EA82T inside , interesting findings .
Posted: Tue Dec 18, 2007 6:10 pm
High all , was back with my engine builder today to see how it all looked pulled apart
. He has started to port the heads and I must say these must be the only pair of first gen turbo heads with no cracks at all in existance - thanks Gee !
We were comparing the ports so far against a set of "used up" 1G heads and I gotta say the std exhaust ports are fairly crude but can be improved easily enough . An interesting point AJ made was that it wouldn't be impossible to fabricate a header with a divider plate reaching inside the exhaust port to the divider . If the header had twin pipes leading from each exhaust port you could get much closer to an 8 port 2 valves per cylinder engine , this would allow warmer cams with more valve overlap to be used because it reduces the cross contamination between adjacent exhaust ports when they are siamesed (ie EA81/82/ER27) . It would also allow the use of a pulse divided header and a twin scroll turbo which is a big if expensive plus .
The other thing AJ's done is CC'd the chambers/piston crowns/head gasket volumes and it turns out that if the pistons were flush with the tops of their bores the static compression ratio would be 8.4 to 1 . As we know the advertised EA82T CR is 7.7 to 1 so the pistons must be down the bore a little wich is not preferable given a choice . A great majority of engines get good combustion characteristics with their pistons either flush with their blocks deck or even a little proud of it . The reason being that the quench or squish area needs to be small and the sort of height between the piston crowns and the head faces typically 25 to 40 thousandths of an inch (0.635 - 1mm) .
AJ said the way to get this is to mill the decks of the cases so that the CR stays the same if the heads need to be changed at any stage .
A problem that does arise is that with less distance between the deck faces the cam timing changes so he's looking at how to modify the std cam pulleys so that the cam timing can be corrected . Basically slotted bolt and dowel pin holes - find the correct point and mark it then weld and redrill the dowel holes . Fixed .
Camshafts . We have 2 sets ATM I think being 85-86 turbo cams and the Vortex ones which may be same as 85-86 MPFI . The early turbo ones have no groove in the A position and one in the B position . The Vortex ones have one groove in the A and B position . The valve timing differences are 10-58 58-10 and 12-58 58-12 . I'm going to look at 87+ profiles to see if theres anything better - possibly the later MPFI cams .
With a CR of ~ 8.5 to one and better cams and header we think this EA82T should make a good road engine .
Cheers A .
. He has started to port the heads and I must say these must be the only pair of first gen turbo heads with no cracks at all in existance - thanks Gee !
We were comparing the ports so far against a set of "used up" 1G heads and I gotta say the std exhaust ports are fairly crude but can be improved easily enough . An interesting point AJ made was that it wouldn't be impossible to fabricate a header with a divider plate reaching inside the exhaust port to the divider . If the header had twin pipes leading from each exhaust port you could get much closer to an 8 port 2 valves per cylinder engine , this would allow warmer cams with more valve overlap to be used because it reduces the cross contamination between adjacent exhaust ports when they are siamesed (ie EA81/82/ER27) . It would also allow the use of a pulse divided header and a twin scroll turbo which is a big if expensive plus .
The other thing AJ's done is CC'd the chambers/piston crowns/head gasket volumes and it turns out that if the pistons were flush with the tops of their bores the static compression ratio would be 8.4 to 1 . As we know the advertised EA82T CR is 7.7 to 1 so the pistons must be down the bore a little wich is not preferable given a choice . A great majority of engines get good combustion characteristics with their pistons either flush with their blocks deck or even a little proud of it . The reason being that the quench or squish area needs to be small and the sort of height between the piston crowns and the head faces typically 25 to 40 thousandths of an inch (0.635 - 1mm) .
AJ said the way to get this is to mill the decks of the cases so that the CR stays the same if the heads need to be changed at any stage .
A problem that does arise is that with less distance between the deck faces the cam timing changes so he's looking at how to modify the std cam pulleys so that the cam timing can be corrected . Basically slotted bolt and dowel pin holes - find the correct point and mark it then weld and redrill the dowel holes . Fixed .
Camshafts . We have 2 sets ATM I think being 85-86 turbo cams and the Vortex ones which may be same as 85-86 MPFI . The early turbo ones have no groove in the A position and one in the B position . The Vortex ones have one groove in the A and B position . The valve timing differences are 10-58 58-10 and 12-58 58-12 . I'm going to look at 87+ profiles to see if theres anything better - possibly the later MPFI cams .
With a CR of ~ 8.5 to one and better cams and header we think this EA82T should make a good road engine .
Cheers A .