Help me optimize my build

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UOP

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Well, where to start. I guess it'll be with a little background on my build. My project is an 86 Mazda RX7 that I've dumped the crappy old rotary for a nice mild 360 Magnum. The reason for this is simple, I want to go drag racing! Why? Well, I already had the engine (built for another project that was abandoned), and the car was sitting in a friend's garage with a blown rotary. I looked under the hood and thought to myself "Wow, look at all that room!!! I bet that 360 will fit in there!!!". So we worked out a deal and I towed it home. Project Mopar RX7 began.

Phase one of the project is complete and the car is running and driving under Mopar power, so now to phase two, upgrade. The current combo is as follows:

-360 Magnum, bone stock rotating assembly
-Stock heads and valve train, except for upgraded valve springs.
-Comp Cams hyd roller: 216/224 @.050, .506/.506, 114 (Comp spec'd it for a boosted application, my abandoned project)
-Edelbrock Airgap intake
-Carter AFB 625
-Stock ignition from a 85 Ramcharger
-1 5/8" block hugger headers (not optimal, I know, but they're the only ones that fit)
-2 1/2" dual exhaust with x-pipe

-Bone stock lock-up 904 and converter

-Stock Mazda Turbo II limited-slip rear, 4.10 ratio. Yes, it "should" be strong enough.

-Car weight is 2890 lbs with a 1/4 tank of fuel and w/o me in it. 52/48% weigh distribution, but I'm still trying to move weight around to get it back to 50/50.




Here's what I've started work on already.

-Tires: M/T ET Street Radials, 255/60-15

-Transmission: Non Lock-up 904 being built with TF-2 shift kit, low first gear, and whatever else my builder is doing to it. Should be finished soon. I don't have a converter on the way since I can't call for a recommendation until I get everything else sorted out. Feel free to make a suggestion if you like.


Ok, so here's a few things I'd like to know.

1.) Cam: I don't think it's the right one for the car, and I'm thinking you all will agree. I've been shopping around for a new roller cam but they seem to have more lift than my stock heads will handle without removing them and cutting down the guides. I'm not trying to cheap out here, but if my heads don't flow well over .500 lift, why go through the expense of machining the heads and possibly having to upgrade my valve springs again when it won't do me any good? So that led me to this. My idea is to contact Comp and ask them to grind a cam similar to, for example, their XE274H cam, but as a roller and with about the same lift as my current cam (.506/.506) so it can be easily swapped without modifying my heads. So the specs would be a roller with 230/236 @ .050, .504/.506 lift, 110 LSA. I'm not sure if the XE274 is the right choice, I was just using that as an example. If a roller ground similar to a XE268 cam would be optimal, great, no problem. What are your thoughts?

2.) Carburetor: I've gotten several different opinions on this(mostly from Chevy or Ford guys), but some input from guys who race a Mopar would be very helpful. I've searched around and I seem to fall right in the middle between a 650dp or 750vs with my gear ratio and weight. A 3310 Holley would be a nice inexpensive choice, but if a dp would be best, then so be it. I'd be happy to answer any more questions about this subject so feel free to ask. I don't particularly care about gas mileage, this is my toy, not my daily driver.



If there is anything else that you need from me, please feel free to ask. I tried to be as specific as possible. Thank you for your time.
 
I see where you're going, and in the future I will build a motor better suited for what I want to do. However, I'm currently just trying to get the most out of what I have. Heads would be GREAT, but they're just not in the budget to get done before spring. I would consider some minor porting, but at this point I'm not comfortable enough to experiment on my heads.
 
UOP said:
I see where you're going, and in the future I will build a motor better suited for what I want to do. However, I'm currently just trying to get the most out of what I have. Heads would be GREAT, but they're just not in the budget to get done before spring. I would consider some minor porting, but at this point I'm not comfortable enough to experiment on my heads.
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Well if you know the size of the valves in your heads that would be awesome, because if they are small, it might be worth it opening them up, to a larger size. (ie. 1.77X1.5 to 1.88X1.6)

If you have the small valves in your heads, the carb you have is OK. But a holley would be better. However if you have the larger valves, you will benefit by going to a larger carb. And as you said the inexpensive 3310 Holley would be great. If you were going to go with a double pumper and put a couple hundred into it, you would do better by getting someone to port your heads and put that money there.

The camshaft you have selected does not sound like such a bad choice, But I am no expert at camshafts.
 
there use to be a guy on the net years ago that had a bad rx7 that was a grude car that went from state to state and took peoples money...been a long time but i use to like to read about him on diff. sites..so way to go be diff. be you go out and race mike
 
Dustin The PcP said:
Well if you know the size of the valves in your heads that would be awesome, because if they are small, it might be worth it opening them up, to a larger size. (ie. 1.77X1.5 to 1.88X1.6)

If you have the small valves in your heads, the carb you have is OK. But a holley would be better. However if you have the larger valves, you will benefit by going to a larger carb. And as you said the inexpensive 3310 Holley would be great. If you were going to go with a double pumper and put a couple hundred into it, you would do better by getting someone to port your heads and put that money there.

The camshaft you have selected does not sound like such a bad choice, But I am no expert at camshafts.
Click to expand...

Valve sizes are 1.92/1.62, and my rocker ratio is 1.6. Here is some info from Hughes' website on the stock head flow if it'll help.


Intake:
.100 - 51.2
.200 - 121.1
.300 - 181.5
.400 - 207.5
.500 - 209.0
.600 - 208.4

Exhaust:
.100 - 55.1
.200 - 109.0
.300 - 148.4
.400 - 170.8
.500 - 176.2
.600 - 178.4
 
Your cam and carb set up as is right now is good. The unported heads are well matched up as well. Leave it as is for the moment. Mike Beck, a guy here, raced his Duster witha Crane cam very similar in specs. 216/228-454/484 lift on a 112 to the tune of low 12's. The Duster was lightened to around your cars weight. He also had 4.10 gears and a 904 with a shift kit. You should follow suite with a basic trans-go performance shifting kit.

As long as your heads (Currently) can handle the lift, spring and clearnace wise, the "Overlifting" of the valve beyond the stall point isn't so bad. But such is not the case as is now or with the intended upgraded cam. I'd also stick with the stock valves for now. A 2.02 wouldn't help much here.

A quick word on weight, if the heavier part is over the rear axle, don't worry about it. Just make sure it launchs straight, drives striaght and stay steady when under power and at speed.
 
The problem will not be lift as much as pressures. You have a lifter that's twice as heavy, a rocker ratio that acts heavier on the spring, and a cam that needs pressure. Unfortunately the head cant accept much for springs. I think you should save a little bit and have a set of LA heads done. Or get a set of take offs from someone upgrading. Run hollow pushrods and you dont need the shaft oiling. the mods to get real springs are costly, and a set of RHSs or Engine Quests will have the same issues... Cost to get usable. Porting wont help if you cant get a spring in it that controls things well.
 
That sounds like a awsome project. I had a 87 rx7 back in the mid 90's. Thing was a blast to drive. I could only imagine with a small block.
 
It's about damn time somone did a project like this. I've been trying to convince my friend to let me drop a slant in his '82 corrola station wagon.
 
rumblefish360 said:
Your cam and carb set up as is right now is good. The unported heads are well matched up as well. Leave it as is for the moment. Mike Beck, a guy here, raced his Duster witha Crane cam very similar in specs. 216/228-454/484 lift on a 112 to the tune of low 12's. The Duster was lightened to around your cars weight. He also had 4.10 gears and a 904 with a shift kit. You should follow suite with a basic trans-go performance shifting kit.

As long as your heads (Currently) can handle the lift, spring and clearnace wise, the "Overlifting" of the valve beyond the stall point isn't so bad. But such is not the case as is now or with the intended upgraded cam. I'd also stick with the stock valves for now. A 2.02 wouldn't help much here.

A quick word on weight, if the heavier part is over the rear axle, don't worry about it. Just make sure it launchs straight, drives striaght and stay steady when under power and at speed.
Click to expand...

Thanks for the reply Rumble. I must say that I'm a little surprised that you think my combo is matched up pretty well. Makes me feel more confident in what I have. I'd sure be happy with a 12 sec car that I built myself in my 1 car garage. :cheers:

I thought for sure everyone would think my cam was not correct. Not so much for duration and lift, but because of the LSA. From what I understand, the wider LSA makes the cam a little "lazy". That's really the reason I was looking to swap to something ground with a 110, to bring the torque on a little harder. Well, that and the fact that you can't even tell I've got a "performance" cam by listening to it, lol.

As for the carb, I still need to buy a new one since the Carter currently on the motor is borrowed. I've already had it longer than I said I would, but so far he's been cool with it. I can't buy it from him since it's destined for another project. I'd like to pick up a Holley of some sort. Gonna think about it a little more.
 
Well, yea, besides the cams short comings, it's not to bad. A change would be better of course.

In general, is this project going to continue as a "On the cheap" project until the money allows for better parts to be purchased? I'll need to know the mind set so I can comment further rather than say, "Oh just spend the mponey on a HOlley 750 HP and be done with it!"

While it would be a great carb to get, the price tag is steep and several parts could be purchased in it's stead.
 
moper said:
The problem will not be lift as much as pressures. You have a lifter that's twice as heavy, a rocker ratio that acts heavier on the spring, and a cam that needs pressure. Unfortunately the head cant accept much for springs. I think you should save a little bit and have a set of LA heads done. Or get a set of take offs from someone upgrading. Run hollow pushrods and you dont need the shaft oiling. the mods to get real springs are costly, and a set of RHSs or Engine Quests will have the same issues... Cost to get usable. Porting wont help if you cant get a spring in it that controls things well.
Click to expand...

Thanks for the input, but you got me thinking about something. Ever since I've had this engine running, I've been a little concerned by the fact that the valvetrain isn't as quiet as I think it should be. Now I've done some searching around this forum and found that others have had the same problem with valvetrain noise when running a Comp XE series cam. I read where someone compared it to a sewing machine, and that's pretty much what I think. But it is quite loud, and is definitely noticeable while driving down the road with the windows up. I'm using MP valve springs, part# P5249464 (rated to .525" lift), that Direct Connection recommended to me when the Comp tech guy said they didn't list a spring for my application. In your opinion, could the added weight and pressures generated by my roller valvetrain be causing the springs to be too weak?

Just so you don't have to go back and look. My current cam specs are 216/224 @ .050", .506"/.506".

Thanks again
 
rumblefish360 said:
Well, yea, besides the cams short comings, it's not to bad. A change would be better of course.

In general, is this project going to continue as a "On the cheap" project until the money allows for better parts to be purchased? I'll need to know the mind set so I can comment further rather than say, "Oh just spend the mponey on a HOlley 750 HP and be done with it!"

While it would be a great carb to get, the price tag is steep and several parts could be purchased in it's stead.
Click to expand...

I don't want to say "On the cheap", but like most I'm on a budget. While I don't exactly have money coming out of my ears, I'm not opposed to spending money where it's needed. Yes, better parts will be purchased in the future as funding allows, but right now I'm just trying to use what I've got to its full potential so I can race this upcoming season. I'm usually not one for buying things twice, but in this case I'd rather have a carb that's just right for this motor, and temporarily too small for the next. There's a new motor in this car's future, but that will be at least a year from now.
 
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