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A 427 at 7000 rpms pulls almost 1.5” manifold vacuum through a dual 63.5mm ported TB. At least mine did. On another engine, 368, was around 1.0” vac through a similarly ported TB.
As Todd has pointed out, of course the LT5 is going another ~ 2000rpm than an L98 or an LT1 motor. Power peak on mine is nearly 6900rpm. And yes its very close to 100kPa at WOT depending on altitude/temp. So the 63mm is utilized.
My manifold is not siamesed, but it is ported to
36mm + as best as the plenum casting will allow.
As Todd has pointed out, of course the LT5 is going another ~ 2000rpm than an L98 or an LT1 motor. Power peak on mine is nearly 6900rpm. And yes its very close to 100kPa at WOT depending on altitude/temp. So the 63mm is utilized.
My manifold is not siamesed, but it is ported to
36mm + as best as the plenum casting will allow.
O.K. So no, a bigger TB or more TB's isn't going to help in a meaningful way on that engine. Thanks for posting that data to clear that up.
That "427" above? Yikes. Something seems amiss there. 1.5" vacuum??
Yes the problem is the TB is too small. Seen it more than once on engines which pump a lot of air. I think we’ve taken this thread down a hole the OP didn’t intend. Sorry.
O.K. So no, a bigger TB or more TB's isn't going to help in a meaningful way on that engine. Thanks for posting that data to clear that up.
That "427" above? Yikes. Something seems amiss there. 1.5" vacuum??
.
For what it is worth, Marc says the 63mm TB is worth ~ 6 hp on a 5.7L motor with full upper/lower (i.e., "510") porting. I ran an analysis of air flow vs HP and cam up with exactly a 6 hp increase, provided the plenum too was opened to 63mm.
Greg Van Deventer built my siamesed plenum, for the stock displacement LT5 in my 1990 #952. Engine had Jeal intake cams and headers so I had it engraved.
I'm thinking ITB as big mods on the factory intake are #@ pricey
I believe I can hack up and mod the inj housing to straighten out the flow and you'll have plenty of intake tb flow by using a lay over crab style itb like the old bb chevy did
for the chapparal team, those old calliope stacks really did make the bb chevys sing and with the right progressive linkage I sure would like to try it out!
all my dollars are just going to get my lsv back on the road with "current technology" but I'm looking to do this if feasible down the road.
I'm thinking ITB as big mods on the factory intake are #@ pricey
I believe I can hack up and mod the inj housing to straighten out the flow and you'll have plenty of intake tb flow by using a lay over crab style itb like the old bb chevy did
for the chapparal team, those old calliope stacks really did make the bb chevys sing and with the right progressive linkage I sure would like to try it out!
all my dollars are just going to get my lsv back on the road with "current technology" but I'm looking to do this if feasible down the road.
No doubt and it would be beautiful wish I had pics of the Lotus Elise GT1s at Sebring who ran LT5 derived motors with ITBs.
04-20-2018, 12:03 PM
