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Old 05-01-2009, 02:20 AM
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best mods for a 1990 chevy 350

i have a 90 Chevy pick up 350 has an rv cam throttle body spacer and a few small upgrades what would be the next best thing to and or change?

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Old 05-01-2009, 03:29 AM
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You already have a 700R4 O/D so I would go to a 3.73 rear end gear or even a 4.10 if you don't do a lot of freeway driving. That change alone will really wake it up.
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Old 05-01-2009, 01:01 PM
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Quote:
Originally Posted by B350
i have a 90 Chevy pick up 350 has an rv cam throttle body spacer and a few small upgrades what would be the next best thing to and or change?
The 90 model has swirl port heads and next to no cam. Changing these makes a huge improvement. The down side is the computer will need a reprogrammed chip, these can be pricey give or take around 400 dollars.

However, most guys go for Vortec heads which also requires a Vortec bolt patter intake to match the TBI to the head. Between the heads and intake and changing how the EGR gets fed will cost about a grand. Without a cam change this will put about 40 more ponies under the hood and extend the rev range to 5500.

For more valve timing there's two ways to go that won't upset the TBI to where it can't be dialed in with a new chip.

1) Go to 1.6 rockers with the existing cam, this will add 15 - 20 hp without having to dig deeper than the rocker covers. Your engine uses self aligning rockers.

2) The Edlebrock 3702 cam is perfect for these TBI engines and about as far as you can go with the factory sensors. But this alone is good for 30-40 hp over what you've got for a cam. The 3702 shouldn't be combined with 1.6 rockers as it pushes the sensor sensitivity to an edge where except for super tuners like TPIS, it's difficult to get programs that work seamlessly with this combo.

But with Vortec heads and intake, the 3702 cam, a new chip, and some decent headers it's easy to get 320-330 hp out of a truck TBI 350.

Bogie
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Old 05-01-2009, 01:38 PM
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Bogie, is there anything that can be done for these swirl-port heads that'll wake them up w/o resorting to heroic measures, porting-wise?

Or are they better left in the "don't bother" pile?
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Old 05-01-2009, 02:03 PM
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well i have an RV cam in that was put in by a miss understanding with the recent rebuilt motor that was put in and i have standard tranny. also i have a flowmaster 40 and im considering putting a glasspack or something like that.
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Old 05-01-2009, 03:20 PM
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Quote:
Originally Posted by cobalt327
Bogie, is there anything that can be done for these swirl-port heads that'll wake them up w/o resorting to heroic measures, porting-wise?

Or are they better left in the "don't bother" pile?
There is a whole group out there that swears by them, being an engineer by trade I do neither, they do a job they were designed for, if you need to change from that job then they're just not the right solution any more.

Basically they are the cast iron 1980s-early 1990s Corvette L-98 head in cast iron with a vane cast on one side of the valve guide. They're super good for a low speed engine doing grunt work like a pickup hauling a ton of stuff in overdrive on the freeway. If you want to get over 4000 RPM with any power they need to be reworked or replaced. Yes the vane can be reduced or removed, but one needs to consider the cost of rebuilding the heads against just getting a new set. While I aimed the conversation at Vortecs because everybody on this planet has heard of them, the aftermarket like Dart and World provide very similar heads that will accept your existing intake at Vortec competitive prices. This really puts a jaundiced look on rebuilding the Swirl Ports.

Your engine will respond to more cam or 1.6 rockers as I sighted without a head change and will also push the rev line up by virtue of holding the valve open further or longer, Longer being more in keeping with overcoming the limitations of port flow in the Swirl Port head than higher lift.

Bogie
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Old 05-01-2009, 03:57 PM
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The best upgrade would be to install a vortec top end (heads and intake). This is a common upgrade with lots of instruction out there on the web.
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Old 05-01-2009, 04:38 PM
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Quote:
Originally Posted by oldbogie
...they do a job they were designed for, if you need to change from that job then they're just not the right solution any more.
That is kind of what I expected. I have a set from a roller-type '92 engine that got a different set of heads altogether.

Thanks.

Quote:
The best upgrade would be to install a vortec top end...
Like the heads below?

Going to put them back on the roller block they came off of. Then put it into my '80 Malibu wagon.
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Old 05-02-2009, 01:06 AM
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350 trucks are the ultimate sleeper

Well, nice to see someone has a shared interest. Okay, so the swirlport heads aren't the best, but what is?! If you have emissions requirements in your area, you can hardly get away with running old double humps with 2.02 and 1.66 valves and 64cc chambers now can we? If no emmisions are required, back date to 1960's fuelie heads, the double humps with the big valves, a single four and ram air. Simple as that. But, if you want to go new school, by all means, upgrade to Vortec heads, use an edelbrock or Holly manifold designed for such heads and TBI, upgrade to holly Venom injectors, keep your spacer and cam, slap a pair of Summit 1988-1995 Chevy Truck headers on it and have fun all day. 1990 to 1994 Chevy trucks were rated at 255 HP from the factory, take a wild guess to what all these mods bring it up to.
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Old 05-03-2009, 07:11 PM
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Quote:
Originally Posted by Speedshift_Sam
Well, nice to see someone has a shared interest. Okay, so the swirlport heads aren't the best, but what is?! If you have emissions requirements in your area, you can hardly get away with running old double humps with 2.02 and 1.66 valves and 64cc chambers now can we? If no emmisions are required, back date to 1960's fuelie heads, the double humps with the big valves, a single four and ram air. Simple as that. But, if you want to go new school, by all means, upgrade to Vortec heads, use an edelbrock or Holly manifold designed for such heads and TBI, upgrade to holly Venom injectors, keep your spacer and cam, slap a pair of Summit 1988-1995 Chevy Truck headers on it and have fun all day. 1990 to 1994 Chevy trucks were rated at 255 HP from the factory, take a wild guess to what all these mods bring it up to.


so some summit headers (long or short?)and the venom injects and a manifold will make a big difference? OK one more thing i have a flowmaster 40 I'm really considering a dynomax race bullet or some cherry bomb glass packs what would you recommend?
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Old 05-07-2009, 08:53 AM
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Do you have single or dual ex?

That I suppose is the next question. By the way you worded that, you are still running the stock cat and y-pipe. Truly, there's no need for a muffler aft of the cat at all. I run my 1990 shortbed the exact same way, it has a decent low thunder, and is not too loud at all. Have a muffler delete (Or y-pipe) made or make it yourself, to go in place of the muffler, and still hook up to your tail pipes. (If you have more than one). That big 3" stock cat is a very good muffler anyway. Where I live, I have no emmisions testing at all, so on my 88 GMC I split it into true duals, and boy what a difference that made. (With no other mods at all, only duals.) And oh yes, the short 1988-1994 truck headers works just fine, They bolt right up to the factory y-pipes, and you can get them without the A.I.R injector ports for the off-road package trucks, and trucks that never came with an A.I.R pump. The long ones may give you a headache with having to create some custom plumbing, or interference with the T-case (If you have a 4X4). But they do perform better than the short variety. Glad to help any way I can.

Last edited by Speedshift_Sam; 05-07-2009 at 08:56 AM. Reason: missed a detail
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Old 05-07-2009, 09:01 AM
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Quote:
Originally Posted by Speedshift_Sam
The long ones may give you a headache
Often they are fouled by the column shifter if you have A/T. Have to then use a floor shifter to get the long tubes to clear.

I'm not sure that your year of truck poses this problem, but something else to check.
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Old 05-07-2009, 10:55 AM
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I bought a tbi motor months ago and the first thing to go on it were those heads. I ended up giving them to a guy at my machine shop.. who did not want them either.. but stated he could get $30 for them or so to buy him lunch for a couple of days.

I would not waste a penny doing anything to those heads. If you must use them, then do as Bogie already commented.. either the 1.6 and or a cam change. I would probably do the simplest/most effective which is a cam change. I look forward to seeing/getting comments from the Bogster because he always right on the money!
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Old 05-08-2009, 12:01 AM
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yea i bought the headers and should be here today i cant wait my engines really clean and with those stupid manifolds were really making me mad so i think I'm gonna be really happy. so what year is considered a classic because they don't have to have a sniffer test and all that correct? but really its not too loud with out a muffler so i wont get stopped or anything. haha lol
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