What is the Difference between the old style SLP runners and the later?
I have the old style gasket matched to Bigmouth Gaskets.

Also, I have just done an upgrade to my 1991 TPI.
What kind of performance/HP am I looking at? Here are the specs.

1991 TPI stock long block 113 heads 10.5:1 compression
Old style SLP runners gasket matched with Bigmouth intake gaskets.
TPIS Bigmouth intake
Ported plenum with 48mm TB
CC502 cam 218/224 @.050/495/503 lift with 1.5 rockers 112lsa
Bosch III 24# injectors and AFPR
Scorpion 1.5 roller rockers
Flow master cat back and TPIS Ypipe (no precats)
It’s a corvette so it has factory shorty headers and I cleaned up the
welds and AIR tubes I couldn’t believe it I got almost a half inch more ID
rear end is a 2.59 (plan on 3.42 in the future)
I got a tune from Scott Hansen

 

bump

 

IMHO the first sytle SLP runners are better for higher horsepower. One side of the runners is already fully siamesed. There are also less restrictions where the bolt bosses bump into the intake tract compared to the 2ns style. For someone modify SLP runners for a high horsepower motor there is a lot less work to do with the first style.

 

I gasket matched them then bolted them on.
Do I need to fully siamese them?

 

For more horsepower yes. Make sure the intake manifold openings are slightly larger than the runners or you will loose power. You don't want a lip in the direction of the airflow.