hey all, i bought the edelbrock base and runners, and am following the info on a few of the threads here on porting and siamesing the runners. i have gotten as far as doing the plenum and the upper runner ports. i am just starting on the lower ports/base. should i siamese these as well or just open them up polish and port match them? where will these modifications put my power band? i have a nice solid 350 (acdelco reman with ~20k on it) with factory heads. basically i want to build a fairly powerful engine based mainly on the street, with the occasional trip to the track. in addition to the porting and intake/runner combo, i am putting 1.6 roller rockers on, headers and 3" y pipe, better ignition coil and module, subframes, strut tower brace, etc. Thanks everyone

what cam are you using?

i'd just siamese the top runners as much as you can, and leave the base alone. Just open up the base as best you can from runner opening to the head intake port opening. That should allow that 350 to breath to 5200-5500 rpms. Good match for mild cams like L98/LT1 cams and some slightly larger cams like comp 502/lingenfelter 211/219, zz9/zz4 etc

it is an L98 engine. the previous owner popped the engine, and filed an insurance claim. they ordered the factory replacement from gm, and i assume it is the original specs (i have the acdelco warranty information/registration sheet they gave me). any ideas on where i could find that out without pulling stuff apart?

well you can check the head specs by the casting number. L98's had '083 heads...last 3 digits that is. other than that, its probly about L98 spec. 9-9.5 to 1 compression. hard to say what internals you have. hopefully it has pistons that will give you near 9.3-9.5 to 1 compression like stock L98's

I'd say mild port job and that little siamesing to the top runner is all you need to do. The stock L98 spec cam will support peak power to 5000 rpms and hold that to 5200-5300. Thats what my HSR setup did but with a lean tune. That TPI setup will support near 4800 rpm peak power i'd say out of the box so you will be fine there. alittle siamesing and porting will give you near 5300 rpm peak power potential and will hold power up to 5600 rpms i'd say on a good cammed/heads 350. Substantial siamesing and porting will support peak power at 5500-5600 and hold that power to 6000.

proper running tune with good exhaust your motor with your TPI intake as shown should dyno near 240-250whp and 330wtq or so. Should be great for low 13's with the right gears/suspension/converter

i will check the casting numbers this evening... thanks. i think the likelyhood of me pushing more than 5500rpm is fairly slim, so i will stick with the upper end siamesed and the lower just ported and matched.

sadly, i don't think i will have time to install a better converter until after my trip in april. i am trying to get this all done for my vacation in florida the last week of april. i am probably going to try to hit the bradenton motorsports park open "test and tune" night. hopefully I will do well.

thanks for the advice

Hi, im looking forward to getting the same Edelbrock High-Flow base and runner kit for my 305 TPI. They say you can gain 18-20HP with stock heads, so when you siamese and port were looking at greater numbers? also when I get this kit, do I need to modify my stock plenum to fit the bigger runner ports? thanks alot.

also, do you think that my 305 will profit from this kit? i mean will it really take in the extra air and get that 18-20hp ? or close

No it won't. You can't siamese port the edelbrock hi-flo runners, all you can do is bore them to some 1.75 inches. Siamesed SLP Runners are much better then edelbrocks. And don't bother porting the baseplate; plenum and runners is all you need. And your 305 most likely won't benefit a whole lot seeing as the tpi system was built for a 305 to be more like a 350 therefore making it a good flowing system for the smaller engine porting is more for the 350. However some mild porting of the plenum and runners definitely won't hurt. You just don't want to overflow the engine.

Holy **** was I wrong. Sorry guys you can siamese the eddy runners. Terribly sorry!