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SmokinVette.com Forums : Corvette Forums : C4 Corvette Forums : C4 Corvette General Discussion : Crate Motor
C4 Corvette General Discussion
1984 - 1996 Corvettes

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Old 07-19-2012, 11:45 AM   #1
CodeGnome
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Default Crate Motor

Alright guys I'm back and looking for crate engine opinions. I won't be doing this until next spring, but want to start planing now. I am considering the flat tappet 375 horse / 400 torque 355 from Blueprint. I could go with more power, but don't see the point as it would be a waste - I already have plenty of fun with the stock engine and I don't want to start breaking other parts. Initially I will leave the stock shorty headers and CFI. I do understand that I would get more with long tubes and better induction, but my thought is to allow room for improvement when I'm ready for it.
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Old 07-19-2012, 12:13 PM   #2
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Quote:
Originally Posted by CodeGnome View Post
Alright guys I'm back and looking for crate engine opinions. I won't be doing this until next spring, but want to start planing now. I am considering the flat tappet 375 horse / 400 torque 355 from Blueprint. I could go with more power, but don't see the point as it would be a waste - I already have plenty of fun with the stock engine and I don't want to start breaking other parts. Initially I will leave the stock shorty headers and CFI. I do understand that I would get more with long tubes and better induction, but my thought is to allow room for improvement when I'm ready for it.

You'll never get 375 horsepower out of it unless you put a Renegade on it as the stock CrossFire intake will only flow 425 cfm. The stock 1-13/16" throttle bodies will flow approximately 567 cfm so your biggest choke point will be the manifold itself. By having your throttle bodies bored to 2" that will increase their flow to a bit over 700 cfm and combined with the 750+ cfm the Renegade will flow you can make your goal.
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Old 07-19-2012, 12:53 PM   #3
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TooBroke - I agree and the induction system will be a later project. I do believe just the motor will net more than the 205hp advertised rating of the current motor.
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Old 07-19-2012, 04:08 PM   #4
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TooBroke - I agree and the induction system will be a later project. I do believe just the motor will net more than the 205hp advertised rating of the current motor.

I'm sure you're right but then it'll fall flat on it's face around 3500 rpm when the stock 425 cfm CrossFire manifold maxes out. The other thing you'll need to do is increase your fuel pressure to around 14 psi by using an '85 or later fuel pump and increasing the spring tension in your pressure regulator by stretching the stock spring about 5/8" to 3/4".

In the meantime you can substantially improve your engine's performance above 3500 rpm by making the fuel modifications right now. Contact me at sw82vette@yahoo.com and I'll walk you thru the process.
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Old 07-19-2012, 05:37 PM   #5
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Since you already are having plenty of fun with the stock engine why not rebuild it. It can be rebuilt at home for not much money using a kit with a machine shop doing the machining or you can pull it and a machine shop will rebuild the long block for you which will still be a lot less than a crate engine.

Truth is to get a lot more hp than the stock 205hp you would have to do serious/expensive work to the induction, computer AND exhaust systems in addition to the crate engine and it still might not be a huge gain without major proper modifications.

Last edited by Slicktop; 07-19-2012 at 05:50 PM.
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Old 07-20-2012, 05:27 AM   #6
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The other thing you'll need to do is increase your fuel pressure to around 14 psi by using an '85 or later fuel pump and increasing the spring tension in your pressure regulator by stretching the stock spring about 5/8" to 3/4".
TooBroke: I've already installed the '85 fuel pump, I'll get in contact with you about the regulator spring. - Thanks
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Old 07-20-2012, 05:37 AM   #7
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Since you already are having plenty of fun with the stock engine why not rebuild it. It can be rebuilt at home for not much money using a kit with a machine shop doing the machining or you can pull it and a machine shop will rebuild the long block for you which will still be a lot less than a crate engine.

Truth is to get a lot more hp than the stock 205hp you would have to do serious/expensive work to the induction, computer AND exhaust systems in addition to the crate engine and it still might not be a huge gain without major proper modifications.
Slick: I'm going with crate engine believing that I'll get more bang for my buck and I'll know exactly what I have. The engine is supposed to be dyno tested & ready to run; and the warranty is far better than I can get from any shop in my area.

As far as performance I agree completely, which is why I'm starting with a heart transplant. As time goes on I can improve the induction, exhaust, etc to release the horses.
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Old 07-20-2012, 07:39 AM   #8
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Good luck! Personally, I would rebuild the original engine, it is still running ok which means that it would be an easy rebuild.
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Old 07-20-2012, 08:14 AM   #9
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TooBroke: I've already installed the '85 fuel pump, I'll get in contact with you about the regulator spring. - Thanks

Back in 2005 I did some extensive testing of my '82 to find out why it seemed to lose power so bad right when it hit 3400-3500 rpm. I started by testing the free flow of my stock pump by powering it with my 4-amp trickle charger and pumping into a big 7-gallon plastic bucket for one minute. Then I multiplied the volume by 60 to determine how much it pumped per hour. About 43-44 gallons per hour which is about the same as a mechanical pump would deliver.

Then I pumped the fuel thru the pressure regulator that was set at 11 psi and the flow dropped to about 22-23 gallons per minute; far short of the 33-34 gallons per minute a 350" engine running at 80% efficiency would require at 6000 rpm. Then I pinched off the fuel return hose to see how much pressure the pump would make before it maxed out and found it signed off at 12 psi when it started bypassing internally.

Not knowing an '85 fuel pump would directly interchange with the '82 thru '84 pumps I installed a rear-frame mounted Hypertech gearotor pump that was rated for 43 gph @ 90 psi at 7-1/2 amps and stretched my pressure regulator spring about 3/4" longer; giving me exactly 14 psi.

Road testing it with a 0-15 psi pressure gauge inside my cabin I found it would maintain a full 14 psi all the way to it's redline and with the increased volume and pressure the Hypertech pump delivered I was astonished over how much additional power it made from about 2800 to 4400 rpm where it suddenly signed off because of the restrictive 425 cfm CrossFire intake manifold. I played around with higher pressure regulator settings and found pressures 2-3 psi above 14 psi produced a lot of black smoke and a loss of power so I settled on the 14 psi as that felt ideal.

Then after boring my throttle bodies to 2.0" and installing my Renegade two years ago my engine will now make terrific power all the way to 6000 rpm but the most noticeable power increase comes between 2800 and 4500 rpm where it's needed the most and I attribute most of that to the fuel system modifications.

The first thing you'll need to do is solder a brass T into your fuel line so you can easily check your pressure with a common 0-15 psi pressure gauge then modify your fuel pressure regulator for easy adjustment (or buy an inexpensive adjustment tool from DCS) and stretch the spring an additional 3/4" to get the desired 14 psi. As you have already installed the '85 pump you'll only need to make the pressure regulator modifications to see a dramatic increase in power from idle up to 4400-4500 rpm..................................





Once the fuel pressure has been increased to 14 psi no further adjustment is needed from then on but the brass pressure tap will always come in handy for future troubleshoooting. To maintain the same bend of the fuel line the tap must be soldered in place (with a propane torch) with the fuel line connected so when you're soldering it in be sure to protect all of the surrounding plastic parts with sheet metal so they won't melt.
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Old 07-20-2012, 08:26 AM   #10
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And one other thing. The stock 1-13/16" throttle bodies will flow 567 cfm so they'll flow plenty to support a stock to mildly modified 350" engine up to 5500 rpm with an automatic transmission. So unless you're planning on exceeding 6000 rpm there's no gain whatsoever in getting them bored to 2.0" (which will flow 719 cfm). And as the stock CrossFire will only flow 425 cfm anyway the choke point will be the CrossFire manifold; not the throttle bodies....................
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