rocker arm stud mounting surfaces on the Dart heads versus the stock 496 heads? ANY DIFFERENCE ?

Dart Machine offers a Tall valve cover for the 8.1L engine.

Thank you,

Tony Hornak

Dart Machinery, LTD.

Keith Atlanta

At least they tried to work with you and give you other options to make it easier..... LOL

Heres how we can help, no, no, probably not and no.

Vortec Bandit

Reason I asked, comparing a few sets from different mans. Found weight range from 538 grams through to nearly 600 grams. Was curious whether the weight difference was around the skirt/pin area or the thickness of the piston top.

Complete assembly will be balanced and PV clearance checked.

Raylar

Most every thing Dart said sounds correct. onely 2 things might be incorrect for the GM iron head.
1 I have a dart 632 i am putting together at this time and fitting the iron GM heads to it. (A class of truck pulling requires correct part number GM heads) Dart sent the correct quanity of head bolts per side in 7/16 for their block. 14 @ 4" long and 4 @2 1/8". The end 2 bolts inside the valve cover need to about 3/4" shorter because the stock head is lower in this area for oil drain back. Other than that, doing ok. (fitment of the engine block into a stock truck accessory drive is adventurous, and the marine 496 is harder )

2 why would you want 3/8 rocker stud holes machined in to the DART heads? stock HI PO GM BBC studs( and ARP and every body else) are 7/16". did I miss read this? I have had several sets machined from 10MM to 7/16" .
Larry Hofer


3 Stock GM 496 head bolts are 10MM metric and DART stayed with 7/16"