Technical Vacuum leak? Early SBC intake on centerbolt engine

I have fitted an early Edelbrock intake on an `87 TBI centerbolt 350 (slotted the 4 center bolt holes).
The engine now seems soggy and vacuum reading is low...Is there some miss-match (Valley angles?) that I have missed...

 

btt

 

I used one recently on one of those engines. The valley angle is the same, just the angle of those four center holes are different than the others. I tig welded all along the edge of the manifold in the center areas and the machined it back down just to add plenty of meat for the gasket surfaces and slotted bolt holes. I then machined four wedge shaped blocks to correct the difference in the angle of the head bolt holes versus the intake holes. It was a lot of work but I couldn't find anyone who makes a three deuce manifold for that engine and the owner was set on having one. Necessity is a mother, lol.

 

I've used the old style intakes on the 86 and up small blocks a few times. No issues. Like you say. .... just get the 4 center bolts to line up. Your good to go.

 

Is that a Doug Nash overdrive?

 

Yes, they are a game-changer on the open road...Have you had any experience with them?

 

Stuart,
If the intake attaches to the heads using 12, 3⁄8-inch bolts (six per side), and the bolts are all at the same slant angle, you have conventional, ’86-and-earlier, cast-iron heads,
If the intake attaches to the heads using just eight, 5⁄16-inch bolts (four per side), and the intake bolt-to-cylinder head installation angle is vertical (the bolts go into the heads “straight-down”), you have ’96-and-later Vortec heads for the Gen I small-block.
http://www.hotrod.com/articles/small-block-intake-swaps-brake-drum-knock-out/
Also check your block for a pump hole as later EFI blocks typically do not have a completed boss and must be modified to allow use of a mechanical fuel pump. They require drilling.
http://www.bhjproducts.com/bhj_content/products/blocktooling/fppr_chs.php

 

A little, mostly as underdrives on motorhomes. Same, but gears swapped.

 

Underdrives, who would have thought...Do you use the regular 90W oil? I have fitted an oil pump and cooler to keep the oil temp. below 85 degrees Centigrade.

 

MGTSTUMPY, as usual, your research and knowledge answers most questions...Thanks to all respondents for your input...Stuart.

 

Yup. The DN overdrive/underdrive was take up by US Gears.

Here's a link to the manual: http://www.dieselwarden.net/temp/usgear/US Gears overdrive manual.pdf

 

I appreciate the inclusion of the pdf, thank you.

 

What's going to make a good donor, for searching purposes ?

 

The early manifolds fit right onto those junky TBI heads with the modification of the 4 center bolt holes. Also TBI manifold will fit onto the early heads too but the 4 center bolts are a bitch to get in, however it's doable.
It is possible to get a vacuume leak with your parts but it should not be from a mismatch in angle provide you have stock parts.