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So, you chopped off a 5.0 upper & used its (mounting flange?) as a grinding template on a 5.8 lower?
No, I used a gasket.
That upper intake stub/flange is for a box upper project.
It was just easy to show how well the ports lined up, and I couldn't find my gasket.
Ok so I'm going with 5.0 upper and gt40 heads. Assuming I use 5.0 gasket between intakes? That a 5.8 lower will match gt40 heads. And when I order headers I need to order for 5.0. If I'm wrong pls let me know.
5.0 upper. 302 and 351 throttle body is the same.
351 lower ported to 5.0 upper gasket, and gt40 intake gasket.
Headers to fit 351 because the engine is taller and wider.
Gt40 heads need head bolt holes opened up to 1/2" for 351 head bolts.
Then get a set of pedestal mount 1.7 roller rockers
Stock gt40 valve springs should be fine, but if you're going to port the heads any, meaning valves will be out, I would get a new set of valve springs because the stock ones are just adequate enough for your application.
Last edited by UNTAMND; Jul 15, 2016 at 11:32 PM.
Reason: Added more stuff
Take the gasket and compare it to the head, then match the ports of the intake to the head. It's ok to have the gasket beca little bigger than the ports, but you want the ports of the intake to match the size of the head.
Just pay attention to how much meat is able to be removed from the intake. It may be thin in some areas.
Yeah I haven't decided where I'm actually going with any of this on my project. Just thought I'd put out some images for the masses to understand the relevant sizes of some of the parts involved/discussed. I am familiar with porting for "steps down" as opposed to "dams" with flow going to a chamber. Trying for an exact match can really mess up parts in many cases & the back sides of the stock truck manifold lower runners are not "meaty" at all.
ahh I see. have to port the upper a bit also to match the lower, especially on the front port...other than that, seems like it all matches up decent except for maybe some thin mating surface between ports.
have you run one of these hybrids? what'd ya notice? the lower seems to be the most abysmal display of flow design, but I wouldn't mind going that route if you noticed some pick-me-up.
I have gotten a few guys to do it, and I've ported their lowers for them.
They claim it to be a noticeable gain.
I have not flow tested one yet.
The 351 lower intake is sunk down that much, so that it consumes the same height as a 302 engine. That's also why the 302 truck lower is tall, and Holley literally copied fords exact design and intake bolt pattern. The Holley systemax intake is one of the best ones for the mustang (because of the shorter large runner design of the upper along with the great lower).
The lower intake flows plenty. Mike over at toohighpsi .com has made about 800 hp with one ported like I typically do them. It's proven to be useable in most applications.
Well, boost sure does mask inadequacies in intakes, but I get the point. Mine runs out of breath around 4k but I'm not sure how much that has to do with the intake, I did hog out the lower enough to have to weld a few spots where I got greedy.
I think I'll go that route, 80% of the performance for 5% of the cost is fine with me for this engine. I'm collecting parts for a real build now, my current setup was a necessity build with jy parts because the 302 seized when I had all my time and money in other projects.
What about just installing some spacers between the 5.0 lower and the head? Seems like it would be less work to me.
Whatever you want.
The price of the intake spacer, you're more than halfway to a great intake.
The hybrid intake is for the budget minded do it yourselfer.
$300 bucks to adapt a stock 302 intake to a 351 isn't my choice.
Unless I had a special intake, I'd stay away from the cost of the spacers.
Epoxy can be used successfully, but there is an inherent risk when doing so....the expansion and contraction of metal can cause it to break free over time and it only has one place to go if it does fail.
